chore: prepare tokio-stream 0.1.9 (#4743)

Co-authored-by: Taiki Endo <[email protected]>

.cargo/audit.toml

@@ -0,0 +1,8 @@
+# See https://github.com/rustsec/rustsec/blob/59e1d2ad0b9cbc6892c26de233d4925074b4b97b/cargo-audit/audit.toml.example for example.
+
+[advisories]
+ignore = [
+    # We depend on nix 0.22 only via mio-aio, a dev-dependency.
+    # https://github.com/tokio-rs/tokio/pull/4255#issuecomment-974786349
+    "RUSTSEC-2021-0119",
+]

.cargo/config

@@ -0,0 +1,2 @@
+# [build]
+# rustflags = ["--cfg", "tokio_unstable"]

.circleci/config.yml

@@ -0,0 +1,25 @@
+version: 2.1        
+jobs:
+  test-arm:
+    machine:
+      image: ubuntu-2004:202101-01
+    resource_class: arm.medium
+    environment:
+      # Change to pin rust versino
+      RUST_STABLE: stable
+    steps:
+      - checkout
+      - run:
+          name: Install Rust
+          command: |
+            curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs -o rustup.sh
+            chmod +x rustup.sh
+            ./rustup.sh -y --default-toolchain $RUST_STABLE
+            source "$HOME"/.cargo/env
+      # Only run Tokio tests
+      - run: cargo test --all-features -p tokio
+
+workflows:
+  ci:
+    jobs:
+      - test-arm

.cirrus.yml

@@ -1,19 +1,51 @@
 freebsd_instance:
-  image: freebsd-12-2-release-amd64
+  image: freebsd-12-3-release-amd64
+env:
+  RUST_STABLE: stable
+  RUST_NIGHTLY: nightly-2022-03-21
+  RUSTFLAGS: -D warnings
 
 # Test FreeBSD in a full VM on cirrus-ci.com.  Test the i686 target too, in the
 # same VM.  The binary will be built in 32-bit mode, but will execute on a
 # 64-bit kernel and in a 64-bit environment.  Our tests don't execute any of
 # the system's binaries, so the environment shouldn't matter.
 task:
-  name: FreeBSD
-  env:
-    LOOM_MAX_PREEMPTIONS: 2
-    RUSTFLAGS: -Dwarnings
+  name: FreeBSD 64-bit
   setup_script:
     - pkg install -y bash curl
     - curl https://sh.rustup.rs -sSf --output rustup.sh
-    - sh rustup.sh -y --profile minimal --default-toolchain stable
+    - sh rustup.sh -y --profile minimal --default-toolchain $RUST_STABLE
+    - . $HOME/.cargo/env
+    - |
+      echo "~~~~ rustc --version ~~~~"
+      rustc --version
+  test_script:
+    - . $HOME/.cargo/env
+    - cargo test --all --all-features
+
+task:
+  name: FreeBSD docs
+  env:
+    RUSTFLAGS: --cfg docsrs --cfg tokio_unstable
+    RUSTDOCFLAGS: --cfg docsrs --cfg tokio_unstable -Dwarnings
+  setup_script:
+    - pkg install -y bash curl
+    - curl https://sh.rustup.rs -sSf --output rustup.sh
+    - sh rustup.sh -y --profile minimal --default-toolchain $RUST_NIGHTLY
+    - . $HOME/.cargo/env
+    - |
+      echo "~~~~ rustc --version ~~~~"
+      rustc --version
+  test_script:
+    - . $HOME/.cargo/env
+    - cargo doc --lib --no-deps --all-features --document-private-items
+
+task:
+  name: FreeBSD 32-bit
+  setup_script:
+    - pkg install -y bash curl
+    - curl https://sh.rustup.rs -sSf --output rustup.sh
+    - sh rustup.sh -y --profile minimal --default-toolchain $RUST_STABLE
     - . $HOME/.cargo/env
     - rustup target add i686-unknown-freebsd
     - |
@@ -21,9 +53,4 @@ task:
       rustc --version
   test_script:
     - . $HOME/.cargo/env
-    - cargo test --all --all-features
-    - cargo doc --all --no-deps
-  i686_test_script:
-    - . $HOME/.cargo/env
-    - |
-      cargo test --all --all-features --target i686-unknown-freebsd
+    - cargo test --all --all-features --target i686-unknown-freebsd

.clippy.toml

@@ -1 +1 @@
-msrv = "1.45"
+msrv = "1.49"

.github/labeler.yml

@@ -0,0 +1,8 @@
+
+R-loom:
+- tokio/src/sync/*
+- tokio/src/sync/**/*
+- tokio-util/src/sync/*
+- tokio-util/src/sync/**/*
+- tokio/src/runtime/*
+- tokio/src/runtime/**/*

.github/workflows/audit.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     if: "!contains(github.event.head_commit.message, 'ci skip')"
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
       - name: Audit Check
         uses: actions-rs/audit-check@v1

.github/workflows/bench.yml

@@ -1,55 +0,0 @@
-name: Benchmark
-on:
-  push:
-    branches:
-      - master
-
-jobs:
-  benchmark:
-    name: Benchmark
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        bench:
-          - rt_multi_threaded
-          - sync_mpsc
-          - sync_rwlock
-          - sync_semaphore
-    steps:
-      - uses: actions/checkout@v2
-      - name: Install Rust
-        run: rustup update stable
-
-      # Run benchmark with `go test -bench` and stores the output to a file
-      - name: Run benchmark
-        run: cargo bench --bench ${{ matrix.bench }} | tee ../output.txt
-        working-directory: benches
-
-      # Download previous benchmark result from cache (if exists)
-      - name: Download previous benchmark data
-        uses: actions/cache@v1
-        with:
-          path: ./cache
-          key: ${{ runner.os }}-benchmark
-
-      # Run `github-action-benchmark` action
-      - name: Store benchmark result
-        uses: rhysd/github-action-benchmark@v1
-        with:
-          name: ${{ matrix.bench }}
-          # What benchmark tool the output.txt came from
-          tool: 'cargo'
-          # Where the output from the benchmark tool is stored
-          output-file-path: output.txt
-          # # Where the previous data file is stored
-          # external-data-json-path: ./cache/benchmark-data.json
-          # Workflow will fail when an alert happens
-          fail-on-alert: true
-          # GitHub API token to make a commit comment
-          github-token: ${{ secrets.GITHUB_TOKEN }}
-          # Enable alert commit comment
-          comment-on-alert: true
-          alert-comment-cc-users: '@tokio-rs/maintainers'
-          auto-push: true
-
-      # Upload the updated cache file for the next job by actions/cache

.github/workflows/ci.yml

@@ -9,8 +9,23 @@ name: CI
 env:
   RUSTFLAGS: -Dwarnings
   RUST_BACKTRACE: 1
-  nightly: nightly-2021-04-25
-  minrust: 1.45.2
+  # Change to specific Rust release to pin
+  rust_stable: stable
+  rust_nightly: nightly-2022-04-18
+  rust_clippy: 1.52.0
+  # When updating this, also update:
+  # - README.md
+  # - tokio/README.md
+  # - CONTRIBUTING.md
+  # - tokio/Cargo.toml
+  # - tokio-util/Cargo.toml
+  # - tokio-test/Cargo.toml
+  # - tokio-stream/Cargo.toml
+  rust_min: 1.49.0
+
+defaults:
+  run:
+    shell: bash
 
 jobs:
   # Depends on all action sthat are required for a "successful" CI run.
@@ -20,6 +35,7 @@ jobs:
     needs:
       - test
       - test-unstable
+      - test-parking_lot
       - miri
       - cross
       - features
@@ -27,8 +43,11 @@ jobs:
       - fmt
       - clippy
       - docs
-      - loom
       - valgrind
+      - loom-compile
+      - check-readme
+      - test-hyper
+      - wasm32-unknown-unknown
     steps:
       - run: exit 0
 
@@ -42,9 +61,15 @@ jobs:
           - ubuntu-latest
           - macos-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: ${{ env.rust_stable }}
+            override: true
       - name: Install Rust
         run: rustup update stable
+      - uses: Swatinem/rust-cache@v1
       - name: Install cargo-hack
         run: cargo install cargo-hack
 
@@ -75,13 +100,41 @@ jobs:
         # bench.yml workflow runs benchmarks only on linux.
         if: startsWith(matrix.os, 'ubuntu')
 
+  test-parking_lot:
+    # The parking_lot crate has a feature called send_guard which changes when
+    # some of its types are Send. Tokio has some measures in place to prevent
+    # this from affecting when Tokio types are Send, and this test exists to
+    # ensure that those measures are working.
+    #
+    # This relies on the potentially affected Tokio type being listed in
+    # `tokio/tokio/tests/async_send_sync.rs`.
+    name: compile tests with parking lot send guards
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: ${{ env.rust_stable }}
+            override: true
+      - uses: Swatinem/rust-cache@v1
+      - name: Enable parking_lot send_guard feature
+        # Inserts the line "plsend = ["parking_lot/send_guard"]" right after [features]
+        run: sed -i '/\[features\]/a plsend = ["parking_lot/send_guard"]' tokio/Cargo.toml
+      - name: Compile tests with all features enabled
+        run: cargo build --workspace --all-features --tests
+
   valgrind:
     name: valgrind
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - name: Install Rust
-        run: rustup update stable
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: ${{ env.rust_stable }}
+            override: true
+      - uses: Swatinem/rust-cache@v1
 
       - name: Install Valgrind
         run: |
@@ -95,7 +148,7 @@ jobs:
 
       # Run with valgrind
       - name: Run valgrind test-mem
-        run: valgrind  --leak-check=full --show-leak-kinds=all ./target/debug/test-mem
+        run: valgrind --error-exitcode=1 --leak-check=full --show-leak-kinds=all ./target/debug/test-mem
 
       # Compile tests
       - name: cargo build test-process-signal
@@ -104,7 +157,7 @@ jobs:
 
       # Run with valgrind
       - name: Run valgrind test-process-signal
-        run: valgrind --leak-check=full --show-leak-kinds=all ./target/debug/test-process-signal
+        run: valgrind --error-exitcode=1 --leak-check=full --show-leak-kinds=all ./target/debug/test-process-signal
 
   test-unstable:
     name: test tokio full --unstable
@@ -116,51 +169,64 @@ jobs:
           - ubuntu-latest
           - macos-latest
     steps:
-      - uses: actions/checkout@v2
-      - name: Install Rust
-        run: rustup update stable
-
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: ${{ env.rust_stable }}
+            override: true
+      - uses: Swatinem/rust-cache@v1
       # Run `tokio` with "unstable" cfg flag.
       - name: test tokio full --cfg unstable
-        run: cargo test --features full
+        run: cargo test --all-features
         working-directory: tokio
         env:
           RUSTFLAGS: --cfg tokio_unstable -Dwarnings
+          # in order to run doctests for unstable features, we must also pass
+          # the unstable cfg to RustDoc
+          RUSTDOCFLAGS: --cfg tokio_unstable
 
   miri:
     name: miri
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_nightly }}
+        uses: actions-rs/toolchain@v1
         with:
-          toolchain: ${{ env.nightly }}
+          toolchain: ${{ env.rust_nightly }}
+          components: miri
           override: true
-      - name: Install Miri
-        run: |
-          set -e
-          rustup component add miri
-          cargo miri setup
-          rm -rf tokio/tests
-
+      - uses: Swatinem/rust-cache@v1
       - name: miri
-        run: cargo miri test --features rt,rt-multi-thread,sync task
-        working-directory: tokio
-  san:
-    name: san
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
-        with:
-          toolchain: ${{ env.nightly }}
-          override: true
-      - name: asan
-        run: cargo test --all-features --target x86_64-unknown-linux-gnu --lib -- --test-threads 1
+        # Many of tests in tokio/tests and doctests use #[tokio::test] or
+        # #[tokio::main] that calls epoll_create1 that Miri does not support.
+        run: cargo miri test --features full --lib --no-fail-fast
         working-directory: tokio
+        env:
+          MIRIFLAGS: -Zmiri-disable-isolation -Zmiri-tag-raw-pointers
+          PROPTEST_CASES: 10
+
+  asan:
+    name: asan
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install llvm
+        # Required to resolve symbols in sanitizer output
+        run: sudo apt-get install -y llvm
+      - name: Install Rust ${{ env.rust_nightly }}
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ env.rust_nightly }}
+          override: true
+      - uses: Swatinem/rust-cache@v1
+      - name: asan
+        run: cargo test --workspace --all-features --target x86_64-unknown-linux-gnu --tests -- --test-threads 1
         env:
           RUSTFLAGS: -Z sanitizer=address
-          ASAN_OPTIONS: detect_leaks=0
+          # Ignore `trybuild` errors as they are irrelevant and flaky on nightly
+          TRYBUILD: overwrite
 
   cross:
     name: cross
@@ -173,34 +239,45 @@ jobs:
           - powerpc64-unknown-linux-gnu
           - mips-unknown-linux-gnu
           - arm-linux-androideabi
+          - mipsel-unknown-linux-musl
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: actions-rs/toolchain@v1
         with:
-          toolchain: stable
+          toolchain: ${{ env.rust_stable }}
           target: ${{ matrix.target }}
           override: true
+      - uses: Swatinem/rust-cache@v1
       - uses: actions-rs/cargo@v1
         with:
           use-cross: true
           command: check
-          args: --workspace --target ${{ matrix.target }}
+          args: --workspace --all-features --target ${{ matrix.target }}
+      - uses: actions-rs/cargo@v1
+        with:
+          use-cross: true
+          command: check
+          args: --workspace --all-features --target ${{ matrix.target }}
+        env:
+          RUSTFLAGS: --cfg tokio_unstable -Dwarnings
 
   features:
     name: features
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_nightly }}
+        uses: actions-rs/toolchain@v1
         with:
-          toolchain: ${{ env.nightly }}
+          toolchain: ${{ env.rust_nightly }}
+          target: ${{ matrix.target }}
           override: true
+      - uses: Swatinem/rust-cache@v1
       - name: Install cargo-hack
         run: cargo install cargo-hack
-
       - name: check --each-feature
         run: cargo hack check --all --each-feature -Z avoid-dev-deps
-
       # Try with unstable feature flags
       - name: check --each-feature --unstable
         run: cargo hack check --all --each-feature -Z avoid-dev-deps
@@ -211,12 +288,13 @@ jobs:
     name: minrust
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_min }}
+        uses: actions-rs/toolchain@v1
         with:
-          toolchain: ${{ env.minrust }}
+          toolchain: ${{ env.rust_min }}
           override: true
-
+      - uses: Swatinem/rust-cache@v1
       - name: "test --workspace --all-features"
         run: cargo check --workspace --all-features
 
@@ -224,11 +302,13 @@ jobs:
     name: minimal-versions
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_nightly }}
+        uses: actions-rs/toolchain@v1
         with:
-          toolchain: ${{ env.nightly }}
+          toolchain: ${{ env.rust_nightly }}
           override: true
+      - uses: Swatinem/rust-cache@v1
       - name: Install cargo-hack
         run: cargo install cargo-hack
       - name: "check --all-features -Z minimal-versions"
@@ -239,23 +319,35 @@ jobs:
           # Update Cargo.lock to minimal version dependencies.
           cargo update -Z minimal-versions
           cargo hack check --all-features --ignore-private
+      - name: "check --all-features --unstable -Z minimal-versions"
+        env:
+          RUSTFLAGS: --cfg tokio_unstable -Dwarnings
+        run: |
+          # Remove dev-dependencies from Cargo.toml to prevent the next `cargo update`
+          # from determining minimal versions based on dev-dependencies.
+          cargo hack --remove-dev-deps --workspace
+          # Update Cargo.lock to minimal version dependencies.
+          cargo update -Z minimal-versions
+          cargo hack check --all-features --ignore-private
 
   fmt:
     name: fmt
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - name: Install Rust
-        run: rustup update stable
-      - name: Install rustfmt
-        run: rustup component add rustfmt
-
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ env.rust_stable }}
+          override: true
+          components: rustfmt
+      - uses: Swatinem/rust-cache@v1
       # Check fmt
       - name: "rustfmt --check"
         # Workaround for rust-lang/cargo#7732
         run: |
-          if ! rustfmt --check --edition 2018 $(find . -name '*.rs' -print); then
-            printf "Please run \`rustfmt --edition 2018 \$(find . -name '*.rs' -print)\` to fix rustfmt errors.\nSee CONTRIBUTING.md for more details.\n" >&2
+          if ! rustfmt --check --edition 2018 $(git ls-files '*.rs'); then
+            printf "Please run \`rustfmt --edition 2018 \$(git ls-files '*.rs')\` to fix rustfmt errors.\nSee CONTRIBUTING.md for more details.\n" >&2
             exit 1
           fi
 
@@ -263,12 +355,14 @@ jobs:
     name: clippy
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - name: Install Rust
-        run: rustup update 1.52.1 && rustup default 1.52.1
-      - name: Install clippy
-        run: rustup component add clippy
-
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_clippy }}
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ env.rust_clippy }}
+          override: true
+          components: clippy
+      - uses: Swatinem/rust-cache@v1
       # Run clippy
       - name: "clippy --all"
         run: cargo clippy --all --tests --all-features
@@ -277,38 +371,95 @@ jobs:
     name: docs
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_nightly }}
+        uses: actions-rs/toolchain@v1
         with:
-          toolchain: ${{ env.nightly }}
+          toolchain: ${{ env.rust_nightly }}
           override: true
-
+      - uses: Swatinem/rust-cache@v1
       - name: "doc --lib --all-features"
         run: cargo doc --lib --no-deps --all-features --document-private-items
         env:
-          RUSTDOCFLAGS: --cfg docsrs -Dwarnings
+          RUSTFLAGS: --cfg docsrs --cfg tokio_unstable
+          RUSTDOCFLAGS: --cfg docsrs --cfg tokio_unstable -Dwarnings
 
-  loom:
-    name: loom
+  loom-compile:
+    name: build loom tests
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        scope:
-          - --skip loom_pool
-          - loom_pool::group_a
-          - loom_pool::group_b
-          - loom_pool::group_c
-          - loom_pool::group_d
-          - time::driver
     steps:
-      - uses: actions/checkout@v2
-      - name: Install Rust
-        run: rustup update stable
-
-      - name: loom ${{ matrix.scope }}
-        run: cargo test --lib --release --features full -- --nocapture $SCOPE
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ env.rust_stable }}
+          override: true
+      - uses: Swatinem/rust-cache@v1
+      - name: build --cfg loom
+        run: cargo test --no-run --lib --features full
         working-directory: tokio
         env:
           RUSTFLAGS: --cfg loom --cfg tokio_unstable -Dwarnings
-          LOOM_MAX_PREEMPTIONS: 2
-          SCOPE: ${{ matrix.scope }}
+
+  check-readme:
+    name: Check README
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Verify that both READMEs are identical
+        run: diff README.md tokio/README.md
+
+      - name: Verify that Tokio version is up to date in README
+        working-directory: tokio
+        run: grep -q "$(sed '/^version = /!d' Cargo.toml | head -n1)" README.md
+
+  test-hyper:
+    name: Test hyper
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os:
+          - windows-latest
+          - ubuntu-latest
+          - macos-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ env.rust_stable }}
+          override: true
+      - uses: Swatinem/rust-cache@v1
+      - name: Test hyper
+        run: |
+          set -x
+          git clone https://github.com/hyperium/hyper.git
+          cd hyper
+          # checkout the latest release because HEAD maybe contains breakage.
+          tag=$(git describe --abbrev=0 --tags)
+          git checkout "${tag}"
+          echo '[workspace]' >>Cargo.toml
+          echo '[patch.crates-io]' >>Cargo.toml
+          echo 'tokio = { path = "../tokio" }' >>Cargo.toml
+          echo 'tokio-util = { path = "../tokio-util" }' >>Cargo.toml
+          echo 'tokio-stream = { path = "../tokio-stream" }' >>Cargo.toml
+          echo 'tokio-test = { path = "../tokio-test" }' >>Cargo.toml
+          git diff
+          cargo test --features full
+
+  wasm32-unknown-unknown:
+    name: test tokio for wasm32-unknown-unknown
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ env.rust_stable }}
+          override: true
+      - uses: Swatinem/rust-cache@v1
+      - name: Install wasm-pack
+        run: curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
+      - name: test tokio
+        run: wasm-pack test --node -- --features "macros sync"
+        working-directory: tokio

.github/workflows/labeler.yml

@@ -0,0 +1,14 @@
+name: "Pull Request Labeler"
+on:
+- pull_request_target
+
+# See .github/labeler.yml file
+
+jobs:
+  triage:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/labeler@v3
+      with:
+        repo-token: "${{ secrets.GITHUB_TOKEN }}"
+        sync-labels: true

.github/workflows/loom.yml

@@ -0,0 +1,45 @@
+on:
+  push:
+    branches: ["master", "tokio-*.x"]
+  pull_request:
+    types: [labeled, opened, synchronize, reopened]
+    branches: ["master", "tokio-*.x"]
+
+name: Loom
+
+env:
+  RUSTFLAGS: -Dwarnings
+  RUST_BACKTRACE: 1
+  # Change to specific Rust release to pin
+  rust_stable: stable
+
+jobs:
+  loom:
+    name: loom
+    # base_ref is null when it's not a pull request
+    if: contains(github.event.pull_request.labels.*.name, 'R-loom') || (github.base_ref == null)
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        scope:
+          - --skip loom_pool
+          - loom_pool::group_a
+          - loom_pool::group_b
+          - loom_pool::group_c
+          - loom_pool::group_d
+          - time::driver
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: ${{ env.rust_stable }}
+            override: true
+      - uses: Swatinem/rust-cache@v1
+      - name: loom ${{ matrix.scope }}
+        run: cargo test --lib --release --features full -- --nocapture $SCOPE
+        working-directory: tokio
+        env:
+          RUSTFLAGS: --cfg loom --cfg tokio_unstable -Dwarnings
+          LOOM_MAX_PREEMPTIONS: 2
+          SCOPE: ${{ matrix.scope }}

.github/workflows/pr-audit.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     if: "!contains(github.event.head_commit.message, 'ci skip')"
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
       - name: Install cargo-audit
         uses: actions-rs/cargo@v1

.github/workflows/stress-test.yml

@@ -5,6 +5,12 @@ on:
     branches:
       - master
 
+env:
+  RUSTFLAGS: -Dwarnings
+  RUST_BACKTRACE: 1
+  # Change to specific Rust release to pin
+  rust_stable: stable
+
 jobs:
   stess-test:
     name: Stress Test
@@ -14,10 +20,13 @@ jobs:
         stress-test:
           - simple_echo_tcp
     steps:
-      - uses: actions/checkout@v2
-      - name: Install Rust
-        run: rustup update stable
-
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: ${{ env.rust_stable }}
+            override: true
+      - uses: Swatinem/rust-cache@v1
       - name: Install Valgrind
         run: |
           sudo apt-get update -y

.gitignore

@@ -1,2 +1,4 @@
 target
 Cargo.lock
+
+.cargo/config.toml

CONTRIBUTING.md

@@ -131,6 +131,24 @@ cargo check --all-features
 cargo test --all-features
 ```
 
+Clippy must be run using the MSRV, so Tokio can avoid having to `#[allow]` new
+lints whose fixes would be incompatible with the current MSRV:
+
+<!--
+When updating this, also update:
+- .github/workflows/ci.yml
+- README.md
+- tokio/README.md
+- tokio/Cargo.toml
+- tokio-util/Cargo.toml
+- tokio-test/Cargo.toml
+- tokio-stream/Cargo.toml
+-->
+
+```
+cargo +1.49.0 clippy --all-features
+```
+
 When building documentation normally, the markers that list the features
 required for various parts of Tokio are missing. To build the documentation
 correctly, use this command:
@@ -139,6 +157,14 @@ correctly, use this command:
 RUSTDOCFLAGS="--cfg docsrs" cargo +nightly doc --all-features
 ```
 
+To build documentation including Tokio's unstable features, it is necessary to
+pass `--cfg tokio_unstable` to both RustDoc *and* rustc. To build the
+documentation for unstable features, use this command:
+
+```
+RUSTDOCFLAGS="--cfg docsrs --cfg tokio_unstable" RUSTFLAGS="--cfg tokio_unstable" cargo +nightly doc --all-features
+```
+
 There is currently a [bug in cargo] that means documentation cannot be built
 from the root of the workspace. If you `cd` into the `tokio` subdirectory the
 command shown above will work.
@@ -150,7 +176,7 @@ command below instead:
 
 ```
 # Mac or Linux
-rustfmt --check --edition 2018 $(find . -name '*.rs' -print)
+rustfmt --check --edition 2018 $(git ls-files '*.rs')
 
 # Powershell
 Get-ChildItem . -Filter "*.rs" -Recurse | foreach { rustfmt --check --edition 2018 $_.FullName }
@@ -165,6 +191,12 @@ LOOM_MAX_PREEMPTIONS=1 RUSTFLAGS="--cfg loom" \
     cargo test --lib --release --features full -- --test-threads=1 --nocapture
 ```
 
+You can run miri tests with
+```
+MIRIFLAGS="-Zmiri-disable-isolation -Zmiri-tag-raw-pointers" PROPTEST_CASES=10 \
+    cargo +nightly miri test --features full --lib
+```
+
 ### Tests
 
 If the change being proposed alters code (as opposed to only documentation for

Cross.toml

@@ -0,0 +1,4 @@
+[build.env]
+passthrough = [
+    "RUSTFLAGS",
+]

LICENSE

@@ -1,4 +1,4 @@
-Copyright (c) 2021 Tokio Contributors
+Copyright (c) 2022 Tokio Contributors
 
 Permission is hereby granted, free of charge, to any
 person obtaining a copy of this software and associated

README.md

@@ -56,7 +56,7 @@ Make sure you activated the full features of the tokio crate on Cargo.toml:
 
 ```toml
 [dependencies]
-tokio = { version = "1.7.0", features = ["full"] }
+tokio = { version = "1.19.0", features = ["full"] }
 ```
 Then, on your main.rs:
 
@@ -140,8 +140,7 @@ several other libraries, including:
 
 * [`tower`]: A library of modular and reusable components for building robust networking clients and servers.
 
-* [`tracing`] (formerly `tokio-trace`): A framework for application-level
-  tracing and async-aware diagnostics.
+* [`tracing`] (formerly `tokio-trace`): A framework for application-level tracing and async-aware diagnostics.
 
 * [`rdbc`]: A Rust database connectivity library for MySQL, Postgres and SQLite.
 
@@ -164,9 +163,48 @@ several other libraries, including:
 
 ## Supported Rust Versions
 
-Tokio is built against the latest stable release. The minimum supported version is 1.45.
-The current Tokio version is not guaranteed to build on Rust versions earlier than the
-minimum supported version.
+<!--
+When updating this, also update:
+- .github/workflows/ci.yml
+- CONTRIBUTING.md
+- README.md
+- tokio/README.md
+- tokio/Cargo.toml
+- tokio-util/Cargo.toml
+- tokio-test/Cargo.toml
+- tokio-stream/Cargo.toml
+-->
+
+Tokio will keep a rolling MSRV (minimum supported rust version) policy of **at
+least** 6 months. When increasing the MSRV, the new Rust version must have been
+released at least six months ago. The current MSRV is 1.49.0.
+
+## Release schedule
+
+Tokio doesn't follow a fixed release schedule, but we typically make one to two
+new minor releases each month. We make patch releases for bugfixes as necessary.
+
+## Bug patching policy
+
+For the purposes of making patch releases with bugfixes, we have designated
+certain minor releases as LTS (long term support) releases. Whenever a bug
+warrants a patch release with a fix for the bug, it will be backported and
+released as a new patch release for each LTS minor version. Our current LTS
+releases are:
+
+ * `1.14.x` - LTS release until June 2022.
+ * `1.18.x` - LTS release until January 2023
+
+Each LTS release will continue to receive backported fixes for at least half a
+year. If you wish to use a fixed minor release in your project, we recommend
+that you use an LTS release.
+
+To use a fixed minor version, you can specify the version with a tilde. For
+example, to specify that you wish to use the newest `1.14.x` patch release, you
+can use the following dependency specification:
+```text
+tokio = { version = "~1.14", features = [...] }
+```
 
 ## License
 

benches/Cargo.toml

@@ -9,7 +9,7 @@ tokio = { version = "1.5.0", path = "../tokio", features = ["full"] }
 bencher = "0.1.5"
 
 [dev-dependencies]
-tokio-util = { version = "0.6.6", path = "../tokio-util", features = ["full"] }
+tokio-util = { version = "0.7.0", path = "../tokio-util", features = ["full"] }
 tokio-stream = { path = "../tokio-stream" }
 
 [target.'cfg(unix)'.dependencies]

benches/fs.rs

@@ -21,7 +21,7 @@ fn rt() -> tokio::runtime::Runtime {
 const BLOCK_COUNT: usize = 1_000;
 
 const BUFFER_SIZE: usize = 4096;
-const DEV_ZERO: &'static str = "/dev/zero";
+const DEV_ZERO: &str = "/dev/zero";
 
 fn async_read_codec(b: &mut Bencher) {
     let rt = rt();

benches/rt_multi_threaded.rs

@@ -1,4 +1,4 @@
-//! Benchmark implementation details of the theaded scheduler. These benches are
+//! Benchmark implementation details of the threaded scheduler. These benches are
 //! intended to be used as a form of regression testing and not as a general
 //! purpose benchmark demonstrating real-world performance.
 

benches/spawn.rs

@@ -2,63 +2,83 @@
 //! This essentially measure the time to enqueue a task in the local and remote
 //! case.
 
