checkpoint

Closes #5011

.cirrus.yml

@@ -11,6 +11,7 @@ env:
 # the system's binaries, so the environment shouldn't matter.
 task:
   name: FreeBSD 64-bit
+  auto_cancellation: $CIRRUS_BRANCH != 'master' && $CIRRUS_BRANCH !=~ 'tokio-.*'
   setup_script:
     - pkg install -y bash curl
     - curl https://sh.rustup.rs -sSf --output rustup.sh
@@ -25,6 +26,7 @@ task:
 
 task:
   name: FreeBSD docs
+  auto_cancellation: $CIRRUS_BRANCH != 'master' && $CIRRUS_BRANCH !=~ 'tokio-.*'
   env:
     RUSTFLAGS: --cfg docsrs --cfg tokio_unstable
     RUSTDOCFLAGS: --cfg docsrs --cfg tokio_unstable -Dwarnings
@@ -42,6 +44,7 @@ task:
 
 task:
   name: FreeBSD 32-bit
+  auto_cancellation: $CIRRUS_BRANCH != 'master' && $CIRRUS_BRANCH !=~ 'tokio-.*'
   setup_script:
     - pkg install -y bash curl
     - curl https://sh.rustup.rs -sSf --output rustup.sh

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,4 @@
+contact_links:
+  - name: Question
+    url: https://github.com/tokio-rs/tokio/discussions
+    about: Questions about Tokio should be posted as a GitHub discussion.

.github/ISSUE_TEMPLATE/question.md

@@ -1,16 +0,0 @@
----
-name: Question
-about: Please use the discussions tab for questions
-title: ''
-labels: ''
-assignees: ''
-
----
-
-Please post your question as a discussion here:
-https://github.com/tokio-rs/tokio/discussions
-
-
-You may also be able to find help here:
-https://discord.gg/tokio
-https://users.rust-lang.org/

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ env:
   RUST_BACKTRACE: 1
   # Change to specific Rust release to pin
   rust_stable: stable
-  rust_nightly: nightly-2022-04-18
+  rust_nightly: nightly-2022-07-26
   rust_clippy: 1.52.0
   # When updating this, also update:
   # - README.md
@@ -34,21 +34,25 @@ jobs:
     runs-on: ubuntu-latest
     needs:
       - test
-      - test-unstable
       - test-parking_lot
+      - valgrind
+      - test-unstable
       - miri
+      - asan
       - cross
       - features
       - minrust
+      - minimal-versions
       - fmt
       - clippy
       - docs
-      - valgrind
       - loom-compile
       - check-readme
       - test-hyper
+      - x86_64-fortanix-unknown-sgx
       - wasm32-unknown-unknown
       - wasm32-wasi
+      - check-external-types
     steps:
       - run: exit 0
 
@@ -72,7 +76,7 @@ jobs:
         run: rustup update stable
       - uses: Swatinem/rust-cache@v1
       - name: Install cargo-hack
-        run: cargo install cargo-hack
+        uses: taiki-e/install-action@cargo-hack
 
       # Run `tokio` with `full` features. This excludes testing utilities which
       # can alter the runtime behavior of Tokio.
@@ -138,9 +142,7 @@ jobs:
       - uses: Swatinem/rust-cache@v1
 
       - name: Install Valgrind
-        run: |
-          sudo apt-get update -y
-          sudo apt-get install -y valgrind
+        uses: taiki-e/install-action@valgrind
 
       # Compile tests
       - name: cargo build test-mem
@@ -195,7 +197,7 @@ jobs:
       - name: Install Rust ${{ env.rust_nightly }}
         uses: actions-rs/toolchain@v1
         with:
-          toolchain: nightly-2022-07-10
+          toolchain: ${{ env.rust_nightly }}
           components: miri
           override: true
       - uses: Swatinem/rust-cache@v1
@@ -275,12 +277,12 @@ jobs:
           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
+        uses: taiki-e/install-action@cargo-hack
+      - name: check --feature-powerset
+        run: cargo hack check --all --feature-powerset --depth 2 -Z avoid-dev-deps --keep-going
       # Try with unstable feature flags
-      - name: check --each-feature --unstable
-        run: cargo hack check --all --each-feature -Z avoid-dev-deps
+      - name: check --feature-powerset --unstable
+        run: cargo hack check --all --feature-powerset --depth 2 -Z avoid-dev-deps --keep-going
         env:
           RUSTFLAGS: --cfg tokio_unstable -Dwarnings
 
@@ -310,7 +312,7 @@ jobs:
           override: true
       - uses: Swatinem/rust-cache@v1
       - name: Install cargo-hack
-        run: cargo install cargo-hack
+        uses: taiki-e/install-action@cargo-hack
       - name: "check --all-features -Z minimal-versions"
         run: |
           # Remove dev-dependencies from Cargo.toml to prevent the next `cargo update`
@@ -447,6 +449,23 @@ jobs:
           git diff
           cargo test --features full
 
+  x86_64-fortanix-unknown-sgx:
+    name: build tokio for x86_64-fortanix-unknown-sgx
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_nightly }}
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ env.rust_nightly }}
+          target: x86_64-fortanix-unknown-sgx
+          override: true
+      - uses: Swatinem/rust-cache@v1
+      # NOTE: Currently the only test we can run is to build tokio with rt and sync features.
+      - name: build tokio
+        run: cargo build --target x86_64-fortanix-unknown-sgx --features rt,sync
+        working-directory: tokio
+
   wasm32-unknown-unknown:
     name: test tokio for wasm32-unknown-unknown
     runs-on: ubuntu-latest
@@ -478,22 +497,59 @@ jobs:
 
       # Install dependencies
       - name: Install cargo-hack
-        run: cargo install cargo-hack
+        uses: taiki-e/install-action@cargo-hack
 
       - name: Install wasm32-wasi target
         run: rustup target add wasm32-wasi
 
       - name: Install wasmtime
-        run: cargo install wasmtime-cli
+        uses: taiki-e/install-action@wasmtime
 
       - name: Install cargo-wasi
         run: cargo install cargo-wasi
 
-      # TODO: Expand this when full WASI support lands.
-      #   Currently, this is a bare bones regression test
-      #   for features that work today with wasi.
+      - name: WASI test tokio full
+        run: cargo test -p tokio --target wasm32-wasi --features full
+        env:
+          CARGO_TARGET_WASM32_WASI_RUNNER: "wasmtime run --"
+          RUSTFLAGS: --cfg tokio_unstable -Dwarnings
+
+      - name: WASI test tokio-util full
+        run: cargo test -p tokio-util --target wasm32-wasi --features full
+        env:
+          CARGO_TARGET_WASM32_WASI_RUNNER: "wasmtime run --"
+          RUSTFLAGS: --cfg tokio_unstable -Dwarnings
+
+      - name: WASI test tokio-stream
+        run: cargo test -p tokio-stream --target wasm32-wasi --features time,net,io-util,sync
+        env:
+          CARGO_TARGET_WASM32_WASI_RUNNER: "wasmtime run --"
+          RUSTFLAGS: --cfg tokio_unstable -Dwarnings
 
       - name: test tests-integration --features wasi-rt
         # TODO: this should become: `cargo hack wasi test --each-feature`
         run: cargo wasi test --test rt_yield --features wasi-rt
         working-directory: tests-integration
+
+  check-external-types:
+    name: check-external-types
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os:
+          - windows-latest
+          - ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Rust ${{ env.rust_nightly }}
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ env.rust_nightly }}
+          override: true
+      - uses: Swatinem/rust-cache@v1
+      - name: check-external-types
+        run: |
+          set -x
+          cargo install cargo-check-external-types --locked --version 0.1.3
+          cargo check-external-types --all-features --config external-types.toml
+        working-directory: tokio

.github/workflows/labeler.yml

@@ -7,6 +7,7 @@ on:
 jobs:
   triage:
     runs-on: ubuntu-latest
+    if: github.repository_owner == 'tokio-rs'
     steps:
     - uses: actions/labeler@v3
       with:

.github/workflows/loom.yml

@@ -17,7 +17,7 @@ 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)
+    if: github.repository_owner == 'tokio-rs' && (contains(github.event.pull_request.labels.*.name, 'R-loom') || (github.base_ref == null))
     runs-on: ubuntu-latest
     strategy:
       matrix:

.github/workflows/stress-test.yml

@@ -12,7 +12,7 @@ env:
   rust_stable: stable
 
 jobs:
-  stess-test:
+  stress-test:
     name: Stress Test
     runs-on: ubuntu-latest
     strategy:
@@ -28,9 +28,7 @@ jobs:
             override: true
       - uses: Swatinem/rust-cache@v1
       - name: Install Valgrind
-        run: |
-          sudo apt-get update -y
-          sudo apt-get install -y valgrind
+        uses: taiki-e/install-action@valgrind
 
       # Compiles each of the stress test examples.
       - name: Compile stress test examples
@@ -38,4 +36,4 @@ jobs:
 
       # Runs each of the examples using Valgrind. Detects leaks and displays them.
       - name: Run valgrind
-        run: valgrind  --leak-check=full --show-leak-kinds=all ./target/release/examples/${{ matrix.stress-test }}
+        run: valgrind --error-exitcode=1 --leak-check=full --show-leak-kinds=all ./target/release/examples/${{ matrix.stress-test }}

CONTRIBUTING.md

@@ -146,7 +146,7 @@ When updating this, also update:
 -->
 
 ```
-cargo +1.49.0 clippy --all-features
+cargo +1.49.0 clippy --all --tests --all-features
 ```
 
 When building documentation normally, the markers that list the features
@@ -154,7 +154,7 @@ required for various parts of Tokio are missing. To build the documentation
 correctly, use this command:
 
 ```
-RUSTDOCFLAGS="--cfg docsrs" cargo +nightly doc --all-features
+RUSTDOCFLAGS="--cfg docsrs" RUSTFLAGS="--cfg docsrs" cargo +nightly doc --all-features
 ```
 
 To build documentation including Tokio's unstable features, it is necessary to
@@ -162,15 +162,9 @@ 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
+RUSTDOCFLAGS="--cfg docsrs --cfg tokio_unstable" RUSTFLAGS="--cfg docsrs --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.
-
-[bug in cargo]: https://github.com/rust-lang/cargo/issues/9274
-
 The `cargo fmt` command does not work on the Tokio codebase. You can use the
 command below instead:
 
@@ -562,7 +556,7 @@ Tokio ≥1.0.0 comes with LTS guarantees:
 
 The goal of these guarantees is to provide stability to the ecosystem.
 
-## Mininum Supported Rust Version (MSRV)
+## Minimum Supported Rust Version (MSRV)
 
  * All Tokio ≥1.0.0 releases will support at least a 6-month old Rust
    compiler release.

README.md

@@ -56,7 +56,7 @@ Make sure you activated the full features of the tokio crate on Cargo.toml:
 
 ```toml
 [dependencies]
-tokio = { version = "1.20.1", features = ["full"] }
+tokio = { version = "1.21.1", features = ["full"] }
 ```
 Then, on your main.rs:
 
@@ -161,6 +161,16 @@ several other libraries, including:
 [`mio`]: https://github.com/tokio-rs/mio
 [`bytes`]: https://github.com/tokio-rs/bytes
 
+## Changelog
+
+The Tokio repository contains multiple crates. Each crate has its own changelog.
+
+ * `tokio` - [view changelog](https://github.com/tokio-rs/tokio/blob/master/tokio/CHANGELOG.md)
+ * `tokio-util` - [view changelog](https://github.com/tokio-rs/tokio/blob/master/tokio-util/CHANGELOG.md)
+ * `tokio-stream` - [view changelog](https://github.com/tokio-rs/tokio/blob/master/tokio-stream/CHANGELOG.md)
+ * `tokio-macros` - [view changelog](https://github.com/tokio-rs/tokio/blob/master/tokio-macros/CHANGELOG.md)
+ * `tokio-test` - [view changelog](https://github.com/tokio-rs/tokio/blob/master/tokio-test/CHANGELOG.md)
+
 ## Supported Rust Versions
 
 <!--
@@ -192,18 +202,18 @@ 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
+ * `1.18.x` - LTS release until June 2023
+ * `1.20.x` - LTS release until September 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.
+Each LTS release will continue to receive backported fixes for at least 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
+example, to specify that you wish to use the newest `1.18.x` patch release, you
 can use the following dependency specification:
 ```text
-tokio = { version = "~1.14", features = [...] }
+tokio = { version = "~1.18", features = [...] }
 ```
 
 ## License

SECURITY.md

@@ -1,13 +1,13 @@
 ## Report a security issue
 
-The Tokio project team welcomes security reports and is committed to providing prompt attention to security issues. Security issues should be reported privately via [[email protected]](mailto:[email protected]). Security issues should not be reported via the public Github Issue tracker.
+The Tokio project team welcomes security reports and is committed to providing prompt attention to security issues. Security issues should be reported privately via [[email protected]](mailto:[email protected]). Security issues should not be reported via the public GitHub Issue tracker.
 
 ## Vulnerability coordination
 
-Remediation of security vulnerabilities is prioritized by the project team. The project team coordinates remediation with third-party project stakeholders via [Github Security Advisories](https://help.github.com/en/github/managing-security-vulnerabilities/about-github-security-advisories). Third-party stakeholders may include the reporter of the issue, affected direct or indirect users of Tokio, and maintainers of upstream dependencies if applicable.
+Remediation of security vulnerabilities is prioritized by the project team. The project team coordinates remediation with third-party project stakeholders via [GitHub Security Advisories](https://help.github.com/en/github/managing-security-vulnerabilities/about-github-security-advisories). Third-party stakeholders may include the reporter of the issue, affected direct or indirect users of Tokio, and maintainers of upstream dependencies if applicable.
 
-Downstream project maintainers and Tokio users can request participation in coordination of applicable security issues by sending your contact email address, Github username(s) and any other salient information to [[email protected]](mailto:[email protected]). Participation in security issue coordination processes is at the discretion of the Tokio team.
+Downstream project maintainers and Tokio users can request participation in coordination of applicable security issues by sending your contact email address, GitHub username(s) and any other salient information to [[email protected]](mailto:[email protected]). Participation in security issue coordination processes is at the discretion of the Tokio team.
 
 ## Security advisories
 
-The project team is committed to transparency in the security issue disclosure process. The Tokio team announces security issues via [project Github Release notes](https://github.com/tokio-rs/tokio/releases) and the [RustSec advisory database](https://github.com/RustSec/advisory-db) (i.e. `cargo-audit`).
+The project team is committed to transparency in the security issue disclosure process. The Tokio team announces security issues via [project GitHub Release notes](https://github.com/tokio-rs/tokio/releases) and the [RustSec advisory database](https://github.com/RustSec/advisory-db) (i.e. `cargo-audit`).

benches/sync_rwlock.rs

@@ -14,7 +14,7 @@ fn read_uncontended(b: &mut Bencher) {
         rt.block_on(async move {
             for _ in 0..6 {
                 let read = lock.read().await;
-                black_box(read);
+                let _read = black_box(read);
             }
         })
     });
@@ -28,7 +28,7 @@ fn read_concurrent_uncontended_multi(b: &mut Bencher) {
 
     async fn task(lock: Arc<RwLock<()>>) {
         let read = lock.read().await;
-        black_box(read);
+        let _read = black_box(read);
     }
 
     let lock = Arc::new(RwLock::new(()));
@@ -55,7 +55,7 @@ fn read_concurrent_uncontended(b: &mut Bencher) {
 
     async fn task(lock: Arc<RwLock<()>>) {
         let read = lock.read().await;
-        black_box(read);
+        let _read = black_box(read);
     }
 
     let lock = Arc::new(RwLock::new(()));
@@ -82,7 +82,7 @@ fn read_concurrent_contended_multi(b: &mut Bencher) {
 
     async fn task(lock: Arc<RwLock<()>>) {
         let read = lock.read().await;
-        black_box(read);
+        let _read = black_box(read);
     }
 
     let lock = Arc::new(RwLock::new(()));
@@ -110,7 +110,7 @@ fn read_concurrent_contended(b: &mut Bencher) {
 
     async fn task(lock: Arc<RwLock<()>>) {
         let read = lock.read().await;
-        black_box(read);
+        let _read = black_box(read);
     }
 
     let lock = Arc::new(RwLock::new(()));

tests-build/README.md

@@ -1,2 +1,10 @@
 Tests the various combination of feature flags. This is broken out to a separate
 crate to work around limitations with cargo features.
+
+To run all of the tests in this directory, run the following commands:
+```
+cargo test --features full
+cargo test --features rt
+```
+If one of the tests fail, you can pass `TRYBUILD=overwrite` to the `cargo test`
+command that failed to have it regenerate the test output.

tests-build/tests/fail/macros_core_no_default.stderr

@@ -1,5 +1,5 @@
 error: The default runtime flavor is `multi_thread`, but the `rt-multi-thread` feature is disabled.
- --> tests/fail/macros_core_no_default.rs:3:1
+ --> $DIR/macros_core_no_default.rs:3:1
   |
 3 | #[tokio::main]
   | ^^^^^^^^^^^^^^

tests-build/tests/fail/macros_dead_code.stderr

@@ -1,4 +1,4 @@
-error: function is never used: `f`
+error: function `f` is never used
  --> $DIR/macros_dead_code.rs:6:10
   |
 6 | async fn f() {}

tests-integration/Cargo.toml

@@ -7,7 +7,6 @@ publish = false
 
 [[bin]]
 name = "test-cat"
-required-features = ["rt-process-io-util"]
 
 [[bin]]
 name = "test-mem"
@@ -31,7 +30,6 @@ name = "rt_yield"
 required-features = ["rt", "macros", "sync"]
 
 [features]
-rt-process-io-util = ["tokio/rt", "tokio/macros", "tokio/process", "tokio/io-util", "tokio/io-std"]
 # For mem check
 rt-net = ["tokio/rt", "tokio/rt-multi-thread", "tokio/net"]
 # For test-process-signal

tests-integration/src/bin/test-cat.rs

@@ -1,14 +1,20 @@
 //! A cat-like utility that can be used as a subprocess to test I/O
 //! stream communication.
 
-use tokio::io::AsyncWriteExt;
+use std::io;
+use std::io::Write;
 
-#[tokio::main(flavor = "current_thread")]
-async fn main() {
-    let mut stdin = tokio::io::stdin();
-    let mut stdout = tokio::io::stdout();
-
-    tokio::io::copy(&mut stdin, &mut stdout).await.unwrap();
-
-    stdout.flush().await.unwrap();
+fn main() {
+    let stdin = io::stdin();
+    let mut stdout = io::stdout();
+    let mut line = String::new();
+    loop {
+        line.clear();
+        stdin.read_line(&mut line).unwrap();
+        if line.is_empty() {
+            break;
+        }
+        stdout.write_all(line.as_bytes()).unwrap();
+    }
+    stdout.flush().unwrap();
 }

tests-integration/tests/macros_main.rs

@@ -1,4 +1,8 @@
-#![cfg(all(feature = "macros", feature = "rt-multi-thread"))]
+#![cfg(all(
+    feature = "macros",
+    feature = "rt-multi-thread",
+    not(target_os = "wasi")
+))]
 
 #[tokio::main]
 async fn basic_main() -> usize {

tests-integration/tests/macros_select.rs

@@ -4,6 +4,7 @@ use futures::channel::oneshot;
 use futures::executor::block_on;
 use std::thread;
 
+#[cfg_attr(target_os = "wasi", ignore = "WASI: std::thread::spawn not supported")]
 #[test]
 fn join_with_select() {
     block_on(async {

tests-integration/tests/process_stdio.rs

@@ -1,5 +1,5 @@
 #![warn(rust_2018_idioms)]
-#![cfg(feature = "full")]
+#![cfg(all(feature = "full", not(target_os = "wasi")))]
 
 use tokio::io::{AsyncBufReadExt, AsyncReadExt, AsyncWriteExt, BufReader};
 use tokio::join;
@@ -8,22 +8,12 @@ use tokio_test::assert_ok;
 
 use futures::future::{self, FutureExt};
 use std::convert::TryInto;
+use std::env;
 use std::io;
 use std::process::{ExitStatus, Stdio};
 
-// so, we need to change this back as a test, but for now this doesn't work because of:
-// https://github.com/rust-lang/rust/pull/95469
-//
-// undo when this is closed: https://github.com/tokio-rs/tokio/issues/4802
-
-// fn cat() -> Command {
-//     let mut cmd = Command::new(std::env!("CARGO_BIN_EXE_test-cat"));
-//     cmd.stdin(Stdio::piped()).stdout(Stdio::piped());
-//     cmd
-// }
-
 fn cat() -> Command {
-    let mut cmd = Command::new("cat");
+    let mut cmd = Command::new(env!("CARGO_BIN_EXE_test-cat"));
     cmd.stdin(Stdio::piped()).stdout(Stdio::piped());
     cmd
 }

tokio-stream/CHANGELOG.md

@@ -1,3 +1,11 @@
+# 0.1.10 (Sept 18, 2022)
+
+- time: add `StreamExt::chunks_timeout` ([#4695])
+- stream: add track_caller to public APIs ([#4786])
+
+[#4695]: https://github.com/tokio-rs/tokio/pull/4695
+[#4786]: https://github.com/tokio-rs/tokio/pull/4786
+
 # 0.1.9 (June 4, 2022)
 
 - deps: upgrade `tokio-util` dependency to `0.7.x` ([#3762])

tokio-stream/Cargo.toml

@@ -4,7 +4,7 @@ name = "tokio-stream"
 # - Remove path dependencies
 # - Update CHANGELOG.md.
 # - Create "tokio-stream-0.1.x" git tag.
-version = "0.1.9"
+version = "0.1.10"
 edition = "2018"
 rust-version = "1.49"
 authors = ["Tokio Contributors <[email protected]>"]
@@ -38,6 +38,7 @@ parking_lot = "0.12.0"
 tokio-test = { path = "../tokio-test" }
 futures = { version = "0.3", default-features = false }
 
+[target.'cfg(not(target_arch = "wasm32"))'.dev-dependencies]
 proptest = "1"
 
 [package.metadata.docs.rs]

tokio-stream/tests/stream_panic.rs

@@ -1,5 +1,5 @@
 #![warn(rust_2018_idioms)]
-#![cfg(feature = "time")]
+#![cfg(all(feature = "time", not(target_os = "wasi")))] // Wasi does not support panic recovery
 
 use parking_lot::{const_mutex, Mutex};
 use std::error::Error;

tokio-stream/tests/stream_stream_map.rs

@@ -325,6 +325,7 @@ fn one_ready_many_none() {
     }
 }
 
+#[cfg(not(target_os = "wasi"))]
 proptest::proptest! {
     #[test]
     fn fuzz_pending_complete_mix(kinds: Vec<bool>) {

tokio-test/src/macros.rs

@@ -260,7 +260,7 @@ macro_rules! assert_err {
     }};
 }
 
-/// Asserts that an exact duration has elapsed since since the start instant ±1ms.
+/// Asserts that an exact duration has elapsed since the start instant ±1ms.
 ///
 /// ```rust
 /// use tokio::time::{self, Instant};

tokio-util/CHANGELOG.md

@@ -1,3 +1,25 @@
+# 0.7.4 (September 8, 2022)
+
+### Added
+
+- io: add `SyncIoBridge::shutdown()` ([#4938])
+- task: improve `LocalPoolHandle` ([#4680])
+
+### Fixed
+
+- util: add `track_caller` to public APIs ([#4785])
+
+### Unstable
+
+- task: fix compilation errors in `JoinMap` with Tokio v1.21.0 ([#4755])
+- task: remove the unstable, deprecated `JoinMap::join_one` ([#4920])
+
+[#4680]: https://github.com/tokio-rs/tokio/pull/4680
+[#4755]: https://github.com/tokio-rs/tokio/pull/4755
+[#4785]: https://github.com/tokio-rs/tokio/pull/4785
+[#4920]: https://github.com/tokio-rs/tokio/pull/4920
+[#4938]: https://github.com/tokio-rs/tokio/pull/4938
+
 # 0.7.3 (June 4, 2022)
 
