fs: add support for non-threadpool executors (#1495)

Provides a thread pool dedicated to running blocking operations (#588)
and update `tokio-fs` to use this pool.

In an effort to make incremental progress, this is an initial step
towards a final solution. First, it provides a very basic pool
implementation with the intend that the pool will be
replaced before the final release. Second, it updates `tokio-fs` to
always use this blocking pool instead of conditionally using
`threadpool::blocking`. Issue #588 contains additional discussion around
potential improvements to the "blocking for all" strategy.

The implementation provided here builds on work started in #954 and
continued in #1045. The general idea is th same as #1045, but the PR
improves on some of the details:

* The number of explicit operations tracked by `File` is reduced only to
  the ones that could interact. All other ops are spawned on the
  blocking pool without being tracked by the `File` instance.

* The `seek` implementation is not backed by a trait and `poll_seek`
  function. This avoids the question of how to model non-blocking seeks
  on top of a blocking file. In this patch, `seek` is represented as an
  `async fn`. If the associated future is dropped before the caller
  observes the return value, we make no effort to define the state in
  which the file ends up.

tokio-executor/Cargo.toml

@@ -21,6 +21,7 @@ keywords = ["futures", "tokio"]
 categories = ["concurrency", "asynchronous"]
 
 [features]
+blocking = ["tokio-sync"]
 current-thread = ["crossbeam-channel"]
 threadpool = [
   "tokio-sync",

tokio-executor/src/blocking.rs

@@ -0,0 +1,142 @@
+//! Thread pool for blocking operations
+
+use tokio_sync::oneshot;
+
+use lazy_static::lazy_static;
+use std::collections::VecDeque;
+use std::future::Future;
+use std::pin::Pin;
+use std::sync::{Condvar, Mutex};
+use std::task::{Context, Poll};
+use std::thread;
+use std::time::Duration;
+
+struct Pool {
+    shared: Mutex<Shared>,
+    condvar: Condvar,
+}
+
+struct Shared {
+    queue: VecDeque<Box<dyn FnOnce() + Send>>,
+    num_th: u32,
+    num_idle: u32,
+}
+
+lazy_static! {
+    static ref POOL: Pool = Pool::new();
+}
+
+const MAX_THREADS: u32 = 1_000;
+const KEEP_ALIVE: Duration = Duration::from_secs(10);
+
+/// Result of a blocking operation running on the blocking thread pool.
+#[derive(Debug)]
+pub struct Blocking<T> {
+    rx: oneshot::Receiver<T>,
+}
+
+/// Run the provided function on a threadpool dedicated to blocking operations.
+pub fn run<F, R>(f: F) -> Blocking<R>
+where
+    F: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
+{
+    let (tx, rx) = oneshot::channel();
+
+    let should_spawn = {
+        let mut shared = POOL.shared.lock().unwrap();
+
+        shared.queue.push_back(Box::new(move || {
+            // The receiver may have dropped
+            let _ = tx.send(f());
+        }));
+
+        if shared.num_idle == 0 {
+            // No threads are able to process the task
+
+            if shared.num_th == MAX_THREADS {
+                // At max number of threads
+                false
+            } else {
+                shared.num_th += 1;
+                true
+            }
+        } else {
+            shared.num_idle -= 1;
+            POOL.condvar.notify_one();
+            false
+        }
+    };
+
+    if should_spawn {
+        spawn_thread();
+    }
+
+    Blocking { rx }
+}
+
+impl<T> Future for Blocking<T> {
+    type Output = T;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        use std::task::Poll::*;
+
+        match Pin::new(&mut self.rx).poll(cx) {
+            Ready(Ok(v)) => Ready(v),
+            Ready(Err(_)) => panic!(
+                "the blocking operation has been dropped before completing. \
+                 This should not happen and is a bug."
+            ),
+            Pending => Pending,
+        }
+    }
+}
+
+fn spawn_thread() {
+    thread::Builder::new()
+        .name("tokio-blocking-driver".to_string())
+        .spawn(|| {
+            'outer: loop {
+                let mut shared = POOL.shared.lock().unwrap();
+
+                if let Some(task) = shared.queue.pop_front() {
+                    drop(shared);
+                    run_task(task);
+                    continue;
+                }
+
+                // IDLE
+                shared.num_idle += 1;
+
+                loop {
+                    shared = POOL.condvar.wait_timeout(shared, KEEP_ALIVE).unwrap().0;
+
+                    if let Some(task) = shared.queue.pop_front() {
+                        drop(shared);
+                        run_task(task);
+                        continue 'outer;
+                    }
+                }
+            }
+        })
+        .unwrap();
+}
+
+fn run_task(f: Box<dyn FnOnce() + Send>) {
+    use std::panic::{catch_unwind, AssertUnwindSafe};
+
+    let _ = catch_unwind(AssertUnwindSafe(|| f()));
+}
+
+impl Pool {
+    fn new() -> Pool {
+        Pool {
+            shared: Mutex::new(Shared {
+                queue: VecDeque::new(),
+                num_th: 0,
+                num_idle: 0,
+            }),
+            condvar: Condvar::new(),
+        }
+    }
+}

tokio-executor/src/lib.rs

@@ -67,6 +67,9 @@ mod global;
 pub mod park;
 mod typed;
 
+#[cfg(feature = "blocking")]
+pub mod blocking;
+
 #[cfg(feature = "current-thread")]
 pub mod current_thread;
 

tokio-fs/Cargo.toml

@@ -23,13 +23,16 @@ categories = ["asynchronous", "network-programming", "filesystem"]
 