+#[macro_use]
+extern crate bencher;
+
 use bencher::{black_box, Bencher};
 
 async fn work() -> usize {
     let val = 1 + 1;
+    tokio::task::yield_now().await;
     black_box(val)
 }
 
-fn basic_scheduler_local_spawn(bench: &mut Bencher) {
+fn basic_scheduler_spawn(bench: &mut Bencher) {
     let runtime = tokio::runtime::Builder::new_current_thread()
         .build()
         .unwrap();
-    runtime.block_on(async {
-        bench.iter(|| {
-            let h = tokio::spawn(work());
-            black_box(h);
-        })
-    });
-}
-
-fn threaded_scheduler_local_spawn(bench: &mut Bencher) {
-    let runtime = tokio::runtime::Builder::new_current_thread()
-        .build()
-        .unwrap();
-    runtime.block_on(async {
-        bench.iter(|| {
-            let h = tokio::spawn(work());
-            black_box(h);
-        })
-    });
-}
-
-fn basic_scheduler_remote_spawn(bench: &mut Bencher) {
-    let runtime = tokio::runtime::Builder::new_current_thread()
-        .build()
-        .unwrap();
-
     bench.iter(|| {
-        let h = runtime.spawn(work());
-        black_box(h);
+        runtime.block_on(async {
+            let h = tokio::spawn(work());
+            assert_eq!(h.await.unwrap(), 2);
+        });
     });
 }
 
-fn threaded_scheduler_remote_spawn(bench: &mut Bencher) {
-    let runtime = tokio::runtime::Builder::new_multi_thread().build().unwrap();
-
+fn basic_scheduler_spawn10(bench: &mut Bencher) {
+    let runtime = tokio::runtime::Builder::new_current_thread()
+        .build()
+        .unwrap();
     bench.iter(|| {
-        let h = runtime.spawn(work());
-        black_box(h);
+        runtime.block_on(async {
+            let mut handles = Vec::with_capacity(10);
+            for _ in 0..10 {
+                handles.push(tokio::spawn(work()));
+            }
+            for handle in handles {
+                assert_eq!(handle.await.unwrap(), 2);
+            }
+        });
+    });
+}
+
+fn threaded_scheduler_spawn(bench: &mut Bencher) {
+    let runtime = tokio::runtime::Builder::new_multi_thread()
+        .worker_threads(1)
+        .build()
+        .unwrap();
+    bench.iter(|| {
+        runtime.block_on(async {
+            let h = tokio::spawn(work());
+            assert_eq!(h.await.unwrap(), 2);
+        });
+    });
+}
+
+fn threaded_scheduler_spawn10(bench: &mut Bencher) {
+    let runtime = tokio::runtime::Builder::new_multi_thread()
+        .worker_threads(1)
+        .build()
+        .unwrap();
+    bench.iter(|| {
+        runtime.block_on(async {
+            let mut handles = Vec::with_capacity(10);
+            for _ in 0..10 {
+                handles.push(tokio::spawn(work()));
+            }
+            for handle in handles {
+                assert_eq!(handle.await.unwrap(), 2);
+            }
+        });
     });
 }
 
 bencher::benchmark_group!(
     spawn,
-    basic_scheduler_local_spawn,
-    threaded_scheduler_local_spawn,
-    basic_scheduler_remote_spawn,
-    threaded_scheduler_remote_spawn
+    basic_scheduler_spawn,
+    basic_scheduler_spawn10,
+    threaded_scheduler_spawn,
+    threaded_scheduler_spawn10,
 );
 
 bencher::benchmark_main!(spawn);

examples/Cargo.toml

@@ -5,14 +5,14 @@ publish = false
 edition = "2018"
 
 # If you copy one of the examples into a new project, you should be using
-# [dependencies] instead.
+# [dependencies] instead, and delete the **path**.
 [dev-dependencies]
-tokio = { version = "1.0.0", path = "../tokio",features = ["full", "tracing"] }
-tokio-util = { version = "0.6.3", path = "../tokio-util",features = ["full"] }
+tokio = { version = "1.0.0", path = "../tokio", features = ["full", "tracing"] }
+tokio-util = { version = "0.7.0", path = "../tokio-util", features = ["full"] }
 tokio-stream = { version = "0.1", path = "../tokio-stream" }
 
 tracing = "0.1"
-tracing-subscriber = { version = "0.2.7", default-features = false, features = ["fmt", "ansi", "env-filter", "chrono", "tracing-log"] }
+tracing-subscriber = { version = "0.3.1", default-features = false, features = ["fmt", "ansi", "env-filter", "tracing-log"] }
 bytes = "1.0.0"
 futures = { version = "0.3.0", features = ["thread-pool"]}
 http = "0.2"
@@ -20,7 +20,7 @@ serde = "1.0"
 serde_derive = "1.0"
 serde_json = "1.0"
 httparse = "1.0"
-time = "0.1"
+httpdate = "1.0"
 once_cell = "1.5.2"
 rand = "0.8.3"
 
@@ -84,6 +84,10 @@ path = "custom-executor-tokio-context.rs"
 name = "named-pipe"
 path = "named-pipe.rs"
 
+[[example]]
+name = "named-pipe-ready"
+path = "named-pipe-ready.rs"
+
 [[example]]
 name = "named-pipe-multi-client"
 path = "named-pipe-multi-client.rs"

examples/named-pipe-ready.rs

@@ -0,0 +1,161 @@
+use std::io;
+
+#[cfg(windows)]
+async fn windows_main() -> io::Result<()> {
+    use tokio::io::Interest;
+    use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
+
+    const PIPE_NAME: &str = r"\\.\pipe\named-pipe-single-client";
+
+    let server = ServerOptions::new().create(PIPE_NAME)?;
+
+    let server = tokio::spawn(async move {
+        // Note: we wait for a client to connect.
+        server.connect().await?;
+
+        let buf = {
+            let mut read_buf = [0u8; 5];
+            let mut read_buf_cursor = 0;
+
+            loop {
+                server.readable().await?;
+
+                let buf = &mut read_buf[read_buf_cursor..];
+
+                match server.try_read(buf) {
+                    Ok(n) => {
+                        read_buf_cursor += n;
+
+                        if read_buf_cursor == read_buf.len() {
+                            break;
+                        }
+                    }
+                    Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+                        continue;
+                    }
+                    Err(e) => {
+                        return Err(e);
+                    }
+                }
+            }
+
+            read_buf
+        };
+
+        {
+            let write_buf = b"pong\n";
+            let mut write_buf_cursor = 0;
+
+            loop {
+                let buf = &write_buf[write_buf_cursor..];
+
+                if buf.is_empty() {
+                    break;
+                }
+
+                server.writable().await?;
+
+                match server.try_write(buf) {
+                    Ok(n) => {
+                        write_buf_cursor += n;
+                    }
+                    Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+                        continue;
+                    }
+                    Err(e) => {
+                        return Err(e);
+                    }
+                }
+            }
+        }
+
+        Ok::<_, io::Error>(buf)
+    });
+
+    let client = tokio::spawn(async move {
+        // There's no need to use a connect loop here, since we know that the
+        // server is already up - `open` was called before spawning any of the
+        // tasks.
+        let client = ClientOptions::new().open(PIPE_NAME)?;
+
+        let mut read_buf = [0u8; 5];
+        let mut read_buf_cursor = 0;
+        let write_buf = b"ping\n";
+        let mut write_buf_cursor = 0;
+
+        loop {
+            let mut interest = Interest::READABLE;
+            if write_buf_cursor < write_buf.len() {
+                interest |= Interest::WRITABLE;
+            }
+
+            let ready = client.ready(interest).await?;
+
+            if ready.is_readable() {
+                let buf = &mut read_buf[read_buf_cursor..];
+
+                match client.try_read(buf) {
+                    Ok(n) => {
+                        read_buf_cursor += n;
+
+                        if read_buf_cursor == read_buf.len() {
+                            break;
+                        }
+                    }
+                    Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+                        continue;
+                    }
+                    Err(e) => {
+                        return Err(e);
+                    }
+                }
+            }
+
+            if ready.is_writable() {
+                let buf = &write_buf[write_buf_cursor..];
+
+                if buf.is_empty() {
+                    continue;
+                }
+
+                match client.try_write(buf) {
+                    Ok(n) => {
+                        write_buf_cursor += n;
+                    }
+                    Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+                        continue;
+                    }
+                    Err(e) => {
+                        return Err(e);
+                    }
+                }
+            }
+        }
+
+        let buf = String::from_utf8_lossy(&read_buf).into_owned();
+
+        Ok::<_, io::Error>(buf)
+    });
+
+    let (server, client) = tokio::try_join!(server, client)?;
+
+    assert_eq!(server?, *b"ping\n");
+    assert_eq!(client?, "pong\n");
+
+    Ok(())
+}
+
+#[tokio::main]
+async fn main() -> io::Result<()> {
+    #[cfg(windows)]
+    {
+        windows_main().await?;
+    }
+
+    #[cfg(not(windows))]
+    {
+        println!("Named pipes are only supported on Windows!");
+    }
+
+    Ok(())
+}

examples/tinydb.rs

@@ -149,7 +149,7 @@ async fn main() -> Result<(), Box<dyn Error>> {
 }
 
 fn handle_request(line: &str, db: &Arc<Database>) -> Response {
-    let request = match Request::parse(&line) {
+    let request = match Request::parse(line) {
         Ok(req) => req,
         Err(e) => return Response::Error { msg: e },
     };

examples/tinyhttp.rs

@@ -221,8 +221,9 @@ mod date {
     use std::cell::RefCell;
     use std::fmt::{self, Write};
     use std::str;
+    use std::time::SystemTime;
 
-    use time::{self, Duration};
+    use httpdate::HttpDate;
 
     pub struct Now(());
 
@@ -252,22 +253,26 @@ mod date {
     struct LastRenderedNow {
         bytes: [u8; 128],
         amt: usize,
-        next_update: time::Timespec,
+        unix_date: u64,
     }
 
     thread_local!(static LAST: RefCell<LastRenderedNow> = RefCell::new(LastRenderedNow {
         bytes: [0; 128],
         amt: 0,
-        next_update: time::Timespec::new(0, 0),
+        unix_date: 0,
     }));
 
     impl fmt::Display for Now {
         fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
             LAST.with(|cache| {
                 let mut cache = cache.borrow_mut();
-                let now = time::get_time();
-                if now >= cache.next_update {
-                    cache.update(now);
+                let now = SystemTime::now();
+                let now_unix = now
+                    .duration_since(SystemTime::UNIX_EPOCH)
+                    .map(|since_epoch| since_epoch.as_secs())
+                    .unwrap_or(0);
+                if cache.unix_date != now_unix {
+                    cache.update(now, now_unix);
                 }
                 f.write_str(cache.buffer())
             })
@@ -279,11 +284,10 @@ mod date {
             str::from_utf8(&self.bytes[..self.amt]).unwrap()
         }
 
-        fn update(&mut self, now: time::Timespec) {
+        fn update(&mut self, now: SystemTime, now_unix: u64) {
             self.amt = 0;
-            write!(LocalBuffer(self), "{}", time::at(now).rfc822()).unwrap();
-            self.next_update = now + Duration::seconds(1);
-            self.next_update.nsec = 0;
+            self.unix_date = now_unix;
+            write!(LocalBuffer(self), "{}", HttpDate::from(now)).unwrap();
         }
     }
 

netlify.toml

@@ -0,0 +1,16 @@
+[build]
+  command = """
+    rustup install nightly --profile minimal && cargo doc --no-deps --all-features
+    """
+  publish = "target/doc"
+
+[build.environment]
+  RUSTDOCFLAGS="""
+    --cfg docsrs \
+    --cfg tokio_unstable \
+    """
+  RUSTFLAGS="--cfg tokio_unstable --cfg docsrs"
+
+[[redirects]]
+  from = "/"
+  to = "/tokio"

tests-build/tests/fail/macros_core_no_default.stderr

@@ -1,7 +1,7 @@
 error: The default runtime flavor is `multi_thread`, but the `rt-multi-thread` feature is disabled.
- --> $DIR/macros_core_no_default.rs:3:1
+ --> tests/fail/macros_core_no_default.rs:3:1
   |
 3 | #[tokio::main]
   | ^^^^^^^^^^^^^^
   |
-  = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)
+  = note: this error originates in the attribute macro `tokio::main` (in Nightly builds, run with -Z macro-backtrace for more info)

tests-build/tests/fail/macros_invalid_input.rs

@@ -1,3 +1,5 @@
+#![deny(duplicate_macro_attributes)]
+
 use tests_build::tokio;
 
 #[tokio::main]
@@ -33,6 +35,15 @@ async fn test_worker_threads_not_int() {}
 #[tokio::test(flavor = "current_thread", worker_threads = 4)]
 async fn test_worker_threads_and_current_thread() {}
 
+#[tokio::test(crate = 456)]
+async fn test_crate_not_ident_int() {}
+
+#[tokio::test(crate = "456")]
+async fn test_crate_not_ident_invalid() {}
+
+#[tokio::test(crate = "abc::edf")]
+async fn test_crate_not_ident_path() {}
+
 #[tokio::test]
 #[test]
 async fn test_has_second_test_attr() {}

tests-build/tests/fail/macros_invalid_input.stderr

@@ -1,71 +1,101 @@
 error: the `async` keyword is missing from the function declaration
- --> $DIR/macros_invalid_input.rs:4:1
+ --> $DIR/macros_invalid_input.rs:6:1
   |
-4 | fn main_is_not_async() {}
+6 | fn main_is_not_async() {}
   | ^^
 
-error: Unknown attribute foo is specified; expected one of: `flavor`, `worker_threads`, `start_paused`
- --> $DIR/macros_invalid_input.rs:6:15
+error: Unknown attribute foo is specified; expected one of: `flavor`, `worker_threads`, `start_paused`, `crate`
+ --> $DIR/macros_invalid_input.rs:8:15
   |
-6 | #[tokio::main(foo)]
+8 | #[tokio::main(foo)]
   |               ^^^
 
 error: Must have specified ident
- --> $DIR/macros_invalid_input.rs:9:15
-  |
-9 | #[tokio::main(threadpool::bar)]
-  |               ^^^^^^^^^^^^^^^
+  --> $DIR/macros_invalid_input.rs:11:15
+   |
+11 | #[tokio::main(threadpool::bar)]
+   |               ^^^^^^^^^^^^^^^
 
 error: the `async` keyword is missing from the function declaration
-  --> $DIR/macros_invalid_input.rs:13:1
+  --> $DIR/macros_invalid_input.rs:15:1
    |
-13 | fn test_is_not_async() {}
+15 | fn test_is_not_async() {}
    | ^^
 
-error: Unknown attribute foo is specified; expected one of: `flavor`, `worker_threads`, `start_paused`
-  --> $DIR/macros_invalid_input.rs:15:15
+error: Unknown attribute foo is specified; expected one of: `flavor`, `worker_threads`, `start_paused`, `crate`
+  --> $DIR/macros_invalid_input.rs:17:15
    |
-15 | #[tokio::test(foo)]
+17 | #[tokio::test(foo)]
    |               ^^^
 
-error: Unknown attribute foo is specified; expected one of: `flavor`, `worker_threads`, `start_paused`
-  --> $DIR/macros_invalid_input.rs:18:15
+error: Unknown attribute foo is specified; expected one of: `flavor`, `worker_threads`, `start_paused`, `crate`
+  --> $DIR/macros_invalid_input.rs:20:15
    |
-18 | #[tokio::test(foo = 123)]
+20 | #[tokio::test(foo = 123)]
    |               ^^^^^^^^^
 
 error: Failed to parse value of `flavor` as string.
-  --> $DIR/macros_invalid_input.rs:21:24
+  --> $DIR/macros_invalid_input.rs:23:24
    |
-21 | #[tokio::test(flavor = 123)]
+23 | #[tokio::test(flavor = 123)]
    |                        ^^^
 
 error: No such runtime flavor `foo`. The runtime flavors are `current_thread` and `multi_thread`.
-  --> $DIR/macros_invalid_input.rs:24:24
+  --> $DIR/macros_invalid_input.rs:26:24
    |
-24 | #[tokio::test(flavor = "foo")]
+26 | #[tokio::test(flavor = "foo")]
    |                        ^^^^^
 
 error: The `start_paused` option requires the `current_thread` runtime flavor. Use `#[tokio::test(flavor = "current_thread")]`
-  --> $DIR/macros_invalid_input.rs:27:55
+  --> $DIR/macros_invalid_input.rs:29:55
    |
-27 | #[tokio::test(flavor = "multi_thread", start_paused = false)]
+29 | #[tokio::test(flavor = "multi_thread", start_paused = false)]
    |                                                       ^^^^^
 
 error: Failed to parse value of `worker_threads` as integer.
-  --> $DIR/macros_invalid_input.rs:30:57
+  --> $DIR/macros_invalid_input.rs:32:57
    |
-30 | #[tokio::test(flavor = "multi_thread", worker_threads = "foo")]
+32 | #[tokio::test(flavor = "multi_thread", worker_threads = "foo")]
    |                                                         ^^^^^
 
 error: The `worker_threads` option requires the `multi_thread` runtime flavor. Use `#[tokio::test(flavor = "multi_thread")]`
-  --> $DIR/macros_invalid_input.rs:33:59
+  --> $DIR/macros_invalid_input.rs:35:59
    |
-33 | #[tokio::test(flavor = "current_thread", worker_threads = 4)]
+35 | #[tokio::test(flavor = "current_thread", worker_threads = 4)]
    |                                                           ^
 
-error: second test attribute is supplied
-  --> $DIR/macros_invalid_input.rs:37:1
+error: Failed to parse value of `crate` as ident.
+  --> $DIR/macros_invalid_input.rs:38:23
    |
-37 | #[test]
+38 | #[tokio::test(crate = 456)]
+   |                       ^^^
+
+error: Failed to parse value of `crate` as ident: "456"
+  --> $DIR/macros_invalid_input.rs:41:23
+   |
+41 | #[tokio::test(crate = "456")]
+   |                       ^^^^^
+
+error: Failed to parse value of `crate` as ident: "abc::edf"
+  --> $DIR/macros_invalid_input.rs:44:23
+   |
+44 | #[tokio::test(crate = "abc::edf")]
+   |                       ^^^^^^^^^^
+
+error: second test attribute is supplied
+  --> $DIR/macros_invalid_input.rs:48:1
+   |
+48 | #[test]
    | ^^^^^^^
+
+error: duplicated attribute
+  --> $DIR/macros_invalid_input.rs:48:1
+   |
+48 | #[test]
+   | ^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/macros_invalid_input.rs:1:9
+   |
+1  | #![deny(duplicate_macro_attributes)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^

tests-build/tests/fail/macros_type_mismatch.rs

@@ -7,12 +7,6 @@ async fn missing_semicolon_or_return_type() {
 
 #[tokio::main]
 async fn missing_return_type() {
-    /* TODO(taiki-e): one of help messages still wrong
-    help: consider using a semicolon here
-       |
-    16 |     return Ok(());;
-       |
-    */
     return Ok(());
 }
 
@@ -21,12 +15,21 @@ async fn extra_semicolon() -> Result<(), ()> {
     /* TODO(taiki-e): help message still wrong
     help: try using a variant of the expected enum
        |
-    29 |     Ok(Ok(());)
+    23 |     Ok(Ok(());)
        |
-    29 |     Err(Ok(());)
+    23 |     Err(Ok(());)
        |
     */
     Ok(());
 }
 
+// https://github.com/tokio-rs/tokio/issues/4635
+#[allow(redundant_semicolons)]
+#[rustfmt::skip]
+#[tokio::main]
+async fn issue_4635() {
+    return 1;
+    ;
+}
+
 fn main() {}

tests-build/tests/fail/macros_type_mismatch.stderr

@@ -1,51 +1,47 @@
 error[E0308]: mismatched types
  --> $DIR/macros_type_mismatch.rs:5:5
   |
+4 | async fn missing_semicolon_or_return_type() {
+  |                                             - help: a return type might be missing here: `-> _`
 5 |     Ok(())
   |     ^^^^^^ expected `()`, found enum `Result`
   |
   = note: expected unit type `()`
                   found enum `Result<(), _>`
-help: consider using a semicolon here
-  |
-5 |     Ok(());
-  |           ^
-help: try adding a return type
-  |
-4 | async fn missing_semicolon_or_return_type() -> Result<(), _> {
-  |                                             ^^^^^^^^^^^^^^^^
 
 error[E0308]: mismatched types
-  --> $DIR/macros_type_mismatch.rs:16:5
+  --> $DIR/macros_type_mismatch.rs:10:5
    |
-16 |     return Ok(());
+9  | async fn missing_return_type() {
+   |                                - help: a return type might be missing here: `-> _`
+10 |     return Ok(());
    |     ^^^^^^^^^^^^^^ expected `()`, found enum `Result`
    |
    = note: expected unit type `()`
                    found enum `Result<(), _>`
-help: consider using a semicolon here
-   |
-16 |     return Ok(());;
-   |                   ^
-help: try adding a return type
-   |
-9  | async fn missing_return_type() -> Result<(), _> {
-   |                                ^^^^^^^^^^^^^^^^
 
 error[E0308]: mismatched types
-  --> $DIR/macros_type_mismatch.rs:29:5
+  --> $DIR/macros_type_mismatch.rs:23:5
    |
-20 | async fn extra_semicolon() -> Result<(), ()> {
+14 | async fn extra_semicolon() -> Result<(), ()> {
    |                               -------------- expected `Result<(), ()>` because of return type
 ...
-29 |     Ok(());
+23 |     Ok(());
    |     ^^^^^^^ expected enum `Result`, found `()`
    |
    = note:   expected enum `Result<(), ()>`
            found unit type `()`
-help: try using a variant of the expected enum
+help: try adding an expression at the end of the block
    |
-29 |     Ok(Ok(());)
+23 ~     Ok(());;
+24 +     Ok(())
    |
-29 |     Err(Ok(());)
+
+error[E0308]: mismatched types
+  --> $DIR/macros_type_mismatch.rs:32:5
    |
+30 | async fn issue_4635() {
+   |                       - help: try adding a return type: `-> i32`
+31 |     return 1;
+32 |     ;
+   |     ^ expected `()`, found integer

tests-build/tests/macros.rs

@@ -5,6 +5,12 @@ fn compile_fail_full() {
     #[cfg(feature = "full")]
     t.pass("tests/pass/forward_args_and_output.rs");
 
+    #[cfg(feature = "full")]
+    t.pass("tests/pass/macros_main_return.rs");
+
+    #[cfg(feature = "full")]
+    t.pass("tests/pass/macros_main_loop.rs");
+
     #[cfg(feature = "full")]
     t.compile_fail("tests/fail/macros_invalid_input.rs");
 

tests-build/tests/macros_clippy.rs

@@ -0,0 +1,7 @@
+#[cfg(feature = "full")]
+#[tokio::test]
+async fn test_with_semicolon_without_return_type() {
+    #![deny(clippy::semicolon_if_nothing_returned)]
+
+    dbg!(0);
+}

tests-build/tests/pass/macros_main_loop.rs

@@ -0,0 +1,14 @@
+use tests_build::tokio;
+
+#[tokio::main]
+async fn main() -> Result<(), ()> {
+    loop {
+        if !never() {
+            return Ok(());
+        }
+    }
+}
+
+fn never() -> bool {
+    std::time::Instant::now() > std::time::Instant::now()
+}

tests-build/tests/pass/macros_main_return.rs

@@ -0,0 +1,6 @@
+use tests_build::tokio;
+
+#[tokio::main]
+async fn main() -> Result<(), ()> {
+    return Ok(());
+}

tests-integration/Cargo.toml

@@ -20,7 +20,7 @@ required-features = ["rt-process-signal"]
 # For mem check
 rt-net = ["tokio/rt", "tokio/rt-multi-thread", "tokio/net"]
 # For test-process-signal
-rt-process-signal = ["rt", "tokio/process", "tokio/signal"]
+rt-process-signal = ["rt-net", "tokio/process", "tokio/signal"]
 
 full = [
     "macros",

tokio-macros/CHANGELOG.md

@@ -1,3 +1,62 @@
+# 1.8.0 (June 4th, 2022)
+
+- macros: always emit return statement ([#4636])
+- macros: support setting a custom crate name for `#[tokio::main]` and `#[tokio::test]` ([#4613])
+
+[#4613]: https://github.com/tokio-rs/tokio/pull/4613
+[#4636]: https://github.com/tokio-rs/tokio/pull/4636
+
+# 1.7.0 (December 15th, 2021)
+
+- macros: address remaining `clippy::semicolon_if_nothing_returned` warning ([#4252])
+
+[#4252]: https://github.com/tokio-rs/tokio/pull/4252
+
+# 1.6.0 (November 16th, 2021)
+
+- macros: fix mut patterns in `select!` macro ([#4211])
+
+[#4211]: https://github.com/tokio-rs/tokio/pull/4211
+
+# 1.5.1 (October 29th, 2021)
+
+- macros: fix type resolution error in `#[tokio::main]` ([#4176])
+
+[#4176]: https://github.com/tokio-rs/tokio/pull/4176
+
+# 1.5.0 (October 13th, 2021)
+
+- macros: make tokio-macros attributes more IDE friendly ([#4162])
+
+[#4162]: https://github.com/tokio-rs/tokio/pull/4162
+
+# 1.4.1 (September 30th, 2021)
+
+Reverted: run `current_thread` inside `LocalSet` ([#4027])
+
+# 1.4.0 (September 29th, 2021)
+
+(yanked)
+
+### Changed
+
+- macros: run `current_thread` inside `LocalSet` ([#4027])
+- macros: explicitly relaxed clippy lint for `.expect()` in runtime entry macro ([#4030])
+
+### Fixed
+
+- macros: fix invalid error messages in functions wrapped with `#[main]` or `#[test]` ([#4067])
+
+[#4027]: https://github.com/tokio-rs/tokio/pull/4027
+[#4030]: https://github.com/tokio-rs/tokio/pull/4030
+[#4067]: https://github.com/tokio-rs/tokio/pull/4067
+
+# 1.3.0 (July 7, 2021)
+
+- macros: don't trigger `clippy::unwrap_used` ([#3926])
+
+[#3926]: https://github.com/tokio-rs/tokio/pull/3926
+
 # 1.2.0 (May 14, 2021)
 
 - macros: forward input arguments in `#[tokio::test]` ([#3691])

tokio-macros/Cargo.toml

@@ -2,17 +2,15 @@
 name = "tokio-macros"
 # When releasing to crates.io:
 # - Remove path dependencies
-# - Update doc url
-#   - Cargo.toml
 # - Update CHANGELOG.md.
 # - Create "tokio-macros-1.0.x" git tag.
-version = "1.2.0"
+version = "1.8.0"
 edition = "2018"
+rust-version = "1.49"
 authors = ["Tokio Contributors <[email protected]>"]
 license = "MIT"
 repository = "https://github.com/tokio-rs/tokio"
 homepage = "https://tokio.rs"
-documentation = "https://docs.rs/tokio-macros/1.2.0/tokio_macros"
 description = """
 Tokio's proc macros.
 """

tokio-macros/LICENSE

@@ -1,4 +1,4 @@
-Copyright (c) 2021 Tokio Contributors
+Copyright (c) 2022 Tokio Contributors
 
 Permission is hereby granted, free of charge, to any
 person obtaining a copy of this software and associated

tokio-macros/src/entry.rs

@@ -1,6 +1,10 @@
 use proc_macro::TokenStream;
-use proc_macro2::Span;
+use proc_macro2::{Ident, Span};
 use quote::{quote, quote_spanned, ToTokens};
+use syn::parse::Parser;
+
+// syn::AttributeArgs does not implement syn::Parse
+type AttributeArgs = syn::punctuated::Punctuated<syn::NestedMeta, syn::Token![,]>;
 
 #[derive(Clone, Copy, PartialEq)]
 enum RuntimeFlavor {
@@ -25,8 +29,17 @@ struct FinalConfig {
     flavor: RuntimeFlavor,
     worker_threads: Option<usize>,
     start_paused: Option<bool>,
+    crate_name: Option<String>,
 }
 
+/// Config used in case of the attribute not being able to build a valid config
+const DEFAULT_ERROR_CONFIG: FinalConfig = FinalConfig {
+    flavor: RuntimeFlavor::CurrentThread,
+    worker_threads: None,
+    start_paused: None,
+    crate_name: None,
+};
+
 struct Configuration {
     rt_multi_thread_available: bool,
     default_flavor: RuntimeFlavor,
@@ -34,6 +47,7 @@ struct Configuration {
     worker_threads: Option<(usize, Span)>,
     start_paused: Option<(bool, Span)>,
     is_test: bool,
+    crate_name: Option<String>,
 }
 
 impl Configuration {
@@ -48,6 +62,7 @@ impl Configuration {
             worker_threads: None,
             start_paused: None,
             is_test,
+            crate_name: None,
         }
     }
 
@@ -93,6 +108,15 @@ impl Configuration {
         Ok(())
     }
 
+    fn set_crate_name(&mut self, name: syn::Lit, span: Span) -> Result<(), syn::Error> {
+        if self.crate_name.is_some() {
+            return Err(syn::Error::new(span, "`crate` set multiple times."));
+        }
+        let name_ident = parse_ident(name, span, "crate")?;
+        self.crate_name = Some(name_ident.to_string());
+        Ok(())
+    }
+
     fn macro_name(&self) -> &'static str {
         if self.is_test {
             "tokio::test"
@@ -140,6 +164,7 @@ impl Configuration {
         };
 
         Ok(FinalConfig {
+            crate_name: self.crate_name.clone(),
             flavor,
             worker_threads,
             start_paused,
@@ -174,6 +199,27 @@ fn parse_string(int: syn::Lit, span: Span, field: &str) -> Result<String, syn::E
     }
 }
 
+fn parse_ident(lit: syn::Lit, span: Span, field: &str) -> Result<Ident, syn::Error> {
+    match lit {
+        syn::Lit::Str(s) => {
+            let err = syn::Error::new(
+                span,
+                format!(
+                    "Failed to parse value of `{}` as ident: \"{}\"",
+                    field,
+                    s.value()
+                ),
+            );
+            let path = s.parse::<syn::Path>().map_err(|_| err.clone())?;
+            path.get_ident().cloned().ok_or(err)
+        }
+        _ => Err(syn::Error::new(
+            span,
+            format!("Failed to parse value of `{}` as ident.", field),
+        )),
+    }
+}
+
 fn parse_bool(bool: syn::Lit, span: Span, field: &str) -> Result<bool, syn::Error> {
     match bool {
         syn::Lit::Bool(b) => Ok(b.value),
@@ -184,13 +230,13 @@ fn parse_bool(bool: syn::Lit, span: Span, field: &str) -> Result<bool, syn::Erro
     }
 }
 
-fn parse_knobs(
-    mut input: syn::ItemFn,
-    args: syn::AttributeArgs,
+fn build_config(
+    input: syn::ItemFn,
+    args: AttributeArgs,
     is_test: bool,
     rt_multi_thread: bool,
-) -> Result<TokenStream, syn::Error> {
-    if input.sig.asyncness.take().is_none() {
+) -> Result<FinalConfig, syn::Error> {
+    if input.sig.asyncness.is_none() {
         let msg = "the `async` keyword is missing from the function declaration";
         return Err(syn::Error::new_spanned(input.sig.fn_token, msg));
     }
@@ -201,12 +247,15 @@ fn parse_knobs(
     for arg in args {
         match arg {
             syn::NestedMeta::Meta(syn::Meta::NameValue(namevalue)) => {
-                let ident = namevalue.path.get_ident();
-                if ident.is_none() {
-                    let msg = "Must have specified ident";
-                    return Err(syn::Error::new_spanned(namevalue, msg));
-                }
-                match ident.unwrap().to_string().to_lowercase().as_str() {
+                let ident = namevalue
+                    .path
+                    .get_ident()
+                    .ok_or_else(|| {
+                        syn::Error::new_spanned(&namevalue, "Must have specified ident")
+                    })?
+                    .to_string()
+                    .to_lowercase();
+                match ident.as_str() {
                     "worker_threads" => {
                         config.set_worker_threads(
                             namevalue.lit.clone(),
@@ -229,9 +278,15 @@ fn parse_knobs(
                         let msg = "Attribute `core_threads` is renamed to `worker_threads`";
                         return Err(syn::Error::new_spanned(namevalue, msg));
                     }
+                    "crate" => {
+                        config.set_crate_name(
+                            namevalue.lit.clone(),
+                            syn::spanned::Spanned::span(&namevalue.lit),
+                        )?;
+                    }
                     name => {
                         let msg = format!(
-                            "Unknown attribute {} is specified; expected one of: `flavor`, `worker_threads`, `start_paused`",
+                            "Unknown attribute {} is specified; expected one of: `flavor`, `worker_threads`, `start_paused`, `crate`",
                             name,
                         );
                         return Err(syn::Error::new_spanned(namevalue, msg));
@@ -239,12 +294,11 @@ fn parse_knobs(
                 }
             }
             syn::NestedMeta::Meta(syn::Meta::Path(path)) => {
-                let ident = path.get_ident();
-                if ident.is_none() {
-                    let msg = "Must have specified ident";
-                    return Err(syn::Error::new_spanned(path, msg));
-                }
-                let name = ident.unwrap().to_string().to_lowercase();
+                let name = path
+                    .get_ident()
+                    .ok_or_else(|| syn::Error::new_spanned(&path, "Must have specified ident"))?
+                    .to_string()
+                    .to_lowercase();
                 let msg = match name.as_str() {
                     "threaded_scheduler" | "multi_thread" => {
                         format!(
@@ -262,7 +316,7 @@ fn parse_knobs(
                         format!("The `{}` attribute requires an argument.", name)
                     }
                     name => {
-                        format!("Unknown attribute {} is specified; expected one of: `flavor`, `worker_threads`, `start_paused`", name)
+                        format!("Unknown attribute {} is specified; expected one of: `flavor`, `worker_threads`, `start_paused`, `crate`", name)
                     }
                 };
                 return Err(syn::Error::new_spanned(path, msg));
@@ -276,7 +330,11 @@ fn parse_knobs(
         }
     }
 
-    let config = config.build()?;
+    config.build()
+}
+
+fn parse_knobs(mut input: syn::ItemFn, is_test: bool, config: FinalConfig) -> TokenStream {
+    input.sig.asyncness = None;
 
     // If type mismatch occurs, the current rustc points to the last statement.
     let (last_stmt_start_span, last_stmt_end_span) = {
@@ -296,12 +354,16 @@ fn parse_knobs(
         (start, end)
     };
 
+    let crate_name = config.crate_name.as_deref().unwrap_or("tokio");
+
+    let crate_ident = Ident::new(crate_name, last_stmt_start_span);
+
     let mut rt = match config.flavor {
         RuntimeFlavor::CurrentThread => quote_spanned! {last_stmt_start_span=>
-            tokio::runtime::Builder::new_current_thread()
+            #crate_ident::runtime::Builder::new_current_thread()
         },
         RuntimeFlavor::Threaded => quote_spanned! {last_stmt_start_span=>
-            tokio::runtime::Builder::new_multi_thread()
+            #crate_ident::runtime::Builder::new_multi_thread()
         },
     };
     if let Some(v) = config.worker_threads {
@@ -323,14 +385,18 @@ fn parse_knobs(
     let brace_token = input.block.brace_token;
     input.block = syn::parse2(quote_spanned! {last_stmt_end_span=>
         {
-            #rt
-                .enable_all()
-                .build()
-                .unwrap()
-                .block_on(async #body)
+            let body = async #body;
+            #[allow(clippy::expect_used, clippy::diverging_sub_expression)]
+            {
+                return #rt
+                    .enable_all()
+                    .build()
+                    .expect("Failed building the Runtime")
+                    .block_on(body);
+            }
         }
     })
-    .unwrap();
+    .expect("Parsing failure");
     input.block.brace_token = brace_token;
 
     let result = quote! {
@@ -338,36 +404,58 @@ fn parse_knobs(
         #input
     };
 
-    Ok(result.into())
+    result.into()
+}
+
+fn token_stream_with_error(mut tokens: TokenStream, error: syn::Error) -> TokenStream {
+    tokens.extend(TokenStream::from(error.into_compile_error()));
+    tokens
 }
 
 #[cfg(not(test))] // Work around for rust-lang/rust#62127
 pub(crate) fn main(args: TokenStream, item: TokenStream, rt_multi_thread: bool) -> TokenStream {
-    let input = syn::parse_macro_input!(item as syn::ItemFn);
-    let args = syn::parse_macro_input!(args as syn::AttributeArgs);
+    // If any of the steps for this macro fail, we still want to expand to an item that is as close
+    // to the expected output as possible. This helps out IDEs such that completions and other
+    // related features keep working.
+    let input: syn::ItemFn = match syn::parse(item.clone()) {
+        Ok(it) => it,
+        Err(e) => return token_stream_with_error(item, e),
+    };
 
-    if input.sig.ident == "main" && !input.sig.inputs.is_empty() {
+    let config = if input.sig.ident == "main" && !input.sig.inputs.is_empty() {
         let msg = "the main function cannot accept arguments";
-        return syn::Error::new_spanned(&input.sig.ident, msg)
-            .to_compile_error()
-            .into();
-    }
+        Err(syn::Error::new_spanned(&input.sig.ident, msg))
+    } else {
+        AttributeArgs::parse_terminated
+            .parse(args)
+            .and_then(|args| build_config(input.clone(), args, false, rt_multi_thread))
+    };
 
-    parse_knobs(input, args, false, rt_multi_thread).unwrap_or_else(|e| e.to_compile_error().into())
+    match config {
+        Ok(config) => parse_knobs(input, false, config),
+        Err(e) => token_stream_with_error(parse_knobs(input, false, DEFAULT_ERROR_CONFIG), e),
+    }
 }
 
 pub(crate) fn test(args: TokenStream, item: TokenStream, rt_multi_thread: bool) -> TokenStream {
-    let input = syn::parse_macro_input!(item as syn::ItemFn);
-    let args = syn::parse_macro_input!(args as syn::AttributeArgs);
+    // If any of the steps for this macro fail, we still want to expand to an item that is as close
+    // to the expected output as possible. This helps out IDEs such that completions and other
+    // related features keep working.
+    let input: syn::ItemFn = match syn::parse(item.clone()) {
+        Ok(it) => it,
+        Err(e) => return token_stream_with_error(item, e),
+    };
+    let config = if let Some(attr) = input.attrs.iter().find(|attr| attr.path.is_ident("test")) {
+        let msg = "second test attribute is supplied";
+        Err(syn::Error::new_spanned(&attr, msg))
+    } else {
+        AttributeArgs::parse_terminated
+            .parse(args)
+            .and_then(|args| build_config(input.clone(), args, true, rt_multi_thread))
+    };
 