 ### Changed

tokio-util/Cargo.toml

@@ -4,7 +4,7 @@ name = "tokio-util"
 # - Remove path dependencies
 # - Update CHANGELOG.md.
 # - Create "tokio-util-0.7.x" git tag.
-version = "0.7.3"
+version = "0.7.4"
 edition = "2018"
 rust-version = "1.49"
 authors = ["Tokio Contributors <[email protected]>"]
@@ -34,7 +34,7 @@ rt = ["tokio/rt", "tokio/sync", "futures-util", "hashbrown"]
 __docs_rs = ["futures-util"]
 
 [dependencies]
-tokio = { version = "1.19.0", path = "../tokio", features = ["sync"] }
+tokio = { version = "1.21.0", path = "../tokio", features = ["sync"] }
 bytes = "1.0.0"
 futures-core = "0.3.0"
 futures-sink = "0.3.0"

tokio-util/src/codec/length_delimited.rs

@@ -522,15 +522,11 @@ impl LengthDelimitedCodec {
             }
         };
 
-        let num_skip = self.builder.get_num_skip();
-
-        if num_skip > 0 {
-            src.advance(num_skip);
-        }
+        src.advance(self.builder.get_num_skip());
 
         // Ensure that the buffer has enough space to read the incoming
         // payload
-        src.reserve(n);
+        src.reserve(n.saturating_sub(src.len()));
 
         Ok(Some(n))
     }
@@ -568,7 +564,7 @@ impl Decoder for LengthDelimitedCodec {
                 self.state = DecodeState::Head;
 
                 // Make sure the buffer has enough space to read the next head
-                src.reserve(self.builder.num_head_bytes());
+                src.reserve(self.builder.num_head_bytes().saturating_sub(src.len()));
 
                 Ok(Some(data))
             }

tokio-util/src/io/stream_reader.rs

@@ -50,9 +50,58 @@ pin_project! {
     /// # }
     /// ```
     ///
+    /// If the stream produces errors which are not [std::io::Error],
+    /// the errors can be converted using [`StreamExt`] to map each
+    /// element.
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    /// use tokio::io::AsyncReadExt;
+    /// use tokio_util::io::StreamReader;
+    /// use tokio_stream::StreamExt;
+    /// # #[tokio::main]
+    /// # async fn main() -> std::io::Result<()> {
+    ///
+    /// // Create a stream from an iterator, including an error.
+    /// let stream = tokio_stream::iter(vec![
+    ///     Result::Ok(Bytes::from_static(&[0, 1, 2, 3])),
+    ///     Result::Ok(Bytes::from_static(&[4, 5, 6, 7])),
+    ///     Result::Err("Something bad happened!")
+    /// ]);
+    ///
+    /// // Use StreamExt to map the stream and error to a std::io::Error
+    /// let stream = stream.map(|result| result.map_err(|err| {
+    ///     std::io::Error::new(std::io::ErrorKind::Other, err)
+    /// }));
+    ///
+    /// // Convert it to an AsyncRead.
+    /// let mut read = StreamReader::new(stream);
+    ///
+    /// // Read five bytes from the stream.
+    /// let mut buf = [0; 5];
+    /// read.read_exact(&mut buf).await?;
+    /// assert_eq!(buf, [0, 1, 2, 3, 4]);
+    ///
+    /// // Read the rest of the current chunk.
+    /// assert_eq!(read.read(&mut buf).await?, 3);
+    /// assert_eq!(&buf[..3], [5, 6, 7]);
+    ///
+    /// // Reading the next chunk will produce an error
+    /// let error = read.read(&mut buf).await.unwrap_err();
+    /// assert_eq!(error.kind(), std::io::ErrorKind::Other);
+    /// assert_eq!(error.into_inner().unwrap().to_string(), "Something bad happened!");
+    ///
+    /// // We have now reached the end.
+    /// assert_eq!(read.read(&mut buf).await?, 0);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
     /// [`AsyncRead`]: tokio::io::AsyncRead
     /// [`Stream`]: futures_core::Stream
     /// [`ReaderStream`]: crate::io::ReaderStream
+    /// [`StreamExt`]: tokio_stream::StreamExt
     #[derive(Debug)]
     pub struct StreamReader<S, B> {
         #[pin]

tokio-util/src/io/sync_bridge.rs

@@ -66,6 +66,21 @@ impl<T: AsyncWrite> SyncIoBridge<T> {
     }
 }
 
+impl<T: AsyncWrite + Unpin> SyncIoBridge<T> {
+    /// Shutdown this writer. This method provides a way to call the [`AsyncWriteExt::shutdown`]
+    /// function of the inner [`tokio::io::AsyncWrite`] instance.
+    ///
+    /// # Errors
+    ///
+    /// This method returns the same errors as [`AsyncWriteExt::shutdown`].
+    ///
+    /// [`AsyncWriteExt::shutdown`]: tokio::io::AsyncWriteExt::shutdown
+    pub fn shutdown(&mut self) -> std::io::Result<()> {
+        let src = &mut self.src;
+        self.rt.block_on(src.shutdown())
+    }
+}
+
 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`].

tokio-util/src/lib.rs

@@ -29,6 +29,7 @@ cfg_codec! {
 }
 
 cfg_net! {
+    #[cfg(not(target_arch = "wasm32"))]
     pub mod udp;
     pub mod net;
 }

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

@@ -200,7 +200,7 @@ where
 /// `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].
+/// To acquire 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());
@@ -218,7 +218,7 @@ fn move_children_to_parent(node: &mut Inner, parent: &mut Inner) {
 /// 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].
+/// To acquire 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;

tokio-util/src/sync/tests/loom_cancellation_token.rs

@@ -80,7 +80,7 @@ fn drop_token_no_child() {
 }
 
 #[test]
-fn drop_token_with_childs() {
+fn drop_token_with_children() {
     loom::model(|| {
         let token1 = CancellationToken::new();
         let child_token1 = token1.child_token();

tokio-util/src/task/join_map.rs

@@ -416,7 +416,6 @@ where
     ///  * `None` if the `JoinMap` is empty.
     ///
     /// [`tokio::select!`]: tokio::select
-    #[doc(alias = "join_one")]
     pub async fn join_next(&mut self) -> Option<(K, Result<V, JoinError>)> {
         let (res, id) = match self.tasks.join_next_with_id().await {
             Some(Ok((id, output))) => (Ok(output), id),
@@ -430,12 +429,6 @@ where
         Some((key, res))
     }
 
-    #[doc(hidden)]
-    #[deprecated(since = "0.7.4", note = "renamed to `JoinMap::join_next`.")]
-    pub async fn join_one(&mut self) -> Option<(K, Result<V, JoinError>)> {
-        self.join_next().await
-    }
-
     /// Aborts all tasks and waits for them to finish shutting down.
     ///
     /// Calling this method is equivalent to calling [`abort_all`] and then calling [`join_next`] in

tokio-util/src/task/mod.rs

@@ -2,7 +2,9 @@
 
 #[cfg(tokio_unstable)]
 mod join_map;
+#[cfg(not(target_os = "wasi"))]
 mod spawn_pinned;
+#[cfg(not(target_os = "wasi"))]
 pub use spawn_pinned::LocalPoolHandle;
 
 #[cfg(tokio_unstable)]

tokio-util/src/time/delay_queue.rs

@@ -190,7 +190,7 @@ impl<T> SlabStorage<T> {
         let key_contained = self.key_map.contains_key(&key.into());
 
         if key_contained {
-            // It's possible that a `compact` call creates capacitiy in `self.inner` in
+            // It's possible that a `compact` call creates capacity in `self.inner` in
             // such a way that a `self.inner.insert` call creates a `key` which was
             // previously given out during an `insert` call prior to the `compact` call.
             // If `key` is contained in `self.key_map`, we have encountered this exact situation,

tokio-util/tests/context.rs

@@ -1,4 +1,5 @@
 #![cfg(feature = "rt")]
+#![cfg(not(target_os = "wasi"))] // Wasi doesn't support threads
 #![warn(rust_2018_idioms)]
 
 use tokio::runtime::Builder;

tokio-util/tests/framed_write.rs

@@ -130,7 +130,7 @@ fn write_hits_backpressure() {
             _ => unreachable!(),
         }
 
-        // Push a new new chunk
+        // Push a new chunk
         mock.calls.push_back(Ok(b[..].to_vec()));
     }
     // 1 'wouldblock', 4 * 2KB buffers, 1 b-byte buffer

tokio-util/tests/io_sync_bridge.rs

@@ -1,8 +1,9 @@
 #![cfg(feature = "io-util")]
+#![cfg(not(target_os = "wasi"))] // Wasi doesn't support threads
 
 use std::error::Error;
-use std::io::{Cursor, Read, Result as IoResult};
-use tokio::io::AsyncRead;
+use std::io::{Cursor, Read, Result as IoResult, Write};
+use tokio::io::{AsyncRead, AsyncReadExt};
 use tokio_util::io::SyncIoBridge;
 
 async fn test_reader_len(
@@ -41,3 +42,21 @@ async fn test_async_write_to_sync() -> Result<(), Box<dyn Error>> {
     assert_eq!(dest.as_slice(), src);
     Ok(())
 }
+
+#[tokio::test]
+async fn test_shutdown() -> Result<(), Box<dyn Error>> {
+    let (s1, mut s2) = tokio::io::duplex(1024);
+    let (_rh, wh) = tokio::io::split(s1);
+    tokio::task::spawn_blocking(move || -> std::io::Result<_> {
+        let mut wh = SyncIoBridge::new(wh);
+        wh.write_all(b"hello")?;
+        wh.shutdown()?;
+        assert!(wh.write_all(b" world").is_err());
+        Ok(())
+    })
+    .await??;
+    let mut buf = vec![];
+    s2.read_to_end(&mut buf).await?;
+    assert_eq!(buf, b"hello");
+    Ok(())
+}

tokio-util/tests/panic.rs

@@ -1,5 +1,5 @@
 #![warn(rust_2018_idioms)]
-#![cfg(feature = "full")]
+#![cfg(all(feature = "full", not(target_os = "wasi")))] // Wasi doesn't support panic recovery
 
 use parking_lot::{const_mutex, Mutex};
 use std::error::Error;

tokio-util/tests/spawn_pinned.rs

@@ -1,4 +1,5 @@
 #![warn(rust_2018_idioms)]
+#![cfg(not(target_os = "wasi"))] // Wasi doesn't support threads
 
 use std::rc::Rc;
 use std::sync::Arc;

tokio-util/tests/sync_cancellation_token.rs

@@ -258,7 +258,7 @@ fn cancel_only_all_descendants() {
     let child2_token = token.child_token();
     let grandchild_token = child1_token.child_token();
     let grandchild2_token = child1_token.child_token();
-    let grandgrandchild_token = grandchild_token.child_token();
+    let great_grandchild_token = grandchild_token.child_token();
 
     assert!(!parent_token.is_cancelled());
     assert!(!token.is_cancelled());
@@ -267,7 +267,7 @@ fn cancel_only_all_descendants() {
     assert!(!child2_token.is_cancelled());
     assert!(!grandchild_token.is_cancelled());
     assert!(!grandchild2_token.is_cancelled());
-    assert!(!grandgrandchild_token.is_cancelled());
+    assert!(!great_grandchild_token.is_cancelled());
 
     let parent_fut = parent_token.cancelled();
     let fut = token.cancelled();
@@ -276,7 +276,7 @@ fn cancel_only_all_descendants() {
     let child2_fut = child2_token.cancelled();
     let grandchild_fut = grandchild_token.cancelled();
     let grandchild2_fut = grandchild2_token.cancelled();
-    let grandgrandchild_fut = grandgrandchild_token.cancelled();
+    let great_grandchild_fut = great_grandchild_token.cancelled();
 
     pin!(parent_fut);
     pin!(fut);
@@ -285,7 +285,7 @@ fn cancel_only_all_descendants() {
     pin!(child2_fut);
     pin!(grandchild_fut);
     pin!(grandchild2_fut);
-    pin!(grandgrandchild_fut);
+    pin!(great_grandchild_fut);
 
     assert_eq!(
         Poll::Pending,
@@ -321,7 +321,7 @@ fn cancel_only_all_descendants() {
     );
     assert_eq!(
         Poll::Pending,
-        grandgrandchild_fut
+        great_grandchild_fut
             .as_mut()
             .poll(&mut Context::from_waker(&waker))
     );
@@ -339,7 +339,7 @@ fn cancel_only_all_descendants() {
     assert!(child2_token.is_cancelled());
     assert!(grandchild_token.is_cancelled());
     assert!(grandchild2_token.is_cancelled());
-    assert!(grandgrandchild_token.is_cancelled());
+    assert!(great_grandchild_token.is_cancelled());
 
     assert_eq!(
         Poll::Ready(()),
@@ -367,7 +367,7 @@ fn cancel_only_all_descendants() {
     );
     assert_eq!(
         Poll::Ready(()),
-        grandgrandchild_fut
+        great_grandchild_fut
             .as_mut()
             .poll(&mut Context::from_waker(&waker))
     );

tokio-util/tests/time_delay_queue.rs

@@ -778,6 +778,7 @@ async fn compact_change_deadline() {
     assert!(entry.is_none());
 }
 
+#[cfg_attr(target_os = "wasi", ignore = "FIXME: Does not seem to work with WASI")]
 #[tokio::test(start_paused = true)]
 async fn remove_after_compact() {
     let now = Instant::now();
@@ -794,6 +795,7 @@ async fn remove_after_compact() {
     assert!(panic.is_err());
 }
 
+#[cfg_attr(target_os = "wasi", ignore = "FIXME: Does not seem to work with WASI")]
 #[tokio::test(start_paused = true)]
 async fn remove_after_compact_poll() {
     let now = Instant::now();

tokio-util/tests/udp.rs

@@ -1,4 +1,5 @@
 #![warn(rust_2018_idioms)]
+#![cfg(not(target_os = "wasi"))] // Wasi doesn't support UDP
 
 use tokio::net::UdpSocket;
 use tokio_stream::StreamExt;

tokio/CHANGELOG.md

@@ -1,3 +1,108 @@
+# 1.21.1 (September 13, 2022)
+
+### Fixed
+
+- net: fix dependency resolution for socket2 ([#5000])
+- task: ignore failure to set TLS in `LocalSet` Drop ([#4976])
+
+[#4976]: https://github.com/tokio-rs/tokio/pull/4976
+[#5000]: https://github.com/tokio-rs/tokio/pull/5000
+
+# 1.21.0 (September 2, 2022)
+
+This release is the first release of Tokio to intentionally support WASM. The
+`sync,macros,io-util,rt,time` features are stabilized on WASM. Additionally the
+wasm32-wasi target is given unstable support for the `net` feature.
+
+### Added
+
+- net: add `device` and `bind_device` methods to TCP/UDP sockets ([#4882])
+- net: add `tos` and `set_tos` methods to TCP and UDP sockets ([#4877])
+- net: add security flags to named pipe `ServerOptions` ([#4845])
+- signal: add more windows signal handlers ([#4924])
+- sync: add `mpsc::Sender::max_capacity` method ([#4904])
+- sync: implement Weak version of `mpsc::Sender` ([#4595])
+- task: add `LocalSet::enter` ([#4765])
+- task: stabilize `JoinSet` and `AbortHandle` ([#4920])
+- tokio: add `track_caller` to public APIs ([#4805], [#4848], [#4852])
+- wasm: initial support for `wasm32-wasi` target ([#4716])
+
+### Fixed
+
+- miri: improve miri compatibility by avoiding temporary references in `linked_list::Link` impls ([#4841])
+- signal: don't register write interest on signal pipe ([#4898])
+- sync: add `#[must_use]` to lock guards ([#4886])
+- sync: fix hang when calling `recv` on closed and reopened broadcast channel ([#4867])
+- task: propagate attributes on task-locals ([#4837])
+
+### Changed
+
+- fs: change panic to error in `File::start_seek` ([#4897])
+- io: reduce syscalls in `poll_read` ([#4840])
+- process: use blocking threadpool for child stdio I/O ([#4824])
+- signal: make `SignalKind` methods const ([#4956])
+
+### Internal changes
+
+- rt: extract `basic_scheduler::Config` ([#4935])
+- rt: move I/O driver into `runtime` module ([#4942])
+- rt: rename internal scheduler types ([#4945])
+
+### Documented
+
+- chore: fix typos and grammar ([#4858], [#4894], [#4928])
+- io: fix typo in `AsyncSeekExt::rewind` docs ([#4893])
+- net: add documentation to `try_read()` for zero-length buffers ([#4937])
+- runtime: remove incorrect panic section for `Builder::worker_threads` ([#4849])
+- sync: doc of `watch::Sender::send` improved ([#4959])
+- task: add cancel safety docs to `JoinHandle` ([#4901])
+- task: expand on cancellation of `spawn_blocking` ([#4811])
+- time: clarify that the first tick of `Interval::tick` happens immediately ([#4951])
+
+### Unstable
+
+- rt: add unstable option to disable the LIFO slot ([#4936])
+- task: fix incorrect signature in `Builder::spawn_on` ([#4953])
+- task: make `task::Builder::spawn*` methods fallible ([#4823])
+
+[#4595]: https://github.com/tokio-rs/tokio/pull/4595
+[#4716]: https://github.com/tokio-rs/tokio/pull/4716
+[#4765]: https://github.com/tokio-rs/tokio/pull/4765
+[#4805]: https://github.com/tokio-rs/tokio/pull/4805
+[#4811]: https://github.com/tokio-rs/tokio/pull/4811
+[#4823]: https://github.com/tokio-rs/tokio/pull/4823
+[#4824]: https://github.com/tokio-rs/tokio/pull/4824
+[#4837]: https://github.com/tokio-rs/tokio/pull/4837
+[#4840]: https://github.com/tokio-rs/tokio/pull/4840
+[#4841]: https://github.com/tokio-rs/tokio/pull/4841
+[#4845]: https://github.com/tokio-rs/tokio/pull/4845
+[#4848]: https://github.com/tokio-rs/tokio/pull/4848
+[#4849]: https://github.com/tokio-rs/tokio/pull/4849
+[#4852]: https://github.com/tokio-rs/tokio/pull/4852
+[#4858]: https://github.com/tokio-rs/tokio/pull/4858
+[#4867]: https://github.com/tokio-rs/tokio/pull/4867
+[#4877]: https://github.com/tokio-rs/tokio/pull/4877
+[#4882]: https://github.com/tokio-rs/tokio/pull/4882
+[#4886]: https://github.com/tokio-rs/tokio/pull/4886
+[#4893]: https://github.com/tokio-rs/tokio/pull/4893
+[#4894]: https://github.com/tokio-rs/tokio/pull/4894
+[#4897]: https://github.com/tokio-rs/tokio/pull/4897
+[#4898]: https://github.com/tokio-rs/tokio/pull/4898
+[#4901]: https://github.com/tokio-rs/tokio/pull/4901
+[#4904]: https://github.com/tokio-rs/tokio/pull/4904
+[#4920]: https://github.com/tokio-rs/tokio/pull/4920
+[#4924]: https://github.com/tokio-rs/tokio/pull/4924
+[#4928]: https://github.com/tokio-rs/tokio/pull/4928
+[#4935]: https://github.com/tokio-rs/tokio/pull/4935
+[#4936]: https://github.com/tokio-rs/tokio/pull/4936
+[#4937]: https://github.com/tokio-rs/tokio/pull/4937
+[#4942]: https://github.com/tokio-rs/tokio/pull/4942
+[#4945]: https://github.com/tokio-rs/tokio/pull/4945
+[#4951]: https://github.com/tokio-rs/tokio/pull/4951
+[#4953]: https://github.com/tokio-rs/tokio/pull/4953
+[#4956]: https://github.com/tokio-rs/tokio/pull/4956
+[#4959]: https://github.com/tokio-rs/tokio/pull/4959
+
 # 1.20.1 (July 25, 2022)
 
 ### Fixed

tokio/Cargo.toml

@@ -6,7 +6,7 @@ name = "tokio"
 #   - README.md
 # - Update CHANGELOG.md.
 # - Create "v1.0.x" git tag.
-version = "1.20.1"
+version = "1.21.1"
 edition = "2018"
 rust-version = "1.49"
 authors = ["Tokio Contributors <[email protected]>"]
@@ -58,6 +58,8 @@ net = [
   "winapi/winbase",
   "winapi/winnt",
   "winapi/minwindef",
+  "winapi/accctrl",
+  "winapi/aclapi",
 ]
 process = [
   "bytes",
@@ -68,11 +70,11 @@ process = [
   "mio/net",
   "signal-hook-registry",
   "winapi/handleapi",
+  "winapi/minwindef",
   "winapi/processthreadsapi",
   "winapi/threadpoollegacyapiset",
   "winapi/winbase",
   "winapi/winnt",
-  "winapi/minwindef",
 ]
 # Includes basic task execution capabilities
 rt = ["once_cell"]
@@ -112,11 +114,13 @@ pin-project-lite = "0.2.0"
 bytes = { version = "1.0.0", optional = true }
 once_cell = { version = "1.5.2", optional = true }
 memchr = { version = "2.2", optional = true }
-mio = { version = "0.8.1", optional = true }
-socket2 = { version = "0.4.4", optional = true, features = [ "all" ] }
+mio = { version = "0.8.4", optional = true }
 num_cpus = { version = "1.8.0", optional = true }
 parking_lot = { version = "0.12.0", optional = true }
 
+[target.'cfg(not(any(target_arch = "wasm32", target_arch = "wasm64")))'.dependencies]
+socket2 = { version = "0.4.4", optional = true, features = [ "all" ] }
+
 # Currently unstable. The API exposed by these features may be broken at any time.
 # Requires `--cfg tokio_unstable` to enable.
 [target.'cfg(tokio_unstable)'.dependencies]
@@ -147,12 +151,14 @@ mockall = "0.11.1"
 tempfile = "3.1.0"
 async-stream = "0.3"
 
-[target.'cfg(not(target_arch = "wasm32"))'.dev-dependencies]
+[target.'cfg(not(any(target_arch = "wasm32", target_arch = "wasm64")))'.dev-dependencies]
 proptest = "1"
-rand = "0.8.0"
 socket2 = "0.4"
 
-[target.'cfg(target_arch = "wasm32")'.dev-dependencies]
+[target.'cfg(not(all(any(target_arch = "wasm32", target_arch = "wasm64"), target_os = "unknown")))'.dev-dependencies]
+rand = "0.8.0"
+
+[target.'cfg(all(any(target_arch = "wasm32", target_arch = "wasm64"), not(target_os = "wasi")))'.dev-dependencies]
 wasm-bindgen-test = "0.3.0"
 
 [target.'cfg(target_os = "freebsd")'.dev-dependencies]

tokio/README.md

@@ -56,7 +56,7 @@ Make sure you activated the full features of the tokio crate on Cargo.toml:
 
 ```toml
 [dependencies]
-tokio = { version = "1.20.1", features = ["full"] }
+tokio = { version = "1.21.1", features = ["full"] }
 ```
 Then, on your main.rs:
 
@@ -161,6 +161,16 @@ several other libraries, including:
 [`mio`]: https://github.com/tokio-rs/mio
 [`bytes`]: https://github.com/tokio-rs/bytes
 