 [dependencies]
 tokio-io = { version = "=0.2.0-alpha.2", features = ["util"], path = "../tokio-io" }
-tokio-executor = { version = "=0.2.0-alpha.2", features = ["threadpool"], path = "../tokio-executor" }
+tokio-executor = { version = "=0.2.0-alpha.2", features = ["blocking"], path = "../tokio-executor" }
+tokio-sync = { version = "=0.2.0-alpha.2", path = "../tokio-sync" }
 
 futures-core-preview = "=0.3.0-alpha.18"
 futures-util-preview = "=0.3.0-alpha.18"
+lazy_static = "1.3.0"
 
 [dev-dependencies]
-tokio = { version = "0.2.0-alpha.1", path = "../tokio" }
+tokio = { version = "=0.2.0-alpha.2", path = "../tokio" }
+tokio-test = { version = "=0.2.0-alpha.2", path = "../tokio-test" }
 
 rand = "0.7"
 tempfile = "3"

tokio-fs/src/blocking.rs

@@ -0,0 +1,252 @@
+use crate::sys;
+
+use tokio_io::{AsyncRead, AsyncWrite};
+
+use futures_core::ready;
+use std::cmp;
+use std::future::Future;
+use std::io;
+use std::io::prelude::*;
+use std::pin::Pin;
+use std::task::Poll::*;
+use std::task::{Context, Poll};
+
+use self::State::*;
+
+/// `T` should not implement _both_ Read and Write.
+#[derive(Debug)]
+pub(crate) struct Blocking<T> {
+    inner: Option<T>,
+    state: State<T>,
+}
+
+#[derive(Debug)]
+pub(crate) struct Buf {
+    buf: Vec<u8>,
+    pos: usize,
+}
+
+pub(crate) const MAX_BUF: usize = 16 * 1024;
+
+#[derive(Debug)]
+enum State<T> {
+    Idle(Option<Buf>),
+    Busy(sys::Blocking<(io::Result<usize>, Buf, T)>),
+}
+
+impl<T> Blocking<T> {
+    pub(crate) fn new(inner: T) -> Blocking<T> {
+        Blocking {
+            inner: Some(inner),
+            state: State::Idle(Some(Buf::with_capacity(0))),
+        }
+    }
+}
+
+impl<T> AsyncRead for Blocking<T>
+where
+    T: Read + Unpin + Send + 'static,
+{
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        dst: &mut [u8],
+    ) -> Poll<io::Result<usize>> {
+        loop {
+            match self.state {
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    if !buf.is_empty() {
+                        let n = buf.copy_to(dst);
+                        *buf_cell = Some(buf);
+                        return Ready(Ok(n));
+                    }
+
+                    buf.ensure_capacity_for(dst);
+                    let mut inner = self.inner.take().unwrap();
+
+                    self.state = Busy(sys::run(move || {
+                        let res = buf.read_from(&mut inner);
+                        (res, buf, inner)
+                    }));
+                }
+                Busy(ref mut rx) => {
+                    let (res, mut buf, inner) = ready!(Pin::new(rx).poll(cx));
+                    self.inner = Some(inner);
+
+                    match res {
+                        Ok(_) => {
+                            let n = buf.copy_to(dst);
+                            self.state = Idle(Some(buf));
+                            return Ready(Ok(n));
+                        }
+                        Err(e) => {
+                            assert!(buf.is_empty());
+
+                            self.state = Idle(Some(buf));
+                            return Ready(Err(e));
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl<T> AsyncWrite for Blocking<T>
+where
+    T: Write + Unpin + Send + 'static,
+{
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        src: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        loop {
+            match self.state {
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    assert!(buf.is_empty());
+
+                    let n = buf.copy_from(src);
+                    let mut inner = self.inner.take().unwrap();
+
+                    self.state = Busy(sys::run(move || {
+                        let n = buf.len();
+                        let res = buf.write_to(&mut inner).map(|_| n);
+
+                        (res, buf, inner)
+                    }));
+
+                    return Ready(Ok(n));
+                }
+                Busy(ref mut rx) => {
+                    let (res, buf, inner) = ready!(Pin::new(rx).poll(cx));
+                    self.state = Idle(Some(buf));
+                    self.inner = Some(inner);
+
+                    // If error, return
+                    res?;
+                }
+            }
+        }
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        let (res, buf, inner) = match self.state {
+            Idle(_) => return Ready(Ok(())),
+            Busy(ref mut rx) => ready!(Pin::new(rx).poll(cx)),
+        };
+
+        // The buffer is not used here
+        self.state = Idle(Some(buf));
+        self.inner = Some(inner);
+
+        Ready(res.map(|_| ()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Poll::Ready(Ok(()))
+    }
+}
+
+/// Repeates operations that are interrupted
+macro_rules! uninterruptibly {
+    ($e:expr) => {{
+        loop {
+            match $e {
+                Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
+                res => break res,
+            }
+        }
+    }};
+}
+
+impl Buf {
+    pub(crate) fn with_capacity(n: usize) -> Buf {
+        Buf {
+            buf: Vec::with_capacity(n),
+            pos: 0,
+        }
+    }
+
+    pub(crate) fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    pub(crate) fn len(&self) -> usize {
+        self.buf.len() - self.pos
+    }
+
+    pub(crate) fn copy_to(&mut self, dst: &mut [u8]) -> usize {
+        let n = cmp::min(self.len(), dst.len());
+        dst[..n].copy_from_slice(&self.bytes()[..n]);
+        self.pos += n;
+
+        if self.pos == self.buf.len() {
+            self.buf.truncate(0);
+            self.pos = 0;
+        }
+
+        n
+    }
+
+    pub(crate) fn copy_from(&mut self, src: &[u8]) -> usize {
+        assert!(self.is_empty());
+
+        let n = cmp::min(src.len(), MAX_BUF);
+
+        self.buf.extend_from_slice(&src[..n]);
+        n
+    }
+
+    pub(crate) fn bytes(&self) -> &[u8] {
+        &self.buf[self.pos..]
+    }
+
+    pub(crate) fn ensure_capacity_for(&mut self, bytes: &[u8]) {
+        assert!(self.is_empty());
+
+        let len = cmp::min(bytes.len(), MAX_BUF);
+
+        if self.buf.len() < len {
+            self.buf.reserve(len - self.buf.len());
+        }
+
+        unsafe {
+            self.buf.set_len(len);
+        }
+    }
+
+    pub(crate) fn read_from<T: Read>(&mut self, rd: &mut T) -> io::Result<usize> {
+        let res = uninterruptibly!(rd.read(&mut self.buf));
+
+        if let Ok(n) = res {
+            self.buf.truncate(n);
+        } else {
+            self.buf.clear();
+        }
+
+        assert_eq!(self.pos, 0);
+
+        res
+    }
+
+    pub(crate) fn write_to<T: Write>(&mut self, wr: &mut T) -> io::Result<()> {
+        assert_eq!(self.pos, 0);
+
+        // `write_all` already ignores interrupts
+        let res = wr.write_all(&self.buf);
+        self.buf.clear();
+        res
+    }
+
+    pub(crate) fn discard_read(&mut self) -> i64 {
+        let ret = -(self.bytes().len() as i64);
+        self.pos = 0;
+        self.buf.truncate(0);
+        ret
+    }
+}