-    for attr in &input.attrs {
-        if attr.path.is_ident("test") {
-            let msg = "second test attribute is supplied";
-            return syn::Error::new_spanned(&attr, msg)
-                .to_compile_error()
-                .into();
-        }
+    match config {
+        Ok(config) => parse_knobs(input, true, config),
+        Err(e) => token_stream_with_error(parse_knobs(input, true, DEFAULT_ERROR_CONFIG), e),
     }
-
-    parse_knobs(input, args, true, rt_multi_thread).unwrap_or_else(|e| e.to_compile_error().into())
 }

tokio-macros/src/lib.rs

@@ -5,7 +5,6 @@
     rust_2018_idioms,
     unreachable_pub
 )]
-#![cfg_attr(docsrs, deny(broken_intra_doc_links))]
 #![doc(test(
     no_crate_inject,
     attr(deny(warnings, rust_2018_idioms), allow(dead_code, unused_variables))
@@ -169,12 +168,32 @@ use proc_macro::TokenStream;
 ///
 /// Note that `start_paused` requires the `test-util` feature to be enabled.
 ///
-/// ### NOTE:
+/// ### Rename package
 ///
-/// If you rename the Tokio crate in your dependencies this macro will not work.
-/// If you must rename the current version of Tokio because you're also using an
-/// older version of Tokio, you _must_ make the current version of Tokio
-/// available as `tokio` in the module where this macro is expanded.
+/// ```rust
+/// use tokio as tokio1;
+///
+/// #[tokio1::main(crate = "tokio1")]
+/// async fn main() {
+///     println!("Hello world");
+/// }
+/// ```
+///
+/// Equivalent code not using `#[tokio::main]`
+///
+/// ```rust
+/// use tokio as tokio1;
+///
+/// fn main() {
+///     tokio1::runtime::Builder::new_multi_thread()
+///         .enable_all()
+///         .build()
+///         .unwrap()
+///         .block_on(async {
+///             println!("Hello world");
+///         })
+/// }
+/// ```
 #[proc_macro_attribute]
 #[cfg(not(test))] // Work around for rust-lang/rust#62127
 pub fn main(args: TokenStream, item: TokenStream) -> TokenStream {
@@ -214,12 +233,32 @@ pub fn main(args: TokenStream, item: TokenStream) -> TokenStream {
 /// }
 /// ```
 ///
-/// ### NOTE:
+/// ### Rename package
 ///
-/// If you rename the Tokio crate in your dependencies this macro will not work.
-/// If you must rename the current version of Tokio because you're also using an
-/// older version of Tokio, you _must_ make the current version of Tokio
-/// available as `tokio` in the module where this macro is expanded.
+/// ```rust
+/// use tokio as tokio1;
+///
+/// #[tokio1::main(crate = "tokio1")]
+/// async fn main() {
+///     println!("Hello world");
+/// }
+/// ```
+///
+/// Equivalent code not using `#[tokio::main]`
+///
+/// ```rust
+/// use tokio as tokio1;
+///
+/// fn main() {
+///     tokio1::runtime::Builder::new_multi_thread()
+///         .enable_all()
+///         .build()
+///         .unwrap()
+///         .block_on(async {
+///             println!("Hello world");
+///         })
+/// }
+/// ```
 #[proc_macro_attribute]
 #[cfg(not(test))] // Work around for rust-lang/rust#62127
 pub fn main_rt(args: TokenStream, item: TokenStream) -> TokenStream {
@@ -261,12 +300,16 @@ pub fn main_rt(args: TokenStream, item: TokenStream) -> TokenStream {
 ///
 /// Note that `start_paused` requires the `test-util` feature to be enabled.
 ///
-/// ### NOTE:
+/// ### Rename package
 ///
-/// If you rename the Tokio crate in your dependencies this macro will not work.
-/// If you must rename the current version of Tokio because you're also using an
-/// older version of Tokio, you _must_ make the current version of Tokio
-/// available as `tokio` in the module where this macro is expanded.
+/// ```rust
+/// use tokio as tokio1;
+///
+/// #[tokio1::test(crate = "tokio1")]
+/// async fn my_test() {
+///     println!("Hello world");
+/// }
+/// ```
 #[proc_macro_attribute]
 pub fn test(args: TokenStream, item: TokenStream) -> TokenStream {
     entry::test(args, item, true)
@@ -282,13 +325,6 @@ pub fn test(args: TokenStream, item: TokenStream) -> TokenStream {
 ///     assert!(true);
 /// }
 /// ```
-///
-/// ### NOTE:
-///
-/// If you rename the Tokio crate in your dependencies this macro will not work.
-/// If you must rename the current version of Tokio because you're also using an
-/// older version of Tokio, you _must_ make the current version of Tokio
-/// available as `tokio` in the module where this macro is expanded.
 #[proc_macro_attribute]
 pub fn test_rt(args: TokenStream, item: TokenStream) -> TokenStream {
     entry::test(args, item, false)
@@ -329,3 +365,11 @@ pub fn test_fail(_args: TokenStream, _item: TokenStream) -> TokenStream {
 pub fn select_priv_declare_output_enum(input: TokenStream) -> TokenStream {
     select::declare_output_enum(input)
 }
+
+/// Implementation detail of the `select!` macro. This macro is **not** intended
+/// to be used as part of the public API and is permitted to change.
+#[proc_macro]
+#[doc(hidden)]
+pub fn select_priv_clean_pattern(input: TokenStream) -> TokenStream {
+    select::clean_pattern_macro(input)
+}

tokio-macros/src/select.rs

@@ -41,3 +41,70 @@ pub(crate) fn declare_output_enum(input: TokenStream) -> TokenStream {
         pub(super) type Mask = #mask;
     })
 }
+
+pub(crate) fn clean_pattern_macro(input: TokenStream) -> TokenStream {
+    // If this isn't a pattern, we return the token stream as-is. The select!
+    // macro is using it in a location requiring a pattern, so an error will be
+    // emitted there.
+    let mut input: syn::Pat = match syn::parse(input.clone()) {
+        Ok(it) => it,
+        Err(_) => return input,
+    };
+
+    clean_pattern(&mut input);
+    quote::ToTokens::into_token_stream(input).into()
+}
+
+// Removes any occurrences of ref or mut in the provided pattern.
+fn clean_pattern(pat: &mut syn::Pat) {
+    match pat {
+        syn::Pat::Box(_box) => {}
+        syn::Pat::Lit(_literal) => {}
+        syn::Pat::Macro(_macro) => {}
+        syn::Pat::Path(_path) => {}
+        syn::Pat::Range(_range) => {}
+        syn::Pat::Rest(_rest) => {}
+        syn::Pat::Verbatim(_tokens) => {}
+        syn::Pat::Wild(_underscore) => {}
+        syn::Pat::Ident(ident) => {
+            ident.by_ref = None;
+            ident.mutability = None;
+            if let Some((_at, pat)) = &mut ident.subpat {
+                clean_pattern(&mut *pat);
+            }
+        }
+        syn::Pat::Or(or) => {
+            for case in or.cases.iter_mut() {
+                clean_pattern(case);
+            }
+        }
+        syn::Pat::Slice(slice) => {
+            for elem in slice.elems.iter_mut() {
+                clean_pattern(elem);
+            }
+        }
+        syn::Pat::Struct(struct_pat) => {
+            for field in struct_pat.fields.iter_mut() {
+                clean_pattern(&mut field.pat);
+            }
+        }
+        syn::Pat::Tuple(tuple) => {
+            for elem in tuple.elems.iter_mut() {
+                clean_pattern(elem);
+            }
+        }
+        syn::Pat::TupleStruct(tuple) => {
+            for elem in tuple.pat.elems.iter_mut() {
+                clean_pattern(elem);
+            }
+        }
+        syn::Pat::Reference(reference) => {
+            reference.mutability = None;
+            clean_pattern(&mut *reference.pat);
+        }
+        syn::Pat::Type(type_pat) => {
+            clean_pattern(&mut *type_pat.pat);
+        }
+        _ => {}
+    }
+}

tokio-stream/CHANGELOG.md

@@ -1,3 +1,43 @@
+# 0.1.9 (June 4, 2022)
+
+- deps: upgrade `tokio-util` dependency to `0.7.x` ([#3762])
+- stream: add `StreamExt::map_while` ([#4351])
+- stream: add `StreamExt::then` ([#4355])
+- stream: add cancel-safety docs to `StreamExt::next` and `try_next` ([#4715])
+- stream: expose `Elapsed` error ([#4502])
+- stream: expose `Timeout` ([#4601])
+- stream: implement `Extend` for `StreamMap` ([#4272])
+- sync: add `Clone` to `RecvError` types ([#4560])
+
+[#3762]: https://github.com/tokio-rs/tokio/pull/3762
+[#4272]: https://github.com/tokio-rs/tokio/pull/4272
+[#4351]: https://github.com/tokio-rs/tokio/pull/4351
+[#4355]: https://github.com/tokio-rs/tokio/pull/4355
+[#4502]: https://github.com/tokio-rs/tokio/pull/4502
+[#4560]: https://github.com/tokio-rs/tokio/pull/4560
+[#4601]: https://github.com/tokio-rs/tokio/pull/4601
+[#4715]: https://github.com/tokio-rs/tokio/pull/4715
+
+# 0.1.8 (October 29, 2021)
+
+- stream: add `From<Receiver<T>>` impl for receiver streams ([#4080])
+- stream: impl `FromIterator` for `StreamMap` ([#4052])
+- signal: make windows docs for signal module show up on unix builds ([#3770])
+
+[#3770]: https://github.com/tokio-rs/tokio/pull/3770
+[#4052]: https://github.com/tokio-rs/tokio/pull/4052
+[#4080]: https://github.com/tokio-rs/tokio/pull/4080
+
+# 0.1.7 (July 7, 2021)
+
+### Fixed
+
+- sync: fix watch wrapper ([#3914])
+- time: fix `Timeout::size_hint` ([#3902])
+
+[#3902]: https://github.com/tokio-rs/tokio/pull/3902
+[#3914]: https://github.com/tokio-rs/tokio/pull/3914
+
 # 0.1.6 (May 14, 2021)
 
 ### Added

tokio-stream/Cargo.toml

@@ -2,17 +2,15 @@
 name = "tokio-stream"
 # When releasing to crates.io:
 # - Remove path dependencies
-# - Update doc url
-#   - Cargo.toml
 # - Update CHANGELOG.md.
 # - Create "tokio-stream-0.1.x" git tag.
-version = "0.1.6"
+version = "0.1.9"
 edition = "2018"
+rust-version = "1.49"
 authors = ["Tokio Contributors <[email protected]>"]
 license = "MIT"
 repository = "https://github.com/tokio-rs/tokio"
 homepage = "https://tokio.rs"
-documentation = "https://docs.rs/tokio-stream/0.1.6/tokio_stream"
 description = """
 Utilities to work with `Stream` and `tokio`.
 """
@@ -30,8 +28,8 @@ signal = ["tokio/signal"]
 [dependencies]
 futures-core = { version = "0.3.0" }
 pin-project-lite = "0.2.0"
-tokio = { version = "1.2.0", path = "../tokio", features = ["sync"] }
-tokio-util = { version = "0.6.3", path = "../tokio-util", optional = true }
+tokio = { version = "1.8.0", path = "../tokio", features = ["sync"] }
+tokio-util = { version = "0.7.0", path = "../tokio-util", optional = true }
 
 [dev-dependencies]
 tokio = { version = "1.2.0", path = "../tokio", features = ["full", "test-util"] }
@@ -44,3 +42,8 @@ proptest = "1"
 [package.metadata.docs.rs]
 all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
+# Issue #3770
+#
+# This should allow `docsrs` to be read across projects, so that `tokio-stream`
+# can pick up stubbed types exported by `tokio`.
+rustc-args = ["--cfg", "docsrs"]

tokio-stream/LICENSE

@@ -1,4 +1,4 @@
-Copyright (c) 2021 Tokio Contributors
+Copyright (c) 2022 Tokio Contributors
 
 Permission is hereby granted, free of charge, to any
 person obtaining a copy of this software and associated

tokio-stream/src/lib.rs

@@ -10,7 +10,6 @@
     unreachable_pub
 )]
 #![cfg_attr(docsrs, feature(doc_cfg))]
-#![cfg_attr(docsrs, deny(broken_intra_doc_links))]
 #![doc(test(
     no_crate_inject,
     attr(deny(warnings, rust_2018_idioms), allow(dead_code, unused_variables))
@@ -78,6 +77,9 @@ pub mod wrappers;
 
 mod stream_ext;
 pub use stream_ext::{collect::FromStream, StreamExt};
+cfg_time! {
+    pub use stream_ext::timeout::{Elapsed, Timeout};
+}
 
 mod empty;
 pub use empty::{empty, Empty};

tokio-stream/src/stream_ext.rs

@@ -1,3 +1,4 @@
+use core::future::Future;
 use futures_core::Stream;
 
 mod all;
@@ -27,6 +28,9 @@ use fuse::Fuse;
 mod map;
 use map::Map;
 
+mod map_while;
+use map_while::MapWhile;
+
 mod merge;
 use merge::Merge;
 
@@ -39,17 +43,20 @@ use skip::Skip;
 mod skip_while;
 use skip_while::SkipWhile;
 
-mod try_next;
-use try_next::TryNext;
-
 mod take;
 use take::Take;
 
 mod take_while;
 use take_while::TakeWhile;
 
+mod then;
+use then::Then;
+
+mod try_next;
+use try_next::TryNext;
+
 cfg_time! {
-    mod timeout;
+    pub(crate) mod timeout;
     use timeout::Timeout;
     use tokio::time::Duration;
     mod throttle;
@@ -106,6 +113,12 @@ pub trait StreamExt: Stream {
     /// pinning it to the stack using the `pin_mut!` macro from the `pin_utils`
     /// crate.
     ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. The returned future only
+    /// holds onto a reference to the underlying stream,
+    /// so dropping it will never lose a value.
+    ///
     /// # Examples
     ///
     /// ```
@@ -142,6 +155,12 @@ pub trait StreamExt: Stream {
     /// an [`Option<Result<T, E>>`](Option), making for easy use
     /// with the [`?`](std::ops::Try) operator.
     ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. The returned future only
+    /// holds onto a reference to the underlying stream,
+    /// so dropping it will never lose a value.
+    ///
     /// # Examples
     ///
     /// ```
@@ -197,6 +216,93 @@ pub trait StreamExt: Stream {
         Map::new(self, f)
     }
 
+    /// Map this stream's items to a different type for as long as determined by
+    /// the provided closure. A stream of the target type will be returned,
+    /// which will yield elements until the closure returns `None`.
+    ///
+    /// The provided closure is executed over all elements of this stream as
+    /// they are made available, until it returns `None`. It is executed inline
+    /// with calls to [`poll_next`](Stream::poll_next). Once `None` is returned,
+    /// the underlying stream will not be polled again.
+    ///
+    /// Note that this function consumes the stream passed into it and returns a
+    /// wrapped version of it, similar to the [`Iterator::map_while`] method in the
+    /// standard library.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// use tokio_stream::{self as stream, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=10);
+    /// let mut stream = stream.map_while(|x| {
+    ///     if x < 4 {
+    ///         Some(x + 3)
+    ///     } else {
+    ///         None
+    ///     }
+    /// });
+    /// assert_eq!(stream.next().await, Some(4));
+    /// assert_eq!(stream.next().await, Some(5));
+    /// assert_eq!(stream.next().await, Some(6));
+    /// assert_eq!(stream.next().await, None);
+    /// # }
+    /// ```
+    fn map_while<T, F>(self, f: F) -> MapWhile<Self, F>
+    where
+        F: FnMut(Self::Item) -> Option<T>,
+        Self: Sized,
+    {
+        MapWhile::new(self, f)
+    }
+
+    /// Maps this stream's items asynchronously to a different type, returning a
+    /// new stream of the resulting type.
+    ///
+    /// The provided closure is executed over all elements of this stream as
+    /// they are made available, and the returned future is executed. Only one
+    /// future is executed at the time.
+    ///
+    /// Note that this function consumes the stream passed into it and returns a
+    /// wrapped version of it, similar to the existing `then` methods in the
+    /// standard library.
+    ///
+    /// Be aware that if the future is not `Unpin`, then neither is the `Stream`
+    /// returned by this method. To handle this, you can use `tokio::pin!` as in
+    /// the example below or put the stream in a `Box` with `Box::pin(stream)`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// use tokio_stream::{self as stream, StreamExt};
+    ///
+    /// async fn do_async_work(value: i32) -> i32 {
+    ///     value + 3
+    /// }
+    ///
+    /// let stream = stream::iter(1..=3);
+    /// let stream = stream.then(do_async_work);
+    ///
+    /// tokio::pin!(stream);
+    ///
+    /// assert_eq!(stream.next().await, Some(4));
+    /// assert_eq!(stream.next().await, Some(5));
+    /// assert_eq!(stream.next().await, Some(6));
+    /// # }
+    /// ```
+    fn then<F, Fut>(self, f: F) -> Then<Self, Fut, F>
+    where
+        F: FnMut(Self::Item) -> Fut,
+        Fut: Future,
+        Self: Sized,
+    {
+        Then::new(self, f)
+    }
+
     /// Combine two streams into one by interleaving the output of both as it
     /// is produced.
     ///
@@ -515,7 +621,7 @@ pub trait StreamExt: Stream {
     /// Skip elements from the underlying stream while the provided predicate
     /// resolves to `true`.
     ///
-    /// This function, like [`Iterator::skip_while`], will ignore elemets from the
+    /// This function, like [`Iterator::skip_while`], will ignore elements from the
     /// stream until the predicate `f` resolves to `false`. Once one element
     /// returns false, the rest of the elements will be yielded.
     ///

tokio-stream/src/stream_ext/collect.rs

@@ -66,17 +66,17 @@ where
         use Poll::Ready;
 
         loop {
-            let mut me = self.as_mut().project();
+            let me = self.as_mut().project();
 
             let item = match ready!(me.stream.poll_next(cx)) {
                 Some(item) => item,
                 None => {
-                    return Ready(U::finalize(sealed::Internal, &mut me.collection));
+                    return Ready(U::finalize(sealed::Internal, me.collection));
                 }
             };
 
-            if !U::extend(sealed::Internal, &mut me.collection, item) {
-                return Ready(U::finalize(sealed::Internal, &mut me.collection));
+            if !U::extend(sealed::Internal, me.collection, item) {
+                return Ready(U::finalize(sealed::Internal, me.collection));
             }
         }
     }
@@ -113,7 +113,7 @@ impl<T: AsRef<str>> sealed::FromStreamPriv<T> for String {
     }
 
     fn finalize(_: sealed::Internal, collection: &mut String) -> String {
-        mem::replace(collection, String::new())
+        mem::take(collection)
     }
 }
 
@@ -132,7 +132,7 @@ impl<T> sealed::FromStreamPriv<T> for Vec<T> {
     }
 
     fn finalize(_: sealed::Internal, collection: &mut Vec<T>) -> Vec<T> {
-        mem::replace(collection, vec![])
+        mem::take(collection)
     }
 }
 

tokio-stream/src/stream_ext/map_while.rs

@@ -0,0 +1,52 @@
+use crate::Stream;
+
+use core::fmt;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`map_while`](super::StreamExt::map_while) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct MapWhile<St, F> {
+        #[pin]
+        stream: St,
+        f: F,
+    }
+}
+
+impl<St, F> fmt::Debug for MapWhile<St, F>
+where
+    St: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("MapWhile")
+            .field("stream", &self.stream)
+            .finish()
+    }
+}
+
+impl<St, F> MapWhile<St, F> {
+    pub(super) fn new(stream: St, f: F) -> Self {
+        MapWhile { stream, f }
+    }
+}
+
+impl<St, F, T> Stream for MapWhile<St, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Option<T>,
+{
+    type Item = T;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
+        let me = self.project();
+        let f = me.f;
+        me.stream.poll_next(cx).map(|opt| opt.and_then(f))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (_, upper) = self.stream.size_hint();
+        (0, upper)
+    }
+}

tokio-stream/src/stream_ext/next.rs

@@ -8,6 +8,13 @@ use pin_project_lite::pin_project;
 
 pin_project! {
     /// Future for the [`next`](super::StreamExt::next) method.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. It only
+    /// holds onto a reference to the underlying stream,
+    /// so dropping it will never lose a value.
+    ///
     #[derive(Debug)]
     #[must_use = "futures do nothing unless you `.await` or poll them"]
     pub struct Next<'a, St: ?Sized> {

tokio-stream/src/stream_ext/then.rs

@@ -0,0 +1,83 @@
+use crate::Stream;
+
+use core::fmt;
+use core::future::Future;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`then`](super::StreamExt::then) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Then<St, Fut, F> {
+        #[pin]
+        stream: St,
+        #[pin]
+        future: Option<Fut>,
+        f: F,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for Then<St, Fut, F>
+where
+    St: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Then")
+            .field("stream", &self.stream)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> Then<St, Fut, F> {
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Then {
+            stream,
+            future: None,
+            f,
+        }
+    }
+}
+
+impl<St, F, Fut> Stream for Then<St, Fut, F>
+where
+    St: Stream,
+    Fut: Future,
+    F: FnMut(St::Item) -> Fut,
+{
+    type Item = Fut::Output;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Fut::Output>> {
+        let mut me = self.project();
+
+        loop {
+            if let Some(future) = me.future.as_mut().as_pin_mut() {
+                match future.poll(cx) {
+                    Poll::Ready(item) => {
+                        me.future.set(None);
+                        return Poll::Ready(Some(item));
+                    }
+                    Poll::Pending => return Poll::Pending,
+                }
+            }
+
+            match me.stream.as_mut().poll_next(cx) {
+                Poll::Ready(Some(item)) => {
+                    me.future.set(Some((me.f)(item)));
+                }
+                Poll::Ready(None) => return Poll::Ready(None),
+                Poll::Pending => return Poll::Pending,
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let future_len = if self.future.is_some() { 1 } else { 0 };
+        let (lower, upper) = self.stream.size_hint();
+
+        let lower = lower.saturating_add(future_len);
+        let upper = upper.and_then(|upper| upper.checked_add(future_len));
+
+        (lower, upper)
+    }
+}

tokio-stream/src/stream_ext/timeout.rs

@@ -69,7 +69,18 @@ impl<S: Stream> Stream for Timeout<S> {
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        self.stream.size_hint()
+        let (lower, upper) = self.stream.size_hint();
+
+        // The timeout stream may insert an error before and after each message
+        // from the underlying stream, but no more than one error between each
+        // message. Hence the upper bound is computed as 2x+1.
+
+        // Using a helper function to enable use of question mark operator.
+        fn twice_plus_one(value: Option<usize>) -> Option<usize> {
+            value?.checked_mul(2)?.checked_add(1)
+        }
+
+        (lower, twice_plus_one(upper))
     }
 }
 

tokio-stream/src/stream_ext/try_next.rs

@@ -9,6 +9,12 @@ use pin_project_lite::pin_project;
 
 pin_project! {
     /// Future for the [`try_next`](super::StreamExt::try_next) method.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. It only
+    /// holds onto a reference to the underlying stream,
+    /// so dropping it will never lose a value.
     #[derive(Debug)]
     #[must_use = "futures do nothing unless you `.await` or poll them"]
     pub struct TryNext<'a, St: ?Sized> {

tokio-stream/src/stream_map.rs

@@ -364,11 +364,11 @@ impl<K, V> StreamMap<K, V> {
     /// # Examples
     ///
     /// ```
-    /// use std::collections::HashMap;
+    /// use tokio_stream::{StreamMap, pending};
     ///
-    /// let mut a = HashMap::new();
+    /// let mut a = StreamMap::new();
     /// assert!(a.is_empty());
-    /// a.insert(1, "a");
+    /// a.insert(1, pending::<i32>());
     /// assert!(!a.is_empty());
     /// ```
     pub fn is_empty(&self) -> bool {
@@ -568,6 +568,32 @@ where
     }
 }
 
+impl<K, V> std::iter::FromIterator<(K, V)> for StreamMap<K, V>
+where
+    K: Hash + Eq,
+{
+    fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> Self {
+        let iterator = iter.into_iter();
+        let (lower_bound, _) = iterator.size_hint();
+        let mut stream_map = Self::with_capacity(lower_bound);
+
+        for (key, value) in iterator {
+            stream_map.insert(key, value);
+        }
+
+        stream_map
+    }
+}
+
+impl<K, V> Extend<(K, V)> for StreamMap<K, V> {
+    fn extend<T>(&mut self, iter: T)
+    where
+        T: IntoIterator<Item = (K, V)>,
+    {
+        self.entries.extend(iter);
+    }
+}
+
 mod rand {
     use std::cell::Cell;
 

tokio-stream/src/wrappers.rs

@@ -1,13 +1,4 @@
 //! Wrappers for Tokio types that implement `Stream`.
-//!
-#![cfg_attr(
-    unix,
-    doc = "You are viewing documentation built under unix. To view windows-specific wrappers, change to the `x86_64-pc-windows-msvc` platform."
-)]
-#![cfg_attr(
-    windows,
-    doc = "You are viewing documentation built under windows. To view unix-specific wrappers, change to the `x86_64-unknown-linux-gnu` platform."
-)]
 
 /// Error types for the wrappers.
 pub mod errors {
@@ -36,9 +27,9 @@ cfg_signal! {
     #[cfg(unix)]
     pub use signal_unix::SignalStream;
 
-    #[cfg(windows)]
+    #[cfg(any(windows, docsrs))]
     mod signal_windows;
-    #[cfg(windows)]
+    #[cfg(any(windows, docsrs))]
     pub use signal_windows::{CtrlCStream, CtrlBreakStream};
 }
 

tokio-stream/src/wrappers/broadcast.rs

@@ -14,11 +14,11 @@ use std::task::{Context, Poll};
 /// [`Stream`]: trait@crate::Stream
 #[cfg_attr(docsrs, doc(cfg(feature = "sync")))]
 pub struct BroadcastStream<T> {
-    inner: ReusableBoxFuture<(Result<T, RecvError>, Receiver<T>)>,
+    inner: ReusableBoxFuture<'static, (Result<T, RecvError>, Receiver<T>)>,
 }
 
 /// An error returned from the inner stream of a [`BroadcastStream`].
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Clone)]
 pub enum BroadcastStreamRecvError {
     /// The receiver lagged too far behind. Attempting to receive again will
     /// return the oldest message still retained by the channel.
@@ -71,3 +71,9 @@ impl<T> fmt::Debug for BroadcastStream<T> {
         f.debug_struct("BroadcastStream").finish()
     }
 }
+
+impl<T: 'static + Clone + Send> From<Receiver<T>> for BroadcastStream<T> {
+    fn from(recv: Receiver<T>) -> Self {
+        Self::new(recv)
+    }
+}

tokio-stream/src/wrappers/mpsc_bounded.rs

@@ -57,3 +57,9 @@ impl<T> AsMut<Receiver<T>> for ReceiverStream<T> {
         &mut self.inner
     }
 }
+
+impl<T> From<Receiver<T>> for ReceiverStream<T> {
+    fn from(recv: Receiver<T>) -> Self {
+        Self::new(recv)
+    }
+}

tokio-stream/src/wrappers/mpsc_unbounded.rs

@@ -51,3 +51,9 @@ impl<T> AsMut<UnboundedReceiver<T>> for UnboundedReceiverStream<T> {
         &mut self.inner
     }
 }
+
+impl<T> From<UnboundedReceiver<T>> for UnboundedReceiverStream<T> {
+    fn from(recv: UnboundedReceiver<T>) -> Self {
+        Self::new(recv)
+    }
+}

tokio-stream/src/wrappers/watch.rs

@@ -11,7 +11,7 @@ use tokio::sync::watch::error::RecvError;
 /// A wrapper around [`tokio::sync::watch::Receiver`] that implements [`Stream`].
 ///
 /// This stream will always start by yielding the current value when the WatchStream is polled,
-/// regardles of whether it was the initial value or sent afterwards.
+/// regardless of whether it was the initial value or sent afterwards.
 ///
 /// # Examples
 ///
@@ -49,7 +49,7 @@ use tokio::sync::watch::error::RecvError;
 /// [`Stream`]: trait@crate::Stream
 #[cfg_attr(docsrs, doc(cfg(feature = "sync")))]
 pub struct WatchStream<T> {
-    inner: ReusableBoxFuture<(Result<(), RecvError>, Receiver<T>)>,
+    inner: ReusableBoxFuture<'static, (Result<(), RecvError>, Receiver<T>)>,
 }
 
 async fn make_future<T: Clone + Send + Sync>(
@@ -59,7 +59,7 @@ async fn make_future<T: Clone + Send + Sync>(
     (result, rx)
 }
 
-impl<T: 'static + Clone + Unpin + Send + Sync> WatchStream<T> {
+impl<T: 'static + Clone + Send + Sync> WatchStream<T> {
     /// Create a new `WatchStream`.
     pub fn new(rx: Receiver<T>) -> Self {
         Self {
@@ -72,10 +72,10 @@ impl<T: Clone + 'static + Send + Sync> Stream for WatchStream<T> {
     type Item = T;
 
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
-        let (result, rx) = ready!(self.inner.poll(cx));
+        let (result, mut rx) = ready!(self.inner.poll(cx));
         match result {
             Ok(_) => {
-                let received = (*rx.borrow()).clone();
+                let received = (*rx.borrow_and_update()).clone();
                 self.inner.set(make_future(rx));
                 Poll::Ready(Some(received))
             }
@@ -94,3 +94,9 @@ impl<T> fmt::Debug for WatchStream<T> {
         f.debug_struct("WatchStream").finish()
     }
 }
+
+impl<T: 'static + Clone + Send + Sync> From<Receiver<T>> for WatchStream<T> {
+    fn from(recv: Receiver<T>) -> Self {
+        Self::new(recv)
+    }
+}

tokio-stream/tests/stream_timeout.rs

@@ -1,10 +1,10 @@
-#![cfg(feature = "full")]
+#![cfg(all(feature = "time", feature = "sync", feature = "io-util"))]
 
 use tokio::time::{self, sleep, Duration};
 use tokio_stream::{self, StreamExt};
 use tokio_test::*;
 
-use futures::StreamExt as _;
+use futures::stream;
 
 async fn maybe_sleep(idx: i32) -> i32 {
     if idx % 2 == 0 {

tokio-stream/tests/time_throttle.rs

@@ -1,5 +1,5 @@
 #![warn(rust_2018_idioms)]
-#![cfg(feature = "full")]
+#![cfg(all(feature = "time", feature = "sync", feature = "io-util"))]
 
 use tokio::time;
 use tokio_stream::StreamExt;

tokio-stream/tests/watch.rs

@@ -0,0 +1,29 @@
+#![cfg(feature = "sync")]
+
+use tokio::sync::watch;
+use tokio_stream::wrappers::WatchStream;
+use tokio_stream::StreamExt;
+
+#[tokio::test]
+async fn message_not_twice() {
+    let (tx, rx) = watch::channel("hello");
+
+    let mut counter = 0;
+    let mut stream = WatchStream::new(rx).map(move |payload| {
+        println!("{}", payload);
+        if payload == "goodbye" {
+            counter += 1;
+        }
+        if counter >= 2 {
+            panic!("too many goodbyes");
+        }
+    });
+
+    let task = tokio::spawn(async move { while stream.next().await.is_some() {} });
+
+    // Send goodbye just once
+    tx.send("goodbye").unwrap();
+
+    drop(tx);
+    task.await.unwrap();
+}

tokio-test/Cargo.toml

@@ -2,17 +2,15 @@
 name = "tokio-test"
 # When releasing to crates.io:
 # - Remove path dependencies
-# - Update doc url
-#   - Cargo.toml
 # - Update CHANGELOG.md.
 # - Create "tokio-test-0.4.x" git tag.
 version = "0.4.2"
 edition = "2018"
+rust-version = "1.49"
 authors = ["Tokio Contributors <[email protected]>"]
 license = "MIT"
 repository = "https://github.com/tokio-rs/tokio"
 homepage = "https://tokio.rs"
-documentation = "https://docs.rs/tokio-test/0.4.2/tokio_test"
 description = """
 Testing utilities for Tokio- and futures-based code
 """
@@ -20,7 +18,7 @@ categories = ["asynchronous", "testing"]
 
 [dependencies]
 tokio = { version = "1.2.0", path = "../tokio", features = ["rt", "sync", "time", "test-util"] }
-tokio-stream = { version = "0.1", path = "../tokio-stream" }
+tokio-stream = { version = "0.1.1", path = "../tokio-stream" }
 async-stream = "0.3"
 
 bytes = "1.0.0"

tokio-test/LICENSE

@@ -1,4 +1,4 @@
-Copyright (c) 2021 Tokio Contributors
+Copyright (c) 2022 Tokio Contributors
 
 Permission is hereby granted, free of charge, to any
 person obtaining a copy of this software and associated

tokio-test/src/lib.rs

@@ -4,13 +4,12 @@
     rust_2018_idioms,
     unreachable_pub
 )]
-#![cfg_attr(docsrs, deny(broken_intra_doc_links))]
 #![doc(test(
     no_crate_inject,
     attr(deny(warnings, rust_2018_idioms), allow(dead_code, unused_variables))
 ))]
 