+## Changelog
+
+The Tokio repository contains multiple crates. Each crate has its own changelog.
+
+ * `tokio` - [view changelog](https://github.com/tokio-rs/tokio/blob/master/tokio/CHANGELOG.md)
+ * `tokio-util` - [view changelog](https://github.com/tokio-rs/tokio/blob/master/tokio-util/CHANGELOG.md)
+ * `tokio-stream` - [view changelog](https://github.com/tokio-rs/tokio/blob/master/tokio-stream/CHANGELOG.md)
+ * `tokio-macros` - [view changelog](https://github.com/tokio-rs/tokio/blob/master/tokio-macros/CHANGELOG.md)
+ * `tokio-test` - [view changelog](https://github.com/tokio-rs/tokio/blob/master/tokio-test/CHANGELOG.md)
+
 ## Supported Rust Versions
 
 <!--
@@ -192,18 +202,18 @@ 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
+ * `1.18.x` - LTS release until June 2023
+ * `1.20.x` - LTS release until September 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.
+Each LTS release will continue to receive backported fixes for at least 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
+example, to specify that you wish to use the newest `1.18.x` patch release, you
 can use the following dependency specification:
 ```text
-tokio = { version = "~1.14", features = [...] }
+tokio = { version = "~1.18", features = [...] }
 ```
 
 ## License

tokio/build.rs

@@ -10,8 +10,16 @@ const CONST_THREAD_LOCAL_PROBE: &str = r#"
 }
 "#;
 
+const ADDR_OF_PROBE: &str = r#"
+{
+    let my_var = 10;
+    ::std::ptr::addr_of!(my_var)
+}
+"#;
+
 fn main() {
     let mut enable_const_thread_local = false;
+    let mut enable_addr_of = false;
 
     match AutoCfg::new() {
         Ok(ac) => {
@@ -34,6 +42,21 @@ fn main() {
                     enable_const_thread_local = true;
                 }
             }
+
+            // The `addr_of` and `addr_of_mut` macros were stabilized in 1.51.
+            if ac.probe_rustc_version(1, 52) {
+                enable_addr_of = true;
+            } else if ac.probe_rustc_version(1, 51) {
+                // This compiler claims to be 1.51, but there are some nightly
+                // compilers that claim to be 1.51 without supporting the
+                // feature. Explicitly probe to check if code using them
+                // compiles.
+                //
+                // The oldest nightly that supports the feature is 2021-01-31.
+                if ac.probe_expression(ADDR_OF_PROBE) {
+                    enable_addr_of = true;
+                }
+            }
         }
 
         Err(e) => {
@@ -54,4 +77,25 @@ fn main() {
         // RUSTFLAGS="--cfg tokio_no_const_thread_local"
         autocfg::emit("tokio_no_const_thread_local")
     }
+
+    if !enable_addr_of {
+        // To disable this feature on compilers that support it, you can
+        // explicitly pass this flag with the following environment variable:
+        //
+        // RUSTFLAGS="--cfg tokio_no_addr_of"
+        autocfg::emit("tokio_no_addr_of")
+    }
+
+    let target = ::std::env::var("TARGET").unwrap_or_default();
+
+    // We emit cfgs instead of using `target_family = "wasm"` that requires Rust 1.54.
+    // Note that these cfgs are unavailable in `Cargo.toml`.
+    if target.starts_with("wasm") {
+        autocfg::emit("tokio_wasm");
+        if target.contains("wasi") {
+            autocfg::emit("tokio_wasi");
+        } else {
+            autocfg::emit("tokio_wasm_not_wasi");
+        }
+    }
 }

tokio/docs/reactor-refactor.md

@@ -188,9 +188,9 @@ readiness, the driver's tick is packed into the atomic `usize`.
 The `ScheduledIo` readiness `AtomicUsize` is structured as:
 
 ```
-| reserved | generation |  driver tick | readinesss |
-|----------+------------+--------------+------------|
-|   1 bit  |   7 bits   +    8 bits    +   16 bits  |
+| reserved | generation |  driver tick | readiness |
+|----------+------------+--------------+-----------|
+|   1 bit  |   7 bits   +    8 bits    +  16 bits  |
 ```
 
 The `reserved` and `generation` components exist today.

tokio/external-types.toml

@@ -0,0 +1,16 @@
+# This config file is for the `cargo-check-external-types` tool that is run in CI.
+
+# The following are types that are allowed to be exposed in Tokio's public API.
+# The standard library is allowed by default.
+allowed_external_types = [
+   "bytes::buf::buf_impl::Buf",
+   "bytes::buf::buf_mut::BufMut",
+
+   "tokio_macros::*",
+
+   # TODO(https://github.com/tokio-rs/tokio/issues/4916): Remove the libc types
+   "libc::unix::gid_t",
+   "libc::unix::pid_t",
+   "libc::unix::uid_t",
+]
+

tokio/src/coop.rs

@@ -207,7 +207,7 @@ cfg_coop! {
 mod test {
     use super::*;
 
-    #[cfg(target_arch = "wasm32")]
+    #[cfg(tokio_wasm_not_wasi)]
     use wasm_bindgen_test::wasm_bindgen_test as test;
 
     fn get() -> Budget {
@@ -215,7 +215,7 @@ mod test {
     }
 
     #[test]
-    fn bugeting() {
+    fn budgeting() {
         use futures::future::poll_fn;
         use tokio_test::*;
 

tokio/src/fs/file.rs

@@ -565,29 +565,30 @@ impl AsyncSeek for File {
         let me = self.get_mut();
         let inner = me.inner.get_mut();
 
-        loop {
-            match inner.state {
-                Busy(_) => panic!("must wait for poll_complete before calling start_seek"),
-                Idle(ref mut buf_cell) => {
-                    let mut buf = buf_cell.take().unwrap();
+        match inner.state {
+            Busy(_) => Err(io::Error::new(
+                io::ErrorKind::Other,
+                "other file operation is pending, call poll_complete before start_seek",
+            )),
+            Idle(ref mut buf_cell) => {
+                let mut buf = buf_cell.take().unwrap();
 
-                    // Factor in any unread data from the buf
-                    if !buf.is_empty() {
-                        let n = buf.discard_read();
+                // Factor in any unread data from the buf
+                if !buf.is_empty() {
+                    let n = buf.discard_read();
 
-                        if let SeekFrom::Current(ref mut offset) = pos {
-                            *offset += n;
-                        }
+                    if let SeekFrom::Current(ref mut offset) = pos {
+                        *offset += n;
                     }
-
-                    let std = me.std.clone();
-
-                    inner.state = Busy(spawn_blocking(move || {
-                        let res = (&*std).seek(pos);
-                        (Operation::Seek(res), buf)
-                    }));
-                    return Ok(());
                 }
+
+                let std = me.std.clone();
+
+                inner.state = Busy(spawn_blocking(move || {
+                    let res = (&*std).seek(pos);
+                    (Operation::Seek(res), buf)
+                }));
+                Ok(())
             }
         }
     }

tokio/src/fs/file/tests.rs

@@ -955,3 +955,24 @@ fn partial_read_set_len_ok() {
     assert_eq!(n, FOO.len());
     assert_eq!(&buf[..n], FOO);
 }
+
+#[test]
+fn busy_file_seek_error() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|_| Err(io::ErrorKind::Other.into()));
+
+    let mut file = crate::io::BufReader::new(File::from_std(file));
+    {
+        let mut t = task::spawn(file.write(HELLO));
+        assert_ready_ok!(t.poll());
+    }
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.seek(SeekFrom::Start(0)));
+    assert_ready_err!(t.poll());
+}

tokio/src/io/async_fd.rs

@@ -1,4 +1,5 @@
-use crate::io::driver::{Handle, Interest, ReadyEvent, Registration};
+use crate::io::Interest;
+use crate::runtime::io::{Handle, ReadyEvent, Registration};
 
 use mio::unix::SourceFd;
 use std::io;

tokio/src/io/blocking.rs

@@ -34,8 +34,9 @@ enum State<T> {
     Busy(sys::Blocking<(io::Result<usize>, Buf, T)>),
 }
 
-cfg_io_std! {
+cfg_io_blocking! {
     impl<T> Blocking<T> {
+        #[cfg_attr(feature = "fs", allow(dead_code))]
         pub(crate) fn new(inner: T) -> Blocking<T> {
             Blocking {
                 inner: Some(inner),

tokio/src/io/bsd/poll_aio.rs

@@ -1,6 +1,7 @@
 //! Use POSIX AIO futures with Tokio.
 
-use crate::io::driver::{Handle, Interest, ReadyEvent, Registration};
+use crate::io::interest::Interest;
+use crate::runtime::io::{Handle, ReadyEvent, Registration};
 use mio::event::Source;
 use mio::Registry;
 use mio::Token;

tokio/src/io/interest.rs

@@ -1,6 +1,6 @@
 #![cfg_attr(not(feature = "net"), allow(dead_code, unreachable_pub))]
 
-use crate::io::driver::Ready;
+use crate::io::ready::Ready;
 
 use std::fmt;
 use std::ops;
@@ -100,7 +100,7 @@ impl Interest {
         self.0
     }
 
-    pub(super) fn mask(self) -> Ready {
+    pub(crate) fn mask(self) -> Ready {
         match self {
             Interest::READABLE => Ready::READABLE | Ready::READ_CLOSED,
             Interest::WRITABLE => Ready::WRITABLE | Ready::WRITE_CLOSED,

tokio/src/io/mod.rs

@@ -1,5 +1,3 @@
-#![cfg_attr(loom, allow(dead_code, unreachable_pub))]
-
 //! Traits, helpers, and type definitions for asynchronous I/O functionality.
 //!
 //! This module is the asynchronous version of `std::io`. Primarily, it
@@ -205,15 +203,19 @@ pub use self::read_buf::ReadBuf;
 pub use std::io::{Error, ErrorKind, Result, SeekFrom};
 
 cfg_io_driver_impl! {
-    pub(crate) mod driver;
+    pub(crate) mod interest;
+    pub(crate) mod ready;
 
     cfg_net! {
-        pub use driver::{Interest, Ready};
+        pub use interest::Interest;
+        pub use ready::Ready;
     }
 
+    #[cfg_attr(tokio_wasi, allow(unused_imports))]
     mod poll_evented;
 
     #[cfg(not(loom))]
+    #[cfg_attr(tokio_wasi, allow(unused_imports))]
     pub(crate) use poll_evented::PollEvented;
 }
 

tokio/src/io/poll_evented.rs

@@ -1,4 +1,5 @@
-use crate::io::driver::{Handle, Interest, Registration};
+use crate::io::interest::Interest;
+use crate::runtime::io::{Handle, Registration};
 
 use mio::event::Source;
 use std::fmt;
@@ -11,7 +12,7 @@ cfg_io_driver! {
     /// [`std::io::Write`] traits with the reactor that drives it.
     ///
     /// `PollEvented` uses [`Registration`] internally to take a type that
-    /// implements [`mio::event::Source`] as well as [`std::io::Read`] and or
+    /// implements [`mio::event::Source`] as well as [`std::io::Read`] and/or
     /// [`std::io::Write`] and associate it with a reactor that will drive it.
     ///
     /// Once the [`mio::event::Source`] type is wrapped by `PollEvented`, it can be
@@ -41,12 +42,12 @@ cfg_io_driver! {
     /// [`poll_read_ready`] again will also indicate read readiness.
     ///
     /// When the operation is attempted and is unable to succeed due to the I/O
-    /// resource not being ready, the caller must call `clear_readiness`.
+    /// resource not being ready, the caller must call [`clear_readiness`].
     /// This clears the readiness state until a new readiness event is received.
     ///
     /// This allows the caller to implement additional functions. For example,
     /// [`TcpListener`] implements poll_accept by using [`poll_read_ready`] and
-    /// `clear_read_ready`.
+    /// [`clear_readiness`].
     ///
     /// ## Platform-specific events
     ///
@@ -57,6 +58,7 @@ cfg_io_driver! {
     /// [`AsyncRead`]: crate::io::AsyncRead
     /// [`AsyncWrite`]: crate::io::AsyncWrite
     /// [`TcpListener`]: crate::net::TcpListener
+    /// [`clear_readiness`]: Registration::clear_readiness
     /// [`poll_read_ready`]: Registration::poll_read_ready
     /// [`poll_write_ready`]: Registration::poll_write_ready
     pub(crate) struct PollEvented<E: Source> {
@@ -77,6 +79,7 @@ impl<E: Source> PollEvented<E> {
     /// The runtime is usually set implicitly when this function is called
     /// from a future driven by a tokio runtime, otherwise runtime can be set
     /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    #[track_caller]
     #[cfg_attr(feature = "signal", allow(unused))]
     pub(crate) fn new(io: E) -> io::Result<Self> {
         PollEvented::new_with_interest(io, Interest::READABLE | Interest::WRITABLE)
@@ -97,6 +100,7 @@ impl<E: Source> PollEvented<E> {
     /// a future driven by a tokio runtime, otherwise runtime can be set
     /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter)
     /// function.
+    #[track_caller]
     #[cfg_attr(feature = "signal", allow(unused))]
     pub(crate) fn new_with_interest(io: E, interest: Interest) -> io::Result<Self> {
         Self::new_with_interest_and_handle(io, interest, Handle::current())
@@ -134,7 +138,7 @@ impl<E: Source> PollEvented<E> {
 }
 
 feature! {
-    #![any(feature = "net", feature = "process")]
+    #![any(feature = "net", all(unix, feature = "process"))]
 
     use crate::io::ReadBuf;
     use std::task::{Context, Poll};
@@ -151,16 +155,32 @@ feature! {
         {
             use std::io::Read;
 
-            let n = ready!(self.registration.poll_read_io(cx, || {
-                let b = &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]);
-                self.io.as_ref().unwrap().read(b)
-            }))?;
+            loop {
+                let evt = ready!(self.registration.poll_read_ready(cx))?;
 
-            // Safety: We trust `TcpStream::read` to have filled up `n` bytes in the
-            // buffer.
-            buf.assume_init(n);
-            buf.advance(n);
-            Poll::Ready(Ok(()))
+                let b = &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]);
+                let len = b.len();
+
+                match self.io.as_ref().unwrap().read(b) {
+                    Ok(n) => {
+                        // if we read a partially full buffer, this is sufficient on unix to show
+                        // that the socket buffer has been drained
+                        if n > 0 && (!cfg!(windows) && n < len) {
+                            self.registration.clear_readiness(evt);
+                        }
+
+                        // Safety: We trust `TcpStream::read` to have filled up `n` bytes in the
+                        // buffer.
+                        buf.assume_init(n);
+                        buf.advance(n);
+                        return Poll::Ready(Ok(()));
+                    },
+                    Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+                        self.registration.clear_readiness(evt);
+                    }
+                    Err(e) => return Poll::Ready(Err(e)),
+                }
+            }
         }
 
         pub(crate) fn poll_write<'a>(&'a self, cx: &mut Context<'_>, buf: &[u8]) -> Poll<io::Result<usize>>
@@ -168,7 +188,26 @@ feature! {
             &'a E: io::Write + 'a,
         {
             use std::io::Write;
-            self.registration.poll_write_io(cx, || self.io.as_ref().unwrap().write(buf))
+
+            loop {
+                let evt = ready!(self.registration.poll_write_ready(cx))?;
+
+                match self.io.as_ref().unwrap().write(buf) {
+                    Ok(n) => {
+                        // if we write only part of our buffer, this is sufficient on unix to show
+                        // that the socket buffer is full
+                        if n > 0 && (!cfg!(windows) && n < buf.len()) {
+                            self.registration.clear_readiness(evt);
+                        }
+
+                        return Poll::Ready(Ok(n));
+                    },
+                    Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+                        self.registration.clear_readiness(evt);
+                    }
+                    Err(e) => return Poll::Ready(Err(e)),
+                }
+            }
         }
 
         #[cfg(feature = "net")]

tokio/src/io/util/async_seek_ext.rs

@@ -69,7 +69,7 @@ cfg_io_util! {
 
         /// Creates a future which will rewind to the beginning of the stream.
         ///
-        /// This is convenience method, equivalent to to `self.seek(SeekFrom::Start(0))`.
+        /// This is convenience method, equivalent to `self.seek(SeekFrom::Start(0))`.
         fn rewind(&mut self) -> Seek<'_, Self>
         where
             Self: Unpin,

tokio/src/lib.rs

@@ -16,6 +16,7 @@
 ))]
 #![cfg_attr(docsrs, feature(doc_cfg))]
 #![cfg_attr(docsrs, allow(unused_attributes))]
+#![cfg_attr(loom, allow(dead_code, unreachable_pub))]
 
 //! A runtime for writing reliable network applications without compromising speed.
 //!
@@ -152,7 +153,7 @@
 //! provide the functionality you need.
 //!
 //! Using the runtime requires the "rt" or "rt-multi-thread" feature flags, to
-//! enable the basic [single-threaded scheduler][rt] and the [thread-pool
+//! enable the current-thread [single-threaded scheduler][rt] and the [multi-thread
 //! scheduler][rt-multi-thread], respectively. See the [`runtime` module
 //! documentation][rt-features] for details. In addition, the "macros" feature
 //! flag enables the `#[tokio::main]` and `#[tokio::test]` attributes.
@@ -309,7 +310,7 @@
 //! need.
 //!
 //! - `full`: Enables all features listed below except `test-util` and `tracing`.
-//! - `rt`: Enables `tokio::spawn`, the basic (current thread) scheduler,
+//! - `rt`: Enables `tokio::spawn`, the current-thread scheduler,
 //!         and non-scheduler utilities.
 //! - `rt-multi-thread`: Enables the heavier, multi-threaded, work-stealing scheduler.
 //! - `io-util`: Enables the IO based `Ext` traits.
@@ -347,9 +348,12 @@
 //!
 //! Likewise, some parts of the API are only available with the same flag:
 //!
-//! - [`task::JoinSet`]
 //! - [`task::Builder`]
-//!  
+//! - Some methods on [`task::JoinSet`]
+//! - [`runtime::RuntimeMetrics`]
+//! - [`runtime::Builder::unhandled_panic`]
+//! - [`task::Id`]
+//!
 //! This flag enables **unstable** features. The public API of these features
 //! may break in 1.x releases. To enable these features, the `--cfg
 //! tokio_unstable` argument must be passed to `rustc` when compiling. This
@@ -379,6 +383,39 @@
 //!
 //! [unstable features]: https://internals.rust-lang.org/t/feature-request-unstable-opt-in-non-transitive-crate-features/16193#why-not-a-crate-feature-2
 //! [feature flags]: https://doc.rust-lang.org/cargo/reference/manifest.html#the-features-section
+//!
+//! ## WASM support
+//!
+//! Tokio has some limited support for the WASM platform. Without the
+//! `tokio_unstable` flag, the following features are supported:
+//!
+//!  * `sync`
+//!  * `macros`
+//!  * `io-util`
+//!  * `rt`
+//!  * `time`
+//!
+//! Enabling any other feature (including `full`) will cause a compilation
+//! failure.
+//!
+//! The `time` module will only work on WASM platforms that have support for
+//! timers (e.g. wasm32-wasi). The timing functions will panic if used on a WASM
+//! platform that does not support timers.
+//!
+//! Note also that if the runtime becomes indefinitely idle, it will panic
+//! immediately instead of blocking forever. On platforms that don't support
+//! time, this means that the runtime can never be idle in any way.
+//!
+//! ### Unstable WASM support
+//!
+//! Tokio also has unstable support for some additional WASM features. This
+//! requires the use of the `tokio_unstable` flag.
+//!
+//! Using this flag enables the use of `tokio::net` on the wasm32-wasi target.
+//! However, not all methods are available on the networking types as WASI
+//! currently does not support the creation of new sockets from within WASM.
+//! Because of this, sockets must currently be created via the `FromRawFd`
+//! trait.
 
 // Test that pointer width is compatible. This asserts that e.g. usize is at
 // least 32 bits, which a lot of components in Tokio currently assumes.
@@ -393,6 +430,37 @@ compile_error! {
     "Tokio requires the platform pointer width to be 32, 64, or 128 bits"
 }
 
+// Ensure that our build script has correctly set cfg flags for wasm.
+//
+// Each condition is written all(a, not(b)). This should be read as
+// "if a, then we must also have b".
+#[cfg(any(
+    all(target_arch = "wasm32", not(tokio_wasm)),
+    all(target_arch = "wasm64", not(tokio_wasm)),
+    all(target_family = "wasm", not(tokio_wasm)),
+    all(target_os = "wasi", not(tokio_wasm)),
+    all(target_os = "wasi", not(tokio_wasi)),
+    all(target_os = "wasi", tokio_wasm_not_wasi),
+    all(tokio_wasm, not(any(target_arch = "wasm32", target_arch = "wasm64"))),
+    all(tokio_wasm_not_wasi, not(tokio_wasm)),
+    all(tokio_wasi, not(tokio_wasm))
+))]
+compile_error!("Tokio's build script has incorrectly detected wasm.");
+
+#[cfg(all(
+    not(tokio_unstable),
+    tokio_wasm,
+    any(
+        feature = "fs",
+        feature = "io-std",
+        feature = "net",
+        feature = "process",
+        feature = "rt-multi-thread",
+        feature = "signal"
+    )
+))]
+compile_error!("Only features sync,macros,io-util,rt,time are supported on wasm.");
+
 // Includes re-exports used by macros.
 //
 // This module is not intended to be part of the public API. In general, any
@@ -417,12 +485,27 @@ cfg_process! {
     pub mod process;
 }
 
-#[cfg(any(feature = "net", feature = "fs", feature = "io-std"))]
+#[cfg(any(
+    feature = "fs",
+    feature = "io-std",
+    feature = "net",
+    all(windows, feature = "process"),
+))]
 mod blocking;
 
 cfg_rt! {
     pub mod runtime;
 }
+cfg_not_rt! {
+    // The `runtime` module is used when the IO or time driver is needed.
+    #[cfg(any(
+        feature = "net",
+        feature = "time",
+        all(unix, feature = "process"),
+        all(unix, feature = "signal"),
+    ))]
+    pub(crate) mod runtime;
+}
 
 pub(crate) mod coop;
 

tokio/src/loom/mocked.rs

@@ -38,3 +38,8 @@ pub(crate) mod sys {
         2
     }
 }
+
+pub(crate) mod thread {
+    pub use loom::lazy_static::AccessError;
+    pub use loom::thread::*;
+}

tokio/src/loom/std/mod.rs

@@ -102,7 +102,7 @@ pub(crate) mod thread {
 
     #[allow(unused_imports)]
     pub(crate) use std::thread::{
-        current, panicking, park, park_timeout, sleep, spawn, Builder, JoinHandle, LocalKey,
-        Result, Thread, ThreadId,
+        current, panicking, park, park_timeout, sleep, spawn, AccessError, Builder, JoinHandle,
+        LocalKey, Result, Thread, ThreadId,
     };
 }

tokio/src/macros/addr_of.rs

@@ -0,0 +1,53 @@
+//! This module defines a macro that lets you go from a raw pointer to a struct
+//! to a raw pointer to a field of the struct.
+
+#[cfg(not(tokio_no_addr_of))]
+macro_rules! generate_addr_of_methods {
+    (
+    impl<$($gen:ident)*> $struct_name:ty {$(
+        $(#[$attrs:meta])*
+        $vis:vis unsafe fn $fn_name:ident(self: NonNull<Self>) -> NonNull<$field_type:ty> {
+            &self$(.$field_name:tt)+
+        }
+    )*}
+    ) => {
+        impl<$($gen)*> $struct_name {$(
+            $(#[$attrs])*
+            $vis unsafe fn $fn_name(me: ::core::ptr::NonNull<Self>) -> ::core::ptr::NonNull<$field_type> {
+                let me = me.as_ptr();
+                let field = ::std::ptr::addr_of_mut!((*me) $(.$field_name)+ );
+                ::core::ptr::NonNull::new_unchecked(field)
+            }
+        )*}
+    };
+}
+
+// The `addr_of_mut!` macro is only available for MSRV at least 1.51.0. This
+// version of the macro uses a workaround for older versions of rustc.
+#[cfg(tokio_no_addr_of)]
+macro_rules! generate_addr_of_methods {
+    (
+    impl<$($gen:ident)*> $struct_name:ty {$(
+        $(#[$attrs:meta])*
+        $vis:vis unsafe fn $fn_name:ident(self: NonNull<Self>) -> NonNull<$field_type:ty> {
+            &self$(.$field_name:tt)+
+        }
+    )*}
+    ) => {
+        impl<$($gen)*> $struct_name {$(
+            $(#[$attrs])*
+            $vis unsafe fn $fn_name(me: ::core::ptr::NonNull<Self>) -> ::core::ptr::NonNull<$field_type> {
+                let me = me.as_ptr();
+                let me_u8 = me as *mut u8;
+
+                let field_offset = {
+                    let me_ref = &*me;
+                    let field_ref_u8 = (&me_ref $(.$field_name)+ ) as *const $field_type as *const u8;
+                    field_ref_u8.offset_from(me_u8)
+                };
+
+                ::core::ptr::NonNull::new_unchecked(me_u8.offset(field_offset).cast())
+            }
+        )*}
+    };
+}

tokio/src/macros/cfg.rs

@@ -61,6 +61,7 @@ macro_rules! cfg_fs {
     ($($item:item)*) => {
         $(
             #[cfg(feature = "fs")]
+            #[cfg(not(tokio_wasi))]
             #[cfg_attr(docsrs, doc(cfg(feature = "fs")))]
             $item
         )*
@@ -69,7 +70,11 @@ macro_rules! cfg_fs {
 
 macro_rules! cfg_io_blocking {
     ($($item:item)*) => {
-        $( #[cfg(any(feature = "io-std", feature = "fs"))] $item )*
+        $( #[cfg(any(
+                feature = "io-std",
+                feature = "fs",
+                all(windows, feature = "process"),
+        ))] $item )*
     }
 }
 