tokio-fs/src/create_dir.rs

@@ -9,5 +9,6 @@ use std::path::Path;
 ///
 /// [std]: https://doc.rust-lang.org/std/fs/fn.create_dir.html
 pub async fn create_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
-    asyncify(|| std::fs::create_dir(&path)).await
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::create_dir(path)).await
 }

tokio-fs/src/create_dir_all.rs

@@ -10,5 +10,6 @@ use std::path::Path;
 ///
 /// [std]: https://doc.rust-lang.org/std/fs/fn.create_dir_all.html
 pub async fn create_dir_all<P: AsRef<Path>>(path: P) -> io::Result<()> {
-    asyncify(|| std::fs::create_dir_all(&path)).await
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::create_dir_all(path)).await
 }

tokio-fs/src/file.rs

@@ -2,17 +2,23 @@
 //!
 //! [`File`]: file/struct.File.html
 
-use crate::{asyncify, blocking_io, OpenOptions};
+use self::State::*;
+use crate::blocking::Buf;
+use crate::{asyncify, sys};
 
 use tokio_io::{AsyncRead, AsyncWrite};
 
-use std::convert::TryFrom;
+use futures_core::ready;
+use std::fmt;
 use std::fs::{Metadata, Permissions};
-use std::io::{self, Read, Seek, Write};
+use std::future::Future;
+use std::io::{self, Seek, SeekFrom};
 use std::path::Path;
 use std::pin::Pin;
+use std::sync::Arc;
 use std::task::Context;
 use std::task::Poll;
+use std::task::Poll::*;
 
 /// A reference to an open file on the filesystem.
 ///
@@ -58,9 +64,27 @@ use std::task::Poll;
 /// # Ok(())
 /// # }
 /// ```
-#[derive(Debug)]
 pub struct File {
-    std: std::fs::File,
+    std: Arc<sys::File>,
+    state: State,
+
+    /// Errors from writes/flushes are returned in write/flush calls. If a write
+    /// error is observed while performing a read, it is saved until the next
+    /// write / flush call.
+    last_write_err: Option<io::ErrorKind>,
+}
+
+#[derive(Debug)]
+enum State {
+    Idle(Option<Buf>),
+    Busy(sys::Blocking<(Operation, Buf)>),
+}
+
+#[derive(Debug)]
+enum Operation {
+    Read(io::Result<usize>),
+    Write(io::Result<()>),
+    Seek(io::Result<u64>),
 }
 
 impl File {
@@ -94,12 +118,12 @@ impl File {
     /// ```
     pub async fn open<P>(path: P) -> io::Result<File>
     where
-        P: AsRef<Path> + Send + Unpin + 'static,
+        P: AsRef<Path>,
     {
-        let mut open_options = OpenOptions::new();
-        open_options.read(true);
+        let path = path.as_ref().to_owned();
+        let std = asyncify(|| sys::File::open(path)).await?;
 
-        open_options.open(path).await
+        Ok(File::from_std(std))
     }
 
     /// Opens a file in write-only mode.
@@ -132,9 +156,10 @@ impl File {
     /// ```
     pub async fn create<P>(path: P) -> io::Result<File>
     where
-        P: AsRef<Path> + Send + Unpin + 'static,
+        P: AsRef<Path>,
     {
-        let std_file = asyncify(|| std::fs::File::create(&path)).await?;
+        let path = path.as_ref().to_owned();
+        let std_file = asyncify(move || sys::File::create(path)).await?;
         Ok(File::from_std(std_file))
     }
 
@@ -151,8 +176,12 @@ impl File {
     /// let std_file = std::fs::File::open("foo.txt").unwrap();
     /// let file = tokio::fs::File::from_std(std_file);
     /// ```
-    pub fn from_std(std: std::fs::File) -> File {
-        File { std }
+    pub fn from_std(std: sys::File) -> File {
+        File {
+            std: Arc::new(std),
+            state: State::Idle(Some(Buf::with_capacity(0))),
+            last_write_err: None,
+        }
     }
 