-//! Tokio and Futures based testing utilites
+//! Tokio and Futures based testing utilities
 
 pub mod io;
 

tokio-test/src/task.rs

@@ -180,7 +180,7 @@ impl ThreadWaker {
         }
     }
 
-    /// Clears any previously received wakes, avoiding potential spurrious
+    /// Clears any previously received wakes, avoiding potential spurious
     /// wake notifications. This should only be called immediately before running the
     /// task.
     fn clear(&self) {

tokio-util/CHANGELOG.md

@@ -1,3 +1,118 @@
+# 0.7.3 (June 4, 2022)
+
+### Changed
+
+- tracing: don't require default tracing features ([#4592])
+- util: simplify implementation of `ReusableBoxFuture` ([#4675])
+
+### Added (unstable)
+
+- task: add `JoinMap` ([#4640], [#4697])
+
+[#4592]: https://github.com/tokio-rs/tokio/pull/4592
+[#4640]: https://github.com/tokio-rs/tokio/pull/4640
+[#4675]: https://github.com/tokio-rs/tokio/pull/4675
+[#4697]: https://github.com/tokio-rs/tokio/pull/4697
+
+# 0.7.2 (May 14, 2022)
+
+This release contains a rewrite of `CancellationToken` that fixes a memory leak. ([#4652])
+
+[#4652]: https://github.com/tokio-rs/tokio/pull/4652
+
+# 0.7.1 (February 21, 2022)
+
+### Added
+
+- codec: add `length_field_type` to `LengthDelimitedCodec` builder ([#4508])
+- io: add `StreamReader::into_inner_with_chunk()` ([#4559])
+
+### Changed
+
+- switch from log to tracing ([#4539])
+
+### Fixed
+
+- sync: fix waker update condition in `CancellationToken` ([#4497])
+- bumped tokio dependency to 1.6 to satisfy minimum requirements ([#4490])
+
+[#4490]: https://github.com/tokio-rs/tokio/pull/4490
+[#4497]: https://github.com/tokio-rs/tokio/pull/4497
+[#4508]: https://github.com/tokio-rs/tokio/pull/4508
+[#4539]: https://github.com/tokio-rs/tokio/pull/4539
+[#4559]: https://github.com/tokio-rs/tokio/pull/4559
+
+# 0.7.0 (February 9, 2022)
+
+### Added
+
+- task: add `spawn_pinned` ([#3370])
+- time: add `shrink_to_fit` and `compact` methods to `DelayQueue` ([#4170])
+- codec: improve `Builder::max_frame_length` docs ([#4352])
+- codec: add mutable reference getters for codecs to pinned `Framed` ([#4372])
+- net: add generic trait to combine `UnixListener` and `TcpListener` ([#4385])
+- codec: implement `Framed::map_codec` ([#4427])
+- codec: implement `Encoder<BytesMut>` for `BytesCodec` ([#4465])
+
+### Changed
+
+- sync: add lifetime parameter to `ReusableBoxFuture` ([#3762])
+- sync: refactored `PollSender<T>` to fix a subtly broken `Sink<T>` implementation ([#4214])
+- time: remove error case from the infallible `DelayQueue::poll_elapsed` ([#4241])
+
+[#3370]: https://github.com/tokio-rs/tokio/pull/3370
+[#4170]: https://github.com/tokio-rs/tokio/pull/4170
+[#4352]: https://github.com/tokio-rs/tokio/pull/4352
+[#4372]: https://github.com/tokio-rs/tokio/pull/4372
+[#4385]: https://github.com/tokio-rs/tokio/pull/4385
+[#4427]: https://github.com/tokio-rs/tokio/pull/4427
+[#4465]: https://github.com/tokio-rs/tokio/pull/4465
+[#3762]: https://github.com/tokio-rs/tokio/pull/3762
+[#4214]: https://github.com/tokio-rs/tokio/pull/4214
+[#4241]: https://github.com/tokio-rs/tokio/pull/4241
+
+# 0.6.10 (May 14, 2021)
+
+This is a backport for the memory leak in `CancellationToken` that was originally fixed in 0.7.2. ([#4652])
+
+[#4652]: https://github.com/tokio-rs/tokio/pull/4652
+
+# 0.6.9 (October 29, 2021)
+
+### Added
+
+- codec: implement `Clone` for `LengthDelimitedCodec` ([#4089])
+- io: add `SyncIoBridge`  ([#4146])
+
+### Fixed
+
+- time: update deadline on removal in `DelayQueue` ([#4178])
+- codec: Update stream impl for Framed to return None after Err ([#4166])
+
+[#4089]: https://github.com/tokio-rs/tokio/pull/4089
+[#4146]: https://github.com/tokio-rs/tokio/pull/4146
+[#4166]: https://github.com/tokio-rs/tokio/pull/4166
+[#4178]: https://github.com/tokio-rs/tokio/pull/4178
+
+# 0.6.8 (September 3, 2021)
+
+### Added
+
+- sync: add drop guard for `CancellationToken` ([#3839])
+- compact: added `AsyncSeek` compat ([#4078])
+- time: expose `Key` used in `DelayQueue`'s `Expired` ([#4081])
+- io: add `with_capacity` to `ReaderStream` ([#4086])
+
+### Fixed
+
+- codec: remove unnecessary `doc(cfg(...))` ([#3989])
+
+[#3839]: https://github.com/tokio-rs/tokio/pull/3839
+[#4078]: https://github.com/tokio-rs/tokio/pull/4078
+[#4081]: https://github.com/tokio-rs/tokio/pull/4081
+[#4086]: https://github.com/tokio-rs/tokio/pull/4086
+[#3989]: https://github.com/tokio-rs/tokio/pull/3989
+
 # 0.6.7 (May 14, 2021)
 
 ### Added

tokio-util/Cargo.toml

@@ -2,17 +2,15 @@
 name = "tokio-util"
 # When releasing to crates.io:
 # - Remove path dependencies
-# - Update doc url
-#   - Cargo.toml
 # - Update CHANGELOG.md.
-# - Create "tokio-util-0.6.x" git tag.
-version = "0.6.7"
+# - Create "tokio-util-0.7.x" git tag.
+version = "0.7.3"
 edition = "2018"
+rust-version = "1.49"
 authors = ["Tokio Contributors <[email protected]>"]
 license = "MIT"
 repository = "https://github.com/tokio-rs/tokio"
 homepage = "https://tokio.rs"
-documentation = "https://docs.rs/tokio-util/0.6.7/tokio_util"
 description = """
 Additional utilities for working with Tokio.
 """
@@ -23,28 +21,31 @@ categories = ["asynchronous"]
 default = []
 
 # Shorthand for enabling everything
-full = ["codec", "compat", "io", "time", "net", "rt"]
+full = ["codec", "compat", "io-util", "time", "net", "rt"]
 
 net = ["tokio/net"]
 compat = ["futures-io",]
-codec = []
+codec = ["tracing"]
 time = ["tokio/time","slab"]
 io = []
-rt = ["tokio/rt"]
+io-util = ["io", "tokio/rt", "tokio/io-util"]
+rt = ["tokio/rt", "tokio/sync", "futures-util", "hashbrown"]
 
 __docs_rs = ["futures-util"]
 
 [dependencies]
-tokio = { version = "1.0.0", path = "../tokio", features = ["sync"] }
-
+tokio = { version = "1.19.0", path = "../tokio", features = ["sync"] }
 bytes = "1.0.0"
 futures-core = "0.3.0"
 futures-sink = "0.3.0"
 futures-io = { version = "0.3.0", optional = true }
 futures-util = { version = "0.3.0", optional = true }
-log = "0.4"
 pin-project-lite = "0.2.0"
-slab = { version = "0.4.1", optional = true } # Backs `DelayQueue`
+slab = { version = "0.4.4", optional = true } # Backs `DelayQueue`
+tracing = { version = "0.1.25", default-features = false, features = ["std"], optional = true }
+
+[target.'cfg(tokio_unstable)'.dependencies]
+hashbrown = { version = "0.12.0", optional = true }
 
 [dev-dependencies]
 tokio = { version = "1.0.0", path = "../tokio", features = ["full"] }
@@ -57,4 +58,8 @@ futures-test = "0.3.5"
 
 [package.metadata.docs.rs]
 all-features = true
-rustdoc-args = ["--cfg", "docsrs"]
+# enable unstable features in the documentation
+rustdoc-args = ["--cfg", "docsrs", "--cfg", "tokio_unstable"]
+# it's necessary to _also_ pass `--cfg tokio_unstable` to rustc, or else
+# dependencies will not be enabled, and the docs build will fail.
+rustc-args = ["--cfg", "docsrs", "--cfg", "tokio_unstable"]

tokio-util/LICENSE

@@ -1,4 +1,4 @@
-Copyright (c) 2021 Tokio Contributors
+Copyright (c) 2022 Tokio Contributors
 
 Permission is hereby granted, free of charge, to any
 person obtaining a copy of this software and associated

tokio-util/README.md

@@ -1,6 +1,6 @@
 # tokio-util
 
-Utilities for encoding and decoding frames.
+Utilities for working with Tokio.
 
 ## License
 

tokio-util/src/cfg.rs

@@ -38,6 +38,18 @@ macro_rules! cfg_io {
     }
 }
 
+cfg_io! {
+    macro_rules! cfg_io_util {
+        ($($item:item)*) => {
+            $(
+                #[cfg(feature = "io-util")]
+                #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+                $item
+            )*
+        }
+    }
+}
+
 macro_rules! cfg_rt {
     ($($item:item)*) => {
         $(

tokio-util/src/codec/any_delimiter_codec.rs

@@ -234,7 +234,7 @@ impl Default for AnyDelimiterCodec {
     }
 }
 
-/// An error occured while encoding or decoding a chunk.
+/// An error occurred while encoding or decoding a chunk.
 #[derive(Debug)]
 pub enum AnyDelimiterCodecError {
     /// The maximum chunk length was exceeded.

tokio-util/src/codec/bytes_codec.rs

@@ -74,3 +74,13 @@ impl Encoder<Bytes> for BytesCodec {
         Ok(())
     }
 }
+
+impl Encoder<BytesMut> for BytesCodec {
+    type Error = io::Error;
+
+    fn encode(&mut self, data: BytesMut, buf: &mut BytesMut) -> Result<(), io::Error> {
+        buf.reserve(data.len());
+        buf.put(data);
+        Ok(())
+    }
+}

tokio-util/src/codec/decoder.rs

@@ -28,7 +28,7 @@ use std::io;
 /// It is up to the Decoder to keep track of a restart after an EOF,
 /// and to decide how to handle such an event by, for example,
 /// allowing frames to cross EOF boundaries, re-emitting opening frames, or
-/// reseting the entire internal state.
+/// resetting the entire internal state.
 ///
 /// [`Framed`]: crate::codec::Framed
 /// [`FramedRead`]: crate::codec::FramedRead

tokio-util/src/codec/framed.rs

@@ -106,6 +106,7 @@ where
                         eof: false,
                         is_readable: false,
                         buffer: BytesMut::with_capacity(capacity),
+                        has_errored: false,
                     },
                     write: WriteFrame::default(),
                 },
@@ -203,6 +204,35 @@ impl<T, U> Framed<T, U> {
         &mut self.inner.codec
     }
 
+    /// Maps the codec `U` to `C`, preserving the read and write buffers
+    /// wrapped by `Framed`.
+    ///
+    /// Note that care should be taken to not tamper with the underlying codec
+    /// as it may corrupt the stream of frames otherwise being worked with.
+    pub fn map_codec<C, F>(self, map: F) -> Framed<T, C>
+    where
+        F: FnOnce(U) -> C,
+    {
+        // This could be potentially simplified once rust-lang/rust#86555 hits stable
+        let parts = self.into_parts();
+        Framed::from_parts(FramedParts {
+            io: parts.io,
+            codec: map(parts.codec),
+            read_buf: parts.read_buf,
+            write_buf: parts.write_buf,
+            _priv: (),
+        })
+    }
+
+    /// Returns a mutable reference to the underlying codec wrapped by
+    /// `Framed`.
+    ///
+    /// Note that care should be taken to not tamper with the underlying codec
+    /// as it may corrupt the stream of frames otherwise being worked with.
+    pub fn codec_pin_mut(self: Pin<&mut Self>) -> &mut U {
+        self.project().inner.project().codec
+    }
+
     /// Returns a reference to the read buffer.
     pub fn read_buffer(&self) -> &BytesMut {
         &self.inner.state.read.buffer

tokio-util/src/codec/framed_impl.rs

@@ -7,12 +7,12 @@ use tokio::io::{AsyncRead, AsyncWrite};
 use bytes::BytesMut;
 use futures_core::ready;
 use futures_sink::Sink;
-use log::trace;
 use pin_project_lite::pin_project;
 use std::borrow::{Borrow, BorrowMut};
 use std::io;
 use std::pin::Pin;
 use std::task::{Context, Poll};
+use tracing::trace;
 
 pin_project! {
     #[derive(Debug)]
@@ -27,10 +27,12 @@ pin_project! {
 const INITIAL_CAPACITY: usize = 8 * 1024;
 const BACKPRESSURE_BOUNDARY: usize = INITIAL_CAPACITY;
 
+#[derive(Debug)]
 pub(crate) struct ReadFrame {
     pub(crate) eof: bool,
     pub(crate) is_readable: bool,
     pub(crate) buffer: BytesMut,
+    pub(crate) has_errored: bool,
 }
 
 pub(crate) struct WriteFrame {
@@ -49,6 +51,7 @@ impl Default for ReadFrame {
             eof: false,
             is_readable: false,
             buffer: BytesMut::with_capacity(INITIAL_CAPACITY),
+            has_errored: false,
         }
     }
 }
@@ -72,6 +75,7 @@ impl From<BytesMut> for ReadFrame {
             buffer,
             is_readable: size > 0,
             eof: false,
+            has_errored: false,
         }
     }
 }
@@ -124,48 +128,64 @@ where
         // to a combination of the `is_readable` and `eof` flags. States persist across
         // loop entries and most state transitions occur with a return.
         //
-        // The intitial state is `reading`.
+        // The initial state is `reading`.
         //
-        // | state   | eof   | is_readable |
-        // |---------|-------|-------------|
-        // | reading | false | false       |
-        // | framing | false | true        |
-        // | pausing | true  | true        |
-        // | paused  | true  | false       |
-        //
-        //                                 `decode_eof`
-        //                                 returns `Some`             read 0 bytes
-        //                                   │       │                 │      │
-        //                                   │       ▼                 │      ▼
-        //                                   ┌───────┐ `decode_eof`    ┌──────┐
-        //                 ┌──read 0 bytes──▶│pausing│─returns `None`─▶│paused│──┐
-        //                 │                 └───────┘                 └──────┘  │
-        // pending read┐   │                     ┌──────┐                  │  ▲  │
-        //      │      │   │                     │      │                  │  │  │
-        //      │      ▼   │                     │  `decode` returns `Some`│ pending read
-        //      │  ╔═══════╗                 ┌───────┐◀─┘                  │
-        //      └──║reading║─read n>0 bytes─▶│framing│                     │
-        //         ╚═══════╝                 └───────┘◀──────read n>0 bytes┘
-        //             ▲                         │
-        //             │                         │
-        //             └─`decode` returns `None`─┘
+        // | state   | eof   | is_readable | has_errored |
+        // |---------|-------|-------------|-------------|
+        // | reading | false | false       | false       |
+        // | framing | false | true        | false       |
+        // | pausing | true  | true        | false       |
+        // | paused  | true  | false       | false       |
+        // | errored | <any> | <any>       | true        |
+        //                                                       `decode_eof` returns Err
+        //                                          ┌────────────────────────────────────────────────────────┐
+        //                   `decode_eof` returns   │                                                        │
+        //                             `Ok(Some)`   │                                                        │
+        //                                 ┌─────┐  │     `decode_eof` returns               After returning │
+        //                Read 0 bytes     ├─────▼──┴┐    `Ok(None)`          ┌────────┐ ◄───┐ `None`    ┌───▼─────┐
+        //               ┌────────────────►│ Pausing ├───────────────────────►│ Paused ├─┐   └───────────┤ Errored │
+        //               │                 └─────────┘                        └─┬──▲───┘ │               └───▲───▲─┘
+        // Pending read  │                                                      │  │     │                   │   │
+        //     ┌──────┐  │            `decode` returns `Some`                   │  └─────┘                   │   │
+        //     │      │  │                   ┌──────┐                           │  Pending                   │   │
+        //     │ ┌────▼──┴─┐ Read n>0 bytes ┌┴──────▼─┐     read n>0 bytes      │  read                      │   │
+        //     └─┤ Reading ├───────────────►│ Framing │◄────────────────────────┘                            │   │
+        //       └──┬─▲────┘                └─────┬──┬┘                                                      │   │
+        //          │ │                           │  │                 `decode` returns Err                  │   │
+        //          │ └───decode` returns `None`──┘  └───────────────────────────────────────────────────────┘   │
+        //          │                             read returns Err                                               │
+        //          └────────────────────────────────────────────────────────────────────────────────────────────┘
         loop {
+            // Return `None` if we have encountered an error from the underlying decoder
+            // See: https://github.com/tokio-rs/tokio/issues/3976
+            if state.has_errored {
+                // preparing has_errored -> paused
+                trace!("Returning None and setting paused");
+                state.is_readable = false;
+                state.has_errored = false;
+                return Poll::Ready(None);
+            }
+
             // Repeatedly call `decode` or `decode_eof` while the buffer is "readable",
             // i.e. it _might_ contain data consumable as a frame or closing frame.
             // Both signal that there is no such data by returning `None`.
             //
             // If `decode` couldn't read a frame and the upstream source has returned eof,
-            // `decode_eof` will attemp to decode the remaining bytes as closing frames.
+            // `decode_eof` will attempt to decode the remaining bytes as closing frames.
             //
             // If the underlying AsyncRead is resumable, we may continue after an EOF,
-            // but must finish emmiting all of it's associated `decode_eof` frames.
+            // but must finish emitting all of it's associated `decode_eof` frames.
             // Furthermore, we don't want to emit any `decode_eof` frames on retried
             // reads after an EOF unless we've actually read more data.
             if state.is_readable {
                 // pausing or framing
                 if state.eof {
                     // pausing
-                    let frame = pinned.codec.decode_eof(&mut state.buffer)?;
+                    let frame = pinned.codec.decode_eof(&mut state.buffer).map_err(|err| {
+                        trace!("Got an error, going to errored state");
+                        state.has_errored = true;
+                        err
+                    })?;
                     if frame.is_none() {
                         state.is_readable = false; // prepare pausing -> paused
                     }
@@ -176,7 +196,11 @@ where
                 // framing
                 trace!("attempting to decode a frame");
 
-                if let Some(frame) = pinned.codec.decode(&mut state.buffer)? {
+                if let Some(frame) = pinned.codec.decode(&mut state.buffer).map_err(|op| {
+                    trace!("Got an error, going to errored state");
+                    state.has_errored = true;
+                    op
+                })? {
                     trace!("frame decoded from buffer");
                     // implicit framing -> framing
                     return Poll::Ready(Some(Ok(frame)));
@@ -190,7 +214,13 @@ where
             // Make sure we've got room for at least one byte to read to ensure
             // that we don't get a spurious 0 that looks like EOF.
             state.buffer.reserve(1);
-            let bytect = match poll_read_buf(pinned.inner.as_mut(), cx, &mut state.buffer)? {
+            let bytect = match poll_read_buf(pinned.inner.as_mut(), cx, &mut state.buffer).map_err(
+                |err| {
+                    trace!("Got an error, going to errored state");
+                    state.has_errored = true;
+                    err
+                },
+            )? {
                 Poll::Ready(ct) => ct,
                 // implicit reading -> reading or implicit paused -> paused
                 Poll::Pending => return Poll::Pending,
@@ -248,7 +278,7 @@ where
 
         while !pinned.state.borrow_mut().buffer.is_empty() {
             let WriteFrame { buffer } = pinned.state.borrow_mut();
-            trace!("writing; remaining={}", buffer.len());
+            trace!(remaining = buffer.len(), "writing;");
 
             let n = ready!(poll_write_buf(pinned.inner.as_mut(), cx, buffer))?;
 

tokio-util/src/codec/framed_read.rs

@@ -51,6 +51,7 @@ where
                     eof: false,
                     is_readable: false,
                     buffer: BytesMut::with_capacity(capacity),
+                    has_errored: false,
                 },
             },
         }
@@ -107,6 +108,32 @@ impl<T, D> FramedRead<T, D> {
         &mut self.inner.codec
     }
 
+    /// Maps the decoder `D` to `C`, preserving the read buffer
+    /// wrapped by `Framed`.
+    pub fn map_decoder<C, F>(self, map: F) -> FramedRead<T, C>
+    where
+        F: FnOnce(D) -> C,
+    {
+        // This could be potentially simplified once rust-lang/rust#86555 hits stable
+        let FramedImpl {
+            inner,
+            state,
+            codec,
+        } = self.inner;
+        FramedRead {
+            inner: FramedImpl {
+                inner,
+                state,
+                codec: map(codec),
+            },
+        }
+    }
+
+    /// Returns a mutable reference to the underlying decoder.
+    pub fn decoder_pin_mut(self: Pin<&mut Self>) -> &mut D {
+        self.project().inner.project().codec
+    }
+
     /// Returns a reference to the read buffer.
     pub fn read_buffer(&self) -> &BytesMut {
         &self.inner.state.buffer

tokio-util/src/codec/framed_write.rs

@@ -88,6 +88,32 @@ impl<T, E> FramedWrite<T, E> {
         &mut self.inner.codec
     }
 
+    /// Maps the encoder `E` to `C`, preserving the write buffer
+    /// wrapped by `Framed`.
+    pub fn map_encoder<C, F>(self, map: F) -> FramedWrite<T, C>
+    where
+        F: FnOnce(E) -> C,
+    {
+        // This could be potentially simplified once rust-lang/rust#86555 hits stable
+        let FramedImpl {
+            inner,
+            state,
+            codec,
+        } = self.inner;
+        FramedWrite {
+            inner: FramedImpl {
+                inner,
+                state,
+                codec: map(codec),
+            },
+        }
+    }
+
+    /// Returns a mutable reference to the underlying encoder.
+    pub fn encoder_pin_mut(self: Pin<&mut Self>) -> &mut E {
+        self.project().inner.project().codec
+    }
+
     /// Returns a reference to the write buffer.
     pub fn write_buffer(&self) -> &BytesMut {
         &self.inner.state.buffer

tokio-util/src/codec/length_delimited.rs

@@ -84,7 +84,7 @@
 //! # fn bind_read<T: AsyncRead>(io: T) {
 //! LengthDelimitedCodec::builder()
 //!     .length_field_offset(0) // default value
-//!     .length_field_length(2)
+//!     .length_field_type::<u16>()
 //!     .length_adjustment(0)   // default value
 //!     .num_skip(0) // Do not strip frame header
 //!     .new_read(io);
@@ -118,7 +118,7 @@
 //! # fn bind_read<T: AsyncRead>(io: T) {
 //! LengthDelimitedCodec::builder()
 //!     .length_field_offset(0) // default value
-//!     .length_field_length(2)
+//!     .length_field_type::<u16>()
 //!     .length_adjustment(0)   // default value
 //!     // `num_skip` is not needed, the default is to skip
 //!     .new_read(io);
@@ -150,7 +150,7 @@
 //! # fn bind_read<T: AsyncRead>(io: T) {
 //! LengthDelimitedCodec::builder()
 //!     .length_field_offset(0) // default value
-//!     .length_field_length(2)
+//!     .length_field_type::<u16>()
 //!     .length_adjustment(-2)  // size of head
 //!     .num_skip(0)
 //!     .new_read(io);
@@ -228,7 +228,7 @@
 //! # fn bind_read<T: AsyncRead>(io: T) {
 //! LengthDelimitedCodec::builder()
 //!     .length_field_offset(1) // length of hdr1
-//!     .length_field_length(2)
+//!     .length_field_type::<u16>()
 //!     .length_adjustment(1)  // length of hdr2
 //!     .num_skip(3) // length of hdr1 + LEN
 //!     .new_read(io);
@@ -274,7 +274,7 @@
 //! # fn bind_read<T: AsyncRead>(io: T) {
 //! LengthDelimitedCodec::builder()
 //!     .length_field_offset(1) // length of hdr1
-//!     .length_field_length(2)
+//!     .length_field_type::<u16>()
 //!     .length_adjustment(-3)  // length of hdr1 + LEN, negative
 //!     .num_skip(3)
 //!     .new_read(io);
@@ -350,7 +350,7 @@
 //! # fn write_frame<T: AsyncWrite>(io: T) {
 //! # let _ =
 //! LengthDelimitedCodec::builder()
-//!     .length_field_length(2)
+//!     .length_field_type::<u16>()
 //!     .new_write(io);
 //! # }
 //! # pub fn main() {}
@@ -379,7 +379,7 @@ use tokio::io::{AsyncRead, AsyncWrite};
 use bytes::{Buf, BufMut, Bytes, BytesMut};
 use std::error::Error as StdError;
 use std::io::{self, Cursor};
-use std::{cmp, fmt};
+use std::{cmp, fmt, mem};
 
 /// Configure length delimited `LengthDelimitedCodec`s.
 ///
@@ -421,7 +421,7 @@ pub struct LengthDelimitedCodecError {
 /// See [module level] documentation for more detail.
 ///
 /// [module level]: index.html
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct LengthDelimitedCodec {
     // Configuration values
     builder: Builder,
@@ -486,7 +486,7 @@ impl LengthDelimitedCodec {
             // Skip the required bytes
             src.advance(self.builder.length_field_offset);
 
-            // match endianess
+            // match endianness
             let n = if self.builder.length_field_is_big_endian {
                 src.get_uint(field_len)
             } else {
@@ -629,6 +629,24 @@ impl Default for LengthDelimitedCodec {
 
 // ===== impl Builder =====
 
+mod builder {
+    /// Types that can be used with `Builder::length_field_type`.
+    pub trait LengthFieldType {}
+
+    impl LengthFieldType for u8 {}
+    impl LengthFieldType for u16 {}
+    impl LengthFieldType for u32 {}
+    impl LengthFieldType for u64 {}
+
+    #[cfg(any(
+        target_pointer_width = "8",
+        target_pointer_width = "16",
+        target_pointer_width = "32",
+        target_pointer_width = "64",
+    ))]
+    impl LengthFieldType for usize {}
+}
+
 impl Builder {
     /// Creates a new length delimited codec builder with default configuration
     /// values.
@@ -642,7 +660,7 @@ impl Builder {
     /// # fn bind_read<T: AsyncRead>(io: T) {
     /// LengthDelimitedCodec::builder()
     ///     .length_field_offset(0)
-    ///     .length_field_length(2)
+    ///     .length_field_type::<u16>()
     ///     .length_adjustment(0)
     ///     .num_skip(0)
     ///     .new_read(io);
@@ -746,7 +764,7 @@ impl Builder {
         }
     }
 
-    /// Sets the max frame length
+    /// Sets the max frame length in bytes
     ///
     /// This configuration option applies to both encoding and decoding. The
     /// default value is 8MB.
@@ -767,7 +785,7 @@ impl Builder {
     ///
     /// # fn bind_read<T: AsyncRead>(io: T) {
     /// LengthDelimitedCodec::builder()
-    ///     .max_frame_length(8 * 1024)
+    ///     .max_frame_length(8 * 1024 * 1024)
     ///     .new_read(io);
     /// # }
     /// # pub fn main() {}
@@ -777,6 +795,42 @@ impl Builder {
         self
     }
 
+    /// Sets the unsigned integer type used to represent the length field.
+    ///
+    /// The default type is [`u32`]. The max type is [`u64`] (or [`usize`] on
+    /// 64-bit targets).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::io::AsyncRead;
+    /// use tokio_util::codec::LengthDelimitedCodec;
+    ///
+    /// # fn bind_read<T: AsyncRead>(io: T) {
+    /// LengthDelimitedCodec::builder()
+    ///     .length_field_type::<u32>()
+    ///     .new_read(io);
+    /// # }
+    /// # pub fn main() {}
+    /// ```
+    ///
+    /// Unlike [`Builder::length_field_length`], this does not fail at runtime
+    /// and instead produces a compile error:
+    ///
+    /// ```compile_fail
+    /// # use tokio::io::AsyncRead;
+    /// # use tokio_util::codec::LengthDelimitedCodec;
+    /// # fn bind_read<T: AsyncRead>(io: T) {
+    /// LengthDelimitedCodec::builder()
+    ///     .length_field_type::<u128>()
+    ///     .new_read(io);
+    /// # }
+    /// # pub fn main() {}
+    /// ```
+    pub fn length_field_type<T: builder::LengthFieldType>(&mut self) -> &mut Self {
+        self.length_field_length(mem::size_of::<T>())
+    }
+
     /// Sets the number of bytes used to represent the length field
     ///
     /// The default value is `4`. The max value is `8`.
@@ -878,7 +932,7 @@ impl Builder {
     /// # pub fn main() {
     /// LengthDelimitedCodec::builder()
     ///     .length_field_offset(0)
-    ///     .length_field_length(2)
+    ///     .length_field_type::<u16>()
     ///     .length_adjustment(0)
     ///     .num_skip(0)
     ///     .new_codec();
@@ -902,7 +956,7 @@ impl Builder {
     /// # fn bind_read<T: AsyncRead>(io: T) {
     /// LengthDelimitedCodec::builder()
     ///     .length_field_offset(0)
-    ///     .length_field_length(2)
+    ///     .length_field_type::<u16>()
     ///     .length_adjustment(0)
     ///     .num_skip(0)
     ///     .new_read(io);
@@ -925,7 +979,7 @@ impl Builder {
     /// # use tokio_util::codec::LengthDelimitedCodec;
     /// # fn write_frame<T: AsyncWrite>(io: T) {
     /// LengthDelimitedCodec::builder()
-    ///     .length_field_length(2)
+    ///     .length_field_type::<u16>()
     ///     .new_write(io);
     /// # }
     /// # pub fn main() {}
@@ -947,7 +1001,7 @@ impl Builder {
     /// # fn write_frame<T: AsyncRead + AsyncWrite>(io: T) {
     /// # let _ =
     /// LengthDelimitedCodec::builder()
-    ///     .length_field_length(2)
+    ///     .length_field_type::<u16>()
     ///     .new_framed(io);
     /// # }
     /// # pub fn main() {}

tokio-util/src/codec/lines_codec.rs

@@ -203,12 +203,12 @@ impl Default for LinesCodec {
     }
 }
 
-/// An error occured while encoding or decoding a line.
+/// An error occurred while encoding or decoding a line.
 #[derive(Debug)]
 pub enum LinesCodecError {
     /// The maximum line length was exceeded.
     MaxLineLengthExceeded,
-    /// An IO error occured.
+    /// An IO error occurred.
     Io(io::Error),
 }
 

tokio-util/src/compat.rs

@@ -13,6 +13,7 @@ pin_project! {
     pub struct Compat<T> {
         #[pin]
         inner: T,
+        seek_pos: Option<io::SeekFrom>,
     }
 }
 
@@ -80,7 +81,10 @@ impl<T: tokio::io::AsyncWrite> TokioAsyncWriteCompatExt for T {}
 
 impl<T> Compat<T> {
     fn new(inner: T) -> Self {
-        Self { inner }
+        Self {
+            inner,
+            seek_pos: None,
+        }
     }
 
     /// Get a reference to the `Future`, `Stream`, `AsyncRead`, or `AsyncWrite` object
@@ -216,6 +220,45 @@ where
     }
 }
 
+impl<T: tokio::io::AsyncSeek> futures_io::AsyncSeek for Compat<T> {
+    fn poll_seek(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        pos: io::SeekFrom,
+    ) -> Poll<io::Result<u64>> {
+        if self.seek_pos != Some(pos) {
+            self.as_mut().project().inner.start_seek(pos)?;
+            *self.as_mut().project().seek_pos = Some(pos);
+        }
+        let res = ready!(self.as_mut().project().inner.poll_complete(cx));
+        *self.as_mut().project().seek_pos = None;
+        Poll::Ready(res.map(|p| p as u64))
+    }
+}
+
+impl<T: futures_io::AsyncSeek> tokio::io::AsyncSeek for Compat<T> {
+    fn start_seek(mut self: Pin<&mut Self>, pos: io::SeekFrom) -> io::Result<()> {
+        *self.as_mut().project().seek_pos = Some(pos);
+        Ok(())
+    }
+
+    fn poll_complete(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
+        let pos = match self.seek_pos {
+            None => {
+                // tokio 1.x AsyncSeek recommends calling poll_complete before start_seek.
+                // We don't have to guarantee that the value returned by
+                // poll_complete called without start_seek is correct,
+                // so we'll return 0.
+                return Poll::Ready(Ok(0));
+            }
+            Some(pos) => pos,
+        };
+        let res = ready!(self.as_mut().project().inner.poll_seek(cx, pos));
+        *self.as_mut().project().seek_pos = None;
+        Poll::Ready(res.map(|p| p as u64))
+    }
+}
+
 #[cfg(unix)]
 impl<T: std::os::unix::io::AsRawFd> std::os::unix::io::AsRawFd for Compat<T> {
     fn as_raw_fd(&self) -> std::os::unix::io::RawFd {

tokio-util/src/either.rs

@@ -67,7 +67,7 @@ pub enum Either<L, R> {
 }
 
 /// A small helper macro which reduces amount of boilerplate in the actual trait method implementation.
-/// It takes an invokation of method as an argument (e.g. `self.poll(cx)`), and redirects it to either
+/// It takes an invocation of method as an argument (e.g. `self.poll(cx)`), and redirects it to either
 /// enum variant held in `self`.
 macro_rules! delegate_call {
     ($self:ident.$method:ident($($args:ident),+)) => {

tokio-util/src/io/mod.rs

@@ -1,14 +1,22 @@
 //! Helpers for IO related tasks.
 //!
-//! These types are often used in combination with hyper or reqwest, as they
+//! The stream types are often used in combination with hyper or reqwest, as they
 //! allow converting between a hyper [`Body`] and [`AsyncRead`].
 //!
+//! The [`SyncIoBridge`] type converts from the world of async I/O
+//! to synchronous I/O; this may often come up when using synchronous APIs
+//! inside [`tokio::task::spawn_blocking`].
+//!
 //! [`Body`]: https://docs.rs/hyper/0.13/hyper/struct.Body.html
 //! [`AsyncRead`]: tokio::io::AsyncRead
 
 mod read_buf;
 mod reader_stream;
 mod stream_reader;
+cfg_io_util! {
+    mod sync_bridge;
+    pub use self::sync_bridge::SyncIoBridge;
+}
 
 pub use self::read_buf::read_buf;
 pub use self::reader_stream::ReaderStream;

tokio-util/src/io/reader_stream.rs

@@ -5,7 +5,7 @@ use std::pin::Pin;
 use std::task::{Context, Poll};
 use tokio::io::AsyncRead;
 