@@ -78,12 +83,12 @@ macro_rules! cfg_io_driver {
         $(
             #[cfg(any(
                 feature = "net",
-                feature = "process",
+                all(unix, feature = "process"),
                 all(unix, feature = "signal"),
             ))]
             #[cfg_attr(docsrs, doc(cfg(any(
                 feature = "net",
-                feature = "process",
+                all(unix, feature = "process"),
                 all(unix, feature = "signal"),
             ))))]
             $item
@@ -96,7 +101,7 @@ macro_rules! cfg_io_driver_impl {
         $(
             #[cfg(any(
                 feature = "net",
-                feature = "process",
+                all(unix, feature = "process"),
                 all(unix, feature = "signal"),
             ))]
             $item
@@ -109,7 +114,7 @@ macro_rules! cfg_not_io_driver {
         $(
             #[cfg(not(any(
                 feature = "net",
-                feature = "process",
+                all(unix, feature = "process"),
                 all(unix, feature = "signal"),
             )))]
             $item
@@ -247,6 +252,7 @@ macro_rules! cfg_process {
             #[cfg(feature = "process")]
             #[cfg_attr(docsrs, doc(cfg(feature = "process")))]
             #[cfg(not(loom))]
+            #[cfg(not(tokio_wasi))]
             $item
         )*
     }
@@ -275,6 +281,7 @@ macro_rules! cfg_signal {
             #[cfg(feature = "signal")]
             #[cfg_attr(docsrs, doc(cfg(feature = "signal")))]
             #[cfg(not(loom))]
+            #[cfg(not(tokio_wasi))]
             $item
         )*
     }
@@ -334,7 +341,7 @@ macro_rules! cfg_not_rt {
 macro_rules! cfg_rt_multi_thread {
     ($($item:item)*) => {
         $(
-            #[cfg(feature = "rt-multi-thread")]
+            #[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
             #[cfg_attr(docsrs, doc(cfg(feature = "rt-multi-thread")))]
             $item
         )*
@@ -451,7 +458,8 @@ macro_rules! cfg_has_atomic_u64 {
                     target_arch = "arm",
                     target_arch = "mips",
                     target_arch = "powerpc",
-                    target_arch = "riscv32"
+                    target_arch = "riscv32",
+                    tokio_wasm
                     )))]
             $item
         )*
@@ -465,9 +473,28 @@ macro_rules! cfg_not_has_atomic_u64 {
                     target_arch = "arm",
                     target_arch = "mips",
                     target_arch = "powerpc",
-                    target_arch = "riscv32"
+                    target_arch = "riscv32",
+                    tokio_wasm
                     ))]
             $item
         )*
     }
 }
+
+macro_rules! cfg_not_wasi {
+    ($($item:item)*) => {
+        $(
+            #[cfg(not(tokio_wasi))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_is_wasm_not_wasi {
+    ($($item:item)*) => {
+        $(
+            #[cfg(tokio_wasm_not_wasi)]
+            $item
+        )*
+    }
+}

tokio/src/macros/mod.rs

@@ -15,6 +15,9 @@ mod ready;
 #[macro_use]
 mod thread_local;
 
+#[macro_use]
+mod addr_of;
+
 cfg_trace! {
     #[macro_use]
     mod trace;

tokio/src/net/mod.rs

@@ -23,8 +23,10 @@
 //! [`UnixDatagram`]: UnixDatagram
 
 mod addr;
-#[cfg(feature = "net")]
-pub(crate) use addr::to_socket_addrs;
+cfg_not_wasi! {
+    #[cfg(feature = "net")]
+    pub(crate) use addr::to_socket_addrs;
+}
 pub use addr::ToSocketAddrs;
 
 cfg_net! {
@@ -33,11 +35,13 @@ cfg_net! {
 
     pub mod tcp;
     pub use tcp::listener::TcpListener;
-    pub use tcp::socket::TcpSocket;
     pub use tcp::stream::TcpStream;
+    cfg_not_wasi! {
+        pub use tcp::socket::TcpSocket;
 
-    mod udp;
-    pub use udp::UdpSocket;
+        mod udp;
+        pub use udp::UdpSocket;
+    }
 }
 
 cfg_net_unix! {

tokio/src/net/tcp/listener.rs

@@ -1,6 +1,9 @@
 use crate::io::{Interest, PollEvented};
 use crate::net::tcp::TcpStream;
-use crate::net::{to_socket_addrs, ToSocketAddrs};
+
+cfg_not_wasi! {
+    use crate::net::{to_socket_addrs, ToSocketAddrs};
+}
 
 use std::convert::TryFrom;
 use std::fmt;
@@ -55,68 +58,70 @@ cfg_net! {
 }
 
 impl TcpListener {
-    /// Creates a new TcpListener, which will be bound to the specified address.
-    ///
-    /// The returned listener is ready for accepting connections.
-    ///
-    /// Binding with a port number of 0 will request that the OS assigns a port
-    /// to this listener. The port allocated can be queried via the `local_addr`
-    /// method.
-    ///
-    /// The address type can be any implementor of the [`ToSocketAddrs`] trait.
-    /// If `addr` yields multiple addresses, bind will be attempted with each of
-    /// the addresses until one succeeds and returns the listener. If none of
-    /// the addresses succeed in creating a listener, the error returned from
-    /// the last attempt (the last address) is returned.
-    ///
-    /// This function sets the `SO_REUSEADDR` option on the socket.
-    ///
-    /// To configure the socket before binding, you can use the [`TcpSocket`]
-    /// type.
-    ///
-    /// [`ToSocketAddrs`]: trait@crate::net::ToSocketAddrs
-    /// [`TcpSocket`]: struct@crate::net::TcpSocket
-    ///
-    /// # Examples
-    ///
-    /// ```no_run
-    /// use tokio::net::TcpListener;
-    ///
-    /// use std::io;
-    ///
-    /// #[tokio::main]
-    /// async fn main() -> io::Result<()> {
-    ///     let listener = TcpListener::bind("127.0.0.1:2345").await?;
-    ///
-    ///     // use the listener
-    ///
-    ///     # let _ = listener;
-    ///     Ok(())
-    /// }
-    /// ```
-    pub async fn bind<A: ToSocketAddrs>(addr: A) -> io::Result<TcpListener> {
-        let addrs = to_socket_addrs(addr).await?;
+    cfg_not_wasi! {
+        /// Creates a new TcpListener, which will be bound to the specified address.
+        ///
+        /// The returned listener is ready for accepting connections.
+        ///
+        /// Binding with a port number of 0 will request that the OS assigns a port
+        /// to this listener. The port allocated can be queried via the `local_addr`
+        /// method.
+        ///
+        /// The address type can be any implementor of the [`ToSocketAddrs`] trait.
+        /// If `addr` yields multiple addresses, bind will be attempted with each of
+        /// the addresses until one succeeds and returns the listener. If none of
+        /// the addresses succeed in creating a listener, the error returned from
+        /// the last attempt (the last address) is returned.
+        ///
+        /// This function sets the `SO_REUSEADDR` option on the socket.
+        ///
+        /// To configure the socket before binding, you can use the [`TcpSocket`]
+        /// type.
+        ///
+        /// [`ToSocketAddrs`]: trait@crate::net::ToSocketAddrs
+        /// [`TcpSocket`]: struct@crate::net::TcpSocket
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::net::TcpListener;
+        ///
+        /// use std::io;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let listener = TcpListener::bind("127.0.0.1:2345").await?;
+        ///
+        ///     // use the listener
+        ///
+        ///     # let _ = listener;
+        ///     Ok(())
+        /// }
+        /// ```
+        pub async fn bind<A: ToSocketAddrs>(addr: A) -> io::Result<TcpListener> {
+            let addrs = to_socket_addrs(addr).await?;
 
-        let mut last_err = None;
+            let mut last_err = None;
 
-        for addr in addrs {
-            match TcpListener::bind_addr(addr) {
-                Ok(listener) => return Ok(listener),
-                Err(e) => last_err = Some(e),
+            for addr in addrs {
+                match TcpListener::bind_addr(addr) {
+                    Ok(listener) => return Ok(listener),
+                    Err(e) => last_err = Some(e),
+                }
             }
+
+            Err(last_err.unwrap_or_else(|| {
+                io::Error::new(
+                    io::ErrorKind::InvalidInput,
+                    "could not resolve to any address",
+                )
+            }))
         }
 
-        Err(last_err.unwrap_or_else(|| {
-            io::Error::new(
-                io::ErrorKind::InvalidInput,
-                "could not resolve to any address",
-            )
-        }))
-    }
-
-    fn bind_addr(addr: SocketAddr) -> io::Result<TcpListener> {
-        let listener = mio::net::TcpListener::bind(addr)?;
-        TcpListener::new(listener)
+        fn bind_addr(addr: SocketAddr) -> io::Result<TcpListener> {
+            let listener = mio::net::TcpListener::bind(addr)?;
+            TcpListener::new(listener)
+        }
     }
 
     /// Accepts a new incoming connection from this listener.
@@ -216,11 +221,13 @@ impl TcpListener {
     ///
     /// # Panics
     ///
-    /// This function panics if thread-local runtime is not set.
+    /// This function panics if it is not called from within a runtime with
+    /// IO enabled.
     ///
     /// The runtime is usually set implicitly when this function is called
     /// from a future driven by a tokio runtime, otherwise runtime can be set
     /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    #[track_caller]
     pub fn from_std(listener: net::TcpListener) -> io::Result<TcpListener> {
         let io = mio::net::TcpListener::from_std(listener);
         let io = PollEvented::new(io)?;
@@ -267,11 +274,22 @@ impl TcpListener {
                 .map(|io| io.into_raw_socket())
                 .map(|raw_socket| unsafe { std::net::TcpListener::from_raw_socket(raw_socket) })
         }
+
+        #[cfg(tokio_wasi)]
+        {
+            use std::os::wasi::io::{FromRawFd, IntoRawFd};
+            self.io
+                .into_inner()
+                .map(|io| io.into_raw_fd())
+                .map(|raw_fd| unsafe { std::net::TcpListener::from_raw_fd(raw_fd) })
+        }
     }
 
-    pub(crate) fn new(listener: mio::net::TcpListener) -> io::Result<TcpListener> {
-        let io = PollEvented::new(listener)?;
-        Ok(TcpListener { io })
+    cfg_not_wasi! {
+        pub(crate) fn new(listener: mio::net::TcpListener) -> io::Result<TcpListener> {
+            let io = PollEvented::new(listener)?;
+            Ok(TcpListener { io })
+        }
     }
 
     /// Returns the local address that this listener is bound to.
@@ -384,6 +402,20 @@ mod sys {
     }
 }
 
+cfg_unstable! {
+    #[cfg(tokio_wasi)]
+    mod sys {
+        use super::TcpListener;
+        use std::os::wasi::prelude::*;
+
+        impl AsRawFd for TcpListener {
+            fn as_raw_fd(&self) -> RawFd {
+                self.io.as_raw_fd()
+            }
+        }
+    }
+}
+
 #[cfg(windows)]
 mod sys {
     use super::TcpListener;

tokio/src/net/tcp/mod.rs

@@ -2,7 +2,9 @@
 
 pub(crate) mod listener;
 
-pub(crate) mod socket;
+cfg_not_wasi! {
+    pub(crate) mod socket;
+}
 
 mod split;
 pub use split::{ReadHalf, WriteHalf};

tokio/src/net/tcp/socket.rs

@@ -398,6 +398,89 @@ impl TcpSocket {
         self.inner.linger()
     }
 
+    /// Gets the value of the `IP_TOS` option for this socket.
+    ///
+    /// For more information about this option, see [`set_tos`].
+    ///
+    /// **NOTE:** On Windows, `IP_TOS` is only supported on [Windows 8+ or
+    /// Windows Server 2012+.](https://docs.microsoft.com/en-us/windows/win32/winsock/ipproto-ip-socket-options)
+    ///
+    /// [`set_tos`]: Self::set_tos
+    // https://docs.rs/socket2/0.4.2/src/socket2/socket.rs.html#1178
+    #[cfg(not(any(
+        target_os = "fuchsia",
+        target_os = "redox",
+        target_os = "solaris",
+        target_os = "illumos",
+    )))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(not(any(
+            target_os = "fuchsia",
+            target_os = "redox",
+            target_os = "solaris",
+            target_os = "illumos",
+        ))))
+    )]
+    pub fn tos(&self) -> io::Result<u32> {
+        self.inner.tos()
+    }
+
+    /// Sets the value for the `IP_TOS` option on this socket.
+    ///
+    /// This value sets the time-to-live field that is used in every packet sent
+    /// from this socket.
+    ///
+    /// **NOTE:** On Windows, `IP_TOS` is only supported on [Windows 8+ or
+    /// Windows Server 2012+.](https://docs.microsoft.com/en-us/windows/win32/winsock/ipproto-ip-socket-options)
+    // https://docs.rs/socket2/0.4.2/src/socket2/socket.rs.html#1178
+    #[cfg(not(any(
+        target_os = "fuchsia",
+        target_os = "redox",
+        target_os = "solaris",
+        target_os = "illumos",
+    )))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(not(any(
+            target_os = "fuchsia",
+            target_os = "redox",
+            target_os = "solaris",
+            target_os = "illumos",
+        ))))
+    )]
+    pub fn set_tos(&self, tos: u32) -> io::Result<()> {
+        self.inner.set_tos(tos)
+    }
+
+    /// Gets the value for the `SO_BINDTODEVICE` option on this socket
+    ///
+    /// This value gets the socket binded device's interface name.
+    #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux",))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux",)))
+    )]
+    pub fn device(&self) -> io::Result<Option<Vec<u8>>> {
+        self.inner.device()
+    }
+
+    /// Sets the value for the `SO_BINDTODEVICE` option on this socket
+    ///
+    /// If a socket is bound to an interface, only packets received from that
+    /// particular interface are processed by the socket. Note that this only
+    /// works for some socket types, particularly `AF_INET` sockets.
+    ///
+    /// If `interface` is `None` or an empty string it removes the binding.
+    #[cfg(all(any(target_os = "android", target_os = "fuchsia", target_os = "linux")))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(all(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))))
+    )]
+    pub fn bind_device(&self, interface: Option<&[u8]>) -> io::Result<()> {
+        self.inner.bind_device(interface)
+    }
+
     /// Gets the local address of this socket.
     ///
     /// Will fail on windows if called before `bind`.

tokio/src/net/tcp/split.rs

@@ -190,8 +190,12 @@ impl ReadHalf<'_> {
     /// # Return
     ///
     /// If data is successfully read, `Ok(n)` is returned, where `n` is the
-    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
-    /// and will no longer yield data. If the stream is not ready to read data
+    /// number of bytes read. If `n` is `0`, then it can indicate one of two scenarios:
+    ///
+    /// 1. The stream's read half is closed and will no longer yield data.
+    /// 2. The specified buffer was 0 bytes in length.
+    ///
+    /// If the stream is not ready to read data,
     /// `Err(io::ErrorKind::WouldBlock)` is returned.
     pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
         self.0.try_read(buf)

tokio/src/net/tcp/split_owned.rs

@@ -245,8 +245,12 @@ impl OwnedReadHalf {
     /// # Return
     ///
     /// If data is successfully read, `Ok(n)` is returned, where `n` is the
-    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
-    /// and will no longer yield data. If the stream is not ready to read data
+    /// number of bytes read. If `n` is `0`, then it can indicate one of two scenarios:
+    ///
+    /// 1. The stream's read half is closed and will no longer yield data.
+    /// 2. The specified buffer was 0 bytes in length.
+    ///
+    /// If the stream is not ready to read data,
     /// `Err(io::ErrorKind::WouldBlock)` is returned.
     pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
         self.inner.try_read(buf)

tokio/src/net/tcp/stream.rs

@@ -1,8 +1,12 @@
-use crate::future::poll_fn;
+cfg_not_wasi! {
+    use crate::future::poll_fn;
+    use crate::net::{to_socket_addrs, ToSocketAddrs};
+    use std::time::Duration;
+}
+
 use crate::io::{AsyncRead, AsyncWrite, Interest, PollEvented, ReadBuf, Ready};
 use crate::net::tcp::split::{split, ReadHalf, WriteHalf};
 use crate::net::tcp::split_owned::{split_owned, OwnedReadHalf, OwnedWriteHalf};
-use crate::net::{to_socket_addrs, ToSocketAddrs};
 
 use std::convert::TryFrom;
 use std::fmt;
@@ -10,7 +14,6 @@ use std::io;
 use std::net::{Shutdown, SocketAddr};
 use std::pin::Pin;
 use std::task::{Context, Poll};
-use std::time::Duration;
 
 cfg_io_util! {
     use bytes::BufMut;
@@ -70,86 +73,88 @@ cfg_net! {
 }
 
 impl TcpStream {
-    /// Opens a TCP connection to a remote host.
-    ///
-    /// `addr` is an address of the remote host. Anything which implements the
-    /// [`ToSocketAddrs`] trait can be supplied as the address.  If `addr`
-    /// yields multiple addresses, connect will be attempted with each of the
-    /// addresses until a connection is successful. If none of the addresses
-    /// result in a successful connection, the error returned from the last
-    /// connection attempt (the last address) is returned.
-    ///
-    /// To configure the socket before connecting, you can use the [`TcpSocket`]
-    /// type.
-    ///
-    /// [`ToSocketAddrs`]: trait@crate::net::ToSocketAddrs
-    /// [`TcpSocket`]: struct@crate::net::TcpSocket
-    ///
-    /// # Examples
-    ///
-    /// ```no_run
-    /// use tokio::net::TcpStream;
-    /// use tokio::io::AsyncWriteExt;
-    /// use std::error::Error;
-    ///
-    /// #[tokio::main]
-    /// async fn main() -> Result<(), Box<dyn Error>> {
-    ///     // Connect to a peer
-    ///     let mut stream = TcpStream::connect("127.0.0.1:8080").await?;
-    ///
-    ///     // Write some data.
-    ///     stream.write_all(b"hello world!").await?;
-    ///
-    ///     Ok(())
-    /// }
-    /// ```
-    ///
-    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
-    ///
-    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
-    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
-    pub async fn connect<A: ToSocketAddrs>(addr: A) -> io::Result<TcpStream> {
-        let addrs = to_socket_addrs(addr).await?;
+    cfg_not_wasi! {
+        /// Opens a TCP connection to a remote host.
+        ///
+        /// `addr` is an address of the remote host. Anything which implements the
+        /// [`ToSocketAddrs`] trait can be supplied as the address.  If `addr`
+        /// yields multiple addresses, connect will be attempted with each of the
+        /// addresses until a connection is successful. If none of the addresses
+        /// result in a successful connection, the error returned from the last
+        /// connection attempt (the last address) is returned.
+        ///
+        /// To configure the socket before connecting, you can use the [`TcpSocket`]
+        /// type.
+        ///
+        /// [`ToSocketAddrs`]: trait@crate::net::ToSocketAddrs
+        /// [`TcpSocket`]: struct@crate::net::TcpSocket
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::net::TcpStream;
+        /// use tokio::io::AsyncWriteExt;
+        /// use std::error::Error;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> Result<(), Box<dyn Error>> {
+        ///     // Connect to a peer
+        ///     let mut stream = TcpStream::connect("127.0.0.1:8080").await?;
+        ///
+        ///     // Write some data.
+        ///     stream.write_all(b"hello world!").await?;
+        ///
+        ///     Ok(())
+        /// }
+        /// ```
+        ///
+        /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
+        ///
+        /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
+        /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+        pub async fn connect<A: ToSocketAddrs>(addr: A) -> io::Result<TcpStream> {
+            let addrs = to_socket_addrs(addr).await?;
 
-        let mut last_err = None;
+            let mut last_err = None;
 
-        for addr in addrs {
-            match TcpStream::connect_addr(addr).await {
-                Ok(stream) => return Ok(stream),
-                Err(e) => last_err = Some(e),
+            for addr in addrs {
+                match TcpStream::connect_addr(addr).await {
+                    Ok(stream) => return Ok(stream),
+                    Err(e) => last_err = Some(e),
+                }
             }
+
+            Err(last_err.unwrap_or_else(|| {
+                io::Error::new(
+                    io::ErrorKind::InvalidInput,
+                    "could not resolve to any address",
+                )
+            }))
         }
 
-        Err(last_err.unwrap_or_else(|| {
-            io::Error::new(
-                io::ErrorKind::InvalidInput,
-                "could not resolve to any address",
-            )
-        }))
-    }
-
-    /// Establishes a connection to the specified `addr`.
-    async fn connect_addr(addr: SocketAddr) -> io::Result<TcpStream> {
-        let sys = mio::net::TcpStream::connect(addr)?;
-        TcpStream::connect_mio(sys).await
-    }
-
-    pub(crate) async fn connect_mio(sys: mio::net::TcpStream) -> io::Result<TcpStream> {
-        let stream = TcpStream::new(sys)?;
-
-        // Once we've connected, wait for the stream to be writable as
-        // that's when the actual connection has been initiated. Once we're
-        // writable we check for `take_socket_error` to see if the connect
-        // actually hit an error or not.
-        //
-        // If all that succeeded then we ship everything on up.
-        poll_fn(|cx| stream.io.registration().poll_write_ready(cx)).await?;
-
-        if let Some(e) = stream.io.take_error()? {
-            return Err(e);
+        /// Establishes a connection to the specified `addr`.
+        async fn connect_addr(addr: SocketAddr) -> io::Result<TcpStream> {
+            let sys = mio::net::TcpStream::connect(addr)?;
+            TcpStream::connect_mio(sys).await
         }
 