     /// Seek to an offset, in bytes, in a stream.
@@ -174,8 +203,42 @@ impl File {
     /// # Ok(())
     /// # }
     /// ```
-    pub async fn seek(&mut self, pos: io::SeekFrom) -> io::Result<u64> {
-        asyncify(|| self.std.seek(pos)).await
+    pub async fn seek(&mut self, mut pos: SeekFrom) -> io::Result<u64> {
+        self.complete_inflight().await;
+
+        let mut buf = match self.state {
+            Idle(ref mut buf_cell) => buf_cell.take().unwrap(),
+            _ => unreachable!(),
+        };
+
+        // 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;
+            }
+        }
+
+        let std = self.std.clone();
+
+        // Start the operation
+        self.state = Busy(sys::run(move || {
+            let res = (&*std).seek(pos);
+            (Operation::Seek(res), buf)
+        }));
+
+        let (op, buf) = match self.state {
+            Idle(_) => unreachable!(),
+            Busy(ref mut rx) => rx.await,
+        };
+
+        self.state = Idle(Some(buf));
+
+        match op {
+            Operation::Seek(res) => res,
+            _ => unreachable!(),
+        }
     }
 
     /// Attempts to sync all OS-internal metadata to disk.
@@ -197,7 +260,10 @@ impl File {
     /// # }
     /// ```
     pub async fn sync_all(&mut self) -> io::Result<()> {
-        asyncify(|| self.std.sync_all()).await
+        self.complete_inflight().await;
+
+        let std = self.std.clone();
+        asyncify(move || std.sync_all()).await
     }
 
     /// This function is similar to `poll_sync_all`, except that it may not
@@ -223,7 +289,10 @@ impl File {
     /// # }
     /// ```
     pub async fn sync_data(&mut self) -> io::Result<()> {
-        asyncify(|| self.std.sync_data()).await
+        self.complete_inflight().await;
+
+        let std = self.std.clone();
+        asyncify(move || std.sync_data()).await
     }
 
     /// Truncates or extends the underlying file, updating the size of this file to become size.
@@ -252,7 +321,44 @@ impl File {
     /// # }
     /// ```
     pub async fn set_len(&mut self, size: u64) -> io::Result<()> {
-        asyncify(|| self.std.set_len(size)).await
+        self.complete_inflight().await;
+
+        let mut buf = match self.state {
+            Idle(ref mut buf_cell) => buf_cell.take().unwrap(),
+            _ => unreachable!(),
+        };
+
+        let seek = if !buf.is_empty() {
+            Some(SeekFrom::Current(buf.discard_read()))
+        } else {
+            None
+        };
+
+        let std = self.std.clone();
+
+        self.state = Busy(sys::run(move || {
+            let res = if let Some(seek) = seek {
+                (&*std).seek(seek).and_then(|_| std.set_len(size))
+            } else {
+                std.set_len(size)
+            }
+            .map(|_| 0); // the value is discarded later
+
+            // Return the result as a seek
+            (Operation::Seek(res), buf)
+        }));
+
+        let (op, buf) = match self.state {
+            Idle(_) => unreachable!(),
+            Busy(ref mut rx) => rx.await,
+        };
+
+        self.state = Idle(Some(buf));
+
+        match op {
+            Operation::Seek(res) => res.map(|_| ()),
+            _ => unreachable!(),
+        }
     }
 
     /// Queries metadata about the underlying file.
@@ -271,7 +377,8 @@ impl File {
     /// # }
     /// ```
     pub async fn metadata(&self) -> io::Result<Metadata> {
-        asyncify(|| self.std.metadata()).await
+        let std = self.std.clone();
+        asyncify(move || std.metadata()).await
     }
 
     /// Create a new `File` instance that shares the same underlying file handle
@@ -290,7 +397,8 @@ impl File {
     /// # }
     /// ```
     pub async fn try_clone(&self) -> io::Result<File> {
-        let std_file = asyncify(|| self.std.try_clone()).await?;
+        let std = self.std.clone();
+        let std_file = asyncify(move || std.try_clone()).await?;
         Ok(File::from_std(std_file))
     }
 
@@ -324,54 +432,162 @@ impl File {
     /// # }
     /// ```
     pub async fn set_permissions(&self, perm: Permissions) -> io::Result<()> {
-        asyncify(|| self.std.set_permissions(perm)).await
+        let std = self.std.clone();
+        asyncify(move || std.set_permissions(perm)).await
     }
 
-    /// Destructures the `tokio_fs::File` into a [`std::fs::File`][std].
-    ///
-    /// # Panics
-    ///
-    /// This function will panic if `shutdown` has been called.
-    ///
-    /// [std]: https://doc.rust-lang.org/std/fs/struct.File.html
-    ///
-    /// # Examples
-    ///
-    /// ```no_run
-    /// use tokio::fs::File;
-    ///
-    /// # async fn dox() -> std::io::Result<()> {
-    /// let file = File::create("foo.txt").await?;
-    /// let std_file = file.into_std();
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub fn into_std(self) -> std::fs::File {
-        self.std
+    async fn complete_inflight(&mut self) {
+        use futures_util::future::poll_fn;
+
+        if let Err(e) = poll_fn(|cx| Pin::new(&mut *self).poll_flush(cx)).await {
+            self.last_write_err = Some(e.kind());
+        }
     }
 }
 