-const CAPACITY: usize = 4096;
+const DEFAULT_CAPACITY: usize = 4096;
 
 pin_project! {
     /// Convert an [`AsyncRead`] into a [`Stream`] of byte chunks.
@@ -50,6 +50,7 @@ pin_project! {
         reader: Option<R>,
         // Working buffer, used to optimize allocations.
         buf: BytesMut,
+        capacity: usize,
     }
 }
 
@@ -63,6 +64,21 @@ impl<R: AsyncRead> ReaderStream<R> {
         ReaderStream {
             reader: Some(reader),
             buf: BytesMut::new(),
+            capacity: DEFAULT_CAPACITY,
+        }
+    }
+
+    /// Convert an [`AsyncRead`] into a [`Stream`] with item type
+    /// `Result<Bytes, std::io::Error>`,
+    /// with a specific read buffer initial capacity.
+    ///
+    /// [`AsyncRead`]: tokio::io::AsyncRead
+    /// [`Stream`]: futures_core::Stream
+    pub fn with_capacity(reader: R, capacity: usize) -> Self {
+        ReaderStream {
+            reader: Some(reader),
+            buf: BytesMut::with_capacity(capacity),
+            capacity,
         }
     }
 }
@@ -80,7 +96,7 @@ impl<R: AsyncRead> Stream for ReaderStream<R> {
         };
 
         if this.buf.capacity() == 0 {
-            this.buf.reserve(CAPACITY);
+            this.buf.reserve(*this.capacity);
         }
 
         match poll_read_buf(reader, cx, &mut this.buf) {

tokio-util/src/io/stream_reader.rs

@@ -84,13 +84,24 @@ where
     }
 
     /// Do we have a chunk and is it non-empty?
-    fn has_chunk(self: Pin<&mut Self>) -> bool {
-        if let Some(chunk) = self.project().chunk {
+    fn has_chunk(&self) -> bool {
+        if let Some(ref chunk) = self.chunk {
             chunk.remaining() > 0
         } else {
             false
         }
     }
+
+    /// Consumes this `StreamReader`, returning a Tuple consisting
+    /// of the underlying stream and an Option of the interal buffer,
+    /// which is Some in case the buffer contains elements.
+    pub fn into_inner_with_chunk(self) -> (S, Option<B>) {
+        if self.has_chunk() {
+            (self.inner, self.chunk)
+        } else {
+            (self.inner, None)
+        }
+    }
 }
 
 impl<S, B> StreamReader<S, B> {
@@ -118,6 +129,10 @@ impl<S, B> StreamReader<S, B> {
     /// Consumes this `BufWriter`, returning the underlying stream.
     ///
     /// Note that any leftover data in the internal buffer is lost.
+    /// If you additionally want access to the internal buffer use
+    /// [`into_inner_with_chunk`].
+    ///
+    /// [`into_inner_with_chunk`]: crate::io::StreamReader::into_inner_with_chunk
     pub fn into_inner(self) -> S {
         self.inner
     }

tokio-util/src/io/sync_bridge.rs

@@ -0,0 +1,103 @@
+use std::io::{Read, Write};
+use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
+
+/// Use a [`tokio::io::AsyncRead`] synchronously as a [`std::io::Read`] or
+/// a [`tokio::io::AsyncWrite`] as a [`std::io::Write`].
+#[derive(Debug)]
+pub struct SyncIoBridge<T> {
+    src: T,
+    rt: tokio::runtime::Handle,
+}
+
+impl<T: AsyncRead + Unpin> Read for SyncIoBridge<T> {
+    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+        let src = &mut self.src;
+        self.rt.block_on(AsyncReadExt::read(src, buf))
+    }
+
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> std::io::Result<usize> {
+        let src = &mut self.src;
+        self.rt.block_on(src.read_to_end(buf))
+    }
+
+    fn read_to_string(&mut self, buf: &mut String) -> std::io::Result<usize> {
+        let src = &mut self.src;
+        self.rt.block_on(src.read_to_string(buf))
+    }
+
+    fn read_exact(&mut self, buf: &mut [u8]) -> std::io::Result<()> {
+        let src = &mut self.src;
+        // The AsyncRead trait returns the count, synchronous doesn't.
+        let _n = self.rt.block_on(src.read_exact(buf))?;
+        Ok(())
+    }
+}
+
+impl<T: AsyncWrite + Unpin> Write for SyncIoBridge<T> {
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        let src = &mut self.src;
+        self.rt.block_on(src.write(buf))
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        let src = &mut self.src;
+        self.rt.block_on(src.flush())
+    }
+
+    fn write_all(&mut self, buf: &[u8]) -> std::io::Result<()> {
+        let src = &mut self.src;
+        self.rt.block_on(src.write_all(buf))
+    }
+
+    fn write_vectored(&mut self, bufs: &[std::io::IoSlice<'_>]) -> std::io::Result<usize> {
+        let src = &mut self.src;
+        self.rt.block_on(src.write_vectored(bufs))
+    }
+}
+
+// Because https://doc.rust-lang.org/std/io/trait.Write.html#method.is_write_vectored is at the time
+// of this writing still unstable, we expose this as part of a standalone method.
+impl<T: AsyncWrite> SyncIoBridge<T> {
+    /// Determines if the underlying [`tokio::io::AsyncWrite`] target supports efficient vectored writes.
+    ///
+    /// See [`tokio::io::AsyncWrite::is_write_vectored`].
+    pub fn is_write_vectored(&self) -> bool {
+        self.src.is_write_vectored()
+    }
+}
+
+impl<T: Unpin> SyncIoBridge<T> {
+    /// Use a [`tokio::io::AsyncRead`] synchronously as a [`std::io::Read`] or
+    /// a [`tokio::io::AsyncWrite`] as a [`std::io::Write`].
+    ///
+    /// When this struct is created, it captures a handle to the current thread's runtime with [`tokio::runtime::Handle::current`].
+    /// It is hence OK to move this struct into a separate thread outside the runtime, as created
+    /// by e.g. [`tokio::task::spawn_blocking`].
+    ///
+    /// Stated even more strongly: to make use of this bridge, you *must* move
+    /// it into a separate thread outside the runtime.  The synchronous I/O will use the
+    /// underlying handle to block on the backing asynchronous source, via
+    /// [`tokio::runtime::Handle::block_on`].  As noted in the documentation for that
+    /// function, an attempt to `block_on` from an asynchronous execution context
+    /// will panic.
+    ///
+    /// # Wrapping `!Unpin` types
+    ///
+    /// Use e.g. `SyncIoBridge::new(Box::pin(src))`.
+    ///
+    /// # Panic
+    ///
+    /// This will panic if called outside the context of a Tokio runtime.
+    pub fn new(src: T) -> Self {
+        Self::new_with_handle(src, tokio::runtime::Handle::current())
+    }
+
+    /// Use a [`tokio::io::AsyncRead`] synchronously as a [`std::io::Read`] or
+    /// a [`tokio::io::AsyncWrite`] as a [`std::io::Write`].
+    ///
+    /// This is the same as [`SyncIoBridge::new`], but allows passing an arbitrary handle and hence may
+    /// be initially invoked outside of an asynchronous context.
+    pub fn new_with_handle(src: T, rt: tokio::runtime::Handle) -> Self {
+        Self { src, rt }
+    }
+}

tokio-util/src/lib.rs

@@ -5,7 +5,6 @@
     rust_2018_idioms,
     unreachable_pub
 )]
-#![cfg_attr(docsrs, deny(broken_intra_doc_links))]
 #![doc(test(
     no_crate_inject,
     attr(deny(warnings, rust_2018_idioms), allow(dead_code, unused_variables))
@@ -31,6 +30,7 @@ cfg_codec! {
 
 cfg_net! {
     pub mod udp;
+    pub mod net;
 }
 
 cfg_compat! {
@@ -43,6 +43,7 @@ cfg_io! {
 
 cfg_rt! {
     pub mod context;
+    pub mod task;
 }
 
 cfg_time! {
@@ -114,6 +115,9 @@ mod util {
 
         let n = {
             let dst = buf.chunk_mut();
+
+            // Safety: `chunk_mut()` returns a `&mut UninitSlice`, and `UninitSlice` is a
+            // transparent wrapper around `[MaybeUninit<u8>]`.
             let dst = unsafe { &mut *(dst as *mut _ as *mut [MaybeUninit<u8>]) };
             let mut buf = ReadBuf::uninit(dst);
             let ptr = buf.filled().as_ptr();

tokio-util/src/net/mod.rs

@@ -0,0 +1,97 @@
+//! TCP/UDP/Unix helpers for tokio.
+
+use crate::either::Either;
+use std::future::Future;
+use std::io::Result;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+#[cfg(unix)]
+pub mod unix;
+
+/// A trait for a listener: `TcpListener` and `UnixListener`.
+pub trait Listener {
+    /// The stream's type of this listener.
+    type Io: tokio::io::AsyncRead + tokio::io::AsyncWrite;
+    /// The socket address type of this listener.
+    type Addr;
+
+    /// Polls to accept a new incoming connection to this listener.
+    fn poll_accept(&mut self, cx: &mut Context<'_>) -> Poll<Result<(Self::Io, Self::Addr)>>;
+
+    /// Accepts a new incoming connection from this listener.
+    fn accept(&mut self) -> ListenerAcceptFut<'_, Self>
+    where
+        Self: Sized,
+    {
+        ListenerAcceptFut { listener: self }
+    }
+
+    /// Returns the local address that this listener is bound to.
+    fn local_addr(&self) -> Result<Self::Addr>;
+}
+
+impl Listener for tokio::net::TcpListener {
+    type Io = tokio::net::TcpStream;
+    type Addr = std::net::SocketAddr;
+
+    fn poll_accept(&mut self, cx: &mut Context<'_>) -> Poll<Result<(Self::Io, Self::Addr)>> {
+        Self::poll_accept(self, cx)
+    }
+
+    fn local_addr(&self) -> Result<Self::Addr> {
+        self.local_addr().map(Into::into)
+    }
+}
+
+/// Future for accepting a new connection from a listener.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct ListenerAcceptFut<'a, L> {
+    listener: &'a mut L,
+}
+
+impl<'a, L> Future for ListenerAcceptFut<'a, L>
+where
+    L: Listener,
+{
+    type Output = Result<(L::Io, L::Addr)>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.listener.poll_accept(cx)
+    }
+}
+
+impl<L, R> Either<L, R>
+where
+    L: Listener,
+    R: Listener,
+{
+    /// Accepts a new incoming connection from this listener.
+    pub async fn accept(&mut self) -> Result<Either<(L::Io, L::Addr), (R::Io, R::Addr)>> {
+        match self {
+            Either::Left(listener) => {
+                let (stream, addr) = listener.accept().await?;
+                Ok(Either::Left((stream, addr)))
+            }
+            Either::Right(listener) => {
+                let (stream, addr) = listener.accept().await?;
+                Ok(Either::Right((stream, addr)))
+            }
+        }
+    }
+
+    /// Returns the local address that this listener is bound to.
+    pub fn local_addr(&self) -> Result<Either<L::Addr, R::Addr>> {
+        match self {
+            Either::Left(listener) => {
+                let addr = listener.local_addr()?;
+                Ok(Either::Left(addr))
+            }
+            Either::Right(listener) => {
+                let addr = listener.local_addr()?;
+                Ok(Either::Right(addr))
+            }
+        }
+    }
+}

tokio-util/src/net/unix/mod.rs

@@ -0,0 +1,18 @@
+//! Unix domain socket helpers.
+
+use super::Listener;
+use std::io::Result;
+use std::task::{Context, Poll};
+
+impl Listener for tokio::net::UnixListener {
+    type Io = tokio::net::UnixStream;
+    type Addr = tokio::net::unix::SocketAddr;
+
+    fn poll_accept(&mut self, cx: &mut Context<'_>) -> Poll<Result<(Self::Io, Self::Addr)>> {
+        Self::poll_accept(self, cx)
+    }
+
+    fn local_addr(&self) -> Result<Self::Addr> {
+        self.local_addr().map(Into::into)
+    }
+}

tokio-util/src/sync/cancellation_token.rs

@@ -1,15 +1,15 @@
 //! An asynchronously awaitable `CancellationToken`.
 //! The token allows to signal a cancellation request to one or more tasks.
+pub(crate) mod guard;
+mod tree_node;
 
-use crate::loom::sync::atomic::AtomicUsize;
-use crate::loom::sync::Mutex;
-use crate::sync::intrusive_double_linked_list::{LinkedList, ListNode};
-
+use crate::loom::sync::Arc;
 use core::future::Future;
 use core::pin::Pin;
-use core::ptr::NonNull;
-use core::sync::atomic::Ordering;
-use core::task::{Context, Poll, Waker};
+use core::task::{Context, Poll};
+
+use guard::DropGuard;
+use pin_project_lite::pin_project;
 
 /// A token which can be used to signal a cancellation request to one or more
 /// tasks.
@@ -21,9 +21,9 @@ use core::task::{Context, Poll, Waker};
 ///
 /// # Examples
 ///
-/// ```ignore
+/// ```no_run
 /// use tokio::select;
-/// use tokio::scope::CancellationToken;
+/// use tokio_util::sync::CancellationToken;
 ///
 /// #[tokio::main]
 /// async fn main() {
@@ -52,31 +52,20 @@ use core::task::{Context, Poll, Waker};
 /// }
 /// ```
 pub struct CancellationToken {
-    inner: NonNull<CancellationTokenState>,
+    inner: Arc<tree_node::TreeNode>,
 }
 
-// Safety: The CancellationToken is thread-safe and can be moved between threads,
-// since all methods are internally synchronized.
-unsafe impl Send for CancellationToken {}
-unsafe impl Sync for CancellationToken {}
-
-/// A Future that is resolved once the corresponding [`CancellationToken`]
-/// was cancelled
-#[must_use = "futures do nothing unless polled"]
-pub struct WaitForCancellationFuture<'a> {
-    /// The CancellationToken that is associated with this WaitForCancellationFuture
-    cancellation_token: Option<&'a CancellationToken>,
-    /// Node for waiting at the cancellation_token
-    wait_node: ListNode<WaitQueueEntry>,
-    /// Whether this future was registered at the token yet as a waiter
-    is_registered: bool,
+pin_project! {
+    /// A Future that is resolved once the corresponding [`CancellationToken`]
+    /// is cancelled.
+    #[must_use = "futures do nothing unless polled"]
+    pub struct WaitForCancellationFuture<'a> {
+        cancellation_token: &'a CancellationToken,
+        #[pin]
+        future: tokio::sync::futures::Notified<'a>,
+    }
 }
 
-// Safety: Futures can be sent between threads as long as the underlying
-// cancellation_token is thread-safe (Sync),
-// which allows to poll/register/unregister from a different thread.
-unsafe impl<'a> Send for WaitForCancellationFuture<'a> {}
-
 // ===== impl CancellationToken =====
 
 impl core::fmt::Debug for CancellationToken {
@@ -89,43 +78,16 @@ impl core::fmt::Debug for CancellationToken {
 
 impl Clone for CancellationToken {
     fn clone(&self) -> Self {
-        // Safety: The state inside a `CancellationToken` is always valid, since
-        // is reference counted
-        let inner = self.state();
-
-        // Tokens are cloned by increasing their refcount
-        let current_state = inner.snapshot();
-        inner.increment_refcount(current_state);
-
-        CancellationToken { inner: self.inner }
+        tree_node::increase_handle_refcount(&self.inner);
+        CancellationToken {
+            inner: self.inner.clone(),
+        }
     }
 }
 
 impl Drop for CancellationToken {
     fn drop(&mut self) {
-        let token_state_pointer = self.inner;
-
-        // Safety: The state inside a `CancellationToken` is always valid, since
-        // is reference counted
-        let inner = unsafe { &mut *self.inner.as_ptr() };
-
-        let mut current_state = inner.snapshot();
-
-        // We need to safe the parent, since the state might be released by the
-        // next call
-        let parent = inner.parent;
-
-        // Drop our own refcount
-        current_state = inner.decrement_refcount(current_state);
-
-        // If this was the last reference, unregister from the parent
-        if current_state.refcount == 0 {
-            if let Some(mut parent) = parent {
-                // Safety: Since we still retain a reference on the parent, it must be valid.
-                let parent = unsafe { parent.as_mut() };
-                parent.unregister_child(token_state_pointer, current_state);
-            }
-        }
+        tree_node::decrease_handle_refcount(&self.inner);
     }
 }
 
@@ -138,29 +100,11 @@ impl Default for CancellationToken {
 impl CancellationToken {
     /// Creates a new CancellationToken in the non-cancelled state.
     pub fn new() -> CancellationToken {
-        let state = Box::new(CancellationTokenState::new(
-            None,
-            StateSnapshot {
-                cancel_state: CancellationState::NotCancelled,
-                has_parent_ref: false,
-                refcount: 1,
-            },
-        ));
-
-        // Safety: We just created the Box. The pointer is guaranteed to be
-        // not null
         CancellationToken {
-            inner: unsafe { NonNull::new_unchecked(Box::into_raw(state)) },
+            inner: Arc::new(tree_node::TreeNode::new()),
         }
     }
 
-    /// Returns a reference to the utilized `CancellationTokenState`.
-    fn state(&self) -> &CancellationTokenState {
-        // Safety: The state inside a `CancellationToken` is always valid, since
-        // is reference counted
-        unsafe { &*self.inner.as_ptr() }
-    }
-
     /// Creates a `CancellationToken` which will get cancelled whenever the
     /// current token gets cancelled.
     ///
@@ -169,9 +113,9 @@ impl CancellationToken {
     ///
     /// # Examples
     ///
-    /// ```ignore
+    /// ```no_run
     /// use tokio::select;
-    /// use tokio::scope::CancellationToken;
+    /// use tokio_util::sync::CancellationToken;
     ///
     /// #[tokio::main]
     /// async fn main() {
@@ -200,56 +144,8 @@ impl CancellationToken {
     /// }
     /// ```
     pub fn child_token(&self) -> CancellationToken {
-        let inner = self.state();
-
-        // Increment the refcount of this token. It will be referenced by the
-        // child, independent of whether the child is immediately cancelled or
-        // not.
-        let _current_state = inner.increment_refcount(inner.snapshot());
-
-        let mut unpacked_child_state = StateSnapshot {
-            has_parent_ref: true,
-            refcount: 1,
-            cancel_state: CancellationState::NotCancelled,
-        };
-        let mut child_token_state = Box::new(CancellationTokenState::new(
-            Some(self.inner),
-            unpacked_child_state,
-        ));
-
-        {
-            let mut guard = inner.synchronized.lock().unwrap();
-            if guard.is_cancelled {
-                // This task was already cancelled. In this case we should not
-                // insert the child into the list, since it would never get removed
-                // from the list.
-                (*child_token_state.synchronized.lock().unwrap()).is_cancelled = true;
-                unpacked_child_state.cancel_state = CancellationState::Cancelled;
-                // Since it's not in the list, the parent doesn't need to retain
-                // a reference to it.
-                unpacked_child_state.has_parent_ref = false;
-                child_token_state
-                    .state
-                    .store(unpacked_child_state.pack(), Ordering::SeqCst);
-            } else {
-                if let Some(mut first_child) = guard.first_child {
-                    child_token_state.from_parent.next_peer = Some(first_child);
-                    // Safety: We manipulate other child task inside the Mutex
-                    // and retain a parent reference on it. The child token can't
-                    // get invalidated while the Mutex is held.
-                    unsafe {
-                        first_child.as_mut().from_parent.prev_peer =
-                            Some((&mut *child_token_state).into())
-                    };
-                }
-                guard.first_child = Some((&mut *child_token_state).into());
-            }
-        };
-
-        let child_token_ptr = Box::into_raw(child_token_state);
-        // Safety: We just created the pointer from a `Box`
         CancellationToken {
-            inner: unsafe { NonNull::new_unchecked(child_token_ptr) },
+            inner: tree_node::child_node(&self.inner),
         }
     }
 
@@ -257,42 +153,42 @@ impl CancellationToken {
     /// derived from it.
     ///
     /// This will wake up all tasks which are waiting for cancellation.
+    ///
+    /// Be aware that cancellation is not an atomic operation. It is possible
+    /// for another thread running in parallel with a call to `cancel` to first
+    /// receive `true` from `is_cancelled` on one child node, and then receive
+    /// `false` from `is_cancelled` on another child node. However, once the
+    /// call to `cancel` returns, all child nodes have been fully cancelled.
     pub fn cancel(&self) {
-        self.state().cancel();
+        tree_node::cancel(&self.inner);
     }
 
-    /// Returns `true` if the `CancellationToken` had been cancelled
+    /// Returns `true` if the `CancellationToken` is cancelled.
     pub fn is_cancelled(&self) -> bool {
-        self.state().is_cancelled()
+        tree_node::is_cancelled(&self.inner)
     }
 
     /// Returns a `Future` that gets fulfilled when cancellation is requested.
+    ///
+    /// The future will complete immediately if the token is already cancelled
+    /// when this method is called.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe.
     pub fn cancelled(&self) -> WaitForCancellationFuture<'_> {
         WaitForCancellationFuture {
-            cancellation_token: Some(self),
-            wait_node: ListNode::new(WaitQueueEntry::new()),
-            is_registered: false,
+            cancellation_token: self,
+            future: self.inner.notified(),
         }
     }
 
-    unsafe fn register(
-        &self,
-        wait_node: &mut ListNode<WaitQueueEntry>,
-        cx: &mut Context<'_>,
-    ) -> Poll<()> {
-        self.state().register(wait_node, cx)
-    }
-
-    fn check_for_cancellation(
-        &self,
-        wait_node: &mut ListNode<WaitQueueEntry>,
-        cx: &mut Context<'_>,
-    ) -> Poll<()> {
-        self.state().check_for_cancellation(wait_node, cx)
-    }
-
-    fn unregister(&self, wait_node: &mut ListNode<WaitQueueEntry>) {
-        self.state().unregister(wait_node)
+    /// Creates a `DropGuard` for this token.
+    ///
+    /// Returned guard will cancel this token (and all its children) on drop
+    /// unless disarmed.
+    pub fn drop_guard(self) -> DropGuard {
+        DropGuard { inner: Some(self) }
     }
 }
 
@@ -308,560 +204,21 @@ impl<'a> Future for WaitForCancellationFuture<'a> {
     type Output = ();
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
-        // Safety: We do not move anything out of `WaitForCancellationFuture`
-        let mut_self: &mut WaitForCancellationFuture<'_> = unsafe { Pin::get_unchecked_mut(self) };
-
-        let cancellation_token = mut_self
-            .cancellation_token
-            .expect("polled WaitForCancellationFuture after completion");
-
-        let poll_res = if !mut_self.is_registered {
-            // Safety: The `ListNode` is pinned through the Future,
-            // and we will unregister it in `WaitForCancellationFuture::drop`
-            // before the Future is dropped and the memory reference is invalidated.
-            unsafe { cancellation_token.register(&mut mut_self.wait_node, cx) }
-        } else {
-            cancellation_token.check_for_cancellation(&mut mut_self.wait_node, cx)
-        };
-
-        if let Poll::Ready(()) = poll_res {
-            // The cancellation_token was signalled
-            mut_self.cancellation_token = None;
-            // A signalled Token means the Waker won't be enqueued anymore
-            mut_self.is_registered = false;
-            mut_self.wait_node.task = None;
-        } else {
-            // This `Future` and its stored `Waker` stay registered at the
-            // `CancellationToken`
-            mut_self.is_registered = true;
-        }
-
-        poll_res
-    }
-}
-
-impl<'a> Drop for WaitForCancellationFuture<'a> {
-    fn drop(&mut self) {
-        // If this WaitForCancellationFuture has been polled and it was added to the
-        // wait queue at the cancellation_token, it must be removed before dropping.
-        // Otherwise the cancellation_token would access invalid memory.
-        if let Some(token) = self.cancellation_token {
-            if self.is_registered {
-                token.unregister(&mut self.wait_node);
-            }
-        }
-    }
-}
-
-/// Tracks how the future had interacted with the [`CancellationToken`]
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
-enum PollState {
-    /// The task has never interacted with the [`CancellationToken`].
-    New,
-    /// The task was added to the wait queue at the [`CancellationToken`].
-    Waiting,
-    /// The task has been polled to completion.
-    Done,
-}
-
-/// Tracks the WaitForCancellationFuture waiting state.
-/// Access to this struct is synchronized through the mutex in the CancellationToken.
-struct WaitQueueEntry {
-    /// The task handle of the waiting task
-    task: Option<Waker>,
-    // Current polling state. This state is only updated inside the Mutex of
-    // the CancellationToken.
-    state: PollState,
-}
-
-impl WaitQueueEntry {
-    /// Creates a new WaitQueueEntry
-    fn new() -> WaitQueueEntry {
-        WaitQueueEntry {
-            task: None,
-            state: PollState::New,
-        }
-    }
-}
-
-struct SynchronizedState {
-    waiters: LinkedList<WaitQueueEntry>,
-    first_child: Option<NonNull<CancellationTokenState>>,
-    is_cancelled: bool,
-}
-
-impl SynchronizedState {
-    fn new() -> Self {
-        Self {
-            waiters: LinkedList::new(),
-            first_child: None,
-            is_cancelled: false,
-        }
-    }
-}
-
-/// Information embedded in child tokens which is synchronized through the Mutex
-/// in their parent.
-struct SynchronizedThroughParent {
-    next_peer: Option<NonNull<CancellationTokenState>>,
-    prev_peer: Option<NonNull<CancellationTokenState>>,
-}
-
-/// Possible states of a `CancellationToken`
-#[derive(Debug, Copy, Clone, PartialEq, Eq)]
-enum CancellationState {
-    NotCancelled = 0,
-    Cancelling = 1,
-    Cancelled = 2,
-}
-
-impl CancellationState {
-    fn pack(self) -> usize {
-        self as usize
-    }
-
-    fn unpack(value: usize) -> Self {
-        match value {
-            0 => CancellationState::NotCancelled,
-            1 => CancellationState::Cancelling,
-            2 => CancellationState::Cancelled,
-            _ => unreachable!("Invalid value"),
-        }
-    }
-}
-
-#[derive(Debug, Copy, Clone, PartialEq, Eq)]
-struct StateSnapshot {
-    /// The amount of references to this particular CancellationToken.
-    /// `CancellationToken` structs hold these references to a `CancellationTokenState`.
-    /// Also the state is referenced by the state of each child.
-    refcount: usize,
-    /// Whether the state is still referenced by it's parent and can therefore
-    /// not be freed.
-    has_parent_ref: bool,
-    /// Whether the token is cancelled
-    cancel_state: CancellationState,
-}
-
-impl StateSnapshot {
-    /// Packs the snapshot into a `usize`
-    fn pack(self) -> usize {
-        self.refcount << 3 | if self.has_parent_ref { 4 } else { 0 } | self.cancel_state.pack()
-    }
-
-    /// Unpacks the snapshot from a `usize`
-    fn unpack(value: usize) -> Self {
-        let refcount = value >> 3;
-        let has_parent_ref = value & 4 != 0;
-        let cancel_state = CancellationState::unpack(value & 0x03);
-
-        StateSnapshot {
-            refcount,
-            has_parent_ref,
-            cancel_state,
-        }
-    }
-
-    /// Whether this `CancellationTokenState` is still referenced by any
-    /// `CancellationToken`.
-    fn has_refs(&self) -> bool {
-        self.refcount != 0 || self.has_parent_ref
-    }
-}
-
-/// The maximum permitted amount of references to a CancellationToken. This
-/// is derived from the intent to never use more than 32bit in the `Snapshot`.
-const MAX_REFS: u32 = (std::u32::MAX - 7) >> 3;
-
-/// Internal state of the `CancellationToken` pair above
-struct CancellationTokenState {
-    state: AtomicUsize,
-    parent: Option<NonNull<CancellationTokenState>>,
-    from_parent: SynchronizedThroughParent,
-    synchronized: Mutex<SynchronizedState>,
-}
-
-impl CancellationTokenState {
-    fn new(
-        parent: Option<NonNull<CancellationTokenState>>,
-        state: StateSnapshot,
-    ) -> CancellationTokenState {
-        CancellationTokenState {
-            parent,
-            from_parent: SynchronizedThroughParent {
-                prev_peer: None,
-                next_peer: None,
-            },
-            state: AtomicUsize::new(state.pack()),
-            synchronized: Mutex::new(SynchronizedState::new()),
-        }
-    }
-
-    /// Returns a snapshot of the current atomic state of the token
-    fn snapshot(&self) -> StateSnapshot {
-        StateSnapshot::unpack(self.state.load(Ordering::SeqCst))
-    }
-
-    fn atomic_update_state<F>(&self, mut current_state: StateSnapshot, func: F) -> StateSnapshot
-    where
-        F: Fn(StateSnapshot) -> StateSnapshot,
-    {
-        let mut current_packed_state = current_state.pack();
+        let mut this = self.project();
         loop {
-            let next_state = func(current_state);
-            match self.state.compare_exchange(
-                current_packed_state,
-                next_state.pack(),
-                Ordering::SeqCst,
-                Ordering::SeqCst,
-            ) {
-                Ok(_) => {
-                    return next_state;
-                }
-                Err(actual) => {
-                    current_packed_state = actual;
-                    current_state = StateSnapshot::unpack(actual);
-                }
-            }
-        }
-    }
-
-    fn increment_refcount(&self, current_state: StateSnapshot) -> StateSnapshot {
-        self.atomic_update_state(current_state, |mut state: StateSnapshot| {
-            if state.refcount >= MAX_REFS as usize {
-                eprintln!("[ERROR] Maximum reference count for CancellationToken was exceeded");
-                std::process::abort();
-            }
-            state.refcount += 1;
-            state
-        })
-    }
-
-    fn decrement_refcount(&self, current_state: StateSnapshot) -> StateSnapshot {
-        let current_state = self.atomic_update_state(current_state, |mut state: StateSnapshot| {
-            state.refcount -= 1;
-            state
-        });
-
-        // Drop the State if it is not referenced anymore
-        if !current_state.has_refs() {
-            // Safety: `CancellationTokenState` is always stored in refcounted
-            // Boxes
-            let _ = unsafe { Box::from_raw(self as *const Self as *mut Self) };
-        }
-
-        current_state
-    }
-
-    fn remove_parent_ref(&self, current_state: StateSnapshot) -> StateSnapshot {
-        let current_state = self.atomic_update_state(current_state, |mut state: StateSnapshot| {
-            state.has_parent_ref = false;
-            state
-        });
-
-        // Drop the State if it is not referenced anymore
-        if !current_state.has_refs() {
-            // Safety: `CancellationTokenState` is always stored in refcounted
-            // Boxes
-            let _ = unsafe { Box::from_raw(self as *const Self as *mut Self) };
-        }
-
-        current_state
-    }
-
-    /// Unregisters a child from the parent token.
-    /// The child tokens state is not exactly known at this point in time.
-    /// If the parent token is cancelled, the child token gets removed from the
-    /// parents list, and might therefore already have been freed. If the parent
-    /// token is not cancelled, the child token is still valid.
-    fn unregister_child(
-        &mut self,
-        mut child_state: NonNull<CancellationTokenState>,
-        current_child_state: StateSnapshot,
-    ) {
-        let removed_child = {
-            // Remove the child toke from the parents linked list
-            let mut guard = self.synchronized.lock().unwrap();
-            if !guard.is_cancelled {
-                // Safety: Since the token was not cancelled, the child must
-                // still be in the list and valid.
-                let mut child_state = unsafe { child_state.as_mut() };
-                debug_assert!(child_state.snapshot().has_parent_ref);
-
-                if guard.first_child == Some(child_state.into()) {
-                    guard.first_child = child_state.from_parent.next_peer;
-                }
-                // Safety: If peers wouldn't be valid anymore, they would try
-                // to remove themselves from the list. This would require locking
-                // the Mutex that we currently own.
-                unsafe {
-                    if let Some(mut prev_peer) = child_state.from_parent.prev_peer {
-                        prev_peer.as_mut().from_parent.next_peer =
-                            child_state.from_parent.next_peer;
-                    }
-                    if let Some(mut next_peer) = child_state.from_parent.next_peer {
-                        next_peer.as_mut().from_parent.prev_peer =
-                            child_state.from_parent.prev_peer;
-                    }
-                }
-                child_state.from_parent.prev_peer = None;
-                child_state.from_parent.next_peer = None;
-
-                // The child is no longer referenced by the parent, since we were able
-                // to remove its reference from the parents list.
-                true
-            } else {
-                // Do not touch the linked list anymore. If the parent is cancelled
-                // it will move all childs outside of the Mutex and manipulate
-                // the pointers there. Manipulating the pointers here too could
-                // lead to races. Therefore leave them just as as and let the
-                // parent deal with it. The parent will make sure to retain a
-                // reference to this state as long as it manipulates the list
-                // pointers. Therefore the pointers are not dangling.
-                false
-            }
-        };
-
-        if removed_child {
-            // If the token removed itself from the parents list, it can reset
-            // the parent ref status. If it is isn't able to do so, because the
-            // parent removed it from the list, there is no need to do this.
-            // The parent ref acts as as another reference count. Therefore
-            // removing this reference can free the object.
-            // Safety: The token was in the list. This means the parent wasn't
-            // cancelled before, and the token must still be alive.
-            unsafe { child_state.as_mut().remove_parent_ref(current_child_state) };
-        }
-
-        // Decrement the refcount on the parent and free it if necessary
-        self.decrement_refcount(self.snapshot());
-    }
-
-    fn cancel(&self) {
-        // Move the state of the CancellationToken from `NotCancelled` to `Cancelling`
-        let mut current_state = self.snapshot();
-
-        let state_after_cancellation = loop {
-            if current_state.cancel_state != CancellationState::NotCancelled {
-                // Another task already initiated the cancellation
-                return;
+            if this.cancellation_token.is_cancelled() {
+                return Poll::Ready(());
             }
 