-        Ok(stream)
+        pub(crate) async fn connect_mio(sys: mio::net::TcpStream) -> io::Result<TcpStream> {
+            let stream = TcpStream::new(sys)?;
+
+            // Once we've connected, wait for the stream to be writable as
+            // that's when the actual connection has been initiated. Once we're
+            // writable we check for `take_socket_error` to see if the connect
+            // actually hit an error or not.
+            //
+            // If all that succeeded then we ship everything on up.
+            poll_fn(|cx| stream.io.registration().poll_write_ready(cx)).await?;
+
+            if let Some(e) = stream.io.take_error()? {
+                return Err(e);
+            }
+
+            Ok(stream)
+        }
     }
 
     pub(crate) fn new(connected: mio::net::TcpStream) -> io::Result<TcpStream> {
@@ -181,11 +186,13 @@ impl TcpStream {
     ///
     /// # Panics
     ///
-    /// This function panics if thread-local runtime is not set.
+    /// This function panics if it is not called from within a runtime with
+    /// IO enabled.
     ///
     /// The runtime is usually set implicitly when this function is called
     /// from a future driven by a tokio runtime, otherwise runtime can be set
     /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    #[track_caller]
     pub fn from_std(stream: std::net::TcpStream) -> io::Result<TcpStream> {
         let io = mio::net::TcpStream::from_std(stream);
         let io = PollEvented::new(io)?;
@@ -244,6 +251,15 @@ impl TcpStream {
                 .map(|io| io.into_raw_socket())
                 .map(|raw_socket| unsafe { std::net::TcpStream::from_raw_socket(raw_socket) })
         }
+
+        #[cfg(tokio_wasi)]
+        {
+            use std::os::wasi::io::{FromRawFd, IntoRawFd};
+            self.io
+                .into_inner()
+                .map(|io| io.into_raw_fd())
+                .map(|raw_fd| unsafe { std::net::TcpStream::from_raw_fd(raw_fd) })
+        }
     }
 
     /// Returns the local address that this stream is bound to.
@@ -531,8 +547,12 @@ impl TcpStream {
     /// # Return
     ///
     /// If data is successfully read, `Ok(n)` is returned, where `n` is the
-    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
-    /// and will no longer yield data. If the stream is not ready to read data
+    /// number of bytes read. If `n` is `0`, then it can indicate one of two scenarios:
+    ///
+    /// 1. The stream's read half is closed and will no longer yield data.
+    /// 2. The specified buffer was 0 bytes in length.
+    ///
+    /// If the stream is not ready to read data,
     /// `Err(io::ErrorKind::WouldBlock)` is returned.
     ///
     /// # Examples
@@ -1077,52 +1097,54 @@ impl TcpStream {
         self.io.set_nodelay(nodelay)
     }
 
-    /// Reads the linger duration for this socket by getting the `SO_LINGER`
-    /// option.
-    ///
-    /// For more information about this option, see [`set_linger`].
-    ///
-    /// [`set_linger`]: TcpStream::set_linger
-    ///
-    /// # Examples
-    ///
-    /// ```no_run
-    /// use tokio::net::TcpStream;
-    ///
-    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
-    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
-    ///
-    /// println!("{:?}", stream.linger()?);
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub fn linger(&self) -> io::Result<Option<Duration>> {
-        socket2::SockRef::from(self).linger()
-    }
+    cfg_not_wasi! {
+        /// Reads the linger duration for this socket by getting the `SO_LINGER`
+        /// option.
+        ///
+        /// For more information about this option, see [`set_linger`].
+        ///
+        /// [`set_linger`]: TcpStream::set_linger
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::net::TcpStream;
+        ///
+        /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+        /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
+        ///
+        /// println!("{:?}", stream.linger()?);
+        /// # Ok(())
+        /// # }
+        /// ```
+        pub fn linger(&self) -> io::Result<Option<Duration>> {
+            socket2::SockRef::from(self).linger()
+        }
 
-    /// Sets the linger duration of this socket by setting the SO_LINGER option.
-    ///
-    /// This option controls the action taken when a stream has unsent messages and the stream is
-    /// closed. If SO_LINGER is set, the system shall block the process until it can transmit the
-    /// data or until the time expires.
-    ///
-    /// If SO_LINGER is not specified, and the stream is closed, the system handles the call in a
-    /// way that allows the process to continue as quickly as possible.
-    ///
-    /// # Examples
-    ///
-    /// ```no_run
-    /// use tokio::net::TcpStream;
-    ///
-    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
-    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
-    ///
-    /// stream.set_linger(None)?;
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub fn set_linger(&self, dur: Option<Duration>) -> io::Result<()> {
-        socket2::SockRef::from(self).set_linger(dur)
+        /// Sets the linger duration of this socket by setting the SO_LINGER option.
+        ///
+        /// This option controls the action taken when a stream has unsent messages and the stream is
+        /// closed. If SO_LINGER is set, the system shall block the process until it can transmit the
+        /// data or until the time expires.
+        ///
+        /// If SO_LINGER is not specified, and the stream is closed, the system handles the call in a
+        /// way that allows the process to continue as quickly as possible.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::net::TcpStream;
+        ///
+        /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+        /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
+        ///
+        /// stream.set_linger(None)?;
+        /// # Ok(())
+        /// # }
+        /// ```
+        pub fn set_linger(&self, dur: Option<Duration>) -> io::Result<()> {
+            socket2::SockRef::from(self).set_linger(dur)
+        }
     }
 
     /// Gets the value of the `IP_TTL` option for this socket.
@@ -1315,3 +1337,15 @@ mod sys {
         }
     }
 }
+
+#[cfg(all(tokio_unstable, tokio_wasi))]
+mod sys {
+    use super::TcpStream;
+    use std::os::wasi::prelude::*;
+
+    impl AsRawFd for TcpStream {
+        fn as_raw_fd(&self) -> RawFd {
+            self.io.as_raw_fd()
+        }
+    }
+}

tokio/src/net/udp.rs

@@ -170,6 +170,7 @@ impl UdpSocket {
         UdpSocket::new(sys)
     }
 
+    #[track_caller]
     fn new(socket: mio::net::UdpSocket) -> io::Result<UdpSocket> {
         let io = PollEvented::new(socket)?;
         Ok(UdpSocket { io })
@@ -210,6 +211,7 @@ impl UdpSocket {
     /// # Ok(())
     /// # }
     /// ```
+    #[track_caller]
     pub fn from_std(socket: net::UdpSocket) -> io::Result<UdpSocket> {
         let io = mio::net::UdpSocket::from_std(socket);
         UdpSocket::new(io)
@@ -257,6 +259,10 @@ impl UdpSocket {
         }
     }
 
+    fn as_socket(&self) -> socket2::SockRef<'_> {
+        socket2::SockRef::from(self)
+    }
+
     /// Returns the local address that this socket is bound to.
     ///
     /// # Example
@@ -1508,6 +1514,89 @@ impl UdpSocket {
         self.io.set_ttl(ttl)
     }
 
+    /// Gets the value of the `IP_TOS` option for this socket.
+    ///
+    /// For more information about this option, see [`set_tos`].
+    ///
+    /// **NOTE:** On Windows, `IP_TOS` is only supported on [Windows 8+ or
+    /// Windows Server 2012+.](https://docs.microsoft.com/en-us/windows/win32/winsock/ipproto-ip-socket-options)
+    ///
+    /// [`set_tos`]: Self::set_tos
+    // https://docs.rs/socket2/0.4.2/src/socket2/socket.rs.html#1178
+    #[cfg(not(any(
+        target_os = "fuchsia",
+        target_os = "redox",
+        target_os = "solaris",
+        target_os = "illumos",
+    )))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(not(any(
+            target_os = "fuchsia",
+            target_os = "redox",
+            target_os = "solaris",
+            target_os = "illumos",
+        ))))
+    )]
+    pub fn tos(&self) -> io::Result<u32> {
+        self.as_socket().tos()
+    }
+
+    /// Sets the value for the `IP_TOS` option on this socket.
+    ///
+    /// This value sets the time-to-live field that is used in every packet sent
+    /// from this socket.
+    ///
+    /// **NOTE:** On Windows, `IP_TOS` is only supported on [Windows 8+ or
+    /// Windows Server 2012+.](https://docs.microsoft.com/en-us/windows/win32/winsock/ipproto-ip-socket-options)
+    // https://docs.rs/socket2/0.4.2/src/socket2/socket.rs.html#1178
+    #[cfg(not(any(
+        target_os = "fuchsia",
+        target_os = "redox",
+        target_os = "solaris",
+        target_os = "illumos",
+    )))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(not(any(
+            target_os = "fuchsia",
+            target_os = "redox",
+            target_os = "solaris",
+            target_os = "illumos",
+        ))))
+    )]
+    pub fn set_tos(&self, tos: u32) -> io::Result<()> {
+        self.as_socket().set_tos(tos)
+    }
+
+    /// Gets the value for the `SO_BINDTODEVICE` option on this socket
+    ///
+    /// This value gets the socket-bound device's interface name.
+    #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux",))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux",)))
+    )]
+    pub fn device(&self) -> io::Result<Option<Vec<u8>>> {
+        self.as_socket().device()
+    }
+
+    /// Sets the value for the `SO_BINDTODEVICE` option on this socket
+    ///
+    /// If a socket is bound to an interface, only packets received from that
+    /// particular interface are processed by the socket. Note that this only
+    /// works for some socket types, particularly `AF_INET` sockets.
+    ///
+    /// If `interface` is `None` or an empty string it removes the binding.
+    #[cfg(all(any(target_os = "android", target_os = "fuchsia", target_os = "linux")))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(all(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))))
+    )]
+    pub fn bind_device(&self, interface: Option<&[u8]>) -> io::Result<()> {
+        self.as_socket().bind_device(interface)
+    }
+
     /// Executes an operation of the `IP_ADD_MEMBERSHIP` type.
     ///
     /// This function specifies a new multicast group for this socket to join.

tokio/src/net/unix/datagram/socket.rs

@@ -430,7 +430,8 @@ impl UnixDatagram {
     ///
     /// # Panics
     ///
-    /// This function panics if thread-local runtime is not set.
+    /// This function panics if it is not called from within a runtime with
+    /// IO enabled.
     ///
     /// The runtime is usually set implicitly when this function is called
     /// from a future driven by a Tokio runtime, otherwise runtime can be set
@@ -457,6 +458,7 @@ impl UnixDatagram {
     /// # Ok(())
     /// # }
     /// ```
+    #[track_caller]
     pub fn from_std(datagram: net::UnixDatagram) -> io::Result<UnixDatagram> {
         let socket = mio::net::UnixDatagram::from_std(datagram);
         let io = PollEvented::new(socket)?;

tokio/src/net/unix/listener.rs

@@ -54,11 +54,13 @@ impl UnixListener {
     ///
     /// # Panics
     ///
-    /// This function panics if thread-local runtime is not set.
+    /// This function panics if it is not called from within a runtime with
+    /// IO enabled.
     ///
     /// The runtime is usually set implicitly when this function is called
     /// from a future driven by a tokio runtime, otherwise runtime can be set
     /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    #[track_caller]
     pub fn bind<P>(path: P) -> io::Result<UnixListener>
     where
         P: AsRef<Path>,
@@ -77,11 +79,13 @@ impl UnixListener {
     ///
     /// # Panics
     ///
-    /// This function panics if thread-local runtime is not set.
+    /// This function panics if it is not called from within a runtime with
+    /// IO enabled.
     ///
     /// The runtime is usually set implicitly when this function is called
     /// from a future driven by a tokio runtime, otherwise runtime can be set
     /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    #[track_caller]
     pub fn from_std(listener: net::UnixListener) -> io::Result<UnixListener> {
         let listener = mio::net::UnixListener::from_std(listener);
         let io = PollEvented::new(listener)?;

tokio/src/net/unix/split.rs

@@ -100,8 +100,12 @@ impl ReadHalf<'_> {
     /// # Return
     ///
     /// If data is successfully read, `Ok(n)` is returned, where `n` is the
-    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
-    /// and will no longer yield data. If the stream is not ready to read data
+    /// number of bytes read. If `n` is `0`, then it can indicate one of two scenarios:
+    ///
+    /// 1. The stream's read half is closed and will no longer yield data.
+    /// 2. The specified buffer was 0 bytes in length.
+    ///
+    /// If the stream is not ready to read data,
     /// `Err(io::ErrorKind::WouldBlock)` is returned.
     pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
         self.0.try_read(buf)

tokio/src/net/unix/split_owned.rs

@@ -155,8 +155,12 @@ impl OwnedReadHalf {
     /// # Return
     ///
     /// If data is successfully read, `Ok(n)` is returned, where `n` is the
-    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
-    /// and will no longer yield data. If the stream is not ready to read data
+    /// number of bytes read. If `n` is `0`, then it can indicate one of two scenarios:
+    ///
+    /// 1. The stream's read half is closed and will no longer yield data.
+    /// 2. The specified buffer was 0 bytes in length.
+    ///
+    /// If the stream is not ready to read data,
     /// `Err(io::ErrorKind::WouldBlock)` is returned.
     pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
         self.inner.try_read(buf)

tokio/src/net/unix/stream.rs

@@ -22,8 +22,8 @@ cfg_io_util! {
 cfg_net_unix! {
     /// A structure representing a connected Unix socket.
     ///
-    /// This socket can be connected directly with `UnixStream::connect` or accepted
-    /// from a listener with `UnixListener::incoming`. Additionally, a pair of
+    /// This socket can be connected directly with [`UnixStream::connect`] or accepted
+    /// from a listener with [`UnixListener::accept`]. Additionally, a pair of
     /// anonymous Unix sockets can be created with `UnixStream::pair`.
     ///
     /// To shut down the stream in the write direction, you can call the
@@ -32,6 +32,7 @@ cfg_net_unix! {
     /// the stream in one direction.
     ///
     /// [`shutdown()`]: fn@crate::io::AsyncWriteExt::shutdown
+    /// [`UnixListener::accept`]: crate::net::UnixListener::accept
     pub struct UnixStream {
         io: PollEvented<mio::net::UnixStream>,
     }
@@ -239,8 +240,12 @@ impl UnixStream {
     /// # Return
     ///
     /// If data is successfully read, `Ok(n)` is returned, where `n` is the
-    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
-    /// and will no longer yield data. If the stream is not ready to read data
+    /// number of bytes read. If `n` is `0`, then it can indicate one of two scenarios:
+    ///
+    /// 1. The stream's read half is closed and will no longer yield data.
+    /// 2. The specified buffer was 0 bytes in length.
+    ///
+    /// If the stream is not ready to read data,
     /// `Err(io::ErrorKind::WouldBlock)` is returned.
     ///
     /// # Examples
@@ -699,11 +704,13 @@ impl UnixStream {
     ///
     /// # Panics
     ///
-    /// This function panics if thread-local runtime is not set.
+    /// This function panics if it is not called from within a runtime with
+    /// IO enabled.
     ///
     /// The runtime is usually set implicitly when this function is called
     /// from a future driven by a tokio runtime, otherwise runtime can be set
     /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    #[track_caller]
     pub fn from_std(stream: net::UnixStream) -> io::Result<UnixStream> {
         let stream = mio::net::UnixStream::from_std(stream);
         let io = PollEvented::new(stream)?;

tokio/src/net/windows/named_pipe.rs

@@ -403,8 +403,12 @@ impl NamedPipeServer {
     /// # Return
     ///
     /// If data is successfully read, `Ok(n)` is returned, where `n` is the
-    /// number of bytes read. `Ok(0)` indicates the pipe's read half is closed
-    /// and will no longer yield data. If the pipe is not ready to read data
+    /// number of bytes read. If `n` is `0`, then it can indicate one of two scenarios:
+    ///
+    /// 1. The pipe's read half is closed and will no longer yield data.
+    /// 2. The specified buffer was 0 bytes in length.
+    ///
+    /// If the pipe is not ready to read data,
     /// `Err(io::ErrorKind::WouldBlock)` is returned.
     ///
     /// # Examples
@@ -1143,8 +1147,12 @@ impl NamedPipeClient {
     /// # Return
     ///
     /// If data is successfully read, `Ok(n)` is returned, where `n` is the
-    /// number of bytes read. `Ok(0)` indicates the pipe's read half is closed
-    /// and will no longer yield data. If the pipe is not ready to read data
+    /// number of bytes read. If `n` is `0`, then it can indicate one of two scenarios:
+    ///
+    /// 1. The pipe's read half is closed and will no longer yield data.
+    /// 2. The specified buffer was 0 bytes in length.
+    ///
+    /// If the pipe is not ready to read data,
     /// `Err(io::ErrorKind::WouldBlock)` is returned.
     ///
     /// # Examples
@@ -1955,6 +1963,106 @@ impl ServerOptions {
         self
     }
 
+    /// Requests permission to modify the pipe's discretionary access control list.
+    ///
+    /// This corresponds to setting [`WRITE_DAC`] in dwOpenMode.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::{io, os::windows::prelude::AsRawHandle, ptr};
+    //
+    /// use tokio::net::windows::named_pipe::ServerOptions;
+    /// use winapi::{
+    ///     shared::winerror::ERROR_SUCCESS,
+    ///     um::{accctrl::SE_KERNEL_OBJECT, aclapi::SetSecurityInfo, winnt::DACL_SECURITY_INFORMATION},
+    /// };
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\write_dac_pipe";
+    ///
+    /// # #[tokio::main] async fn main() -> io::Result<()> {
+    /// let mut pipe_template = ServerOptions::new();
+    /// pipe_template.write_dac(true);
+    /// let pipe = pipe_template.create(PIPE_NAME)?;
+    ///
+    /// unsafe {
+    ///     assert_eq!(
+    ///         ERROR_SUCCESS,
+    ///         SetSecurityInfo(
+    ///             pipe.as_raw_handle(),
+    ///             SE_KERNEL_OBJECT,
+    ///             DACL_SECURITY_INFORMATION,
+    ///             ptr::null_mut(),
+    ///             ptr::null_mut(),
+    ///             ptr::null_mut(),
+    ///             ptr::null_mut(),
+    ///         )
+    ///     );
+    /// }
+    ///
+    /// # Ok(()) }
+    /// ```
+    ///
+    /// ```
+    /// use std::{io, os::windows::prelude::AsRawHandle, ptr};
+    //
+    /// use tokio::net::windows::named_pipe::ServerOptions;
+    /// use winapi::{
+    ///     shared::winerror::ERROR_ACCESS_DENIED,
+    ///     um::{accctrl::SE_KERNEL_OBJECT, aclapi::SetSecurityInfo, winnt::DACL_SECURITY_INFORMATION},
+    /// };
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\write_dac_pipe_fail";
+    ///
+    /// # #[tokio::main] async fn main() -> io::Result<()> {
+    /// let mut pipe_template = ServerOptions::new();
+    /// pipe_template.write_dac(false);
+    /// let pipe = pipe_template.create(PIPE_NAME)?;
+    ///
+    /// unsafe {
+    ///     assert_eq!(
+    ///         ERROR_ACCESS_DENIED,
+    ///         SetSecurityInfo(
+    ///             pipe.as_raw_handle(),
+    ///             SE_KERNEL_OBJECT,
+    ///             DACL_SECURITY_INFORMATION,
+    ///             ptr::null_mut(),
+    ///             ptr::null_mut(),
+    ///             ptr::null_mut(),
+    ///             ptr::null_mut(),
+    ///         )
+    ///     );
+    /// }
+    ///
+    /// # Ok(()) }
+    /// ```
+    ///
+    /// [`WRITE_DAC`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
+    pub fn write_dac(&mut self, requested: bool) -> &mut Self {
+        bool_flag!(self.open_mode, requested, winnt::WRITE_DAC);
+        self
+    }
+
+    /// Requests permission to modify the pipe's owner.
+    ///
+    /// This corresponds to setting [`WRITE_OWNER`] in dwOpenMode.
+    ///
+    /// [`WRITE_OWNER`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
+    pub fn write_owner(&mut self, requested: bool) -> &mut Self {
+        bool_flag!(self.open_mode, requested, winnt::WRITE_OWNER);
+        self
+    }
+
+    /// Requests permission to modify the pipe's system access control list.
+    ///
+    /// This corresponds to setting [`ACCESS_SYSTEM_SECURITY`] in dwOpenMode.
+    ///
+    /// [`ACCESS_SYSTEM_SECURITY`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
+    pub fn access_system_security(&mut self, requested: bool) -> &mut Self {
+        bool_flag!(self.open_mode, requested, winnt::ACCESS_SYSTEM_SECURITY);
+        self
+    }
+
     /// Indicates whether this server can accept remote clients or not. Remote
     /// clients are disabled by default.
     ///
@@ -2020,6 +2128,7 @@ impl ServerOptions {
     /// let builder = ServerOptions::new().max_instances(255);
     /// # Ok(()) }
     /// ```
+    #[track_caller]
     pub fn max_instances(&mut self, instances: usize) -> &mut Self {
         assert!(instances < 255, "cannot specify more than 254 instances");
         self.max_instances = instances as DWORD;

tokio/src/park/either.rs

@@ -1,74 +0,0 @@
-#![cfg_attr(not(feature = "full"), allow(dead_code))]
-
-use crate::park::{Park, Unpark};
-
-use std::fmt;
-use std::time::Duration;
-
-pub(crate) enum Either<A, B> {
-    A(A),
-    B(B),
-}
-
-impl<A, B> Park for Either<A, B>
-where
-    A: Park,
-    B: Park,
-{
-    type Unpark = Either<A::Unpark, B::Unpark>;
-    type Error = Either<A::Error, B::Error>;
-
-    fn unpark(&self) -> Self::Unpark {
-        match self {
-            Either::A(a) => Either::A(a.unpark()),
-            Either::B(b) => Either::B(b.unpark()),
-        }
-    }
-
-    fn park(&mut self) -> Result<(), Self::Error> {
-        match self {
-            Either::A(a) => a.park().map_err(Either::A),
-            Either::B(b) => b.park().map_err(Either::B),
-        }
-    }
-
-    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
-        match self {
-            Either::A(a) => a.park_timeout(duration).map_err(Either::A),
-            Either::B(b) => b.park_timeout(duration).map_err(Either::B),
-        }
-    }
-
-    fn shutdown(&mut self) {
-        match self {
-            Either::A(a) => a.shutdown(),
-            Either::B(b) => b.shutdown(),
-        }
-    }
-}
-
-impl<A, B> Unpark for Either<A, B>
-where
-    A: Unpark,
-    B: Unpark,
-{
-    fn unpark(&self) {
-        match self {
-            Either::A(a) => a.unpark(),
-            Either::B(b) => b.unpark(),
-        }
-    }
-}
-
-impl<A, B> fmt::Debug for Either<A, B>
-where
-    A: fmt::Debug,
-    B: fmt::Debug,
-{
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Either::A(a) => a.fmt(fmt),
-            Either::B(b) => b.fmt(fmt),
-        }
-    }
-}

tokio/src/park/mod.rs

@@ -34,84 +34,4 @@
 //! * `park_timeout` does the same as `park` but allows specifying a maximum
 //!   time to block the thread for.
 