 impl AsyncRead for File {
     fn poll_read(
-        self: Pin<&mut Self>,
-        _cx: &mut Context<'_>,
-        buf: &mut [u8],
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        dst: &mut [u8],
     ) -> Poll<io::Result<usize>> {
-        blocking_io(|| (&self.std).read(buf))
+        loop {
+            match self.state {
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    if !buf.is_empty() {
+                        let n = buf.copy_to(dst);
+                        *buf_cell = Some(buf);
+                        return Ready(Ok(n));
+                    }
+
+                    buf.ensure_capacity_for(dst);
+                    let std = self.std.clone();
+
+                    self.state = Busy(sys::run(move || {
+                        let res = buf.read_from(&mut &*std);
+                        (Operation::Read(res), buf)
+                    }));
+                }
+                Busy(ref mut rx) => {
+                    let (op, mut buf) = ready!(Pin::new(rx).poll(cx));
+
+                    match op {
+                        Operation::Read(Ok(_)) => {
+                            let n = buf.copy_to(dst);
+                            self.state = Idle(Some(buf));
+                            return Ready(Ok(n));
+                        }
+                        Operation::Read(Err(e)) => {
+                            assert!(buf.is_empty());
+
+                            self.state = Idle(Some(buf));
+                            return Ready(Err(e));
+                        }
+                        Operation::Write(Ok(_)) => {
+                            assert!(buf.is_empty());
+                            self.state = Idle(Some(buf));
+                            continue;
+                        }
+                        Operation::Write(Err(e)) => {
+                            assert!(self.last_write_err.is_none());
+                            self.last_write_err = Some(e.kind());
+                            self.state = Idle(Some(buf));
+                        }
+                        Operation::Seek(_) => {
+                            assert!(buf.is_empty());
+                            self.state = Idle(Some(buf));
+                            continue;
+                        }
+                    }
+                }
+            }
+        }
     }
 }
 
 impl AsyncWrite for File {
     fn poll_write(
-        self: Pin<&mut Self>,
-        _cx: &mut Context<'_>,
-        buf: &[u8],
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        src: &[u8],
     ) -> Poll<io::Result<usize>> {
-        blocking_io(|| (&self.std).write(buf))
+        if let Some(e) = self.last_write_err.take() {
+            return Ready(Err(e.into()));
+        }
+
+        loop {
+            match self.state {
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    let seek = if !buf.is_empty() {
+                        Some(SeekFrom::Current(buf.discard_read()))
+                    } else {
+                        None
+                    };
+
+                    let n = buf.copy_from(src);
+                    let std = self.std.clone();
+
+                    self.state = Busy(sys::run(move || {
+                        let res = if let Some(seek) = seek {
+                            (&*std).seek(seek).and_then(|_| buf.write_to(&mut &*std))
+                        } else {
+                            buf.write_to(&mut &*std)
+                        };
+
+                        (Operation::Write(res), buf)
+                    }));
+
+                    return Ready(Ok(n));
+                }
+                Busy(ref mut rx) => {
+                    let (op, buf) = ready!(Pin::new(rx).poll(cx));
+                    self.state = Idle(Some(buf));
+
+                    match op {
+                        Operation::Read(_) => {
+                            // We don't care about the result here. The fact
+                            // that the cursor has advanced will be reflected in
+                            // the next iteration of the loop
+                            continue;
+                        }
+                        Operation::Write(res) => {
+                            // If the previous write was successful, continue.
+                            // Otherwise, error.
+                            res?;
+                            continue;
+                        }
+                        Operation::Seek(_) => {
+                            // Ignore the seek
+                            continue;
+                        }
+                    }
+                }
+            }
+        }
     }
 
-    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
-        blocking_io(|| (&self.std).flush())
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        if let Some(e) = self.last_write_err.take() {
+            return Ready(Err(e.into()));
+        }
+
+        let (op, buf) = match self.state {
+            Idle(_) => return Ready(Ok(())),
+            Busy(ref mut rx) => ready!(Pin::new(rx).poll(cx)),
+        };
+
+        // The buffer is not used here
+        self.state = Idle(Some(buf));
+
+        match op {
+            Operation::Read(_) => Ready(Ok(())),
+            Operation::Write(res) => Ready(res),
+            Operation::Seek(_) => Ready(Ok(())),
+        }
     }
 
     fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
@@ -379,16 +595,16 @@ impl AsyncWrite for File {
     }
 }
 
-impl From<std::fs::File> for File {
-    fn from(std: std::fs::File) -> Self {
+impl From<sys::File> for File {
+    fn from(std: sys::File) -> Self {
         Self::from_std(std)
     }
 }
 
-impl TryFrom<File> for std::fs::File {
-    type Error = io::Error;
-
-    fn try_from(file: File) -> Result<Self, Self::Error> {
-        Ok(file.std)
+impl fmt::Debug for File {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("tokio::fs::File")
+            .field("std", &self.std)
+            .finish()
     }
 }

tokio-fs/src/hard_link.rs

@@ -12,5 +12,8 @@ use std::path::Path;
 ///
 /// [std]: https://doc.rust-lang.org/std/fs/fn.hard_link.html
 pub async fn hard_link<P: AsRef<Path>, Q: AsRef<Path>>(src: P, dst: Q) -> io::Result<()> {
-    asyncify(|| std::fs::hard_link(&src, &dst)).await
+    let src = src.as_ref().to_owned();
+    let dst = dst.as_ref().to_owned();
+
+    asyncify(move || std::fs::hard_link(src, dst)).await
 }

tokio-fs/src/lib.rs

@@ -34,6 +34,7 @@
 //! [`AsyncRead`]: https://docs.rs/tokio-io/0.1/tokio_io/trait.AsyncRead.html
 //! [tokio-executor]: https://docs.rs/tokio-executor/0.2.0-alpha.2/tokio_executor/threadpool/index.html
 