-            let mut next_state = current_state;
-            next_state.cancel_state = CancellationState::Cancelling;
-            match self.state.compare_exchange(
-                current_state.pack(),
-                next_state.pack(),
-                Ordering::SeqCst,
-                Ordering::SeqCst,
-            ) {
-                Ok(_) => break next_state,
-                Err(actual) => current_state = StateSnapshot::unpack(actual),
+            // No wakeups can be lost here because there is always a call to
+            // `is_cancelled` between the creation of the future and the call to
+            // `poll`, and the code that sets the cancelled flag does so before
+            // waking the `Notified`.
+            if this.future.as_mut().poll(cx).is_pending() {
+                return Poll::Pending;
             }
-        };
 
-        // This task cancelled the token
-
-        // Take the task list out of the Token
-        // We do not want to cancel child token inside this lock. If one of the
-        // child tasks would have additional child tokens, we would recursively
-        // take locks.
-
-        // Doing this action has an impact if the child token is dropped concurrently:
-        // It will try to deregister itself from the parent task, but can not find
-        // itself in the task list anymore. Therefore it needs to assume the parent
-        // has extracted the list and will process it. It may not modify the list.
-        // This is OK from a memory safety perspective, since the parent still
-        // retains a reference to the child task until it finished iterating over
-        // it.
-
-        let mut first_child = {
-            let mut guard = self.synchronized.lock().unwrap();
-            // Save the cancellation also inside the Mutex
-            // This allows child tokens which want to detach themselves to detect
-            // that this is no longer required since the parent cleared the list.
-            guard.is_cancelled = true;
-
-            // Wakeup all waiters
-            // This happens inside the lock to make cancellation reliable
-            // If we would access waiters outside of the lock, the pointers
-            // may no longer be valid.
-            // Typically this shouldn't be an issue, since waking a task should
-            // only move it from the blocked into the ready state and not have
-            // further side effects.
-
-            // Use a reverse iterator, so that the oldest waiter gets
-            // scheduled first
-            guard.waiters.reverse_drain(|waiter| {
-                // We are not allowed to move the `Waker` out of the list node.
-                // The `Future` relies on the fact that the old `Waker` stays there
-                // as long as the `Future` has not completed in order to perform
-                // the `will_wake()` check.
-                // Therefore `wake_by_ref` is used instead of `wake()`
-                if let Some(handle) = &mut waiter.task {
-                    handle.wake_by_ref();
-                }
-                // Mark the waiter to have been removed from the list.
-                waiter.state = PollState::Done;
-            });
-
-            guard.first_child.take()
-        };
-
-        while let Some(mut child) = first_child {
-            // Safety: We know this is a valid pointer since it is in our child pointer
-            // list. It can't have been freed in between, since we retain a a reference
-            // to each child.
-            let mut_child = unsafe { child.as_mut() };
-
-            // Get the next child and clean up list pointers
-            first_child = mut_child.from_parent.next_peer;
-            mut_child.from_parent.prev_peer = None;
-            mut_child.from_parent.next_peer = None;
-
-            // Cancel the child task
-            mut_child.cancel();
-
-            // Drop the parent reference. This `CancellationToken` is not interested
-            // in interacting with the child anymore.
-            // This is ONLY allowed once we promised not to touch the state anymore
-            // after this interaction.
-            mut_child.remove_parent_ref(mut_child.snapshot());
+            this.future.set(this.cancellation_token.inner.notified());
         }
-
-        // The cancellation has completed
-        // At this point in time tasks which registered a wait node can be sure
-        // that this wait node already had been dequeued from the list without
-        // needing to inspect the list.
-        self.atomic_update_state(state_after_cancellation, |mut state| {
-            state.cancel_state = CancellationState::Cancelled;
-            state
-        });
-    }
-
-    /// Returns `true` if the `CancellationToken` had been cancelled
-    fn is_cancelled(&self) -> bool {
-        let current_state = self.snapshot();
-        current_state.cancel_state != CancellationState::NotCancelled
-    }
-
-    /// Registers a waiting task at the `CancellationToken`.
-    /// Safety: This method is only safe as long as the waiting waiting task
-    /// will properly unregister the wait node before it gets moved.
-    unsafe fn register(
-        &self,
-        wait_node: &mut ListNode<WaitQueueEntry>,
-        cx: &mut Context<'_>,
-    ) -> Poll<()> {
-        debug_assert_eq!(PollState::New, wait_node.state);
-        let current_state = self.snapshot();
-
-        // Perform an optimistic cancellation check before. This is not strictly
-        // necessary since we also check for cancellation in the Mutex, but
-        // reduces the necessary work to be performed for tasks which already
-        // had been cancelled.
-        if current_state.cancel_state != CancellationState::NotCancelled {
-            return Poll::Ready(());
-        }
-
-        // So far the token is not cancelled. However it could be cancelld before
-        // we get the chance to store the `Waker`. Therfore we need to check
-        // for cancellation again inside the mutex.
-        let mut guard = self.synchronized.lock().unwrap();
-        if guard.is_cancelled {
-            // Cancellation was signalled
-            wait_node.state = PollState::Done;
-            Poll::Ready(())
-        } else {
-            // Added the task to the wait queue
-            wait_node.task = Some(cx.waker().clone());
-            wait_node.state = PollState::Waiting;
-            guard.waiters.add_front(wait_node);
-            Poll::Pending
-        }
-    }
-
-    fn check_for_cancellation(
-        &self,
-        wait_node: &mut ListNode<WaitQueueEntry>,
-        cx: &mut Context<'_>,
-    ) -> Poll<()> {
-        debug_assert!(
-            wait_node.task.is_some(),
-            "Method can only be called after task had been registered"
-        );
-
-        let current_state = self.snapshot();
-
-        if current_state.cancel_state != CancellationState::NotCancelled {
-            // If the cancellation had been fully completed we know that our `Waker`
-            // is no longer registered at the `CancellationToken`.
-            // Otherwise the cancel call may or may not yet have iterated
-            // through the waiters list and removed the wait nodes.
-            // If it hasn't yet, we need to remove it. Otherwise an attempt to
-            // reuse the `wait_node´ might get freed due to the `WaitForCancellationFuture`
-            // getting dropped before the cancellation had interacted with it.
-            if current_state.cancel_state != CancellationState::Cancelled {
-                self.unregister(wait_node);
-            }
-            Poll::Ready(())
-        } else {
-            // Check if we need to swap the `Waker`. This will make the check more
-            // expensive, since the `Waker` is synchronized through the Mutex.
-            // If we don't need to perform a `Waker` update, an atomic check for
-            // cancellation is sufficient.
-            let need_waker_update = wait_node
-                .task
-                .as_ref()
-                .map(|waker| waker.will_wake(cx.waker()))
-                .unwrap_or(true);
-
-            if need_waker_update {
-                let guard = self.synchronized.lock().unwrap();
-                if guard.is_cancelled {
-                    // Cancellation was signalled. Since this cancellation signal
-                    // is set inside the Mutex, the old waiter must already have
-                    // been removed from the waiting list
-                    debug_assert_eq!(PollState::Done, wait_node.state);
-                    wait_node.task = None;
-                    Poll::Ready(())
-                } else {
-                    // The WaitForCancellationFuture is already in the queue.
-                    // The CancellationToken can't have been cancelled,
-                    // since this would change the is_cancelled flag inside the mutex.
-                    // Therefore we just have to update the Waker. A follow-up
-                    // cancellation will always use the new waker.
-                    wait_node.task = Some(cx.waker().clone());
-                    Poll::Pending
-                }
-            } else {
-                // Do nothing. If the token gets cancelled, this task will get
-                // woken again and can fetch the cancellation.
-                Poll::Pending
-            }
-        }
-    }
-
-    fn unregister(&self, wait_node: &mut ListNode<WaitQueueEntry>) {
-        debug_assert!(
-            wait_node.task.is_some(),
-            "waiter can not be active without task"
-        );
-
-        let mut guard = self.synchronized.lock().unwrap();
-        // WaitForCancellationFuture only needs to get removed if it has been added to
-        // the wait queue of the CancellationToken.
-        // This has happened in the PollState::Waiting case.
-        if let PollState::Waiting = wait_node.state {
-            // Safety: Due to the state, we know that the node must be part
-            // of the waiter list
-            if !unsafe { guard.waiters.remove(wait_node) } {
-                // Panic if the address isn't found. This can only happen if the contract was
-                // violated, e.g. the WaitQueueEntry got moved after the initial poll.
-                panic!("Future could not be removed from wait queue");
-            }
-            wait_node.state = PollState::Done;
-        }
-        wait_node.task = None;
     }
 }

tokio-util/src/sync/cancellation_token/guard.rs

@@ -0,0 +1,27 @@
+use crate::sync::CancellationToken;
+
+/// A wrapper for cancellation token which automatically cancels
+/// it on drop. It is created using `drop_guard` method on the `CancellationToken`.
+#[derive(Debug)]
+pub struct DropGuard {
+    pub(super) inner: Option<CancellationToken>,
+}
+
+impl DropGuard {
+    /// Returns stored cancellation token and removes this drop guard instance
+    /// (i.e. it will no longer cancel token). Other guards for this token
+    /// are not affected.
+    pub fn disarm(mut self) -> CancellationToken {
+        self.inner
+            .take()
+            .expect("`inner` can be only None in a destructor")
+    }
+}
+
+impl Drop for DropGuard {
+    fn drop(&mut self) {
+        if let Some(inner) = &self.inner {
+            inner.cancel();
+        }
+    }
+}

tokio-util/src/sync/cancellation_token/tree_node.rs

@@ -0,0 +1,373 @@
+//! This mod provides the logic for the inner tree structure of the CancellationToken.
+//!
+//! CancellationTokens are only light handles with references to TreeNode.
+//! All the logic is actually implemented in the TreeNode.
+//!
+//! A TreeNode is part of the cancellation tree and may have one parent and an arbitrary number of
+//! children.
+//!
+//! A TreeNode can receive the request to perform a cancellation through a CancellationToken.
+//! This cancellation request will cancel the node and all of its descendants.
+//!
+//! As soon as a node cannot get cancelled any more (because it was already cancelled or it has no
+//! more CancellationTokens pointing to it any more), it gets removed from the tree, to keep the
+//! tree as small as possible.
+//!
+//! # Invariants
+//!
+//! Those invariants shall be true at any time.
+//!
+//! 1. A node that has no parents and no handles can no longer be cancelled.
+//!     This is important during both cancellation and refcounting.
+//!
+//! 2. If node B *is* or *was* a child of node A, then node B was created *after* node A.
+//!     This is important for deadlock safety, as it is used for lock order.
+//!     Node B can only become the child of node A in two ways:
+//!         - being created with `child_node()`, in which case it is trivially true that
+//!           node A already existed when node B was created
+//!         - being moved A->C->B to A->B because node C was removed in `decrease_handle_refcount()`
+//!           or `cancel()`. In this case the invariant still holds, as B was younger than C, and C
+//!           was younger than A, therefore B is also younger than A.
+//!
+//! 3. If two nodes are both unlocked and node A is the parent of node B, then node B is a child of
+//!    node A. It is important to always restore that invariant before dropping the lock of a node.
+//!
+//! # Deadlock safety
+//!
+//! We always lock in the order of creation time. We can prove this through invariant #2.
+//! Specifically, through invariant #2, we know that we always have to lock a parent
+//! before its child.
+//!
+use crate::loom::sync::{Arc, Mutex, MutexGuard};
+
+/// A node of the cancellation tree structure
+///
+/// The actual data it holds is wrapped inside a mutex for synchronization.
+pub(crate) struct TreeNode {
+    inner: Mutex<Inner>,
+    waker: tokio::sync::Notify,
+}
+impl TreeNode {
+    pub(crate) fn new() -> Self {
+        Self {
+            inner: Mutex::new(Inner {
+                parent: None,
+                parent_idx: 0,
+                children: vec![],
+                is_cancelled: false,
+                num_handles: 1,
+            }),
+            waker: tokio::sync::Notify::new(),
+        }
+    }
+
+    pub(crate) fn notified(&self) -> tokio::sync::futures::Notified<'_> {
+        self.waker.notified()
+    }
+}
+
+/// The data contained inside a TreeNode.
+///
+/// This struct exists so that the data of the node can be wrapped
+/// in a Mutex.
+struct Inner {
+    parent: Option<Arc<TreeNode>>,
+    parent_idx: usize,
+    children: Vec<Arc<TreeNode>>,
+    is_cancelled: bool,
+    num_handles: usize,
+}
+
+/// Returns whether or not the node is cancelled
+pub(crate) fn is_cancelled(node: &Arc<TreeNode>) -> bool {
+    node.inner.lock().unwrap().is_cancelled
+}
+
+/// Creates a child node
+pub(crate) fn child_node(parent: &Arc<TreeNode>) -> Arc<TreeNode> {
+    let mut locked_parent = parent.inner.lock().unwrap();
+
+    // Do not register as child if we are already cancelled.
+    // Cancelled trees can never be uncancelled and therefore
+    // need no connection to parents or children any more.
+    if locked_parent.is_cancelled {
+        return Arc::new(TreeNode {
+            inner: Mutex::new(Inner {
+                parent: None,
+                parent_idx: 0,
+                children: vec![],
+                is_cancelled: true,
+                num_handles: 1,
+            }),
+            waker: tokio::sync::Notify::new(),
+        });
+    }
+
+    let child = Arc::new(TreeNode {
+        inner: Mutex::new(Inner {
+            parent: Some(parent.clone()),
+            parent_idx: locked_parent.children.len(),
+            children: vec![],
+            is_cancelled: false,
+            num_handles: 1,
+        }),
+        waker: tokio::sync::Notify::new(),
+    });
+
+    locked_parent.children.push(child.clone());
+
+    child
+}
+
+/// Disconnects the given parent from all of its children.
+///
+/// Takes a reference to [Inner] to make sure the parent is already locked.
+fn disconnect_children(node: &mut Inner) {
+    for child in std::mem::take(&mut node.children) {
+        let mut locked_child = child.inner.lock().unwrap();
+        locked_child.parent_idx = 0;
+        locked_child.parent = None;
+    }
+}
+
+/// Figures out the parent of the node and locks the node and its parent atomically.
+///
+/// The basic principle of preventing deadlocks in the tree is
+/// that we always lock the parent first, and then the child.
+/// For more info look at *deadlock safety* and *invariant #2*.
+///
+/// Sadly, it's impossible to figure out the parent of a node without
+/// locking it. To then achieve locking order consistency, the node
+/// has to be unlocked before the parent gets locked.
+/// This leaves a small window where we already assume that we know the parent,
+/// but neither the parent nor the node is locked. Therefore, the parent could change.
+///
+/// To prevent that this problem leaks into the rest of the code, it is abstracted
+/// in this function.
+///
+/// The locked child and optionally its locked parent, if a parent exists, get passed
+/// to the `func` argument via (node, None) or (node, Some(parent)).
+fn with_locked_node_and_parent<F, Ret>(node: &Arc<TreeNode>, func: F) -> Ret
+where
+    F: FnOnce(MutexGuard<'_, Inner>, Option<MutexGuard<'_, Inner>>) -> Ret,
+{
+    let mut potential_parent = {
+        let locked_node = node.inner.lock().unwrap();
+        match locked_node.parent.clone() {
+            Some(parent) => parent,
+            // If we locked the node and its parent is `None`, we are in a valid state
+            // and can return.
+            None => return func(locked_node, None),
+        }
+    };
+
+    loop {
+        // Deadlock safety:
+        //
+        // Due to invariant #2, we know that we have to lock the parent first, and then the child.
+        // This is true even if the potential_parent is no longer the current parent or even its
+        // sibling, as the invariant still holds.
+        let locked_parent = potential_parent.inner.lock().unwrap();
+        let locked_node = node.inner.lock().unwrap();
+
+        let actual_parent = match locked_node.parent.clone() {
+            Some(parent) => parent,
+            // If we locked the node and its parent is `None`, we are in a valid state
+            // and can return.
+            None => {
+                // Was the wrong parent, so unlock it before calling `func`
+                drop(locked_parent);
+                return func(locked_node, None);
+            }
+        };
+
+        // Loop until we managed to lock both the node and its parent
+        if Arc::ptr_eq(&actual_parent, &potential_parent) {
+            return func(locked_node, Some(locked_parent));
+        }
+
+        // Drop locked_parent before reassigning to potential_parent,
+        // as potential_parent is borrowed in it
+        drop(locked_node);
+        drop(locked_parent);
+
+        potential_parent = actual_parent;
+    }
+}
+
+/// Moves all children from `node` to `parent`.
+///
+/// `parent` MUST have been a parent of the node when they both got locked,
+/// otherwise there is a potential for a deadlock as invariant #2 would be violated.
+///
+/// To aquire the locks for node and parent, use [with_locked_node_and_parent].
+fn move_children_to_parent(node: &mut Inner, parent: &mut Inner) {
+    // Pre-allocate in the parent, for performance
+    parent.children.reserve(node.children.len());
+
+    for child in std::mem::take(&mut node.children) {
+        {
+            let mut child_locked = child.inner.lock().unwrap();
+            child_locked.parent = node.parent.clone();
+            child_locked.parent_idx = parent.children.len();
+        }
+        parent.children.push(child);
+    }
+}
+
+/// Removes a child from the parent.
+///
+/// `parent` MUST be the parent of `node`.
+/// To aquire the locks for node and parent, use [with_locked_node_and_parent].
+fn remove_child(parent: &mut Inner, mut node: MutexGuard<'_, Inner>) {
+    // Query the position from where to remove a node
+    let pos = node.parent_idx;
+    node.parent = None;
+    node.parent_idx = 0;
+
+    // Unlock node, so that only one child at a time is locked.
+    // Otherwise we would violate the lock order (see 'deadlock safety') as we
+    // don't know the creation order of the child nodes
+    drop(node);
+
+    // If `node` is the last element in the list, we don't need any swapping
+    if parent.children.len() == pos + 1 {
+        parent.children.pop().unwrap();
+    } else {
+        // If `node` is not the last element in the list, we need to
+        // replace it with the last element
+        let replacement_child = parent.children.pop().unwrap();
+        replacement_child.inner.lock().unwrap().parent_idx = pos;
+        parent.children[pos] = replacement_child;
+    }
+
+    let len = parent.children.len();
+    if 4 * len <= parent.children.capacity() {
+        // equal to:
+        //    parent.children.shrink_to(2 * len);
+        // but shrink_to was not yet stabilized in our minimal compatible version
+        let old_children = std::mem::replace(&mut parent.children, Vec::with_capacity(2 * len));
+        parent.children.extend(old_children);
+    }
+}
+
+/// Increases the reference count of handles.
+pub(crate) fn increase_handle_refcount(node: &Arc<TreeNode>) {
+    let mut locked_node = node.inner.lock().unwrap();
+
+    // Once no handles are left over, the node gets detached from the tree.
+    // There should never be a new handle once all handles are dropped.
+    assert!(locked_node.num_handles > 0);
+
+    locked_node.num_handles += 1;
+}
+
+/// Decreases the reference count of handles.
+///
+/// Once no handle is left, we can remove the node from the
+/// tree and connect its parent directly to its children.
+pub(crate) fn decrease_handle_refcount(node: &Arc<TreeNode>) {
+    let num_handles = {
+        let mut locked_node = node.inner.lock().unwrap();
+        locked_node.num_handles -= 1;
+        locked_node.num_handles
+    };
+
+    if num_handles == 0 {
+        with_locked_node_and_parent(node, |mut node, parent| {
+            // Remove the node from the tree
+            match parent {
+                Some(mut parent) => {
+                    // As we want to remove ourselves from the tree,
+                    // we have to move the children to the parent, so that
+                    // they still receive the cancellation event without us.
+                    // Moving them does not violate invariant #1.
+                    move_children_to_parent(&mut node, &mut parent);
+
+                    // Remove the node from the parent
+                    remove_child(&mut parent, node);
+                }
+                None => {
+                    // Due to invariant #1, we can assume that our
+                    // children can no longer be cancelled through us.
+                    // (as we now have neither a parent nor handles)
+                    // Therefore we can disconnect them.
+                    disconnect_children(&mut node);
+                }
+            }
+        });
+    }
+}
+
+/// Cancels a node and its children.
+pub(crate) fn cancel(node: &Arc<TreeNode>) {
+    let mut locked_node = node.inner.lock().unwrap();
+
+    if locked_node.is_cancelled {
+        return;
+    }
+
+    // One by one, adopt grandchildren and then cancel and detach the child
+    while let Some(child) = locked_node.children.pop() {
+        // This can't deadlock because the mutex we are already
+        // holding is the parent of child.
+        let mut locked_child = child.inner.lock().unwrap();
+
+        // Detach the child from node
+        // No need to modify node.children, as the child already got removed with `.pop`
+        locked_child.parent = None;
+        locked_child.parent_idx = 0;
+
+        // If child is already cancelled, detaching is enough
+        if locked_child.is_cancelled {
+            continue;
+        }
+
+        // Cancel or adopt grandchildren
+        while let Some(grandchild) = locked_child.children.pop() {
+            // This can't deadlock because the two mutexes we are already
+            // holding is the parent and grandparent of grandchild.
+            let mut locked_grandchild = grandchild.inner.lock().unwrap();
+
+            // Detach the grandchild
+            locked_grandchild.parent = None;
+            locked_grandchild.parent_idx = 0;
+
+            // If grandchild is already cancelled, detaching is enough
+            if locked_grandchild.is_cancelled {
+                continue;
+            }
+
+            // For performance reasons, only adopt grandchildren that have children.
+            // Otherwise, just cancel them right away, no need for another iteration.
+            if locked_grandchild.children.is_empty() {
+                // Cancel the grandchild
+                locked_grandchild.is_cancelled = true;
+                locked_grandchild.children = Vec::new();
+                drop(locked_grandchild);
+                grandchild.waker.notify_waiters();
+            } else {
+                // Otherwise, adopt grandchild
+                locked_grandchild.parent = Some(node.clone());
+                locked_grandchild.parent_idx = locked_node.children.len();
+                drop(locked_grandchild);
+                locked_node.children.push(grandchild);
+            }
+        }
+
+        // Cancel the child
+        locked_child.is_cancelled = true;
+        locked_child.children = Vec::new();
+        drop(locked_child);
+        child.waker.notify_waiters();
+
+        // Now the child is cancelled and detached and all its children are adopted.
+        // Just continue until all (including adopted) children are cancelled and detached.
+    }
+
+    // Cancel the node itself.
+    locked_node.is_cancelled = true;
+    locked_node.children = Vec::new();
+    drop(locked_node);
+    node.waker.notify_waiters();
+}