-cfg_rt! {
-    pub(crate) mod either;
-}
-
-#[cfg(any(feature = "rt", feature = "sync"))]
 pub(crate) mod thread;
-
-use std::fmt::Debug;
-use std::sync::Arc;
-use std::time::Duration;
-
-/// Blocks the current thread.
-pub(crate) trait Park {
-    /// Unpark handle type for the `Park` implementation.
-    type Unpark: Unpark;
-
-    /// Error returned by `park`.
-    type Error: Debug;
-
-    /// Gets a new `Unpark` handle associated with this `Park` instance.
-    fn unpark(&self) -> Self::Unpark;
-
-    /// Blocks the current thread unless or until the token is available.
-    ///
-    /// A call to `park` does not guarantee that the thread will remain blocked
-    /// forever, and callers should be prepared for this possibility. This
-    /// function may wakeup spuriously for any reason.
-    ///
-    /// # Panics
-    ///
-    /// This function **should** not panic, but ultimately, panics are left as
-    /// an implementation detail. Refer to the documentation for the specific
-    /// `Park` implementation.
-    fn park(&mut self) -> Result<(), Self::Error>;
-
-    /// Parks the current thread for at most `duration`.
-    ///
-    /// This function is the same as `park` but allows specifying a maximum time
-    /// to block the thread for.
-    ///
-    /// Same as `park`, there is no guarantee that the thread will remain
-    /// blocked for any amount of time. Spurious wakeups are permitted for any
-    /// reason.
-    ///
-    /// # Panics
-    ///
-    /// This function **should** not panic, but ultimately, panics are left as
-    /// an implementation detail. Refer to the documentation for the specific
-    /// `Park` implementation.
-    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error>;
-
-    /// Releases all resources held by the parker for proper leak-free shutdown.
-    fn shutdown(&mut self);
-}
-
-/// Unblock a thread blocked by the associated `Park` instance.
-pub(crate) trait Unpark: Sync + Send + 'static {
-    /// Unblocks a thread that is blocked by the associated `Park` handle.
-    ///
-    /// Calling `unpark` atomically makes available the unpark token, if it is
-    /// not already available.
-    ///
-    /// # Panics
-    ///
-    /// This function **should** not panic, but ultimately, panics are left as
-    /// an implementation detail. Refer to the documentation for the specific
-    /// `Unpark` implementation.
-    fn unpark(&self);
-}
-
-impl Unpark for Box<dyn Unpark> {
-    fn unpark(&self) {
-        (**self).unpark()
-    }
-}
-
-impl Unpark for Arc<dyn Unpark> {
-    fn unpark(&self) {
-        (**self).unpark()
-    }
-}

tokio/src/park/thread.rs

@@ -2,7 +2,6 @@
 
 use crate::loom::sync::atomic::AtomicUsize;
 use crate::loom::sync::{Arc, Condvar, Mutex};
-use crate::park::{Park, Unpark};
 
 use std::sync::atomic::Ordering::SeqCst;
 use std::time::Duration;
@@ -12,8 +11,6 @@ pub(crate) struct ParkThread {
     inner: Arc<Inner>,
 }
 
-pub(crate) type ParkError = ();
-
 /// Unblocks a thread that was blocked by `ParkThread`.
 #[derive(Clone, Debug)]
 pub(crate) struct UnparkThread {
@@ -47,28 +44,25 @@ impl ParkThread {
             }),
         }
     }
-}
 
-impl Park for ParkThread {
-    type Unpark = UnparkThread;
-    type Error = ParkError;
-
-    fn unpark(&self) -> Self::Unpark {
+    pub(crate) fn unpark(&self) -> UnparkThread {
         let inner = self.inner.clone();
         UnparkThread { inner }
     }
 
-    fn park(&mut self) -> Result<(), Self::Error> {
+    pub(crate) fn park(&mut self) {
         self.inner.park();
-        Ok(())
     }
 
-    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+    pub(crate) fn park_timeout(&mut self, duration: Duration) {
+        // Wasm doesn't have threads, so just sleep.
+        #[cfg(not(tokio_wasm))]
         self.inner.park_timeout(duration);
-        Ok(())
+        #[cfg(tokio_wasm)]
+        std::thread::sleep(duration);
     }
 
-    fn shutdown(&mut self) {
+    pub(crate) fn shutdown(&mut self) {
         self.inner.shutdown();
     }
 }
@@ -208,12 +202,13 @@ impl Default for ParkThread {
 
 // ===== impl UnparkThread =====
 
-impl Unpark for UnparkThread {
-    fn unpark(&self) {
+impl UnparkThread {
+    pub(crate) fn unpark(&self) {
         self.inner.unpark();
     }
 }
 
+use crate::loom::thread::AccessError;
 use std::future::Future;
 use std::marker::PhantomData;
 use std::mem;
@@ -237,24 +232,38 @@ impl CachedParkThread {
         }
     }
 
-    pub(crate) fn get_unpark(&self) -> Result<UnparkThread, ParkError> {
+    pub(crate) fn waker(&self) -> Result<Waker, AccessError> {
+        self.unpark().map(|unpark| unpark.into_waker())
+    }
+
+    fn unpark(&self) -> Result<UnparkThread, AccessError> {
         self.with_current(|park_thread| park_thread.unpark())
     }
 
+    pub(crate) fn park(&mut self) {
+        self.with_current(|park_thread| park_thread.inner.park())
+            .unwrap();
+    }
+
+    pub(crate) fn park_timeout(&mut self, duration: Duration) {
+        self.with_current(|park_thread| park_thread.inner.park_timeout(duration))
+            .unwrap();
+    }
+
     /// Gets a reference to the `ParkThread` handle for this thread.
-    fn with_current<F, R>(&self, f: F) -> Result<R, ParkError>
+    fn with_current<F, R>(&self, f: F) -> Result<R, AccessError>
     where
         F: FnOnce(&ParkThread) -> R,
     {
-        CURRENT_PARKER.try_with(|inner| f(inner)).map_err(|_| ())
+        CURRENT_PARKER.try_with(|inner| f(inner))
     }
 
-    pub(crate) fn block_on<F: Future>(&mut self, f: F) -> Result<F::Output, ParkError> {
+    pub(crate) fn block_on<F: Future>(&mut self, f: F) -> Result<F::Output, AccessError> {
         use std::task::Context;
         use std::task::Poll::Ready;
 
         // `get_unpark()` should not return a Result
-        let waker = self.get_unpark()?.into_waker();
+        let waker = self.waker()?;
         let mut cx = Context::from_waker(&waker);
 
         pin!(f);
@@ -264,34 +273,11 @@ impl CachedParkThread {
                 return Ok(v);
             }
 
-            self.park()?;
+            self.park();
         }
     }
 }
 
-impl Park for CachedParkThread {
-    type Unpark = UnparkThread;
-    type Error = ParkError;
-
-    fn unpark(&self) -> Self::Unpark {
-        self.get_unpark().unwrap()
-    }
-
-    fn park(&mut self) -> Result<(), Self::Error> {
-        self.with_current(|park_thread| park_thread.inner.park())?;
-        Ok(())
-    }
-
-    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
-        self.with_current(|park_thread| park_thread.inner.park_timeout(duration))?;
-        Ok(())
-    }
-
-    fn shutdown(&mut self) {
-        let _ = self.with_current(|park_thread| park_thread.inner.shutdown());
-    }
-}
-
 impl UnparkThread {
     pub(crate) fn into_waker(self) -> Waker {
         unsafe {

tokio/src/process/mod.rs

@@ -1285,41 +1285,39 @@ impl ChildStderr {
 
 impl AsyncWrite for ChildStdin {
     fn poll_write(
-        self: Pin<&mut Self>,
+        mut self: Pin<&mut Self>,
         cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<io::Result<usize>> {
-        self.inner.poll_write(cx, buf)
+        Pin::new(&mut self.inner).poll_write(cx, buf)
     }
 
-    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        Poll::Ready(Ok(()))
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.inner).poll_flush(cx)
     }
 
-    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        Poll::Ready(Ok(()))
+    fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.inner).poll_shutdown(cx)
     }
 }
 
 impl AsyncRead for ChildStdout {
     fn poll_read(
-        self: Pin<&mut Self>,
+        mut self: Pin<&mut Self>,
         cx: &mut Context<'_>,
         buf: &mut ReadBuf<'_>,
     ) -> Poll<io::Result<()>> {
-        // Safety: pipes support reading into uninitialized memory
-        unsafe { self.inner.poll_read(cx, buf) }
+        Pin::new(&mut self.inner).poll_read(cx, buf)
     }
 }
 
 impl AsyncRead for ChildStderr {
     fn poll_read(
-        self: Pin<&mut Self>,
+        mut self: Pin<&mut Self>,
         cx: &mut Context<'_>,
         buf: &mut ReadBuf<'_>,
     ) -> Poll<io::Result<()>> {
-        // Safety: pipes support reading into uninitialized memory
-        unsafe { self.inner.poll_read(cx, buf) }
+        Pin::new(&mut self.inner).poll_read(cx, buf)
     }
 }
 

tokio/src/process/unix/driver.rs

@@ -2,11 +2,9 @@
 
 //! Process driver.
 
-use crate::park::Park;
 use crate::process::unix::GlobalOrphanQueue;
 use crate::signal::unix::driver::{Driver as SignalDriver, Handle as SignalHandle};
 
-use std::io;
 use std::time::Duration;
 
 /// Responsible for cleaning up orphaned child processes on Unix platforms.
@@ -28,31 +26,18 @@ impl Driver {
             signal_handle,
         }
     }
-}
 
-// ===== impl Park for Driver =====
-
-impl Park for Driver {
-    type Unpark = <SignalDriver as Park>::Unpark;
-    type Error = io::Error;
-
-    fn unpark(&self) -> Self::Unpark {
-        self.park.unpark()
-    }
-
-    fn park(&mut self) -> Result<(), Self::Error> {
-        self.park.park()?;
+    pub(crate) fn park(&mut self) {
+        self.park.park();
         GlobalOrphanQueue::reap_orphans(&self.signal_handle);
-        Ok(())
     }
 
-    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
-        self.park.park_timeout(duration)?;
+    pub(crate) fn park_timeout(&mut self, duration: Duration) {
+        self.park.park_timeout(duration);
         GlobalOrphanQueue::reap_orphans(&self.signal_handle);
-        Ok(())
     }
 
-    fn shutdown(&mut self) {
+    pub(crate) fn shutdown(&mut self) {
         self.park.shutdown()
     }
 }

tokio/src/process/unix/mod.rs

@@ -29,7 +29,7 @@ use orphan::{OrphanQueue, OrphanQueueImpl, Wait};
 mod reap;
 use reap::Reaper;
 
-use crate::io::PollEvented;
+use crate::io::{AsyncRead, AsyncWrite, PollEvented, ReadBuf};
 use crate::process::kill::Kill;
 use crate::process::SpawnedChild;
 use crate::signal::unix::driver::Handle as SignalHandle;
@@ -177,8 +177,8 @@ impl AsRawFd for Pipe {
     }
 }
 
-pub(crate) fn convert_to_stdio(io: PollEvented<Pipe>) -> io::Result<Stdio> {
-    let mut fd = io.into_inner()?.fd;
+pub(crate) fn convert_to_stdio(io: ChildStdio) -> io::Result<Stdio> {
+    let mut fd = io.inner.into_inner()?.fd;
 
     // Ensure that the fd to be inherited is set to *blocking* mode, as this
     // is the default that virtually all programs expect to have. Those
@@ -213,7 +213,50 @@ impl Source for Pipe {
     }
 }
 
-pub(crate) type ChildStdio = PollEvented<Pipe>;
+pub(crate) struct ChildStdio {
+    inner: PollEvented<Pipe>,
+}
+
+impl fmt::Debug for ChildStdio {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.inner.fmt(fmt)
+    }
+}
+
+impl AsRawFd for ChildStdio {
+    fn as_raw_fd(&self) -> RawFd {
+        self.inner.as_raw_fd()
+    }
+}
+
+impl AsyncWrite for ChildStdio {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.inner.poll_write(cx, buf)
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl AsyncRead for ChildStdio {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        // Safety: pipes support reading into uninitialized memory
+        unsafe { self.inner.poll_read(cx, buf) }
+    }
+}
 
 fn set_nonblocking<T: AsRawFd>(fd: &mut T, nonblocking: bool) -> io::Result<()> {
     unsafe {
@@ -238,7 +281,7 @@ fn set_nonblocking<T: AsRawFd>(fd: &mut T, nonblocking: bool) -> io::Result<()>
     Ok(())
 }
 
-pub(super) fn stdio<T>(io: T) -> io::Result<PollEvented<Pipe>>
+pub(super) fn stdio<T>(io: T) -> io::Result<ChildStdio>
 where
     T: IntoRawFd,
 {
@@ -246,5 +289,5 @@ where
     let mut pipe = Pipe::from(io);
     set_nonblocking(&mut pipe, true)?;
 
-    PollEvented::new(pipe)
+    PollEvented::new(pipe).map(|inner| ChildStdio { inner })
 }

tokio/src/process/unix/orphan.rs

@@ -120,7 +120,7 @@ where
 #[cfg(all(test, not(loom)))]
 pub(crate) mod test {
     use super::*;
-    use crate::io::driver::Driver as IoDriver;
+    use crate::runtime::io::Driver as IoDriver;
     use crate::signal::unix::driver::{Driver as SignalDriver, Handle as SignalHandle};
     use crate::sync::watch;
     use std::cell::{Cell, RefCell};

tokio/src/process/windows.rs

@@ -15,22 +15,22 @@
 //! `RegisterWaitForSingleObject` and then wait on the other end of the oneshot
 //! from then on out.
 
-use crate::io::PollEvented;
+use crate::io::{blocking::Blocking, AsyncRead, AsyncWrite, ReadBuf};
 use crate::process::kill::Kill;
 use crate::process::SpawnedChild;
 use crate::sync::oneshot;
 
-use mio::windows::NamedPipe;
 use std::fmt;
+use std::fs::File as StdFile;
 use std::future::Future;
 use std::io;
-use std::os::windows::prelude::{AsRawHandle, FromRawHandle, IntoRawHandle, RawHandle};
+use std::os::windows::prelude::{AsRawHandle, IntoRawHandle, RawHandle};
 use std::pin::Pin;
 use std::process::Stdio;
 use std::process::{Child as StdChild, Command as StdCommand, ExitStatus};
 use std::ptr;
-use std::task::Context;
-use std::task::Poll;
+use std::sync::Arc;
+use std::task::{Context, Poll};
 use winapi::shared::minwindef::{DWORD, FALSE};
 use winapi::um::handleapi::{DuplicateHandle, INVALID_HANDLE_VALUE};
 use winapi::um::processthreadsapi::GetCurrentProcess;
@@ -167,28 +167,97 @@ unsafe extern "system" fn callback(ptr: PVOID, _timer_fired: BOOLEAN) {
     let _ = complete.take().unwrap().send(());
 }
 
-pub(crate) type ChildStdio = PollEvented<NamedPipe>;
+#[derive(Debug)]
+struct ArcFile(Arc<StdFile>);
 
-pub(super) fn stdio<T>(io: T) -> io::Result<PollEvented<NamedPipe>>
+impl io::Read for ArcFile {
+    fn read(&mut self, bytes: &mut [u8]) -> io::Result<usize> {
+        (&*self.0).read(bytes)
+    }
+}
+
+impl io::Write for ArcFile {
+    fn write(&mut self, bytes: &[u8]) -> io::Result<usize> {
+        (&*self.0).write(bytes)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        (&*self.0).flush()
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct ChildStdio {
+    // Used for accessing the raw handle, even if the io version is busy
+    raw: Arc<StdFile>,
+    // For doing I/O operations asynchronously
+    io: Blocking<ArcFile>,
+}
+
+impl AsRawHandle for ChildStdio {
+    fn as_raw_handle(&self) -> RawHandle {
+        self.raw.as_raw_handle()
+    }
+}
+
+impl AsyncRead for ChildStdio {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.io).poll_read(cx, buf)
+    }
+}
+
+impl AsyncWrite for ChildStdio {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Pin::new(&mut self.io).poll_write(cx, buf)
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.io).poll_flush(cx)
+    }
+
+    fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.io).poll_shutdown(cx)
+    }
+}
+
+pub(super) fn stdio<T>(io: T) -> io::Result<ChildStdio>
 where
     T: IntoRawHandle,
 {
-    let pipe = unsafe { NamedPipe::from_raw_handle(io.into_raw_handle()) };
-    PollEvented::new(pipe)
+    use std::os::windows::prelude::FromRawHandle;
+
+    let raw = Arc::new(unsafe { StdFile::from_raw_handle(io.into_raw_handle()) });
+    let io = Blocking::new(ArcFile(raw.clone()));
+    Ok(ChildStdio { raw, io })
 }
 
-pub(crate) fn convert_to_stdio(io: PollEvented<NamedPipe>) -> io::Result<Stdio> {
-    let named_pipe = io.into_inner()?;
+pub(crate) fn convert_to_stdio(child_stdio: ChildStdio) -> io::Result<Stdio> {
+    let ChildStdio { raw, io } = child_stdio;
+    drop(io); // Try to drop the Arc count here
+
+    Arc::try_unwrap(raw)
+        .or_else(|raw| duplicate_handle(&*raw))
+        .map(Stdio::from)
+}
+
+fn duplicate_handle<T: AsRawHandle>(io: &T) -> io::Result<StdFile> {
+    use std::os::windows::prelude::FromRawHandle;
 
-    // Mio does not implement `IntoRawHandle` for `NamedPipe`, so we'll manually
-    // duplicate the handle here...
     unsafe {
         let mut dup_handle = INVALID_HANDLE_VALUE;
         let cur_proc = GetCurrentProcess();
 
         let status = DuplicateHandle(
             cur_proc,
-            named_pipe.as_raw_handle(),
+            io.as_raw_handle(),
             cur_proc,
             &mut dup_handle,
             0 as DWORD,
@@ -200,6 +269,6 @@ pub(crate) fn convert_to_stdio(io: PollEvented<NamedPipe>) -> io::Result<Stdio>
             return Err(io::Error::last_os_error());
         }
 
-        Ok(Stdio::from_raw_handle(dup_handle))
+        Ok(StdFile::from_raw_handle(dup_handle))
     }
 }

tokio/src/runtime/blocking/mod.rs

@@ -4,15 +4,20 @@
 //! compilation.
 
 mod pool;
-pub(crate) use pool::{spawn_blocking, BlockingPool, Mandatory, Spawner, Task};
+pub(crate) use pool::{spawn_blocking, BlockingPool, Spawner};
 
 cfg_fs! {
     pub(crate) use pool::spawn_mandatory_blocking;
 }
 
+cfg_trace! {
+    pub(crate) use pool::Mandatory;
+}
+
 mod schedule;
 mod shutdown;
 mod task;
+#[cfg(all(test, not(tokio_wasm)))]
 pub(crate) use schedule::NoopSchedule;
 pub(crate) use task::BlockingTask;
 

tokio/src/runtime/blocking/pool.rs

@@ -3,14 +3,16 @@
 use crate::loom::sync::{Arc, Condvar, Mutex};
 use crate::loom::thread;
 use crate::runtime::blocking::schedule::NoopSchedule;
-use crate::runtime::blocking::shutdown;
+use crate::runtime::blocking::{shutdown, BlockingTask};
 use crate::runtime::builder::ThreadNameFn;
 use crate::runtime::context;
 use crate::runtime::task::{self, JoinHandle};
-use crate::runtime::{Builder, Callback, ToHandle};
+use crate::runtime::{Builder, Callback, Handle};
+use crate::util::{replace_thread_rng, RngSeedGenerator};
 
 use std::collections::{HashMap, VecDeque};
 use std::fmt;
+use std::io;
 use std::time::Duration;
 
 pub(crate) struct BlockingPool {
@@ -47,6 +49,9 @@ struct Inner {
 
     // Customizable wait timeout.
     keep_alive: Duration,
+
+    // Random number seed
+    seed_generator: RngSeedGenerator,
 }
 
 struct Shared {
@@ -82,6 +87,25 @@ pub(crate) enum Mandatory {
     NonMandatory,
 }
 
+pub(crate) enum SpawnError {
+    /// Pool is shutting down and the task was not scheduled
+    ShuttingDown,
+    /// There are no worker threads available to take the task
+    /// and the OS failed to spawn a new one
+    NoThreads(io::Error),
+}
+
+impl From<SpawnError> for io::Error {
+    fn from(e: SpawnError) -> Self {
+        match e {
+            SpawnError::ShuttingDown => {
+                io::Error::new(io::ErrorKind::Other, "blocking pool shutting down")
+            }
+            SpawnError::NoThreads(e) => e,
+        }
+    }
+}
+
 impl Task {
     pub(crate) fn new(task: task::UnownedTask<NoopSchedule>, mandatory: Mandatory) -> Task {
         Task { task, mandatory }
@@ -105,6 +129,7 @@ const KEEP_ALIVE: Duration = Duration::from_secs(10);
 /// Tasks will be scheduled as non-mandatory, meaning they may not get executed
 /// in case of runtime shutdown.
 #[track_caller]
+#[cfg_attr(tokio_wasi, allow(dead_code))]
 pub(crate) fn spawn_blocking<F, R>(func: F) -> JoinHandle<R>
 where
     F: FnOnce() -> R + Send + 'static,
@@ -129,7 +154,7 @@ cfg_fs! {
         R: Send + 'static,
     {
         let rt = context::current();
-        rt.as_inner().spawn_mandatory_blocking(&rt, func)
+        rt.inner.blocking_spawner().spawn_mandatory_blocking(&rt, func)
     }
 }
 
@@ -161,6 +186,7 @@ impl BlockingPool {
                     before_stop: builder.before_stop.clone(),
                     thread_cap,
                     keep_alive,
+                    seed_generator: builder.seed_generator.next_generator(),
                 }),
             },
             shutdown_rx,
@@ -220,7 +246,103 @@ impl fmt::Debug for BlockingPool {
 // ===== impl Spawner =====
 
 impl Spawner {
-    pub(crate) fn spawn(&self, task: Task, rt: &dyn ToHandle) -> Result<(), ()> {
+    #[track_caller]
+    pub(crate) fn spawn_blocking<F, R>(&self, rt: &Handle, func: F) -> JoinHandle<R>
+    where
+        F: FnOnce() -> R + Send + 'static,
+        R: Send + 'static,
+    {
+        let (join_handle, spawn_result) =
+            if cfg!(debug_assertions) && std::mem::size_of::<F>() > 2048 {
+                self.spawn_blocking_inner(Box::new(func), Mandatory::NonMandatory, None, rt)
+            } else {
+                self.spawn_blocking_inner(func, Mandatory::NonMandatory, None, rt)
+            };
+
+        match spawn_result {
+            Ok(()) => join_handle,
+            // Compat: do not panic here, return the join_handle even though it will never resolve
+            Err(SpawnError::ShuttingDown) => join_handle,
+            Err(SpawnError::NoThreads(e)) => {
+                panic!("OS can't spawn worker thread: {}", e)
+            }
+        }
+    }
+
+    cfg_fs! {
+        #[track_caller]
+        #[cfg_attr(any(
+            all(loom, not(test)), // the function is covered by loom tests
+            test
+        ), allow(dead_code))]
+        pub(crate) fn spawn_mandatory_blocking<F, R>(&self, rt: &Handle, func: F) -> Option<JoinHandle<R>>
+        where
+            F: FnOnce() -> R + Send + 'static,
+            R: Send + 'static,
+        {
+            let (join_handle, spawn_result) = if cfg!(debug_assertions) && std::mem::size_of::<F>() > 2048 {
+                self.spawn_blocking_inner(
+                    Box::new(func),
+                    Mandatory::Mandatory,
+                    None,
+                    rt,
+                )
+            } else {
+                self.spawn_blocking_inner(
+                    func,
+                    Mandatory::Mandatory,
+                    None,
+                    rt,
+                )
+            };
+
+            if spawn_result.is_ok() {
+                Some(join_handle)
+            } else {
+                None
+            }
+        }
+    }
+
+    #[track_caller]
+    pub(crate) fn spawn_blocking_inner<F, R>(
+        &self,
+        func: F,
+        is_mandatory: Mandatory,
+        name: Option<&str>,
+        rt: &Handle,
+    ) -> (JoinHandle<R>, Result<(), SpawnError>)
+    where
+        F: FnOnce() -> R + Send + 'static,
+        R: Send + 'static,
+    {
+        let fut = BlockingTask::new(func);
+        let id = task::Id::next();
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let fut = {
+            use tracing::Instrument;
+            let location = std::panic::Location::caller();
+            let span = tracing::trace_span!(
+                target: "tokio::task::blocking",
+                "runtime.spawn",
+                kind = %"blocking",
+                task.name = %name.unwrap_or_default(),
+                task.id = id.as_u64(),
+                "fn" = %std::any::type_name::<F>(),
+                spawn.location = %format_args!("{}:{}:{}", location.file(), location.line(), location.column()),
+            );
+            fut.instrument(span)
+        };
+
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let _ = name;
+
+        let (task, handle) = task::unowned(fut, NoopSchedule, id);
+        let spawned = self.spawn_task(Task::new(task, is_mandatory), rt);
+        (handle, spawned)
+    }
+
+    fn spawn_task(&self, task: Task, rt: &Handle) -> Result<(), SpawnError> {
         let mut shared = self.inner.shared.lock();
 
         if shared.shutdown {
@@ -230,7 +352,7 @@ impl Spawner {
             task.task.shutdown();
 