+mod blocking;
 mod create_dir;
 mod create_dir_all;
 mod file;
@@ -76,37 +77,18 @@ pub use crate::symlink_metadata::symlink_metadata;
 pub use crate::write::write;
 
 use std::io;
-use std::io::ErrorKind::Other;
-use std::task::Poll;
-use std::task::Poll::*;
-
-fn blocking_io<F, T>(f: F) -> Poll<io::Result<T>>
-where
-    F: FnOnce() -> io::Result<T>,
-{
-    use tokio_executor::threadpool::blocking;
-
-    match blocking(f) {
-        Ready(Ok(v)) => Ready(v),
-        Ready(Err(_)) => Ready(Err(blocking_err())),
-        Pending => Pending,
-    }
-}
 
 async fn asyncify<F, T>(f: F) -> io::Result<T>
 where
-    F: FnOnce() -> io::Result<T>,
+    F: FnOnce() -> io::Result<T> + Send + 'static,
+    T: Send + 'static,
 {
-    use futures_util::future::poll_fn;
-
-    let mut f = Some(f);
-    poll_fn(move |_| blocking_io(|| f.take().unwrap()())).await
+    sys::run(f).await
 }
 
-fn blocking_err() -> io::Error {
-    io::Error::new(
-        Other,
-        "`blocking` annotated I/O must be called \
-         from the context of the Tokio runtime.",
-    )
+/// Types in this module can be mocked out in tests.
+mod sys {
+    pub(crate) use std::fs::File;
+
+    pub(crate) use tokio_executor::blocking::{run, Blocking};
 }

tokio-fs/src/metadata.rs

@@ -7,7 +7,8 @@ use std::path::Path;
 /// Queries the file system metadata for a path.
 pub async fn metadata<P>(path: P) -> io::Result<Metadata>
 where
-    P: AsRef<Path> + Send + 'static,
+    P: AsRef<Path>,
 {
-    asyncify(|| std::fs::metadata(&path)).await
+    let path = path.as_ref().to_owned();
+    asyncify(|| std::fs::metadata(path)).await
 }

tokio-fs/src/open_options.rs

@@ -1,6 +1,5 @@
-use super::File;
+use crate::{asyncify, File};
 
-use futures_util::future::poll_fn;
 use std::io;
 use std::path::Path;
 
@@ -91,10 +90,13 @@ impl OpenOptions {
     /// [`open`]: https://doc.rust-lang.org/std/fs/struct.OpenOptions.html#method.open
     pub async fn open<P>(&self, path: P) -> io::Result<File>
     where
-        P: AsRef<Path> + Send + Unpin + 'static,
+        P: AsRef<Path>,
     {
-        let std_file = poll_fn(|_| crate::blocking_io(|| self.0.open(&path))).await?;
-        Ok(File::from_std(std_file))
+        let path = path.as_ref().to_owned();
+        let opts = self.0.clone();
+
+        let std = asyncify(move || opts.open(path)).await?;
+        Ok(File::from_std(std))
     }
 }
 

tokio-fs/src/os/unix/symlink.rs

@@ -11,5 +11,8 @@ use std::path::Path;
 ///
 /// [std]: https://doc.rust-lang.org/std/os/unix/fs/fn.symlink.html
 pub async fn symlink<P: AsRef<Path>, Q: AsRef<Path>>(src: P, dst: Q) -> io::Result<()> {
-    asyncify(|| std::os::unix::fs::symlink(&src, &dst)).await
+    let src = src.as_ref().to_owned();
+    let dst = dst.as_ref().to_owned();
+
+    asyncify(move || std::os::unix::fs::symlink(src, dst)).await
 }

tokio-fs/src/os/windows/symlink_dir.rs

@@ -12,5 +12,8 @@ use std::path::Path;
 ///
 /// [std]: https://doc.rust-lang.org/std/os/windows/fs/fn.symlink_dir.html
 pub async fn symlink_dir<P: AsRef<Path>, Q: AsRef<Path>>(src: P, dst: Q) -> io::Result<()> {
-    asyncify(|| std::os::windows::fs::symlink_dir(&src, &dst)).await
+    let src = src.as_ref().to_owned();
+    let dst = dst.as_ref().to_owned();
+
+    asyncify(move || std::os::windows::fs::symlink_dir(src, dst)).await
 }

tokio-fs/src/os/windows/symlink_file.rs

@@ -12,5 +12,8 @@ use std::path::Path;
 ///
 /// [std]: https://doc.rust-lang.org/std/os/windows/fs/fn.symlink_file.html
 pub async fn symlink_file<P: AsRef<Path>, Q: AsRef<Path>>(src: P, dst: Q) -> io::Result<()> {
-    asyncify(|| std::os::windows::fs::symlink_file(&src, &dst)).await
+    let src = src.as_ref().to_owned();
+    let dst = dst.as_ref().to_owned();
+
+    asyncify(move || std::os::windows::fs::symlink_file(src, dst)).await
 }

tokio-fs/src/read.rs

@@ -1,6 +1,4 @@
-use crate::File;
-
-use tokio_io::AsyncReadExt;
+use crate::asyncify;
 
 use std::{io, path::Path};
 