tokio-util/src/sync/intrusive_double_linked_list.rs

@@ -1,788 +0,0 @@
-//! An intrusive double linked list of data
-
-#![allow(dead_code, unreachable_pub)]
-
-use core::{
-    marker::PhantomPinned,
-    ops::{Deref, DerefMut},
-    ptr::NonNull,
-};
-
-/// A node which carries data of type `T` and is stored in an intrusive list
-#[derive(Debug)]
-pub struct ListNode<T> {
-    /// The previous node in the list. `None` if there is no previous node.
-    prev: Option<NonNull<ListNode<T>>>,
-    /// The next node in the list. `None` if there is no previous node.
-    next: Option<NonNull<ListNode<T>>>,
-    /// The data which is associated to this list item
-    data: T,
-    /// Prevents `ListNode`s from being `Unpin`. They may never be moved, since
-    /// the list semantics require addresses to be stable.
-    _pin: PhantomPinned,
-}
-
-impl<T> ListNode<T> {
-    /// Creates a new node with the associated data
-    pub fn new(data: T) -> ListNode<T> {
-        Self {
-            prev: None,
-            next: None,
-            data,
-            _pin: PhantomPinned,
-        }
-    }
-}
-
-impl<T> Deref for ListNode<T> {
-    type Target = T;
-
-    fn deref(&self) -> &T {
-        &self.data
-    }
-}
-
-impl<T> DerefMut for ListNode<T> {
-    fn deref_mut(&mut self) -> &mut T {
-        &mut self.data
-    }
-}
-
-/// An intrusive linked list of nodes, where each node carries associated data
-/// of type `T`.
-#[derive(Debug)]
-pub struct LinkedList<T> {
-    head: Option<NonNull<ListNode<T>>>,
-    tail: Option<NonNull<ListNode<T>>>,
-}
-
-impl<T> LinkedList<T> {
-    /// Creates an empty linked list
-    pub fn new() -> Self {
-        LinkedList::<T> {
-            head: None,
-            tail: None,
-        }
-    }
-
-    /// Adds a node at the front of the linked list.
-    /// Safety: This function is only safe as long as `node` is guaranteed to
-    /// get removed from the list before it gets moved or dropped.
-    /// In addition to this `node` may not be added to another other list before
-    /// it is removed from the current one.
-    pub unsafe fn add_front(&mut self, node: &mut ListNode<T>) {
-        node.next = self.head;
-        node.prev = None;
-        if let Some(mut head) = self.head {
-            head.as_mut().prev = Some(node.into())
-        };
-        self.head = Some(node.into());
-        if self.tail.is_none() {
-            self.tail = Some(node.into());
-        }
-    }
-
-    /// Inserts a node into the list in a way that the list keeps being sorted.
-    /// Safety: This function is only safe as long as `node` is guaranteed to
-    /// get removed from the list before it gets moved or dropped.
-    /// In addition to this `node` may not be added to another other list before
-    /// it is removed from the current one.
-    pub unsafe fn add_sorted(&mut self, node: &mut ListNode<T>)
-    where
-        T: PartialOrd,
-    {
-        if self.head.is_none() {
-            // First node in the list
-            self.head = Some(node.into());
-            self.tail = Some(node.into());
-            return;
-        }
-
-        let mut prev: Option<NonNull<ListNode<T>>> = None;
-        let mut current = self.head;
-
-        while let Some(mut current_node) = current {
-            if node.data < current_node.as_ref().data {
-                // Need to insert before the current node
-                current_node.as_mut().prev = Some(node.into());
-                match prev {
-                    Some(mut prev) => {
-                        prev.as_mut().next = Some(node.into());
-                    }
-                    None => {
-                        // We are inserting at the beginning of the list
-                        self.head = Some(node.into());
-                    }
-                }
-                node.next = current;
-                node.prev = prev;
-                return;
-            }
-            prev = current;
-            current = current_node.as_ref().next;
-        }
-
-        // We looped through the whole list and the nodes data is bigger or equal
-        // than everything we found up to now.
-        // Insert at the end. Since we checked before that the list isn't empty,
-        // tail always has a value.
-        node.prev = self.tail;
-        node.next = None;
-        self.tail.as_mut().unwrap().as_mut().next = Some(node.into());
-        self.tail = Some(node.into());
-    }
-
-    /// Returns the first node in the linked list without removing it from the list
-    /// The function is only safe as long as valid pointers are stored inside
-    /// the linked list.
-    /// The returned pointer is only guaranteed to be valid as long as the list
-    /// is not mutated
-    pub fn peek_first(&self) -> Option<&mut ListNode<T>> {
-        // Safety: When the node was inserted it was promised that it is alive
-        // until it gets removed from the list.
-        // The returned node has a pointer which constrains it to the lifetime
-        // of the list. This is ok, since the Node is supposed to outlive
-        // its insertion in the list.
-        unsafe {
-            self.head
-                .map(|mut node| &mut *(node.as_mut() as *mut ListNode<T>))
-        }
-    }
-
-    /// Returns the last node in the linked list without removing it from the list
-    /// The function is only safe as long as valid pointers are stored inside
-    /// the linked list.
-    /// The returned pointer is only guaranteed to be valid as long as the list
-    /// is not mutated
-    pub fn peek_last(&self) -> Option<&mut ListNode<T>> {
-        // Safety: When the node was inserted it was promised that it is alive
-        // until it gets removed from the list.
-        // The returned node has a pointer which constrains it to the lifetime
-        // of the list. This is ok, since the Node is supposed to outlive
-        // its insertion in the list.
-        unsafe {
-            self.tail
-                .map(|mut node| &mut *(node.as_mut() as *mut ListNode<T>))
-        }
-    }
-
-    /// Removes the first node from the linked list
-    pub fn remove_first(&mut self) -> Option<&mut ListNode<T>> {
-        #![allow(clippy::debug_assert_with_mut_call)]
-
-        // Safety: When the node was inserted it was promised that it is alive
-        // until it gets removed from the list
-        unsafe {
-            let mut head = self.head?;
-            self.head = head.as_mut().next;
-
-            let first_ref = head.as_mut();
-            match first_ref.next {
-                None => {
-                    // This was the only node in the list
-                    debug_assert_eq!(Some(first_ref.into()), self.tail);
-                    self.tail = None;
-                }
-                Some(mut next) => {
-                    next.as_mut().prev = None;
-                }
-            }
-
-            first_ref.prev = None;
-            first_ref.next = None;
-            Some(&mut *(first_ref as *mut ListNode<T>))
-        }
-    }
-
-    /// Removes the last node from the linked list and returns it
-    pub fn remove_last(&mut self) -> Option<&mut ListNode<T>> {
-        #![allow(clippy::debug_assert_with_mut_call)]
-
-        // Safety: When the node was inserted it was promised that it is alive
-        // until it gets removed from the list
-        unsafe {
-            let mut tail = self.tail?;
-            self.tail = tail.as_mut().prev;
-
-            let last_ref = tail.as_mut();
-            match last_ref.prev {
-                None => {
-                    // This was the last node in the list
-                    debug_assert_eq!(Some(last_ref.into()), self.head);
-                    self.head = None;
-                }
-                Some(mut prev) => {
-                    prev.as_mut().next = None;
-                }
-            }
-
-            last_ref.prev = None;
-            last_ref.next = None;
-            Some(&mut *(last_ref as *mut ListNode<T>))
-        }
-    }
-
-    /// Returns whether the linked list doesn not contain any node
-    pub fn is_empty(&self) -> bool {
-        if self.head.is_some() {
-            return false;
-        }
-
-        debug_assert!(self.tail.is_none());
-        true
-    }
-
-    /// Removes the given `node` from the linked list.
-    /// Returns whether the `node` was removed.
-    /// It is also only safe if it is known that the `node` is either part of this
-    /// list, or of no list at all. If `node` is part of another list, the
-    /// behavior is undefined.
-    pub unsafe fn remove(&mut self, node: &mut ListNode<T>) -> bool {
-        #![allow(clippy::debug_assert_with_mut_call)]
-
-        match node.prev {
-            None => {
-                // This might be the first node in the list. If it is not, the
-                // node is not in the list at all. Since our precondition is that
-                // the node must either be in this list or in no list, we check that
-                // the node is really in no list.
-                if self.head != Some(node.into()) {
-                    debug_assert!(node.next.is_none());
-                    return false;
-                }
-                self.head = node.next;
-            }
-            Some(mut prev) => {
-                debug_assert_eq!(prev.as_ref().next, Some(node.into()));
-                prev.as_mut().next = node.next;
-            }
-        }
-
-        match node.next {
-            None => {
-                // This must be the last node in our list. Otherwise the list
-                // is inconsistent.
-                debug_assert_eq!(self.tail, Some(node.into()));
-                self.tail = node.prev;
-            }
-            Some(mut next) => {
-                debug_assert_eq!(next.as_mut().prev, Some(node.into()));
-                next.as_mut().prev = node.prev;
-            }
-        }
-
-        node.next = None;
-        node.prev = None;
-
-        true
-    }
-
-    /// Drains the list iby calling a callback on each list node
-    ///
-    /// The method does not return an iterator since stopping or deferring
-    /// draining the list is not permitted. If the method would push nodes to
-    /// an iterator we could not guarantee that the nodes do not get utilized
-    /// after having been removed from the list anymore.
-    pub fn drain<F>(&mut self, mut func: F)
-    where
-        F: FnMut(&mut ListNode<T>),
-    {
-        let mut current = self.head;
-        self.head = None;
-        self.tail = None;
-
-        while let Some(mut node) = current {
-            // Safety: The nodes have not been removed from the list yet and must
-            // therefore contain valid data. The nodes can also not be added to
-            // the list again during iteration, since the list is mutably borrowed.
-            unsafe {
-                let node_ref = node.as_mut();
-                current = node_ref.next;
-
-                node_ref.next = None;
-                node_ref.prev = None;
-
-                // Note: We do not reset the pointers from the next element in the
-                // list to the current one since we will iterate over the whole
-                // list anyway, and therefore clean up all pointers.
-
-                func(node_ref);
-            }
-        }
-    }
-
-    /// Drains the list in reverse order by calling a callback on each list node
-    ///
-    /// The method does not return an iterator since stopping or deferring
-    /// draining the list is not permitted. If the method would push nodes to
-    /// an iterator we could not guarantee that the nodes do not get utilized
-    /// after having been removed from the list anymore.
-    pub fn reverse_drain<F>(&mut self, mut func: F)
-    where
-        F: FnMut(&mut ListNode<T>),
-    {
-        let mut current = self.tail;
-        self.head = None;
-        self.tail = None;
-
-        while let Some(mut node) = current {
-            // Safety: The nodes have not been removed from the list yet and must
-            // therefore contain valid data. The nodes can also not be added to
-            // the list again during iteration, since the list is mutably borrowed.
-            unsafe {
-                let node_ref = node.as_mut();
-                current = node_ref.prev;
-
-                node_ref.next = None;
-                node_ref.prev = None;
-
-                // Note: We do not reset the pointers from the next element in the
-                // list to the current one since we will iterate over the whole
-                // list anyway, and therefore clean up all pointers.
-
-                func(node_ref);
-            }
-        }
-    }
-}
-
-#[cfg(all(test, feature = "std"))] // Tests make use of Vec at the moment
-mod tests {
-    use super::*;
-
-    fn collect_list<T: Copy>(mut list: LinkedList<T>) -> Vec<T> {
-        let mut result = Vec::new();
-        list.drain(|node| {
-            result.push(**node);
-        });
-        result
-    }
-
-    fn collect_reverse_list<T: Copy>(mut list: LinkedList<T>) -> Vec<T> {
-        let mut result = Vec::new();
-        list.reverse_drain(|node| {
-            result.push(**node);
-        });
-        result
-    }
-
-    unsafe fn add_nodes(list: &mut LinkedList<i32>, nodes: &mut [&mut ListNode<i32>]) {
-        for node in nodes.iter_mut() {
-            list.add_front(node);
-        }
-    }
-
-    unsafe fn assert_clean<T>(node: &mut ListNode<T>) {
-        assert!(node.next.is_none());
-        assert!(node.prev.is_none());
-    }
-
-    #[test]
-    fn insert_and_iterate() {
-        unsafe {
-            let mut a = ListNode::new(5);
-            let mut b = ListNode::new(7);
-            let mut c = ListNode::new(31);
-
-            let mut setup = |list: &mut LinkedList<i32>| {
-                assert_eq!(true, list.is_empty());
-                list.add_front(&mut c);
-                assert_eq!(31, **list.peek_first().unwrap());
-                assert_eq!(false, list.is_empty());
-                list.add_front(&mut b);
-                assert_eq!(7, **list.peek_first().unwrap());
-                list.add_front(&mut a);
-                assert_eq!(5, **list.peek_first().unwrap());
-            };
-
-            let mut list = LinkedList::new();
-            setup(&mut list);
-            let items: Vec<i32> = collect_list(list);
-            assert_eq!([5, 7, 31].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            setup(&mut list);
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert_eq!([31, 7, 5].to_vec(), items);
-        }
-    }
-
-    #[test]
-    fn add_sorted() {
-        unsafe {
-            let mut a = ListNode::new(5);
-            let mut b = ListNode::new(7);
-            let mut c = ListNode::new(31);
-            let mut d = ListNode::new(99);
-
-            let mut list = LinkedList::new();
-            list.add_sorted(&mut a);
-            let items: Vec<i32> = collect_list(list);
-            assert_eq!([5].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            list.add_sorted(&mut a);
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert_eq!([5].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut d, &mut c, &mut b]);
-            list.add_sorted(&mut a);
-            let items: Vec<i32> = collect_list(list);
-            assert_eq!([5, 7, 31, 99].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut d, &mut c, &mut b]);
-            list.add_sorted(&mut a);
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert_eq!([99, 31, 7, 5].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut d, &mut c, &mut a]);
-            list.add_sorted(&mut b);
-            let items: Vec<i32> = collect_list(list);
-            assert_eq!([5, 7, 31, 99].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut d, &mut c, &mut a]);
-            list.add_sorted(&mut b);
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert_eq!([99, 31, 7, 5].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut d, &mut b, &mut a]);
-            list.add_sorted(&mut c);
-            let items: Vec<i32> = collect_list(list);
-            assert_eq!([5, 7, 31, 99].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut d, &mut b, &mut a]);
-            list.add_sorted(&mut c);
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert_eq!([99, 31, 7, 5].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-            list.add_sorted(&mut d);
-            let items: Vec<i32> = collect_list(list);
-            assert_eq!([5, 7, 31, 99].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-            list.add_sorted(&mut d);
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert_eq!([99, 31, 7, 5].to_vec(), items);
-        }
-    }
-
-    #[test]
-    fn drain_and_collect() {
-        unsafe {
-            let mut a = ListNode::new(5);
-            let mut b = ListNode::new(7);
-            let mut c = ListNode::new(31);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-
-            let taken_items: Vec<i32> = collect_list(list);
-            assert_eq!([5, 7, 31].to_vec(), taken_items);
-        }
-    }
-
-    #[test]
-    fn peek_last() {
-        unsafe {
-            let mut a = ListNode::new(5);
-            let mut b = ListNode::new(7);
-            let mut c = ListNode::new(31);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-
-            let last = list.peek_last();
-            assert_eq!(31, **last.unwrap());
-            list.remove_last();
-
-            let last = list.peek_last();
-            assert_eq!(7, **last.unwrap());
-            list.remove_last();
-
-            let last = list.peek_last();
-            assert_eq!(5, **last.unwrap());
-            list.remove_last();
-
-            let last = list.peek_last();
-            assert!(last.is_none());
-        }
-    }
-
-    #[test]
-    fn remove_first() {
-        unsafe {
-            // We iterate forward and backwards through the manipulated lists
-            // to make sure pointers in both directions are still ok.
-            let mut a = ListNode::new(5);
-            let mut b = ListNode::new(7);
-            let mut c = ListNode::new(31);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-            let removed = list.remove_first().unwrap();
-            assert_clean(removed);
-            assert!(!list.is_empty());
-            let items: Vec<i32> = collect_list(list);
-            assert_eq!([7, 31].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-            let removed = list.remove_first().unwrap();
-            assert_clean(removed);
-            assert!(!list.is_empty());
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert_eq!([31, 7].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut b, &mut a]);
-            let removed = list.remove_first().unwrap();
-            assert_clean(removed);
-            assert!(!list.is_empty());
-            let items: Vec<i32> = collect_list(list);
-            assert_eq!([7].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut b, &mut a]);
-            let removed = list.remove_first().unwrap();
-            assert_clean(removed);
-            assert!(!list.is_empty());
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert_eq!([7].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut a]);
-            let removed = list.remove_first().unwrap();
-            assert_clean(removed);
-            assert!(list.is_empty());
-            let items: Vec<i32> = collect_list(list);
-            assert!(items.is_empty());
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut a]);
-            let removed = list.remove_first().unwrap();
-            assert_clean(removed);
-            assert!(list.is_empty());
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert!(items.is_empty());
-        }
-    }
-
-    #[test]
-    fn remove_last() {
-        unsafe {
-            // We iterate forward and backwards through the manipulated lists
-            // to make sure pointers in both directions are still ok.
-            let mut a = ListNode::new(5);
-            let mut b = ListNode::new(7);
-            let mut c = ListNode::new(31);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-            let removed = list.remove_last().unwrap();
-            assert_clean(removed);
-            assert!(!list.is_empty());
-            let items: Vec<i32> = collect_list(list);
-            assert_eq!([5, 7].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-            let removed = list.remove_last().unwrap();
-            assert_clean(removed);
-            assert!(!list.is_empty());
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert_eq!([7, 5].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut b, &mut a]);
-            let removed = list.remove_last().unwrap();
-            assert_clean(removed);
-            assert!(!list.is_empty());
-            let items: Vec<i32> = collect_list(list);
-            assert_eq!([5].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut b, &mut a]);
-            let removed = list.remove_last().unwrap();
-            assert_clean(removed);
-            assert!(!list.is_empty());
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert_eq!([5].to_vec(), items);
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut a]);
-            let removed = list.remove_last().unwrap();
-            assert_clean(removed);
-            assert!(list.is_empty());
-            let items: Vec<i32> = collect_list(list);
-            assert!(items.is_empty());
-
-            let mut list = LinkedList::new();
-            add_nodes(&mut list, &mut [&mut a]);
-            let removed = list.remove_last().unwrap();
-            assert_clean(removed);
-            assert!(list.is_empty());
-            let items: Vec<i32> = collect_reverse_list(list);
-            assert!(items.is_empty());
-        }
-    }
-
-    #[test]
-    fn remove_by_address() {
-        unsafe {
-            let mut a = ListNode::new(5);
-            let mut b = ListNode::new(7);
-            let mut c = ListNode::new(31);
-
-            {
-                // Remove first
-                let mut list = LinkedList::new();
-                add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-                assert_eq!(true, list.remove(&mut a));
-                assert_clean((&mut a).into());
-                // a should be no longer there and can't be removed twice
-                assert_eq!(false, list.remove(&mut a));
-                assert_eq!(Some((&mut b).into()), list.head);
-                assert_eq!(Some((&mut c).into()), b.next);
-                assert_eq!(Some((&mut b).into()), c.prev);
-                let items: Vec<i32> = collect_list(list);
-                assert_eq!([7, 31].to_vec(), items);
-
-                let mut list = LinkedList::new();
-                add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-                assert_eq!(true, list.remove(&mut a));
-                assert_clean((&mut a).into());
-                // a should be no longer there and can't be removed twice
-                assert_eq!(false, list.remove(&mut a));
-                assert_eq!(Some((&mut c).into()), b.next);
-                assert_eq!(Some((&mut b).into()), c.prev);
-                let items: Vec<i32> = collect_reverse_list(list);
-                assert_eq!([31, 7].to_vec(), items);
-            }
-
-            {
-                // Remove middle
-                let mut list = LinkedList::new();
-                add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-                assert_eq!(true, list.remove(&mut b));
-                assert_clean((&mut b).into());
-                assert_eq!(Some((&mut c).into()), a.next);
-                assert_eq!(Some((&mut a).into()), c.prev);
-                let items: Vec<i32> = collect_list(list);
-                assert_eq!([5, 31].to_vec(), items);
-
-                let mut list = LinkedList::new();
-                add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-                assert_eq!(true, list.remove(&mut b));
-                assert_clean((&mut b).into());
-                assert_eq!(Some((&mut c).into()), a.next);
-                assert_eq!(Some((&mut a).into()), c.prev);
-                let items: Vec<i32> = collect_reverse_list(list);
-                assert_eq!([31, 5].to_vec(), items);
-            }
-
-            {
-                // Remove last
-                let mut list = LinkedList::new();
-                add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-                assert_eq!(true, list.remove(&mut c));
-                assert_clean((&mut c).into());
-                assert!(b.next.is_none());
-                assert_eq!(Some((&mut b).into()), list.tail);
-                let items: Vec<i32> = collect_list(list);
-                assert_eq!([5, 7].to_vec(), items);
-
-                let mut list = LinkedList::new();
-                add_nodes(&mut list, &mut [&mut c, &mut b, &mut a]);
-                assert_eq!(true, list.remove(&mut c));
-                assert_clean((&mut c).into());
-                assert!(b.next.is_none());
-                assert_eq!(Some((&mut b).into()), list.tail);
-                let items: Vec<i32> = collect_reverse_list(list);
-                assert_eq!([7, 5].to_vec(), items);
-            }
-
-            {
-                // Remove first of two
-                let mut list = LinkedList::new();
-                add_nodes(&mut list, &mut [&mut b, &mut a]);
-                assert_eq!(true, list.remove(&mut a));
-                assert_clean((&mut a).into());
-                // a should be no longer there and can't be removed twice
-                assert_eq!(false, list.remove(&mut a));
-                assert_eq!(Some((&mut b).into()), list.head);
-                assert_eq!(Some((&mut b).into()), list.tail);
-                assert!(b.next.is_none());
-                assert!(b.prev.is_none());
-                let items: Vec<i32> = collect_list(list);
-                assert_eq!([7].to_vec(), items);
-
-                let mut list = LinkedList::new();
-                add_nodes(&mut list, &mut [&mut b, &mut a]);
-                assert_eq!(true, list.remove(&mut a));
-                assert_clean((&mut a).into());
-                // a should be no longer there and can't be removed twice
-                assert_eq!(false, list.remove(&mut a));
-                assert_eq!(Some((&mut b).into()), list.head);
-                assert_eq!(Some((&mut b).into()), list.tail);
-                assert!(b.next.is_none());
-                assert!(b.prev.is_none());
-                let items: Vec<i32> = collect_reverse_list(list);
-                assert_eq!([7].to_vec(), items);
-            }
-
-            {
-                // Remove last of two
-                let mut list = LinkedList::new();
-                add_nodes(&mut list, &mut [&mut b, &mut a]);
-                assert_eq!(true, list.remove(&mut b));
-                assert_clean((&mut b).into());
-                assert_eq!(Some((&mut a).into()), list.head);
-                assert_eq!(Some((&mut a).into()), list.tail);
-                assert!(a.next.is_none());
-                assert!(a.prev.is_none());
-                let items: Vec<i32> = collect_list(list);
-                assert_eq!([5].to_vec(), items);
-
-                let mut list = LinkedList::new();
-                add_nodes(&mut list, &mut [&mut b, &mut a]);
-                assert_eq!(true, list.remove(&mut b));
-                assert_clean((&mut b).into());
-                assert_eq!(Some((&mut a).into()), list.head);
-                assert_eq!(Some((&mut a).into()), list.tail);
-                assert!(a.next.is_none());
-                assert!(a.prev.is_none());
-                let items: Vec<i32> = collect_reverse_list(list);
-                assert_eq!([5].to_vec(), items);
-            }
-
-            {
-                // Remove last item
-                let mut list = LinkedList::new();
-                add_nodes(&mut list, &mut [&mut a]);
-                assert_eq!(true, list.remove(&mut a));
-                assert_clean((&mut a).into());
-                assert!(list.head.is_none());
-                assert!(list.tail.is_none());
-                let items: Vec<i32> = collect_list(list);
-                assert!(items.is_empty());
-            }
-
-            {
-                // Remove missing
-                let mut list = LinkedList::new();
-                list.add_front(&mut b);
-                list.add_front(&mut a);
-                assert_eq!(false, list.remove(&mut c));
-            }
-        }
-    }
-}

tokio-util/src/sync/mod.rs

@@ -1,12 +1,10 @@
 //! Synchronization primitives
 
 mod cancellation_token;
-pub use cancellation_token::{CancellationToken, WaitForCancellationFuture};
-
-mod intrusive_double_linked_list;
+pub use cancellation_token::{guard::DropGuard, CancellationToken, WaitForCancellationFuture};
 
 mod mpsc;
-pub use mpsc::PollSender;
+pub use mpsc::{PollSendError, PollSender};
 
 mod poll_semaphore;
 pub use poll_semaphore::PollSemaphore;

tokio-util/src/sync/mpsc.rs

@@ -1,221 +1,283 @@
-use futures_core::ready;
 use futures_sink::Sink;
 use std::pin::Pin;
-use std::sync::Arc;
 use std::task::{Context, Poll};
-use tokio::sync::mpsc::{error::SendError, Sender};
+use std::{fmt, mem};
+use tokio::sync::mpsc::OwnedPermit;
+use tokio::sync::mpsc::Sender;
 
 use super::ReusableBoxFuture;
 
-// This implementation was chosen over something based on permits because to get a
-// `tokio::sync::mpsc::Permit` out of the `inner` future, you must transmute the
-// lifetime on the permit to `'static`.
+/// Error returned by the `PollSender` when the channel is closed.
+#[derive(Debug)]
+pub struct PollSendError<T>(Option<T>);
+
+impl<T> PollSendError<T> {
+    /// Consumes the stored value, if any.
+    ///
+    /// If this error was encountered when calling `start_send`/`send_item`, this will be the item
+    /// that the caller attempted to send.  Otherwise, it will be `None`.
+    pub fn into_inner(self) -> Option<T> {
+        self.0
+    }
+}
+
+impl<T> fmt::Display for PollSendError<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "channel closed")
+    }
+}
+
+impl<T: fmt::Debug> std::error::Error for PollSendError<T> {}
+
+#[derive(Debug)]
+enum State<T> {
+    Idle(Sender<T>),
+    Acquiring,
+    ReadyToSend(OwnedPermit<T>),
+    Closed,
+}
 
 /// A wrapper around [`mpsc::Sender`] that can be polled.
 ///
 /// [`mpsc::Sender`]: tokio::sync::mpsc::Sender
 #[derive(Debug)]
 pub struct PollSender<T> {
-    /// is none if closed
-    sender: Option<Arc<Sender<T>>>,
-    is_sending: bool,
-    inner: ReusableBoxFuture<Result<(), SendError<T>>>,
+    sender: Option<Sender<T>>,
+    state: State<T>,
+    acquire: ReusableBoxFuture<'static, Result<OwnedPermit<T>, PollSendError<T>>>,
 }
 
-// By reusing the same async fn for both Some and None, we make sure every
-// future passed to ReusableBoxFuture has the same underlying type, and hence
-// the same size and alignment.
-async fn make_future<T>(data: Option<(Arc<Sender<T>>, T)>) -> Result<(), SendError<T>> {
+// Creates a future for acquiring a permit from the underlying channel.  This is used to ensure
+// there's capacity for a send to complete.
+//
+// By reusing the same async fn for both `Some` and `None`, we make sure every future passed to
+// ReusableBoxFuture has the same underlying type, and hence the same size and alignment.
+async fn make_acquire_future<T>(
+    data: Option<Sender<T>>,
+) -> Result<OwnedPermit<T>, PollSendError<T>> {
     match data {
-        Some((sender, value)) => sender.send(value).await,
-        None => unreachable!(
-            "This future should not be pollable, as is_sending should be set to false."
-        ),
+        Some(sender) => sender
+            .reserve_owned()
+            .await
+            .map_err(|_| PollSendError(None)),
+        None => unreachable!("this future should not be pollable in this state"),
     }
 }
 
 impl<T: Send + 'static> PollSender<T> {
-    /// Create a new `PollSender`.
+    /// Creates a new `PollSender`.
     pub fn new(sender: Sender<T>) -> Self {
         Self {
-            sender: Some(Arc::new(sender)),
-            is_sending: false,
-            inner: ReusableBoxFuture::new(make_future(None)),
+            sender: Some(sender.clone()),
+            state: State::Idle(sender),
+            acquire: ReusableBoxFuture::new(make_acquire_future(None)),
         }
     }
 
-    /// Start sending a new item.
+    fn take_state(&mut self) -> State<T> {
+        mem::replace(&mut self.state, State::Closed)
+    }
+
+    /// Attempts to prepare the sender to receive a value.
     ///
-    /// This method panics if a send is currently in progress. To ensure that no
-    /// send is in progress, call `poll_send_done` first until it returns
-    /// `Poll::Ready`.
+    /// This method must be called and return `Poll::Ready(Ok(()))` prior to each call to
+    /// `send_item`.
     ///
-    /// If this method returns an error, that indicates that the channel is
-    /// closed. Note that this method is not guaranteed to return an error if
-    /// the channel is closed, but in that case the error would be reported by
-    /// the first call to `poll_send_done`.
-    pub fn start_send(&mut self, value: T) -> Result<(), SendError<T>> {
-        if self.is_sending {
-            panic!("start_send called while not ready.");
-        }
-        match self.sender.clone() {
-            Some(sender) => {
-                self.inner.set(make_future(Some((sender, value))));
-                self.is_sending = true;
-                Ok(())
+    /// This method returns `Poll::Ready` once the underlying channel is ready to receive a value,
+    /// by reserving a slot in the channel for the item to be sent. If this method returns
+    /// `Poll::Pending`, the current task is registered to be notified (via
+    /// `cx.waker().wake_by_ref()`) when `poll_reserve` should be called again.
+    ///
+    /// # Errors
+    ///
+    /// If the channel is closed, an error will be returned.  This is a permanent state.
+    pub fn poll_reserve(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), PollSendError<T>>> {
+        loop {
+            let (result, next_state) = match self.take_state() {
+                State::Idle(sender) => {
+                    // Start trying to acquire a permit to reserve a slot for our send, and
+                    // immediately loop back around to poll it the first time.
+                    self.acquire.set(make_acquire_future(Some(sender)));
+                    (None, State::Acquiring)
+                }
+                State::Acquiring => match self.acquire.poll(cx) {
+                    // Channel has capacity.
+                    Poll::Ready(Ok(permit)) => {
+                        (Some(Poll::Ready(Ok(()))), State::ReadyToSend(permit))
+                    }
+                    // Channel is closed.
+                    Poll::Ready(Err(e)) => (Some(Poll::Ready(Err(e))), State::Closed),
+                    // Channel doesn't have capacity yet, so we need to wait.
+                    Poll::Pending => (Some(Poll::Pending), State::Acquiring),
+                },
+                // We're closed, either by choice or because the underlying sender was closed.
+                s @ State::Closed => (Some(Poll::Ready(Err(PollSendError(None)))), s),
+                // We're already ready to send an item.
+                s @ State::ReadyToSend(_) => (Some(Poll::Ready(Ok(()))), s),
+            };
+
+            self.state = next_state;
+            if let Some(result) = result {
+                return result;
             }
-            None => Err(SendError(value)),
         }
     }
 
-    /// If a send is in progress, poll for its completion. If no send is in progress,
-    /// this method returns `Poll::Ready(Ok(()))`.
+    /// Sends an item to the channel.
     ///
-    /// This method can return the following values:
+    /// Before calling `send_item`, `poll_reserve` must be called with a successful return
+    /// value of `Poll::Ready(Ok(()))`.
     ///
-    ///  - `Poll::Ready(Ok(()))` if the in-progress send has been completed, or there is
-    ///    no send in progress (even if the channel is closed).
-    ///  - `Poll::Ready(Err(err))` if the in-progress send failed because the channel has
-    ///    been closed.
-    ///  - `Poll::Pending` if a send is in progress, but it could not complete now.
+    /// # Errors
     ///
-    /// When this method returns `Poll::Pending`, the current task is scheduled
-    /// to receive a wakeup when the message is sent, or when the entire channel
-    /// is closed (but not if just this sender is closed by
-    /// `close_this_sender`). Note that on multiple calls to `poll_send_done`,
-    /// only the `Waker` from the `Context` passed to the most recent call is
-    /// scheduled to receive a wakeup.
+    /// If the channel is closed, an error will be returned.  This is a permanent state.
     ///
-    /// If this method returns `Poll::Ready`, then `start_send` is guaranteed to
-    /// not panic.
-    pub fn poll_send_done(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), SendError<T>>> {
-        if !self.is_sending {
-            return Poll::Ready(Ok(()));
-        }
+    /// # Panics
+    ///
+    /// If `poll_reserve` was not successfully called prior to calling `send_item`, then this method
+    /// will panic.
+    pub fn send_item(&mut self, value: T) -> Result<(), PollSendError<T>> {
+        let (result, next_state) = match self.take_state() {
+            State::Idle(_) | State::Acquiring => {
+                panic!("`send_item` called without first calling `poll_reserve`")
+            }
+            // We have a permit to send our item, so go ahead, which gets us our sender back.
+            State::ReadyToSend(permit) => (Ok(()), State::Idle(permit.send(value))),
+            // We're closed, either by choice or because the underlying sender was closed.
+            State::Closed => (Err(PollSendError(Some(value))), State::Closed),
+        };
 
-        let result = self.inner.poll(cx);
-        if result.is_ready() {
-            self.is_sending = false;
-        }
-        if let Poll::Ready(Err(_)) = &result {
-            self.sender = None;
-        }
+        // Handle deferred closing if `close` was called between `poll_reserve` and `send_item`.
+        self.state = if self.sender.is_some() {
+            next_state
+        } else {
+            State::Closed
+        };
         result
     }
 
-    /// Check whether the channel is ready to send more messages now.
+    /// Checks whether this sender is been closed.
     ///
-    /// If this method returns `true`, then `start_send` is guaranteed to not
-    /// panic.
-    ///
-    /// If the channel is closed, this method returns `true`.
-    pub fn is_ready(&self) -> bool {
-        !self.is_sending
-    }
-
-    /// Check whether the channel has been closed.
+    /// The underlying channel that this sender was wrapping may still be open.
     pub fn is_closed(&self) -> bool {
-        match &self.sender {
-            Some(sender) => sender.is_closed(),
-            None => true,
-        }
+        matches!(self.state, State::Closed) || self.sender.is_none()
     }
 
-    /// Clone the underlying `Sender`.
+    /// Gets a reference to the `Sender` of the underlying channel.
     ///
-    /// If this method returns `None`, then the channel is closed. (But it is
-    /// not guaranteed to return `None` if the channel is closed.)
-    pub fn clone_inner(&self) -> Option<Sender<T>> {
-        self.sender.as_ref().map(|sender| (&**sender).clone())
+    /// If `PollSender` has been closed, `None` is returned. The underlying channel that this sender
+    /// was wrapping may still be open.
+    pub fn get_ref(&self) -> Option<&Sender<T>> {
+        self.sender.as_ref()
     }
 
-    /// Access the underlying `Sender`.
+    /// Closes this sender.
     ///
-    /// If this method returns `None`, then the channel is closed. (But it is
-    /// not guaranteed to return `None` if the channel is closed.)
-    pub fn inner_ref(&self) -> Option<&Sender<T>> {
-        self.sender.as_deref()
-    }
-
-    // This operation is supported because it is required by the Sink trait.
-    /// Close this sender. No more messages can be sent from this sender.
+    /// No more messages will be able to be sent from this sender, but the underlying channel will
+    /// remain open until all senders have dropped, or until the [`Receiver`] closes the channel.
     ///
-    /// Note that this only closes the channel from the view-point of this
-    /// sender. The channel remains open until all senders have gone away, or
-    /// until the [`Receiver`] closes the channel.
-    ///
-    /// If there is a send in progress when this method is called, that send is
-    /// unaffected by this operation, and `poll_send_done` can still be called
-    /// to complete that send.
+    /// If a slot was previously reserved by calling `poll_reserve`, then a final call can be made
+    /// to `send_item` in order to consume the reserved slot.  After that, no further sends will be
+    /// possible.  If you do not intend to send another item, you can release the reserved slot back
+    /// to the underlying sender by calling [`abort_send`].
     ///
+    /// [`abort_send`]: crate::sync::PollSender::abort_send
     /// [`Receiver`]: tokio::sync::mpsc::Receiver
-    pub fn close_this_sender(&mut self) {
+    pub fn close(&mut self) {
+        // Mark ourselves officially closed by dropping our main sender.
         self.sender = None;
+
+        // If we're already idle, closed, or we haven't yet reserved a slot, we can quickly
+        // transition to the closed state.  Otherwise, leave the existing permit in place for the
+        // caller if they want to complete the send.
+        match self.state {
+            State::Idle(_) => self.state = State::Closed,
+            State::Acquiring => {
+                self.acquire.set(make_acquire_future(None));
+                self.state = State::Closed;
+            }
+            _ => {}
+        }
     }
 
-    /// Abort the current in-progress send, if any.
+    /// Aborts the current in-progress send, if any.
     ///
-    /// Returns `true` if a send was aborted.
+    /// Returns `true` if a send was aborted.  If the sender was closed prior to calling
+    /// `abort_send`, then the sender will remain in the closed state, otherwise the sender will be
+    /// ready to attempt another send.
     pub fn abort_send(&mut self) -> bool {
-        if self.is_sending {
-            self.inner.set(make_future(None));
-            self.is_sending = false;
-            true
-        } else {
-            false
-        }
+        // We may have been closed in the meantime, after a call to `poll_reserve` already
+        // succeeded.  We'll check if `self.sender` is `None` to see if we should transition to the
+        // closed state when we actually abort a send, rather than resetting ourselves back to idle.
+
+        let (result, next_state) = match self.take_state() {
+            // We're currently trying to reserve a slot to send into.
+            State::Acquiring => {
+                // Replacing the future drops the in-flight one.
+                self.acquire.set(make_acquire_future(None));
+
+                // If we haven't closed yet, we have to clone our stored sender since we have no way
+                // to get it back from the acquire future we just dropped.
+                let state = match self.sender.clone() {
+                    Some(sender) => State::Idle(sender),
+                    None => State::Closed,
+                };
+                (true, state)
+            }
+            // We got the permit.  If we haven't closed yet, get the sender back.
+            State::ReadyToSend(permit) => {
+                let state = if self.sender.is_some() {
+                    State::Idle(permit.release())
+                } else {
+                    State::Closed
+                };
+                (true, state)
+            }
+            s => (false, s),
+        };
+
+        self.state = next_state;
+        result
     }
 }
 
 impl<T> Clone for PollSender<T> {
-    /// Clones this `PollSender`. The resulting clone will not have any
-    /// in-progress send operations, even if the current `PollSender` does.
+    /// Clones this `PollSender`.
+    ///
+    /// The resulting `PollSender` will have an initial state identical to calling `PollSender::new`.
     fn clone(&self) -> PollSender<T> {
+        let (sender, state) = match self.sender.clone() {
+            Some(sender) => (Some(sender.clone()), State::Idle(sender)),
+            None => (None, State::Closed),
+        };
+
         Self {
-            sender: self.sender.clone(),
-            is_sending: false,
-            inner: ReusableBoxFuture::new(async { unreachable!() }),
+            sender,
+            state,
+            // We don't use `make_acquire_future` here because our relaxed bounds on `T` are not
+            // compatible with the transitive bounds required by `Sender<T>`.
+            acquire: ReusableBoxFuture::new(async { unreachable!() }),
         }
     }
 }
 
 impl<T: Send + 'static> Sink<T> for PollSender<T> {
-    type Error = SendError<T>;
+    type Error = PollSendError<T>;
 
-    /// This is equivalent to calling [`poll_send_done`].
-    ///
-    /// [`poll_send_done`]: PollSender::poll_send_done
     fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
-        Pin::into_inner(self).poll_send_done(cx)
+        Pin::into_inner(self).poll_reserve(cx)
     }
 
-    /// This is equivalent to calling [`poll_send_done`].
-    ///
-    /// [`poll_send_done`]: PollSender::poll_send_done
-    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
-        Pin::into_inner(self).poll_send_done(cx)
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
     }
 
-    /// This is equivalent to calling [`start_send`].
-    ///
-    /// [`start_send`]: PollSender::start_send
     fn start_send(self: Pin<&mut Self>, item: T) -> Result<(), Self::Error> {
-        Pin::into_inner(self).start_send(item)
+        Pin::into_inner(self).send_item(item)
     }
 
-    /// This method will first flush the `PollSender`, and then close it by
-    /// calling [`close_this_sender`].
-    ///
-    /// If a send fails while flushing because the [`Receiver`] has gone away,
-    /// then this function returns an error. The channel is still successfully
-    /// closed in this situation.
-    ///
-    /// [`close_this_sender`]: PollSender::close_this_sender
-    /// [`Receiver`]: tokio::sync::mpsc::Receiver
-    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
-        ready!(self.as_mut().poll_flush(cx))?;
-
-        Pin::into_inner(self).close_this_sender();
+    fn poll_close(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Pin::into_inner(self).close();
         Poll::Ready(Ok(()))
     }
 }

tokio-util/src/sync/poll_semaphore.rs

@@ -12,7 +12,7 @@ use super::ReusableBoxFuture;
 /// [`Semaphore`]: tokio::sync::Semaphore
 pub struct PollSemaphore {
     semaphore: Arc<Semaphore>,
-    permit_fut: Option<ReusableBoxFuture<Result<OwnedSemaphorePermit, AcquireError>>>,
+    permit_fut: Option<ReusableBoxFuture<'static, Result<OwnedSemaphorePermit, AcquireError>>>,
 }
 
 impl PollSemaphore {

tokio-util/src/sync/reusable_box.rs

@@ -1,33 +1,29 @@
 use std::alloc::Layout;
+use std::fmt;
 use std::future::Future;
-use std::panic::AssertUnwindSafe;
+use std::marker::PhantomData;
+use std::mem::{self, ManuallyDrop};
 use std::pin::Pin;
-use std::ptr::{self, NonNull};
+use std::ptr;
 use std::task::{Context, Poll};
-use std::{fmt, panic};
 
-/// A reusable `Pin<Box<dyn Future<Output = T> + Send>>`.
+/// A reusable `Pin<Box<dyn Future<Output = T> + Send + 'a>>`.
 ///
 /// This type lets you replace the future stored in the box without
 /// reallocating when the size and alignment permits this.
-pub struct ReusableBoxFuture<T> {
-    boxed: NonNull<dyn Future<Output = T> + Send>,
+pub struct ReusableBoxFuture<'a, T> {
+    boxed: Pin<Box<dyn Future<Output = T> + Send + 'a>>,
 }
 
-impl<T> ReusableBoxFuture<T> {
+impl<'a, T> ReusableBoxFuture<'a, T> {
     /// Create a new `ReusableBoxFuture<T>` containing the provided future.
     pub fn new<F>(future: F) -> Self
     where
-        F: Future<Output = T> + Send + 'static,
+        F: Future<Output = T> + Send + 'a,
     {
-        let boxed: Box<dyn Future<Output = T> + Send> = Box::new(future);
-
-        let boxed = Box::into_raw(boxed);
-
-        // SAFETY: Box::into_raw does not return null pointers.
-        let boxed = unsafe { NonNull::new_unchecked(boxed) };
-
-        Self { boxed }
+        Self {
+            boxed: Box::pin(future),
+        }
     }
 
     /// Replace the future currently stored in this box.
@@ -36,7 +32,7 @@ impl<T> ReusableBoxFuture<T> {
     /// different from the layout of the currently stored future.
     pub fn set<F>(&mut self, future: F)
     where
-        F: Future<Output = T> + Send + 'static,
+        F: Future<Output = T> + Send + 'a,
     {
         if let Err(future) = self.try_set(future) {
             *self = Self::new(future);
@@ -50,64 +46,31 @@ impl<T> ReusableBoxFuture<T> {
     /// future.
     pub fn try_set<F>(&mut self, future: F) -> Result<(), F>
     where
-        F: Future<Output = T> + Send + 'static,
+        F: Future<Output = T> + Send + 'a,
     {
-        // SAFETY: The pointer is not dangling.
-        let self_layout = {
-            let dyn_future: &(dyn Future<Output = T> + Send) = unsafe { self.boxed.as_ref() };
-            Layout::for_value(dyn_future)
-        };
-
-        if Layout::new::<F>() == self_layout {
-            // SAFETY: We just checked that the layout of F is correct.
-            unsafe {
-                self.set_same_layout(future);
-            }
-
-            Ok(())
-        } else {
-            Err(future)
+        // If we try to inline the contents of this function, the type checker complains because
+        // the bound `T: 'a` is not satisfied in the call to `pending()`. But by putting it in an
+        // inner function that doesn't have `T` as a generic parameter, we implicitly get the bound
+        // `F::Output: 'a` transitively through `F: 'a`, allowing us to call `pending()`.
+        #[inline(always)]
+        fn real_try_set<'a, F>(
+            this: &mut ReusableBoxFuture<'a, F::Output>,
+            future: F,
+        ) -> Result<(), F>
+        where
+            F: Future + Send + 'a,
+        {
+            // future::Pending<T> is a ZST so this never allocates.
+            let boxed = mem::replace(&mut this.boxed, Box::pin(Pending(PhantomData)));
+            reuse_pin_box(boxed, future, |boxed| this.boxed = Pin::from(boxed))
         }
-    }
 