             // no need to even push this task; it would never get picked up
-            return Err(());
+            return Err(SpawnError::ShuttingDown);
         }
 
         shared.queue.push_back(task);
@@ -261,7 +383,7 @@ impl Spawner {
                         Err(e) => {
                             // The OS refused to spawn the thread and there is no thread
                             // to pick up the task that has just been pushed to the queue.
-                            panic!("OS can't spawn worker thread: {}", e)
+                            return Err(SpawnError::NoThreads(e));
                         }
                     }
                 }
@@ -283,7 +405,7 @@ impl Spawner {
     fn spawn_thread(
         &self,
         shutdown_tx: shutdown::Sender,
-        rt: &dyn ToHandle,
+        rt: &Handle,
         id: usize,
     ) -> std::io::Result<thread::JoinHandle<()>> {
         let mut builder = thread::Builder::new().name((self.inner.thread_name)());
@@ -292,12 +414,12 @@ impl Spawner {
             builder = builder.stack_size(stack_size);
         }
 
-        let rt = rt.to_handle();
+        let rt = rt.clone();
 
         builder.spawn(move || {
             // Only the reference should be moved into the closure
             let _enter = crate::runtime::context::enter(rt.clone());
-            rt.as_inner().blocking_spawner.inner.run(id);
+            rt.inner.blocking_spawner().inner.run(id);
             drop(shutdown_tx);
         })
     }
@@ -314,6 +436,8 @@ impl Inner {
         if let Some(f) = &self.after_start {
             f()
         }
+        // We own this thread so there is no need to replace the RngSeed once we're done.
+        let _ = replace_thread_rng(self.seed_generator.next_seed());
 
         let mut shared = self.shared.lock();
         let mut join_on_thread = None;

tokio/src/runtime/builder.rs

@@ -1,5 +1,6 @@
 use crate::runtime::handle::Handle;
-use crate::runtime::{blocking, driver, Callback, Runtime, Spawner};
+use crate::runtime::{blocking, driver, Callback, Runtime};
+use crate::util::{RngSeed, RngSeedGenerator};
 
 use std::fmt;
 use std::io;
@@ -85,6 +86,14 @@ pub struct Builder {
     /// How many ticks before yielding to the driver for timer and I/O events?
     pub(super) event_interval: u32,
 
+    /// When true, the multi-threade scheduler LIFO slot should not be used.
+    ///
+    /// This option should only be exposed as unstable.
+    pub(super) disable_lifo_slot: bool,
+
+    /// Specify a random number generator seed to provide deterministic results
+    pub(super) seed_generator: RngSeedGenerator,
+
     #[cfg(tokio_unstable)]
     pub(super) unhandled_panic: UnhandledPanic,
 }
@@ -174,7 +183,7 @@ pub(crate) type ThreadNameFn = std::sync::Arc<dyn Fn() -> String + Send + Sync +
 
 pub(crate) enum Kind {
     CurrentThread,
-    #[cfg(feature = "rt-multi-thread")]
+    #[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
     MultiThread,
 }
 
@@ -197,14 +206,16 @@ impl Builder {
         Builder::new(Kind::CurrentThread, 31, EVENT_INTERVAL)
     }
 
-    /// Returns a new builder with the multi thread scheduler selected.
-    ///
-    /// Configuration methods can be chained on the return value.
-    #[cfg(feature = "rt-multi-thread")]
-    #[cfg_attr(docsrs, doc(cfg(feature = "rt-multi-thread")))]
-    pub fn new_multi_thread() -> Builder {
-        // The number `61` is fairly arbitrary. I believe this value was copied from golang.
-        Builder::new(Kind::MultiThread, 61, 61)
+    cfg_not_wasi! {
+        /// Returns a new builder with the multi thread scheduler selected.
+        ///
+        /// Configuration methods can be chained on the return value.
+        #[cfg(feature = "rt-multi-thread")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "rt-multi-thread")))]
+        pub fn new_multi_thread() -> Builder {
+            // The number `61` is fairly arbitrary. I believe this value was copied from golang.
+            Builder::new(Kind::MultiThread, 61, 61)
+        }
     }
 
     /// Returns a new runtime builder initialized with default configuration
@@ -248,8 +259,12 @@ impl Builder {
             global_queue_interval,
             event_interval,
 
+            seed_generator: RngSeedGenerator::new(RngSeed::new()),
+
             #[cfg(tokio_unstable)]
             unhandled_panic: UnhandledPanic::Ignore,
+
+            disable_lifo_slot: false,
         }
     }
 
@@ -270,7 +285,11 @@ impl Builder {
     ///     .unwrap();
     /// ```
     pub fn enable_all(&mut self) -> &mut Self {
-        #[cfg(any(feature = "net", feature = "process", all(unix, feature = "signal")))]
+        #[cfg(any(
+            feature = "net",
+            all(unix, feature = "process"),
+            all(unix, feature = "signal")
+        ))]
         self.enable_io();
         #[cfg(feature = "time")]
         self.enable_time();
@@ -287,11 +306,7 @@ impl Builder {
     ///
     /// The default value is the number of cores available to the system.
     ///
-    /// # Panics
-    ///
-    /// When using the `current_thread` runtime this method will panic, since
-    /// those variants do not allow setting worker thread counts.
-    ///
+    /// When using the `current_thread` runtime this method has no effect.
     ///
     /// # Examples
     ///
@@ -616,8 +631,8 @@ impl Builder {
     /// ```
     pub fn build(&mut self) -> io::Result<Runtime> {
         match &self.kind {
-            Kind::CurrentThread => self.build_basic_runtime(),
-            #[cfg(feature = "rt-multi-thread")]
+            Kind::CurrentThread => self.build_current_thread_runtime(),
+            #[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
             Kind::MultiThread => self.build_threaded_runtime(),
         }
     }
@@ -626,7 +641,7 @@ impl Builder {
         driver::Cfg {
             enable_pause_time: match self.kind {
                 Kind::CurrentThread => true,
-                #[cfg(feature = "rt-multi-thread")]
+                #[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
                 Kind::MultiThread => false,
             },
             enable_io: self.enable_io,
@@ -736,7 +751,7 @@ impl Builder {
         /// * `UnhandledPanic::ShutdownRuntime` will force the runtime to
         ///   shutdown immediately when a spawned task panics even if that
         ///   task's `JoinHandle` has not been dropped. All other spawned tasks
-        ///   will immediatetly terminate and further calls to
+        ///   will immediately terminate and further calls to
         ///   [`Runtime::block_on`] will panic.
         ///
         /// # Unstable
@@ -779,33 +794,108 @@ impl Builder {
             self.unhandled_panic = behavior;
             self
         }
+
+        /// Disables the LIFO task scheduler heuristic.
+        ///
+        /// The multi-threaded scheduler includes a heuristic for optimizing
+        /// message-passing patterns. This heuristic results in the **last**
+        /// scheduled task being polled first.
+        ///
+        /// To implement this heuristic, each worker thread has a slot which
+        /// holds the task that should be polled next. However, this slot cannot
+        /// be stolen by other worker threads, which can result in lower total
+        /// throughput when tasks tend to have longer poll times.
+        ///
+        /// This configuration option will disable this heuristic resulting in
+        /// all scheduled tasks being pushed into the worker-local queue, which
+        /// is stealable.
+        ///
+        /// Consider trying this option when the task "scheduled" time is high
+        /// but the runtime is underutilized. Use tokio-rs/tokio-metrics to
+        /// collect this data.
+        ///
+        /// # Unstable
+        ///
+        /// This configuration option is considered a workaround for the LIFO
+        /// slot not being stealable. When the slot becomes stealable, we will
+        /// revisit whther or not this option is necessary. See
+        /// tokio-rs/tokio#4941.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::runtime;
+        ///
+        /// let rt = runtime::Builder::new_multi_thread()
+        ///     .disable_lifo_slot()
+        ///     .build()
+        ///     .unwrap();
+        /// ```
+        pub fn disable_lifo_slot(&mut self) -> &mut Self {
+            self.disable_lifo_slot = true;
+            self
+        }
+
+        /// Specifies the random number generation seed to use within all threads associated
+        /// with the runtime being built.
+        ///
+        /// This option is intended to make certain parts of the runtime deterministic.
+        /// Specifically, it affects the [`tokio::select!`] macro and the work stealing
+        /// algorithm. In the case of [`tokio::select!`] it will ensure that the order that
+        /// branches are polled is deterministic.
+        ///
+        /// In the case of work stealing, it's a little more complicated. Each worker will
+        /// be given a deterministic seed so that the starting peer for each work stealing
+        /// search will be deterministic.
+        ///
+        /// In addition to the code specifying `rng_seed` and interacting with the runtime,
+        /// the internals of Tokio and the Rust compiler may affect the sequences of random
+        /// numbers. In order to ensure repeatable results, the version of Tokio, the versions
+        /// of all other dependencies that interact with Tokio, and the Rust compiler version
+        /// should also all remain constant.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// # use tokio::runtime::{self, RngSeed};
+        /// # pub fn main() {
+        /// let seed = RngSeed::from_bytes(b"place your seed here");
+        /// let rt = runtime::Builder::new_current_thread()
+        ///     .rng_seed(seed)
+        ///     .build();
+        /// # }
+        /// ```
+        ///
+        /// [`tokio::select!`]: crate::select
+        pub fn rng_seed(&mut self, seed: RngSeed) -> &mut Self {
+            self.seed_generator = RngSeedGenerator::new(seed);
+            self
+        }
     }
 
-    fn build_basic_runtime(&mut self) -> io::Result<Runtime> {
-        use crate::runtime::basic_scheduler::Config;
-        use crate::runtime::{BasicScheduler, HandleInner, Kind};
+    fn build_current_thread_runtime(&mut self) -> io::Result<Runtime> {
+        use crate::runtime::scheduler::{self, CurrentThread};
+        use crate::runtime::{Config, Scheduler};
 
-        let (driver, resources) = driver::Driver::new(self.get_cfg())?;
+        let (driver, driver_handle) = driver::Driver::new(self.get_cfg())?;
 
         // Blocking pool
         let blocking_pool = blocking::create_blocking_pool(self, self.max_blocking_threads);
         let blocking_spawner = blocking_pool.spawner().clone();
 
-        let handle_inner = HandleInner {
-            io_handle: resources.io_handle,
-            time_handle: resources.time_handle,
-            signal_handle: resources.signal_handle,
-            clock: resources.clock,
-            blocking_spawner,
-        };
+        // Generate a rng seed for this runtime.
+        let seed_generator_1 = self.seed_generator.next_generator();
+        let seed_generator_2 = self.seed_generator.next_generator();
 
         // And now put a single-threaded scheduler on top of the timer. When
         // there are no futures ready to do something, it'll let the timer or
         // the reactor to generate some new stimuli for the futures to continue
         // in their life.
-        let scheduler = BasicScheduler::new(
+        let scheduler = CurrentThread::new(
             driver,
-            handle_inner,
+            driver_handle,
+            blocking_spawner,
+            seed_generator_2,
             Config {
                 before_park: self.before_park.clone(),
                 after_unpark: self.after_unpark.clone(),
@@ -813,13 +903,16 @@ impl Builder {
                 event_interval: self.event_interval,
                 #[cfg(tokio_unstable)]
                 unhandled_panic: self.unhandled_panic.clone(),
+                disable_lifo_slot: self.disable_lifo_slot,
+                seed_generator: seed_generator_1,
             },
         );
-        let spawner = Spawner::Basic(scheduler.spawner().clone());
+
+        let handle = scheduler::Handle::CurrentThread(scheduler.handle().clone());
 
         Ok(Runtime {
-            kind: Kind::CurrentThread(scheduler),
-            handle: Handle { spawner },
+            scheduler: Scheduler::CurrentThread(scheduler),
+            handle: Handle { inner: handle },
             blocking_pool,
         })
     }
@@ -901,45 +994,49 @@ cfg_rt_multi_thread! {
     impl Builder {
         fn build_threaded_runtime(&mut self) -> io::Result<Runtime> {
             use crate::loom::sys::num_cpus;
-            use crate::runtime::{HandleInner, Kind, ThreadPool};
+            use crate::runtime::{Config, Scheduler};
+            use crate::runtime::scheduler::{self, MultiThread};
 
             let core_threads = self.worker_threads.unwrap_or_else(num_cpus);
 
-            let (driver, resources) = driver::Driver::new(self.get_cfg())?;
+            let (driver, driver_handle) = driver::Driver::new(self.get_cfg())?;
 
             // Create the blocking pool
             let blocking_pool =
                 blocking::create_blocking_pool(self, self.max_blocking_threads + core_threads);
             let blocking_spawner = blocking_pool.spawner().clone();
 
-            let handle_inner = HandleInner {
-                io_handle: resources.io_handle,
-                time_handle: resources.time_handle,
-                signal_handle: resources.signal_handle,
-                clock: resources.clock,
-                blocking_spawner,
-            };
+            // Generate a rng seed for this runtime.
+            let seed_generator_1 = self.seed_generator.next_generator();
+            let seed_generator_2 = self.seed_generator.next_generator();
 
-            let (scheduler, launch) = ThreadPool::new(
+            let (scheduler, launch) = MultiThread::new(
                 core_threads,
                 driver,
-                handle_inner,
-                self.before_park.clone(),
-                self.after_unpark.clone(),
-                self.global_queue_interval,
-                self.event_interval,
+                driver_handle,
+                blocking_spawner,
+                seed_generator_2,
+                Config {
+                    before_park: self.before_park.clone(),
+                    after_unpark: self.after_unpark.clone(),
+                    global_queue_interval: self.global_queue_interval,
+                    event_interval: self.event_interval,
+                    #[cfg(tokio_unstable)]
+                    unhandled_panic: self.unhandled_panic.clone(),
+                    disable_lifo_slot: self.disable_lifo_slot,
+                    seed_generator: seed_generator_1,
+                },
             );
-            let spawner = Spawner::ThreadPool(scheduler.spawner().clone());
 
-            // Create the runtime handle
-            let handle = Handle { spawner };
+            let handle = scheduler::Handle::MultiThread(scheduler.handle().clone());
+            let handle = Handle { inner: handle };
 
             // Spawn the thread pool workers
             let _enter = crate::runtime::context::enter(handle.clone());
             launch.launch();
 
             Ok(Runtime {
-                kind: Kind::ThreadPool(scheduler),
+                scheduler: Scheduler::MultiThread(scheduler),
                 handle,
                 blocking_pool,
             })

tokio/src/runtime/config.rs

@@ -0,0 +1,34 @@
+#![cfg_attr(any(not(feature = "full"), tokio_wasm), allow(dead_code))]
+use crate::runtime::Callback;
+use crate::util::RngSeedGenerator;
+
+pub(crate) struct Config {
+    /// How many ticks before pulling a task from the global/remote queue?
+    pub(crate) global_queue_interval: u32,
+
+    /// How many ticks before yielding to the driver for timer and I/O events?
+    pub(crate) event_interval: u32,
+
+    /// Callback for a worker parking itself
+    pub(crate) before_park: Option<Callback>,
+
+    /// Callback for a worker unparking itself
+    pub(crate) after_unpark: Option<Callback>,
+
+    /// The multi-threaded scheduler includes a per-worker LIFO slot used to
+    /// store the last scheduled task. This can improve certain usage patterns,
+    /// especially message passing between tasks. However, this LIFO slot is not
+    /// currently stealable.
+    ///
+    /// Eventually, the LIFO slot **will** become stealable, however as a
+    /// stop-gap, this unstable option lets users disable the LIFO task.
+    pub(crate) disable_lifo_slot: bool,
+
+    /// Random number generator seed to configure runtimes to act in a
+    /// deterministic way.
+    pub(crate) seed_generator: RngSeedGenerator,
+
+    #[cfg(tokio_unstable)]
+    /// How to respond to unhandled task panics.
+    pub(crate) unhandled_panic: crate::runtime::UnhandledPanic,
+}

tokio/src/runtime/context.rs

@@ -1,5 +1,6 @@
 //! Thread local runtime context
 use crate::runtime::{Handle, TryCurrentError};
+use crate::util::{replace_thread_rng, RngSeed};
 
 use std::cell::RefCell;
 
@@ -24,10 +25,16 @@ pub(crate) fn current() -> Handle {
 }
 
 cfg_io_driver! {
+    #[track_caller]
     pub(crate) fn io_handle() -> crate::runtime::driver::IoHandle {
         match CONTEXT.try_with(|ctx| {
             let ctx = ctx.borrow();
-            ctx.as_ref().expect(crate::util::error::CONTEXT_MISSING_ERROR).as_inner().io_handle.clone()
+            ctx.as_ref()
+                .expect(crate::util::error::CONTEXT_MISSING_ERROR)
+                .inner
+                .driver()
+                .io
+                .clone()
         }) {
             Ok(io_handle) => io_handle,
             Err(_) => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
@@ -40,7 +47,11 @@ cfg_signal_internal! {
     pub(crate) fn signal_handle() -> crate::runtime::driver::SignalHandle {
         match CONTEXT.try_with(|ctx| {
             let ctx = ctx.borrow();
-            ctx.as_ref().expect(crate::util::error::CONTEXT_MISSING_ERROR).as_inner().signal_handle.clone()
+            ctx.as_ref()
+                .expect(crate::util::error::CONTEXT_MISSING_ERROR)
+                .inner
+                .signal()
+                .clone()
         }) {
             Ok(signal_handle) => signal_handle,
             Err(_) => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
@@ -49,19 +60,14 @@ cfg_signal_internal! {
 }
 
 cfg_time! {
-    pub(crate) fn time_handle() -> crate::runtime::driver::TimeHandle {
-        match CONTEXT.try_with(|ctx| {
-            let ctx = ctx.borrow();
-            ctx.as_ref().expect(crate::util::error::CONTEXT_MISSING_ERROR).as_inner().time_handle.clone()
-        }) {
-            Ok(time_handle) => time_handle,
-            Err(_) => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
-        }
-    }
-
     cfg_test_util! {
         pub(crate) fn clock() -> Option<crate::runtime::driver::Clock> {
-            match CONTEXT.try_with(|ctx| (*ctx.borrow()).as_ref().map(|ctx| ctx.as_inner().clock.clone())) {
+            match CONTEXT.try_with(|ctx| {
+                let ctx = ctx.borrow();
+                ctx
+                    .as_ref()
+                    .map(|ctx| ctx.inner.clock().clone())
+            }) {
                 Ok(clock) => clock,
                 Err(_) => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
             }
@@ -69,15 +75,6 @@ cfg_time! {
     }
 }
 
-cfg_rt! {
-    pub(crate) fn spawn_handle() -> Option<crate::runtime::Spawner> {
-        match CONTEXT.try_with(|ctx| (*ctx.borrow()).as_ref().map(|ctx| ctx.spawner.clone())) {
-            Ok(spawner) => spawner,
-            Err(_) => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
-        }
-    }
-}
-
 /// Sets this [`Handle`] as the current active [`Handle`].
 ///
 /// [`Handle`]: Handle
@@ -92,21 +89,29 @@ pub(crate) fn enter(new: Handle) -> EnterGuard {
 ///
 /// [`Handle`]: Handle
 pub(crate) fn try_enter(new: Handle) -> Option<EnterGuard> {
-    CONTEXT
-        .try_with(|ctx| {
-            let old = ctx.borrow_mut().replace(new);
-            EnterGuard(old)
-        })
-        .ok()
+    let rng_seed = new.inner.seed_generator().next_seed();
+    let old_handle = CONTEXT.try_with(|ctx| ctx.borrow_mut().replace(new)).ok()?;
+
+    let old_seed = replace_thread_rng(rng_seed);
+
+    Some(EnterGuard {
+        old_handle,
+        old_seed,
+    })
 }
 
 #[derive(Debug)]
-pub(crate) struct EnterGuard(Option<Handle>);
+pub(crate) struct EnterGuard {
+    old_handle: Option<Handle>,
+    old_seed: RngSeed,
+}
 
 impl Drop for EnterGuard {
     fn drop(&mut self) {
         CONTEXT.with(|ctx| {
-            *ctx.borrow_mut() = self.0.take();
+            *ctx.borrow_mut() = self.old_handle.take();
         });
+        // We discard the RngSeed associated with this guard
+        let _ = replace_thread_rng(self.old_seed.clone());
     }
 }

tokio/src/runtime/driver.rs

@@ -1,45 +1,192 @@
 //! Abstracts out the entire chain of runtime sub-drivers into common types.
-use crate::park::thread::ParkThread;
-use crate::park::Park;
+
+// Eventually, this file will see significant refactoring / cleanup. For now, we
+// don't need to worry much about dead code with certain feature permutations.
+#![cfg_attr(not(feature = "full"), allow(dead_code))]
+
+use crate::park::thread::{ParkThread, UnparkThread};
 
 use std::io;
 use std::time::Duration;
 
+#[derive(Debug)]
+pub(crate) struct Driver {
+    inner: TimeDriver,
+}
+
+#[derive(Debug)]
+pub(crate) struct Handle {
+    /// IO driver handle
+    pub(crate) io: IoHandle,
+
+    /// Signal driver handle
+    #[cfg_attr(any(not(unix), loom), allow(dead_code))]
+    pub(crate) signal: SignalHandle,
+
+    /// Time driver handle
+    pub(crate) time: TimeHandle,
+
+    /// Source of `Instant::now()`
+    #[cfg_attr(not(all(feature = "time", feature = "test-util")), allow(dead_code))]
+    pub(crate) clock: Clock,
+}
+
+pub(crate) struct Cfg {
+    pub(crate) enable_io: bool,
+    pub(crate) enable_time: bool,
+    pub(crate) enable_pause_time: bool,
+    pub(crate) start_paused: bool,
+}
+
+impl Driver {
+    pub(crate) fn new(cfg: Cfg) -> io::Result<(Self, Handle)> {
+        let (io_stack, io_handle, signal_handle) = create_io_stack(cfg.enable_io)?;
+
+        let clock = create_clock(cfg.enable_pause_time, cfg.start_paused);
+
+        let (time_driver, time_handle) =
+            create_time_driver(cfg.enable_time, io_stack, clock.clone());
+
+        Ok((
+            Self { inner: time_driver },
+            Handle {
+                io: io_handle,
+                signal: signal_handle,
+                time: time_handle,
+                clock,
+            },
+        ))
+    }
+
+    pub(crate) fn park(&mut self) {
+        self.inner.park()
+    }
+
+    pub(crate) fn park_timeout(&mut self, duration: Duration) {
+        self.inner.park_timeout(duration)
+    }
+
+    pub(crate) fn shutdown(&mut self) {
+        self.inner.shutdown()
+    }
+}
+
+impl Handle {
+    pub(crate) fn unpark(&self) {
+        #[cfg(feature = "time")]
+        if let Some(handle) = &self.time {
+            handle.unpark();
+        }
+
+        self.io.unpark();
+    }
+}
+
 // ===== io driver =====
 
 cfg_io_driver! {
-    type IoDriver = crate::io::driver::Driver;
-    type IoStack = crate::park::either::Either<ProcessDriver, ParkThread>;
-    pub(crate) type IoHandle = Option<crate::io::driver::Handle>;
+    pub(crate) type IoDriver = crate::runtime::io::Driver;
+
+    #[derive(Debug)]
+    pub(crate) enum IoStack {
+        Enabled(ProcessDriver),
+        Disabled(ParkThread),
+    }
+
+    #[derive(Debug, Clone)]
+    pub(crate) enum IoHandle {
+        Enabled(crate::runtime::io::Handle),
+        Disabled(UnparkThread),
+    }
 
     fn create_io_stack(enabled: bool) -> io::Result<(IoStack, IoHandle, SignalHandle)> {
-        use crate::park::either::Either;
-
         #[cfg(loom)]
         assert!(!enabled);
 
         let ret = if enabled {
-            let io_driver = crate::io::driver::Driver::new()?;
+            let io_driver = crate::runtime::io::Driver::new()?;
             let io_handle = io_driver.handle();
 
             let (signal_driver, signal_handle) = create_signal_driver(io_driver)?;
             let process_driver = create_process_driver(signal_driver);
 