@@ -22,12 +20,8 @@ use std::{io, path::Path};
 /// ```
 pub async fn read<P>(path: P) -> io::Result<Vec<u8>>
 where
-    P: AsRef<Path> + Send + Unpin + 'static,
+    P: AsRef<Path>,
 {
-    let mut file = File::open(path).await?;
-    let metadata = file.metadata().await?;
-
-    let mut contents = Vec::with_capacity(metadata.len() as usize + 1);
-    file.read_to_end(&mut contents).await?;
-    Ok(contents)
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::read(path)).await
 }

tokio-fs/src/read_dir.rs

@@ -1,13 +1,16 @@
-use crate::{asyncify, blocking_io};
+use crate::{asyncify, sys};
 
+use futures_core::ready;
 use futures_core::stream::Stream;
 use std::ffi::OsString;
-use std::fs::{DirEntry as StdDirEntry, FileType, Metadata};
+use std::fs::{FileType, Metadata};
+use std::future::Future;
 use std::io;
 #[cfg(unix)]
 use std::os::unix::fs::DirEntryExt;
 use std::path::{Path, PathBuf};
 use std::pin::Pin;
+use std::sync::Arc;
 use std::task::Context;
 use std::task::Poll;
 
@@ -20,8 +23,10 @@ pub async fn read_dir<P>(path: P) -> io::Result<ReadDir>
 where
     P: AsRef<Path> + Send + 'static,
 {
-    let std = asyncify(|| std::fs::read_dir(&path)).await?;
-    Ok(ReadDir(std))
+    let path = path.as_ref().to_owned();
+    let std = asyncify(|| std::fs::read_dir(path)).await?;
+
+    Ok(ReadDir(State::Idle(Some(std))))
 }
 
 /// Stream of the entries in a directory.
@@ -42,22 +47,37 @@ where
 /// [`Err`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Err
 #[derive(Debug)]
 #[must_use = "streams do nothing unless polled"]
-pub struct ReadDir(std::fs::ReadDir);
+pub struct ReadDir(State);
+
+#[derive(Debug)]
+enum State {
+    Idle(Option<std::fs::ReadDir>),
+    Pending(sys::Blocking<(Option<io::Result<std::fs::DirEntry>>, std::fs::ReadDir)>),
+}
 
 impl Stream for ReadDir {
     type Item = io::Result<DirEntry>;
 
-    fn poll_next(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
-        let res = blocking_io(|| match self.0.next() {
-            Some(Err(err)) => Err(err),
-            Some(Ok(item)) => Ok(Some(Ok(DirEntry(item)))),
-            None => Ok(None),
-        });
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        loop {
+            match self.0 {
+                State::Idle(ref mut std) => {
+                    let mut std = std.take().unwrap();
 
-        match res {
-            Poll::Ready(Err(err)) => Poll::Ready(Some(Err(err))),
-            Poll::Ready(Ok(v)) => Poll::Ready(v),
-            Poll::Pending => Poll::Pending,
+                    self.0 = State::Pending(sys::run(move || {
+                        let ret = std.next();
+                        (ret, std)
+                    }));
+                }
+                State::Pending(ref mut rx) => {
+                    let (ret, std) = ready!(Pin::new(rx).poll(cx));
+                    self.0 = State::Idle(Some(std));
+
+                    let ret = ret.map(|res| res.map(|std| DirEntry(Arc::new(std))));
+
+                    return Poll::Ready(ret);
+                }
+            }
         }
     }
 }
@@ -75,16 +95,9 @@ impl Stream for ReadDir {
 ///
 /// [std]: https://doc.rust-lang.org/std/fs/struct.DirEntry.html
 #[derive(Debug)]
-pub struct DirEntry(StdDirEntry);
+pub struct DirEntry(Arc<std::fs::DirEntry>);
 
 impl DirEntry {
-    /// Destructures the `tokio_fs::DirEntry` into a [`std::fs::DirEntry`][std].
-    ///
-    /// [std]: https://doc.rust-lang.org/std/fs/struct.DirEntry.html
-    pub fn into_std(self) -> StdDirEntry {
-        self.0
-    }
-
     /// Returns the full path to the file that this entry represents.
     ///
     /// The full path is created by joining the original path to `read_dir`
@@ -177,7 +190,8 @@ impl DirEntry {
     /// # }
     /// ```
     pub async fn metadata(&self) -> io::Result<Metadata> {
-        asyncify(|| self.0.metadata()).await
+        let std = self.0.clone();
+        asyncify(move || std.metadata()).await
     }
 
     /// Return the file type for the file that this entry points at.
@@ -214,7 +228,8 @@ impl DirEntry {
     /// # }
     /// ```
     pub async fn file_type(&self) -> io::Result<FileType> {
-        asyncify(|| self.0.file_type()).await
+        let std = self.0.clone();
+        asyncify(move || std.file_type()).await
     }
 }
 

tokio-fs/src/read_link.rs

@@ -9,5 +9,6 @@ use std::path::{Path, PathBuf};
 ///
 /// [std]: https://doc.rust-lang.org/std/fs/fn.read_link.html
 pub async fn read_link<P: AsRef<Path>>(path: P) -> io::Result<PathBuf> {
-    asyncify(|| std::fs::read_link(&path)).await
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::read_link(path)).await
 }

tokio-fs/src/remove_dir.rs

@@ -9,5 +9,6 @@ use std::path::Path;
 ///
 /// [std]: https://doc.rust-lang.org/std/fs/fn.remove_dir.html
 pub async fn remove_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
-    asyncify(|| std::fs::remove_dir(&path)).await
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::remove_dir(path)).await
 }

tokio-fs/src/remove_dir_all.rs

@@ -9,5 +9,6 @@ use std::path::Path;
 ///
 /// [std]: https://doc.rust-lang.org/std/fs/fn.remove_dir_all.html
 pub async fn remove_dir_all<P: AsRef<Path>>(path: P) -> io::Result<()> {
-    asyncify(|| std::fs::remove_dir_all(&path)).await
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::remove_dir_all(path)).await
 }