-    /// Set the current future.
-    ///
-    /// # Safety
-    ///
-    /// This function requires that the layout of the provided future is the
-    /// same as `self.layout`.
-    unsafe fn set_same_layout<F>(&mut self, future: F)
-    where
-        F: Future<Output = T> + Send + 'static,
-    {
-        // Drop the existing future, catching any panics.
-        let result = panic::catch_unwind(AssertUnwindSafe(|| {
-            ptr::drop_in_place(self.boxed.as_ptr());
-        }));
-
-        // Overwrite the future behind the pointer. This is safe because the
-        // allocation was allocated with the same size and alignment as the type F.
-        let self_ptr: *mut F = self.boxed.as_ptr() as *mut F;
-        ptr::write(self_ptr, future);
-
-        // Update the vtable of self.boxed. The pointer is not null because we
-        // just got it from self.boxed, which is not null.
-        self.boxed = NonNull::new_unchecked(self_ptr);
-
-        // If the old future's destructor panicked, resume unwinding.
-        match result {
-            Ok(()) => {}
-            Err(payload) => {
-                panic::resume_unwind(payload);
-            }
-        }
+        real_try_set(self, future)
     }
 
     /// Get a pinned reference to the underlying future.
     pub fn get_pin(&mut self) -> Pin<&mut (dyn Future<Output = T> + Send)> {
-        // SAFETY: The user of this box cannot move the box, and we do not move it
-        // either.
-        unsafe { Pin::new_unchecked(self.boxed.as_mut()) }
+        self.boxed.as_mut()
     }
 
     /// Poll the future stored inside this box.
@@ -116,7 +79,7 @@ impl<T> ReusableBoxFuture<T> {
     }
 }
 
-impl<T> Future for ReusableBoxFuture<T> {
+impl<T> Future for ReusableBoxFuture<'_, T> {
     type Output = T;
 
     /// Poll the future stored inside this box.
@@ -125,27 +88,84 @@ impl<T> Future for ReusableBoxFuture<T> {
     }
 }
 
-// The future stored inside ReusableBoxFuture<T> must be Send.
-unsafe impl<T> Send for ReusableBoxFuture<T> {}
-
 // The only method called on self.boxed is poll, which takes &mut self, so this
 // struct being Sync does not permit any invalid access to the Future, even if
 // the future is not Sync.
-unsafe impl<T> Sync for ReusableBoxFuture<T> {}
+unsafe impl<T> Sync for ReusableBoxFuture<'_, T> {}
 
-// Just like a Pin<Box<dyn Future>> is always Unpin, so is this type.
-impl<T> Unpin for ReusableBoxFuture<T> {}
-
-impl<T> Drop for ReusableBoxFuture<T> {
-    fn drop(&mut self) {
-        unsafe {
-            drop(Box::from_raw(self.boxed.as_ptr()));
-        }
-    }
-}
-
-impl<T> fmt::Debug for ReusableBoxFuture<T> {
+impl<T> fmt::Debug for ReusableBoxFuture<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("ReusableBoxFuture").finish()
     }
 }
+
+fn reuse_pin_box<T: ?Sized, U, O, F>(boxed: Pin<Box<T>>, new_value: U, callback: F) -> Result<O, U>
+where
+    F: FnOnce(Box<U>) -> O,
+{
+    let layout = Layout::for_value::<T>(&*boxed);
+    if layout != Layout::new::<U>() {
+        return Err(new_value);
+    }
+
+    // SAFETY: We don't ever construct a non-pinned reference to the old `T` from now on, and we
+    // always drop the `T`.
+    let raw: *mut T = Box::into_raw(unsafe { Pin::into_inner_unchecked(boxed) });
+
+    // When dropping the old value panics, we still want to call `callback` — so move the rest of
+    // the code into a guard type.
+    let guard = CallOnDrop::new(|| {
+        let raw: *mut U = raw.cast::<U>();
+        unsafe { raw.write(new_value) };
+
+        // SAFETY:
+        // - `T` and `U` have the same layout.
+        // - `raw` comes from a `Box` that uses the same allocator as this one.
+        // - `raw` points to a valid instance of `U` (we just wrote it in).
+        let boxed = unsafe { Box::from_raw(raw) };
+
+        callback(boxed)
+    });
+
+    // Drop the old value.
+    unsafe { ptr::drop_in_place(raw) };
+
+    // Run the rest of the code.
+    Ok(guard.call())
+}
+
+struct CallOnDrop<O, F: FnOnce() -> O> {
+    f: ManuallyDrop<F>,
+}
+
+impl<O, F: FnOnce() -> O> CallOnDrop<O, F> {
+    fn new(f: F) -> Self {
+        let f = ManuallyDrop::new(f);
+        Self { f }
+    }
+    fn call(self) -> O {
+        let mut this = ManuallyDrop::new(self);
+        let f = unsafe { ManuallyDrop::take(&mut this.f) };
+        f()
+    }
+}
+
+impl<O, F: FnOnce() -> O> Drop for CallOnDrop<O, F> {
+    fn drop(&mut self) {
+        let f = unsafe { ManuallyDrop::take(&mut self.f) };
+        f();
+    }
+}
+
+/// The same as `std::future::Pending<T>`; we can't use that type directly because on rustc
+/// versions <1.60 it didn't unconditionally implement `Send`.
+// FIXME: use `std::future::Pending<T>` once the MSRV is >=1.60
+struct Pending<T>(PhantomData<fn() -> T>);
+
+impl<T> Future for Pending<T> {
+    type Output = T;
+
+    fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Poll::Pending
+    }
+}

tokio-util/src/task/join_map.rs

@@ -0,0 +1,810 @@
+use hashbrown::hash_map::RawEntryMut;
+use hashbrown::HashMap;
+use std::borrow::Borrow;
+use std::collections::hash_map::RandomState;
+use std::fmt;
+use std::future::Future;
+use std::hash::{BuildHasher, Hash, Hasher};
+use tokio::runtime::Handle;
+use tokio::task::{AbortHandle, Id, JoinError, JoinSet, LocalSet};
+
+/// A collection of tasks spawned on a Tokio runtime, associated with hash map
+/// keys.
+///
+/// This type is very similar to the [`JoinSet`] type in `tokio::task`, with the
+/// addition of a  set of keys associated with each task. These keys allow
+/// [cancelling a task][abort] or [multiple tasks][abort_matching] in the
+/// `JoinMap` based on   their keys, or [test whether a task corresponding to a
+/// given key exists][contains] in the `JoinMap`.
+///
+/// In addition, when tasks in the `JoinMap` complete, they will return the
+/// associated key along with the value returned by the task, if any.
+///
+/// A `JoinMap` can be used to await the completion of some or all of the tasks
+/// in the map. The map is not ordered, and the tasks will be returned in the
+/// order they complete.
+///
+/// All of the tasks must have the same return type `V`.
+///
+/// When the `JoinMap` is dropped, all tasks in the `JoinMap` are immediately aborted.
+///
+/// **Note**: This type depends on Tokio's [unstable API][unstable]. See [the
+/// documentation on unstable features][unstable] for details on how to enable
+/// Tokio's unstable features.
+///
+/// # Examples
+///
+/// Spawn multiple tasks and wait for them:
+///
+/// ```
+/// use tokio_util::task::JoinMap;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut map = JoinMap::new();
+///
+///     for i in 0..10 {
+///         // Spawn a task on the `JoinMap` with `i` as its key.
+///         map.spawn(i, async move { /* ... */ });
+///     }
+///
+///     let mut seen = [false; 10];
+///
+///     // When a task completes, `join_one` returns the task's key along
+///     // with its output.
+///     while let Some((key, res)) = map.join_one().await {
+///         seen[key] = true;
+///         assert!(res.is_ok(), "task {} completed successfully!", key);
+///     }
+///
+///     for i in 0..10 {
+///         assert!(seen[i]);
+///     }
+/// }
+/// ```
+///
+/// Cancel tasks based on their keys:
+///
+/// ```
+/// use tokio_util::task::JoinMap;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut map = JoinMap::new();
+///
+///     map.spawn("hello world", async move { /* ... */ });
+///     map.spawn("goodbye world", async move { /* ... */});
+///
+///     // Look up the "goodbye world" task in the map and abort it.
+///     let aborted = map.abort("goodbye world");
+///
+///     // `JoinMap::abort` returns `true` if a task existed for the
+///     // provided key.
+///     assert!(aborted);
+///
+///     while let Some((key, res)) = map.join_one().await {
+///         if key == "goodbye world" {
+///             // The aborted task should complete with a cancelled `JoinError`.
+///             assert!(res.unwrap_err().is_cancelled());
+///         } else {
+///             // Other tasks should complete normally.
+///             assert!(res.is_ok());
+///         }
+///     }
+/// }
+/// ```
+///
+/// [`JoinSet`]: tokio::task::JoinSet
+/// [unstable]: tokio#unstable-features
+/// [abort]: fn@Self::abort
+/// [abort_matching]: fn@Self::abort_matching
+/// [contains]: fn@Self::contains_key
+#[cfg_attr(docsrs, doc(cfg(all(feature = "rt", tokio_unstable))))]
+pub struct JoinMap<K, V, S = RandomState> {
+    /// A map of the [`AbortHandle`]s of the tasks spawned on this `JoinMap`,
+    /// indexed by their keys and task IDs.
+    ///
+    /// The [`Key`] type contains both the task's `K`-typed key provided when
+    /// spawning tasks, and the task's IDs. The IDs are stored here to resolve
+    /// hash collisions when looking up tasks based on their pre-computed hash
+    /// (as stored in the `hashes_by_task` map).
+    tasks_by_key: HashMap<Key<K>, AbortHandle, S>,
+
+    /// A map from task IDs to the hash of the key associated with that task.
+    ///
+    /// This map is used to perform reverse lookups of tasks in the
+    /// `tasks_by_key` map based on their task IDs. When a task terminates, the
+    /// ID is provided to us by the `JoinSet`, so we can look up the hash value
+    /// of that task's key, and then remove it from the `tasks_by_key` map using
+    /// the raw hash code, resolving collisions by comparing task IDs.
+    hashes_by_task: HashMap<Id, u64, S>,
+
+    /// The [`JoinSet`] that awaits the completion of tasks spawned on this
+    /// `JoinMap`.
+    tasks: JoinSet<V>,
+}
+
+/// A [`JoinMap`] key.
+///
+/// This holds both a `K`-typed key (the actual key as seen by the user), _and_
+/// a task ID, so that hash collisions between `K`-typed keys can be resolved
+/// using either `K`'s `Eq` impl *or* by checking the task IDs.
+///
+/// This allows looking up a task using either an actual key (such as when the
+/// user queries the map with a key), *or* using a task ID and a hash (such as
+/// when removing completed tasks from the map).
+#[derive(Debug)]
+struct Key<K> {
+    key: K,
+    id: Id,
+}
+
+impl<K, V> JoinMap<K, V> {
+    /// Creates a new empty `JoinMap`.
+    ///
+    /// The `JoinMap` is initially created with a capacity of 0, so it will not
+    /// allocate until a task is first spawned on it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio_util::task::JoinMap;
+    /// let map: JoinMap<&str, i32> = JoinMap::new();
+    /// ```
+    #[inline]
+    #[must_use]
+    pub fn new() -> Self {
+        Self::with_hasher(RandomState::new())
+    }
+
+    /// Creates an empty `JoinMap` with the specified capacity.
+    ///
+    /// The `JoinMap` will be able to hold at least `capacity` tasks without
+    /// reallocating.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio_util::task::JoinMap;
+    /// let map: JoinMap<&str, i32> = JoinMap::with_capacity(10);
+    /// ```
+    #[inline]
+    #[must_use]
+    pub fn with_capacity(capacity: usize) -> Self {
+        JoinMap::with_capacity_and_hasher(capacity, Default::default())
+    }
+}
+
+impl<K, V, S: Clone> JoinMap<K, V, S> {
+    /// Creates an empty `JoinMap` which will use the given hash builder to hash
+    /// keys.
+    ///
+    /// The created map has the default initial capacity.
+    ///
+    /// Warning: `hash_builder` is normally randomly generated, and
+    /// is designed to allow `JoinMap` to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    ///
+    /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
+    /// the `JoinMap` to be useful, see its documentation for details.
+    #[inline]
+    #[must_use]
+    pub fn with_hasher(hash_builder: S) -> Self {
+        Self::with_capacity_and_hasher(0, hash_builder)
+    }
+
+    /// Creates an empty `JoinMap` with the specified capacity, using `hash_builder`
+    /// to hash the keys.
+    ///
+    /// The `JoinMap` will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the `JoinMap` will not allocate.
+    ///
+    /// Warning: `hash_builder` is normally randomly generated, and
+    /// is designed to allow HashMaps to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    ///
+    /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
+    /// the `JoinMap`to be useful, see its documentation for details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// use tokio_util::task::JoinMap;
+    /// use std::collections::hash_map::RandomState;
+    ///
+    /// let s = RandomState::new();
+    /// let mut map = JoinMap::with_capacity_and_hasher(10, s);
+    /// map.spawn(1, async move { "hello world!" });
+    /// # }
+    /// ```
+    #[inline]
+    #[must_use]
+    pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Self {
+        Self {
+            tasks_by_key: HashMap::with_capacity_and_hasher(capacity, hash_builder.clone()),
+            hashes_by_task: HashMap::with_capacity_and_hasher(capacity, hash_builder),
+            tasks: JoinSet::new(),
+        }
+    }
+
+    /// Returns the number of tasks currently in the `JoinMap`.
+    pub fn len(&self) -> usize {
+        let len = self.tasks_by_key.len();
+        debug_assert_eq!(len, self.hashes_by_task.len());
+        len
+    }
+
+    /// Returns whether the `JoinMap` is empty.
+    pub fn is_empty(&self) -> bool {
+        let empty = self.tasks_by_key.is_empty();
+        debug_assert_eq!(empty, self.hashes_by_task.is_empty());
+        empty
+    }
+
+    /// Returns the number of tasks the map can hold without reallocating.
+    ///
+    /// This number is a lower bound; the `JoinMap` might be able to hold
+    /// more, but is guaranteed to be able to hold at least this many.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio_util::task::JoinMap;
+    ///
+    /// let map: JoinMap<i32, i32> = JoinMap::with_capacity(100);
+    /// assert!(map.capacity() >= 100);
+    /// ```
+    #[inline]
+    pub fn capacity(&self) -> usize {
+        let capacity = self.tasks_by_key.capacity();
+        debug_assert_eq!(capacity, self.hashes_by_task.capacity());
+        capacity
+    }
+}
+
+impl<K, V, S> JoinMap<K, V, S>
+where
+    K: Hash + Eq,
+    V: 'static,
+    S: BuildHasher,
+{
+    /// Spawn the provided task and store it in this `JoinMap` with the provided
+    /// key.
+    ///
+    /// If a task previously existed in the `JoinMap` for this key, that task
+    /// will be cancelled and replaced with the new one. The previous task will
+    /// be removed from the `JoinMap`; a subsequent call to [`join_one`] will
+    /// *not* return a cancelled [`JoinError`] for that task.
+    ///
+    /// # Panics
+    ///
+    /// This method panics if called outside of a Tokio runtime.
+    ///
+    /// [`join_one`]: Self::join_one
+    #[track_caller]
+    pub fn spawn<F>(&mut self, key: K, task: F)
+    where
+        F: Future<Output = V>,
+        F: Send + 'static,
+        V: Send,
+    {
+        let task = self.tasks.spawn(task);
+        self.insert(key, task)
+    }
+
+    /// Spawn the provided task on the provided runtime and store it in this
+    /// `JoinMap` with the provided key.
+    ///
+    /// If a task previously existed in the `JoinMap` for this key, that task
+    /// will be cancelled and replaced with the new one. The previous task will
+    /// be removed from the `JoinMap`; a subsequent call to [`join_one`] will
+    /// *not* return a cancelled [`JoinError`] for that task.
+    ///
+    /// [`join_one`]: Self::join_one
+    #[track_caller]
+    pub fn spawn_on<F>(&mut self, key: K, task: F, handle: &Handle)
+    where
+        F: Future<Output = V>,
+        F: Send + 'static,
+        V: Send,
+    {
+        let task = self.tasks.spawn_on(task, handle);
+        self.insert(key, task);
+    }
+
+    /// Spawn the provided task on the current [`LocalSet`] and store it in this
+    /// `JoinMap` with the provided key.
+    ///
+    /// If a task previously existed in the `JoinMap` for this key, that task
+    /// will be cancelled and replaced with the new one. The previous task will
+    /// be removed from the `JoinMap`; a subsequent call to [`join_one`] will
+    /// *not* return a cancelled [`JoinError`] for that task.
+    ///
+    /// # Panics
+    ///
+    /// This method panics if it is called outside of a `LocalSet`.
+    ///
+    /// [`LocalSet`]: tokio::task::LocalSet
+    /// [`join_one`]: Self::join_one
+    #[track_caller]
+    pub fn spawn_local<F>(&mut self, key: K, task: F)
+    where
+        F: Future<Output = V>,
+        F: 'static,
+    {
+        let task = self.tasks.spawn_local(task);
+        self.insert(key, task);
+    }
+
+    /// Spawn the provided task on the provided [`LocalSet`] and store it in
+    /// this `JoinMap` with the provided key.
+    ///
+    /// If a task previously existed in the `JoinMap` for this key, that task
+    /// will be cancelled and replaced with the new one. The previous task will
+    /// be removed from the `JoinMap`; a subsequent call to [`join_one`] will
+    /// *not* return a cancelled [`JoinError`] for that task.
+    ///
+    /// [`LocalSet`]: tokio::task::LocalSet
+    /// [`join_one`]: Self::join_one
+    #[track_caller]
+    pub fn spawn_local_on<F>(&mut self, key: K, task: F, local_set: &LocalSet)
+    where
+        F: Future<Output = V>,
+        F: 'static,
+    {
+        let task = self.tasks.spawn_local_on(task, local_set);
+        self.insert(key, task)
+    }
+
+    fn insert(&mut self, key: K, abort: AbortHandle) {
+        let hash = self.hash(&key);
+        let id = abort.id();
+        let map_key = Key {
+            id: id.clone(),
+            key,
+        };
+
+        // Insert the new key into the map of tasks by keys.
+        let entry = self
+            .tasks_by_key
+            .raw_entry_mut()
+            .from_hash(hash, |k| k.key == map_key.key);
+        match entry {
+            RawEntryMut::Occupied(mut occ) => {
+                // There was a previous task spawned with the same key! Cancel
+                // that task, and remove its ID from the map of hashes by task IDs.
+                let Key { id: prev_id, .. } = occ.insert_key(map_key);
+                occ.insert(abort).abort();
+                let _prev_hash = self.hashes_by_task.remove(&prev_id);
+                debug_assert_eq!(Some(hash), _prev_hash);
+            }
+            RawEntryMut::Vacant(vac) => {
+                vac.insert(map_key, abort);
+            }
+        };
+
+        // Associate the key's hash with this task's ID, for looking up tasks by ID.
+        let _prev = self.hashes_by_task.insert(id, hash);
+        debug_assert!(_prev.is_none(), "no prior task should have had the same ID");
+    }
+
+    /// Waits until one of the tasks in the map completes and returns its
+    /// output, along with the key corresponding to that task.
+    ///
+    /// Returns `None` if the map is empty.
+    ///
+    /// # Cancel Safety
+    ///
+    /// This method is cancel safe. If `join_one` is used as the event in a [`tokio::select!`]
+    /// statement and some other branch completes first, it is guaranteed that no tasks were
+    /// removed from this `JoinMap`.
+    ///
+    /// # Returns
+    ///
+    /// This function returns:
+    ///
+    ///  * `Some((key, Ok(value)))` if one of the tasks in this `JoinMap` has
+    ///    completed. The `value` is the return value of that ask, and `key` is
+    ///    the key associated with the task.
+    ///  * `Some((key, Err(err))` if one of the tasks in this JoinMap` has
+    ///    panicked or been aborted. `key` is the key associated  with the task
+    ///    that panicked or was aborted.
+    ///  * `None` if the `JoinMap` is empty.
+    ///
+    /// [`tokio::select!`]: tokio::select
+    pub async fn join_one(&mut self) -> Option<(K, Result<V, JoinError>)> {
+        let (res, id) = match self.tasks.join_one_with_id().await {
+            Some(Ok((id, output))) => (Ok(output), id),
+            Some(Err(e)) => {
+                let id = e.id();
+                (Err(e), id)
+            }
+            None => return None,
+        };
+        let key = self.remove_by_id(id)?;
+        Some((key, res))
+    }
+
+    /// Aborts all tasks and waits for them to finish shutting down.
+    ///
+    /// Calling this method is equivalent to calling [`abort_all`] and then calling [`join_one`] in
+    /// a loop until it returns `None`.
+    ///
+    /// This method ignores any panics in the tasks shutting down. When this call returns, the
+    /// `JoinMap` will be empty.
+    ///
+    /// [`abort_all`]: fn@Self::abort_all
+    /// [`join_one`]: fn@Self::join_one
+    pub async fn shutdown(&mut self) {
+        self.abort_all();
+        while self.join_one().await.is_some() {}
+    }
+
+    /// Abort the task corresponding to the provided `key`.
+    ///
+    /// If this `JoinMap` contains a task corresponding to `key`, this method
+    /// will abort that task and return `true`. Otherwise, if no task exists for
+    /// `key`, this method returns `false`.
+    ///
+    /// # Examples
+    ///
+    /// Aborting a task by key:
+    ///
+    /// ```
+    /// use tokio_util::task::JoinMap;
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let mut map = JoinMap::new();
+    ///
+    /// map.spawn("hello world", async move { /* ... */ });
+    /// map.spawn("goodbye world", async move { /* ... */});
+    ///
+    /// // Look up the "goodbye world" task in the map and abort it.
+    /// map.abort("goodbye world");
+    ///
+    /// while let Some((key, res)) = map.join_one().await {
+    ///     if key == "goodbye world" {
+    ///         // The aborted task should complete with a cancelled `JoinError`.
+    ///         assert!(res.unwrap_err().is_cancelled());
+    ///     } else {
+    ///         // Other tasks should complete normally.
+    ///         assert!(res.is_ok());
+    ///     }
+    /// }
+    /// # }
+    /// ```
+    ///
+    /// `abort` returns `true` if a task was aborted:
+    /// ```
+    /// use tokio_util::task::JoinMap;
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let mut map = JoinMap::new();
+    ///
+    /// map.spawn("hello world", async move { /* ... */ });
+    /// map.spawn("goodbye world", async move { /* ... */});
+    ///
+    /// // A task for the key "goodbye world" should exist in the map:
+    /// assert!(map.abort("goodbye world"));
+    ///
+    /// // Aborting a key that does not exist will return `false`:
+    /// assert!(!map.abort("goodbye universe"));
+    /// # }
+    /// ```
+    pub fn abort<Q: ?Sized>(&mut self, key: &Q) -> bool
+    where
+        Q: Hash + Eq,
+        K: Borrow<Q>,
+    {
+        match self.get_by_key(key) {
+            Some((_, handle)) => {
+                handle.abort();
+                true
+            }
+            None => false,
+        }
+    }
+
+    /// Aborts all tasks with keys matching `predicate`.
+    ///
+    /// `predicate` is a function called with a reference to each key in the
+    /// map. If it returns `true` for a given key, the corresponding task will
+    /// be cancelled.
+    ///
+    /// # Examples
+    /// ```
+    /// use tokio_util::task::JoinMap;
+    ///
+    /// # // use the current thread rt so that spawned tasks don't
+    /// # // complete in the background before they can be aborted.
+    /// # #[tokio::main(flavor = "current_thread")]
+    /// # async fn main() {
+    /// let mut map = JoinMap::new();
+    ///
+    /// map.spawn("hello world", async move {
+    ///     // ...
+    ///     # tokio::task::yield_now().await; // don't complete immediately, get aborted!
+    /// });
+    /// map.spawn("goodbye world", async move {
+    ///     // ...
+    ///     # tokio::task::yield_now().await; // don't complete immediately, get aborted!
+    /// });
+    /// map.spawn("hello san francisco", async move {
+    ///     // ...
+    ///     # tokio::task::yield_now().await; // don't complete immediately, get aborted!
+    /// });
+    /// map.spawn("goodbye universe", async move {
+    ///     // ...
+    ///     # tokio::task::yield_now().await; // don't complete immediately, get aborted!
+    /// });
+    ///
+    /// // Abort all tasks whose keys begin with "goodbye"
+    /// map.abort_matching(|key| key.starts_with("goodbye"));
+    ///
+    /// let mut seen = 0;
+    /// while let Some((key, res)) = map.join_one().await {
+    ///     seen += 1;
+    ///     if key.starts_with("goodbye") {
+    ///         // The aborted task should complete with a cancelled `JoinError`.
+    ///         assert!(res.unwrap_err().is_cancelled());
+    ///     } else {
+    ///         // Other tasks should complete normally.
+    ///         assert!(key.starts_with("hello"));
+    ///         assert!(res.is_ok());
+    ///     }
+    /// }
+    ///
+    /// // All spawned tasks should have completed.
+    /// assert_eq!(seen, 4);
+    /// # }
+    /// ```
+    pub fn abort_matching(&mut self, mut predicate: impl FnMut(&K) -> bool) {
+        // Note: this method iterates over the tasks and keys *without* removing
+        // any entries, so that the keys from aborted tasks can still be
+        // returned when calling `join_one` in the future.
+        for (Key { ref key, .. }, task) in &self.tasks_by_key {
+            if predicate(key) {
+                task.abort();
+            }
+        }
+    }
+
+    /// Returns `true` if this `JoinMap` contains a task for the provided key.
+    ///
+    /// If the task has completed, but its output hasn't yet been consumed by a
+    /// call to [`join_one`], this method will still return `true`.
+    ///
+    /// [`join_one`]: fn@Self::join_one
+    pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool
+    where
+        Q: Hash + Eq,
+        K: Borrow<Q>,
+    {
+        self.get_by_key(key).is_some()
+    }
+
+    /// Returns `true` if this `JoinMap` contains a task with the provided
+    /// [task ID].
+    ///
+    /// If the task has completed, but its output hasn't yet been consumed by a
+    /// call to [`join_one`], this method will still return `true`.
+    ///
+    /// [`join_one`]: fn@Self::join_one
+    /// [task ID]: tokio::task::Id
+    pub fn contains_task(&self, task: &Id) -> bool {
+        self.get_by_id(task).is_some()
+    }
+
+    /// Reserves capacity for at least `additional` more tasks to be spawned
+    /// on this `JoinMap` without reallocating for the map of task keys. The
+    /// collection may reserve more space to avoid frequent reallocations.
+    ///
+    /// Note that spawning a task will still cause an allocation for the task
+    /// itself.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new allocation size overflows [`usize`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio_util::task::JoinMap;
+    ///
+    /// let mut map: JoinMap<&str, i32> = JoinMap::new();
+    /// map.reserve(10);
+    /// ```
+    #[inline]
+    pub fn reserve(&mut self, additional: usize) {
+        self.tasks_by_key.reserve(additional);
+        self.hashes_by_task.reserve(additional);
+    }
+
+    /// Shrinks the capacity of the `JoinMap` as much as possible. It will drop
+    /// down as much as possible while maintaining the internal rules
+    /// and possibly leaving some space in accordance with the resize policy.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// use tokio_util::task::JoinMap;
+    ///
+    /// let mut map: JoinMap<i32, i32> = JoinMap::with_capacity(100);
+    /// map.spawn(1, async move { 2 });
+    /// map.spawn(3, async move { 4 });
+    /// assert!(map.capacity() >= 100);
+    /// map.shrink_to_fit();
+    /// assert!(map.capacity() >= 2);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn shrink_to_fit(&mut self) {
+        self.hashes_by_task.shrink_to_fit();
+        self.tasks_by_key.shrink_to_fit();
+    }
+
+    /// Shrinks the capacity of the map with a lower limit. It will drop
+    /// down no lower than the supplied limit while maintaining the internal rules
+    /// and possibly leaving some space in accordance with the resize policy.
+    ///
+    /// If the current capacity is less than the lower limit, this is a no-op.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// use tokio_util::task::JoinMap;
+    ///
+    /// let mut map: JoinMap<i32, i32> = JoinMap::with_capacity(100);
+    /// map.spawn(1, async move { 2 });
+    /// map.spawn(3, async move { 4 });
+    /// assert!(map.capacity() >= 100);
+    /// map.shrink_to(10);
+    /// assert!(map.capacity() >= 10);
+    /// map.shrink_to(0);
+    /// assert!(map.capacity() >= 2);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn shrink_to(&mut self, min_capacity: usize) {
+        self.hashes_by_task.shrink_to(min_capacity);
+        self.tasks_by_key.shrink_to(min_capacity)
+    }
+
+    /// Look up a task in the map by its key, returning the key and abort handle.
+    fn get_by_key<'map, Q: ?Sized>(&'map self, key: &Q) -> Option<(&'map Key<K>, &'map AbortHandle)>
+    where
+        Q: Hash + Eq,
+        K: Borrow<Q>,
+    {
+        let hash = self.hash(key);
+        self.tasks_by_key
+            .raw_entry()
+            .from_hash(hash, |k| k.key.borrow() == key)
+    }
+
+    /// Look up a task in the map by its task ID, returning the key and abort handle.
+    fn get_by_id<'map>(&'map self, id: &Id) -> Option<(&'map Key<K>, &'map AbortHandle)> {
+        let hash = self.hashes_by_task.get(id)?;
+        self.tasks_by_key
+            .raw_entry()
+            .from_hash(*hash, |k| &k.id == id)
+    }
+
+    /// Remove a task from the map by ID, returning the key for that task.
+    fn remove_by_id(&mut self, id: Id) -> Option<K> {
+        // Get the hash for the given ID.
+        let hash = self.hashes_by_task.remove(&id)?;
+
+        // Remove the entry for that hash.
+        let entry = self
+            .tasks_by_key
+            .raw_entry_mut()
+            .from_hash(hash, |k| k.id == id);
+        let (Key { id: _key_id, key }, handle) = match entry {
+            RawEntryMut::Occupied(entry) => entry.remove_entry(),
+            _ => return None,
+        };
+        debug_assert_eq!(_key_id, id);
+        debug_assert_eq!(id, handle.id());
+        self.hashes_by_task.remove(&id);
+        Some(key)
+    }
+
+    /// Returns the hash for a given key.
+    #[inline]
+    fn hash<Q: ?Sized>(&self, key: &Q) -> u64
+    where
+        Q: Hash,
+    {
+        let mut hasher = self.tasks_by_key.hasher().build_hasher();
+        key.hash(&mut hasher);
+        hasher.finish()
+    }
+}
+
+impl<K, V, S> JoinMap<K, V, S>
+where
+    V: 'static,
+{
+    /// Aborts all tasks on this `JoinMap`.
+    ///
+    /// This does not remove the tasks from the `JoinMap`. To wait for the tasks to complete
+    /// cancellation, you should call `join_one` in a loop until the `JoinMap` is empty.
+    pub fn abort_all(&mut self) {
+        self.tasks.abort_all()
+    }
+
+    /// Removes all tasks from this `JoinMap` without aborting them.
+    ///
+    /// The tasks removed by this call will continue to run in the background even if the `JoinMap`
+    /// is dropped. They may still be aborted by key.
+    pub fn detach_all(&mut self) {
+        self.tasks.detach_all();
+        self.tasks_by_key.clear();
+        self.hashes_by_task.clear();
+    }
+}
+
+// Hand-written `fmt::Debug` implementation in order to avoid requiring `V:
+// Debug`, since no value is ever actually stored in the map.
+impl<K: fmt::Debug, V, S> fmt::Debug for JoinMap<K, V, S> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // format the task keys and abort handles a little nicer by just
+        // printing the key and task ID pairs, without format the `Key` struct
+        // itself or the `AbortHandle`, which would just format the task's ID
+        // again.
+        struct KeySet<'a, K: fmt::Debug, S>(&'a HashMap<Key<K>, AbortHandle, S>);
+        impl<K: fmt::Debug, S> fmt::Debug for KeySet<'_, K, S> {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                f.debug_map()
+                    .entries(self.0.keys().map(|Key { key, id }| (key, id)))
+                    .finish()
+            }
+        }
+
+        f.debug_struct("JoinMap")
+            // The `tasks_by_key` map is the only one that contains information
+            // that's really worth formatting for the user, since it contains
+            // the tasks' keys and IDs. The other fields are basically
+            // implementation details.
+            .field("tasks", &KeySet(&self.tasks_by_key))
+            .finish()
+    }
+}
+
+impl<K, V> Default for JoinMap<K, V> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+// === impl Key ===
+
+impl<K: Hash> Hash for Key<K> {
+    // Don't include the task ID in the hash.
+    #[inline]
+    fn hash<H: Hasher>(&self, hasher: &mut H) {
+        self.key.hash(hasher);
+    }
+}
+
+// Because we override `Hash` for this type, we must also override the
+// `PartialEq` impl, so that all instances with the same hash are equal.
+impl<K: PartialEq> PartialEq for Key<K> {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        self.key == other.key
+    }
+}
+
+impl<K: Eq> Eq for Key<K> {}

tokio-util/src/task/mod.rs

@@ -0,0 +1,10 @@
+//! Extra utilities for spawning tasks
+
+#[cfg(tokio_unstable)]
+mod join_map;
+mod spawn_pinned;
+pub use spawn_pinned::LocalPoolHandle;
+
+#[cfg(tokio_unstable)]
+#[cfg_attr(docsrs, doc(cfg(all(tokio_unstable, feature = "rt"))))]
+pub use join_map::JoinMap;