-            (Either::A(process_driver), Some(io_handle), signal_handle)
+            (IoStack::Enabled(process_driver), IoHandle::Enabled(io_handle), signal_handle)
         } else {
-            (Either::B(ParkThread::new()), Default::default(), Default::default())
+            let park_thread = ParkThread::new();
+            let unpark_thread = park_thread.unpark();
+            (IoStack::Disabled(park_thread), IoHandle::Disabled(unpark_thread), Default::default())
         };
 
         Ok(ret)
     }
+
+    impl IoStack {
+        /*
+        pub(crate) fn handle(&self) -> IoHandle {
+            match self {
+                IoStack::Enabled(v) => IoHandle::Enabled(v.handle()),
+                IoStack::Disabled(v) => IoHandle::Disabled(v.unpark()),
+            }
+        }]
+        */
+
+        pub(crate) fn park(&mut self) {
+            match self {
+                IoStack::Enabled(v) => v.park(),
+                IoStack::Disabled(v) => v.park(),
+            }
+        }
+
+        pub(crate) fn park_timeout(&mut self, duration: Duration) {
+            match self {
+                IoStack::Enabled(v) => v.park_timeout(duration),
+                IoStack::Disabled(v) => v.park_timeout(duration),
+            }
+        }
+
+        pub(crate) fn shutdown(&mut self) {
+            match self {
+                IoStack::Enabled(v) => v.shutdown(),
+                IoStack::Disabled(v) => v.shutdown(),
+            }
+        }
+    }
+
+    impl IoHandle {
+        pub(crate) fn unpark(&self) {
+            match self {
+                IoHandle::Enabled(handle) => handle.unpark(),
+                IoHandle::Disabled(handle) => handle.unpark(),
+            }
+        }
+
+        #[track_caller]
+        pub(crate) fn expect(self, msg: &'static str) -> crate::runtime::io::Handle {
+            match self {
+                IoHandle::Enabled(v) => v,
+                IoHandle::Disabled(..) => panic!("{}", msg),
+            }
+        }
+
+        cfg_unstable! {
+            pub(crate) fn as_ref(&self) -> Option<&crate::runtime::io::Handle> {
+                match self {
+                    IoHandle::Enabled(v) => Some(v),
+                    IoHandle::Disabled(..) => None,
+                }
+            }
+        }
+    }
 }
 
 cfg_not_io_driver! {
-    pub(crate) type IoHandle = ();
-    type IoStack = ParkThread;
+    pub(crate) type IoHandle = UnparkThread;
+    pub(crate) type IoStack = ParkThread;
 
     fn create_io_stack(_enabled: bool) -> io::Result<(IoStack, IoHandle, SignalHandle)> {
-        Ok((ParkThread::new(), Default::default(), Default::default()))
+        let park_thread = ParkThread::new();
+        let unpark_thread = park_thread.unpark();
+        Ok((park_thread, unpark_thread, Default::default()))
     }
 }
 
@@ -98,10 +245,17 @@ cfg_not_process_driver! {
 // ===== time driver =====
 
 cfg_time! {
-    type TimeDriver = crate::park::either::Either<crate::time::driver::Driver<IoStack>, IoStack>;
+    #[derive(Debug)]
+    pub(crate) enum TimeDriver {
+        Enabled {
+            driver: crate::runtime::time::Driver,
+            handle: crate::runtime::time::Handle,
+        },
+        Disabled(IoStack),
+    }
 
     pub(crate) type Clock = crate::time::Clock;
-    pub(crate) type TimeHandle = Option<crate::time::driver::Handle>;
+    pub(crate) type TimeHandle = Option<crate::runtime::time::Handle>;
 
     fn create_clock(enable_pausing: bool, start_paused: bool) -> Clock {
         crate::time::Clock::new(enable_pausing, start_paused)
@@ -112,15 +266,35 @@ cfg_time! {
         io_stack: IoStack,
         clock: Clock,
     ) -> (TimeDriver, TimeHandle) {
-        use crate::park::either::Either;
-
         if enable {
-            let driver = crate::time::driver::Driver::new(io_stack, clock);
-            let handle = driver.handle();
+            let (driver, handle) = crate::runtime::time::Driver::new(io_stack, clock);
 
-            (Either::A(driver), Some(handle))
+            (TimeDriver::Enabled { driver, handle: handle.clone() }, Some(handle))
         } else {
-            (Either::B(io_stack), None)
+            (TimeDriver::Disabled(io_stack), None)
+        }
+    }
+
+    impl TimeDriver {
+        pub(crate) fn park(&mut self) {
+            match self {
+                TimeDriver::Enabled { driver, handle } => driver.park(handle),
+                TimeDriver::Disabled(v) => v.park(),
+            }
+        }
+
+        pub(crate) fn park_timeout(&mut self, duration: Duration) {
+            match self {
+                TimeDriver::Enabled { driver, handle } => driver.park_timeout(handle, duration),
+                TimeDriver::Disabled(v) => v.park_timeout(duration),
+            }
+        }
+
+        pub(crate) fn shutdown(&mut self) {
+            match self {
+                TimeDriver::Enabled { driver, handle } => driver.shutdown(handle),
+                TimeDriver::Disabled(v) => v.shutdown(),
+            }
         }
     }
 }
@@ -143,66 +317,3 @@ cfg_not_time! {
         (io_stack, ())
     }
 }
-
-// ===== runtime driver =====
-
-#[derive(Debug)]
-pub(crate) struct Driver {
-    inner: TimeDriver,
-}
-
-pub(crate) struct Resources {
-    pub(crate) io_handle: IoHandle,
-    pub(crate) signal_handle: SignalHandle,
-    pub(crate) time_handle: TimeHandle,
-    pub(crate) clock: Clock,
-}
-
-pub(crate) struct Cfg {
-    pub(crate) enable_io: bool,
-    pub(crate) enable_time: bool,
-    pub(crate) enable_pause_time: bool,
-    pub(crate) start_paused: bool,
-}
-
-impl Driver {
-    pub(crate) fn new(cfg: Cfg) -> io::Result<(Self, Resources)> {
-        let (io_stack, io_handle, signal_handle) = create_io_stack(cfg.enable_io)?;
-
-        let clock = create_clock(cfg.enable_pause_time, cfg.start_paused);
-
-        let (time_driver, time_handle) =
-            create_time_driver(cfg.enable_time, io_stack, clock.clone());
-
-        Ok((
-            Self { inner: time_driver },
-            Resources {
-                io_handle,
-                signal_handle,
-                time_handle,
-                clock,
-            },
-        ))
-    }
-}
-
-impl Park for Driver {
-    type Unpark = <TimeDriver as Park>::Unpark;
-    type Error = <TimeDriver as Park>::Error;
-
-    fn unpark(&self) -> Self::Unpark {
-        self.inner.unpark()
-    }
-
-    fn park(&mut self) -> Result<(), Self::Error> {
-        self.inner.park()
-    }
-
-    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
-        self.inner.park_timeout(duration)
-    }
-
-    fn shutdown(&mut self) {
-        self.inner.shutdown()
-    }
-}

tokio/src/runtime/enter.rs

@@ -25,8 +25,6 @@ pub(crate) struct Enter {
 }
 
 cfg_rt! {
-    use crate::park::thread::ParkError;
-
     use std::time::Duration;
 
     /// Marks the current thread as being within the dynamic extent of an
@@ -139,10 +137,12 @@ cfg_rt_multi_thread! {
 }
 
 cfg_rt! {
+    use crate::loom::thread::AccessError;
+
     impl Enter {
         /// Blocks the thread on the specified future, returning the value with
         /// which that future completes.
-        pub(crate) fn block_on<F>(&mut self, f: F) -> Result<F::Output, ParkError>
+        pub(crate) fn block_on<F>(&mut self, f: F) -> Result<F::Output, AccessError>
         where
             F: std::future::Future,
         {
@@ -156,18 +156,17 @@ cfg_rt! {
         ///
         /// If the future completes before `timeout`, the result is returned. If
         /// `timeout` elapses, then `Err` is returned.
-        pub(crate) fn block_on_timeout<F>(&mut self, f: F, timeout: Duration) -> Result<F::Output, ParkError>
+        pub(crate) fn block_on_timeout<F>(&mut self, f: F, timeout: Duration) -> Result<F::Output, ()>
         where
             F: std::future::Future,
         {
-            use crate::park::Park;
             use crate::park::thread::CachedParkThread;
             use std::task::Context;
             use std::task::Poll::Ready;
             use std::time::Instant;
 
             let mut park = CachedParkThread::new();
-            let waker = park.get_unpark()?.into_waker();
+            let waker = park.waker().map_err(|_| ())?;
             let mut cx = Context::from_waker(&waker);
 
             pin!(f);
@@ -184,7 +183,7 @@ cfg_rt! {
                     return Err(());
                 }
 
-                park.park_timeout(when - now)?;
+                park.park_timeout(when - now);
             }
         }
     }

tokio/src/runtime/handle.rs

@@ -1,11 +1,4 @@
-use crate::runtime::blocking::{BlockingTask, NoopSchedule};
-use crate::runtime::task::{self, JoinHandle};
-use crate::runtime::{blocking, context, driver, Spawner};
-use crate::util::error::{CONTEXT_MISSING_ERROR, THREAD_LOCAL_DESTROYED_ERROR};
-
-use std::future::Future;
-use std::marker::PhantomData;
-use std::{error, fmt};
+use crate::runtime::scheduler;
 
 /// Handle to the runtime.
 ///
@@ -14,47 +7,19 @@ use std::{error, fmt};
 ///
 /// [`Runtime::handle`]: crate::runtime::Runtime::handle()
 #[derive(Debug, Clone)]
+// When the `rt` feature is *not* enabled, this type is still defined, but not
+// included in the public API.
 pub struct Handle {
-    pub(super) spawner: Spawner,
+    pub(crate) inner: scheduler::Handle,
 }
 
-/// All internal handles that are *not* the scheduler's spawner.
-#[derive(Debug)]
-pub(crate) struct HandleInner {
-    /// Handles to the I/O drivers
-    #[cfg_attr(
-        not(any(feature = "net", feature = "process", all(unix, feature = "signal"))),
-        allow(dead_code)
-    )]
-    pub(super) io_handle: driver::IoHandle,
+use crate::runtime::context;
+use crate::runtime::task::JoinHandle;
+use crate::util::error::{CONTEXT_MISSING_ERROR, THREAD_LOCAL_DESTROYED_ERROR};
 
-    /// Handles to the signal drivers
-    #[cfg_attr(
-        any(
-            loom,
-            not(all(unix, feature = "signal")),
-            not(all(unix, feature = "process")),
-        ),
-        allow(dead_code)
-    )]
-    pub(super) signal_handle: driver::SignalHandle,
-
-    /// Handles to the time drivers
-    #[cfg_attr(not(feature = "time"), allow(dead_code))]
-    pub(super) time_handle: driver::TimeHandle,
-
-    /// Source of `Instant::now()`
-    #[cfg_attr(not(all(feature = "time", feature = "test-util")), allow(dead_code))]
-    pub(super) clock: driver::Clock,
-
-    /// Blocking pool spawner
-    pub(super) blocking_spawner: blocking::Spawner,
-}
-
-/// Create a new runtime handle.
-pub(crate) trait ToHandle {
-    fn to_handle(&self) -> Handle;
-}
+use std::future::Future;
+use std::marker::PhantomData;
+use std::{error, fmt};
 
 /// Runtime context guard.
 ///
@@ -204,11 +169,7 @@ impl Handle {
         F: FnOnce() -> R + Send + 'static,
         R: Send + 'static,
     {
-        self.as_inner().spawn_blocking(self, func)
-    }
-
-    pub(crate) fn as_inner(&self) -> &HandleInner {
-        self.spawner.as_handle_inner()
+        self.inner.blocking_spawner().spawn_blocking(self, func)
     }
 
     /// Runs a future to completion on this `Handle`'s associated `Runtime`.
@@ -308,17 +269,7 @@ impl Handle {
         let id = crate::runtime::task::Id::next();
         #[cfg(all(tokio_unstable, feature = "tracing"))]
         let future = crate::util::trace::task(future, "task", _name, id.as_u64());
-        self.spawner.spawn(future, id)
-    }
-
-    pub(crate) fn shutdown(mut self) {
-        self.spawner.shutdown();
-    }
-}
-
-impl ToHandle for Handle {
-    fn to_handle(&self) -> Handle {
-        self.clone()
+        self.inner.spawn(future, id)
     }
 }
 
@@ -334,100 +285,6 @@ cfg_metrics! {
     }
 }
 
-impl HandleInner {
-    #[track_caller]
-    pub(crate) fn spawn_blocking<F, R>(&self, rt: &dyn ToHandle, func: F) -> JoinHandle<R>
-    where
-        F: FnOnce() -> R + Send + 'static,
-        R: Send + 'static,
-    {
-        let (join_handle, _was_spawned) = if cfg!(debug_assertions)
-            && std::mem::size_of::<F>() > 2048
-        {
-            self.spawn_blocking_inner(Box::new(func), blocking::Mandatory::NonMandatory, None, rt)
-        } else {
-            self.spawn_blocking_inner(func, blocking::Mandatory::NonMandatory, None, rt)
-        };
-
-        join_handle
-    }
-
-    cfg_fs! {
-        #[track_caller]
-        #[cfg_attr(any(
-            all(loom, not(test)), // the function is covered by loom tests
-            test
-        ), allow(dead_code))]
-        pub(crate) fn spawn_mandatory_blocking<F, R>(&self, rt: &dyn ToHandle, func: F) -> Option<JoinHandle<R>>
-        where
-            F: FnOnce() -> R + Send + 'static,
-            R: Send + 'static,
-        {
-            let (join_handle, was_spawned) = if cfg!(debug_assertions) && std::mem::size_of::<F>() > 2048 {
-                self.spawn_blocking_inner(
-                    Box::new(func),
-                    blocking::Mandatory::Mandatory,
-                    None,
-                    rt,
-                )
-            } else {
-                self.spawn_blocking_inner(
-                    func,
-                    blocking::Mandatory::Mandatory,
-                    None,
-                    rt,
-                )
-            };
-
-            if was_spawned {
-                Some(join_handle)
-            } else {
-                None
-            }
-        }
-    }
-
-    #[track_caller]
-    pub(crate) fn spawn_blocking_inner<F, R>(
-        &self,
-        func: F,
-        is_mandatory: blocking::Mandatory,
-        name: Option<&str>,
-        rt: &dyn ToHandle,
-    ) -> (JoinHandle<R>, bool)
-    where
-        F: FnOnce() -> R + Send + 'static,
-        R: Send + 'static,
-    {
-        let fut = BlockingTask::new(func);
-        let id = super::task::Id::next();
-        #[cfg(all(tokio_unstable, feature = "tracing"))]
-        let fut = {
-            use tracing::Instrument;
-            let location = std::panic::Location::caller();
-            let span = tracing::trace_span!(
-                target: "tokio::task::blocking",
-                "runtime.spawn",
-                kind = %"blocking",
-                task.name = %name.unwrap_or_default(),
-                task.id = id.as_u64(),
-                "fn" = %std::any::type_name::<F>(),
-                spawn.location = %format_args!("{}:{}:{}", location.file(), location.line(), location.column()),
-            );
-            fut.instrument(span)
-        };
-
-        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
-        let _ = name;
-
-        let (task, handle) = task::unowned(fut, NoopSchedule, id);
-        let spawned = self
-            .blocking_spawner
-            .spawn(blocking::Task::new(task, is_mandatory), rt);
-        (handle, spawned.is_ok())
-    }
-}
-
 /// Error returned by `try_current` when no Runtime has been started
 #[derive(Debug)]
 pub struct TryCurrentError {

tokio/src/runtime/io/mod.rs

@@ -1,13 +1,5 @@
 #![cfg_attr(not(feature = "rt"), allow(dead_code))]
 
-mod interest;
-#[allow(unreachable_pub)]
-pub use interest::Interest;
-
-mod ready;
-#[allow(unreachable_pub)]
-pub use ready::Ready;
-
 mod registration;
 pub(crate) use registration::Registration;
 
@@ -16,7 +8,8 @@ use scheduled_io::ScheduledIo;
 
 mod metrics;
 
-use crate::park::{Park, Unpark};
+use crate::io::interest::Interest;
+use crate::io::ready::Ready;
 use crate::util::slab::{self, Slab};
 use crate::{loom::sync::RwLock, util::bit};
 
@@ -72,6 +65,8 @@ pub(super) struct Inner {
     io_dispatch: RwLock<IoDispatcher>,
 
     /// Used to wake up the reactor from a call to `turn`.
+    /// Not supported on Wasi due to lack of threading support.
+    #[cfg(not(tokio_wasi))]
     waker: mio::Waker,
 
     metrics: IoDriverMetrics,
@@ -115,6 +110,7 @@ impl Driver {
     /// creation.
     pub(crate) fn new() -> io::Result<Driver> {
         let poll = mio::Poll::new()?;
+        #[cfg(not(tokio_wasi))]
         let waker = mio::Waker::new(poll.registry(), TOKEN_WAKEUP)?;
         let registry = poll.registry().try_clone()?;
 
@@ -129,6 +125,7 @@ impl Driver {
             inner: Arc::new(Inner {
                 registry,
                 io_dispatch: RwLock::new(IoDispatcher::new(allocator)),
+                #[cfg(not(tokio_wasi))]
                 waker,
                 metrics: IoDriverMetrics::default(),
             }),
@@ -147,7 +144,26 @@ impl Driver {
         }
     }
 
-    fn turn(&mut self, max_wait: Option<Duration>) -> io::Result<()> {
+    pub(crate) fn park(&mut self) {
+        self.turn(None);
+    }
+
+    pub(crate) fn park_timeout(&mut self, duration: Duration) {
+        self.turn(Some(duration));
+    }
+
+    pub(crate) fn shutdown(&mut self) {
+        if self.inner.shutdown() {
+            self.resources.for_each(|io| {
+                // If a task is waiting on the I/O resource, notify it. The task
+                // will then attempt to use the I/O resource and fail due to the
+                // driver being shutdown. And shutdown will clear all wakers.
+                io.shutdown();
+            });
+        }
+    }
+
+    fn turn(&mut self, max_wait: Option<Duration>) {
         // How often to call `compact()` on the resource slab
         const COMPACT_INTERVAL: u8 = 255;
 
@@ -164,7 +180,12 @@ impl Driver {
         match self.poll.poll(&mut events, max_wait) {
             Ok(_) => {}
             Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
-            Err(e) => return Err(e),
+            #[cfg(tokio_wasi)]
+            Err(e) if e.kind() == io::ErrorKind::InvalidInput => {
+                // In case of wasm32_wasi this error happens, when trying to poll without subscriptions
+                // just return from the park, as there would be nothing, which wakes us up.
+            }
+            Err(e) => panic!("unexpected error when polling the I/O driver: {:?}", e),
         }
 
         // Process all the events that came in, dispatching appropriately
@@ -181,8 +202,6 @@ impl Driver {
         self.inner.metrics.incr_ready_count_by(ready_count);
 
         self.events = Some(events);
-
-        Ok(())
     }
 
     fn dispatch(&mut self, token: mio::Token, ready: Ready) {
@@ -206,42 +225,6 @@ impl Driver {
     }
 }
 
-impl Drop for Driver {
-    fn drop(&mut self) {
-        self.shutdown();
-    }
-}
-
-impl Park for Driver {
-    type Unpark = Handle;
-    type Error = io::Error;
-
-    fn unpark(&self) -> Self::Unpark {
-        self.handle()
-    }
-
-    fn park(&mut self) -> io::Result<()> {
-        self.turn(None)?;
-        Ok(())
-    }
-
-    fn park_timeout(&mut self, duration: Duration) -> io::Result<()> {
-        self.turn(Some(duration))?;
-        Ok(())
-    }
-
-    fn shutdown(&mut self) {
-        if self.inner.shutdown() {
-            self.resources.for_each(|io| {
-                // If a task is waiting on the I/O resource, notify it. The task
-                // will then attempt to use the I/O resource and fail due to the
-                // driver being shutdown. And shutdown will clear all wakers.
-                io.shutdown();
-            });
-        }
-    }
-}
-
 impl fmt::Debug for Driver {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "Driver")
@@ -259,7 +242,7 @@ cfg_rt! {
         /// This function panics if there is no current reactor set and `rt` feature
         /// flag is not enabled.
         #[track_caller]
-        pub(super) fn current() -> Self {
+        pub(crate) fn current() -> Self {
             crate::runtime::context::io_handle().expect("A Tokio 1.x context was found, but IO is disabled. Call `enable_io` on the runtime builder to enable IO.")
         }
     }
@@ -273,7 +256,8 @@ cfg_not_rt! {
         ///
         /// This function panics if there is no current reactor set, or if the `rt`
         /// feature flag is not enabled.
-        pub(super) fn current() -> Self {
+        #[track_caller]
+        pub(crate) fn current() -> Self {
             panic!("{}", crate::util::error::CONTEXT_MISSING_ERROR)
         }
     }
@@ -299,17 +283,12 @@ impl Handle {
     /// after this method has been called. If the reactor is not currently
     /// blocked in `turn`, then the next call to `turn` will not block and
     /// return immediately.
-    fn wakeup(&self) {
+    pub(crate) fn unpark(&self) {
+        #[cfg(not(tokio_wasi))]
         self.inner.waker.wake().expect("failed to wake I/O driver");
     }
 }
 
-impl Unpark for Handle {
-    fn unpark(&self) {
-        self.wakeup();
-    }
-}
-
 impl fmt::Debug for Handle {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "Handle")

tokio/src/runtime/io/registration.rs

@@ -1,6 +1,7 @@
 #![cfg_attr(not(feature = "net"), allow(dead_code))]
 
-use crate::io::driver::{Direction, Handle, Interest, ReadyEvent, ScheduledIo};
+use crate::io::interest::Interest;
+use crate::runtime::io::{Direction, Handle, ReadyEvent, ScheduledIo};
 use crate::util::slab;
 
 use mio::event::Source;
@@ -56,10 +57,8 @@ unsafe impl Sync for Registration {}
 // ===== impl Registration =====
 
 impl Registration {
-    /// Registers the I/O resource with the default reactor, for a specific
-    /// `Interest`. `new_with_interest` should be used over `new` when you need
-    /// control over the readiness state, such as when a file descriptor only
-    /// allows reads. This does not add `hup` or `error` so if you are
+    /// Registers the I/O resource with the reactor for the provided handle, for
+    /// a specific `Interest`. This does not add `hup` or `error` so if you are
     /// interested in those states, you will need to add them to the readiness
     /// state passed to this function.
     ///
@@ -115,6 +114,7 @@ impl Registration {
 
     // Uses the poll path, requiring the caller to ensure mutual exclusion for
     // correctness. Only the last task to call this function is notified.
+    #[cfg(not(tokio_wasi))]
     pub(crate) fn poll_read_io<R>(
         &self,
         cx: &mut Context<'_>,