tokio-fs/src/remove_file.rs

@@ -13,5 +13,6 @@ use std::path::Path;
 ///
 /// [std]: https://doc.rust-lang.org/std/fs/fn.remove_file.html
 pub async fn remove_file<P: AsRef<Path>>(path: P) -> io::Result<()> {
-    asyncify(|| std::fs::remove_file(&path)).await
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::remove_file(path)).await
 }

tokio-fs/src/rename.rs

@@ -12,5 +12,8 @@ use std::path::Path;
 ///
 /// [std]: https://doc.rust-lang.org/std/fs/fn.rename.html
 pub async fn rename<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> io::Result<()> {
-    asyncify(|| std::fs::rename(&from, &to)).await
+    let from = from.as_ref().to_owned();
+    let to = to.as_ref().to_owned();
+
+    asyncify(move || std::fs::rename(from, to)).await
 }

tokio-fs/src/set_permissions.rs

@@ -10,5 +10,6 @@ use std::path::Path;
 ///
 /// [std]: https://doc.rust-lang.org/std/fs/fn.set_permissions.html
 pub async fn set_permissions<P: AsRef<Path>>(path: P, perm: Permissions) -> io::Result<()> {
-    asyncify(|| std::fs::set_permissions(&path, perm)).await
+    let path = path.as_ref().to_owned();
+    asyncify(|| std::fs::set_permissions(path, perm)).await
 }

tokio-fs/src/stderr.rs

@@ -1,8 +1,8 @@
-use crate::blocking_io;
+use crate::blocking::Blocking;
 
 use tokio_io::AsyncWrite;
 
-use std::io::{self, Write};
+use std::io;
 use std::pin::Pin;
 use std::task::Context;
 use std::task::Poll;
@@ -18,7 +18,7 @@ use std::task::Poll;
 /// [`AsyncWrite`]: trait.AsyncWrite.html
 #[derive(Debug)]
 pub struct Stderr {
-    std: std::io::Stderr,
+    std: Blocking<std::io::Stderr>,
 }
 
 /// Constructs a new handle to the standard error of the current process.
@@ -27,23 +27,28 @@ pub struct Stderr {
 /// Tokio runtime.
 pub fn stderr() -> Stderr {
     let std = io::stderr();
-    Stderr { std }
+    Stderr {
+        std: Blocking::new(std),
+    }
 }
 
 impl AsyncWrite for Stderr {
     fn poll_write(
         mut self: Pin<&mut Self>,
-        _cx: &mut Context<'_>,
+        cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<io::Result<usize>> {
-        blocking_io(|| (&mut self.std).write(buf))
+        Pin::new(&mut self.std).poll_write(cx, buf)
     }
 
-    fn poll_flush(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
-        blocking_io(|| (&mut self.std).flush())
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.std).poll_flush(cx)
     }
 
-    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
-        Poll::Ready(Ok(()))
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.std).poll_shutdown(cx)
     }
 }

tokio-fs/src/stdin.rs

@@ -1,8 +1,8 @@
-use crate::blocking_io;
+use crate::blocking::Blocking;
 
 use tokio_io::AsyncRead;
 
-use std::io::{self, Read};
+use std::io;
 use std::pin::Pin;
 use std::task::Context;
 use std::task::Poll;
@@ -24,7 +24,7 @@ use std::task::Poll;
 /// [`AsyncRead`]: trait.AsyncRead.html
 #[derive(Debug)]
 pub struct Stdin {
-    std: std::io::Stdin,
+    std: Blocking<std::io::Stdin>,
 }
 
 /// Constructs a new handle to the standard input of the current process.
@@ -33,15 +33,17 @@ pub struct Stdin {
 /// Tokio runtime.
 pub fn stdin() -> Stdin {
     let std = io::stdin();
-    Stdin { std }
+    Stdin {
+        std: Blocking::new(std),
+    }
 }
 
 impl AsyncRead for Stdin {
     fn poll_read(
         mut self: Pin<&mut Self>,
-        _cx: &mut Context<'_>,
+        cx: &mut Context<'_>,
         buf: &mut [u8],
     ) -> Poll<io::Result<usize>> {
-        blocking_io(|| (&mut self.std).read(buf))
+        Pin::new(&mut self.std).poll_read(cx, buf)
     }
 }

tokio-fs/src/stdout.rs

@@ -1,8 +1,8 @@
-use crate::blocking_io;
+use crate::blocking::Blocking;
 
 use tokio_io::AsyncWrite;
 
-use std::io::{self, Write};
+use std::io;
 use std::pin::Pin;
 use std::task::Context;
 use std::task::Poll;
@@ -18,7 +18,7 @@ use std::task::Poll;
 /// [`AsyncWrite`]: trait.AsyncWrite.html
 #[derive(Debug)]
 pub struct Stdout {
-    std: std::io::Stdout,
+    std: Blocking<std::io::Stdout>,
 }
 
 /// Constructs a new handle to the standard output of the current process.
@@ -27,23 +27,28 @@ pub struct Stdout {
 /// runtime.
 pub fn stdout() -> Stdout {
     let std = io::stdout();
-    Stdout { std }
+    Stdout {
+        std: Blocking::new(std),
+    }
 }
 
 impl AsyncWrite for Stdout {
     fn poll_write(
         mut self: Pin<&mut Self>,
-        _cx: &mut Context<'_>,
+        cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<io::Result<usize>> {
-        blocking_io(|| (&mut self.std).write(buf))
+        Pin::new(&mut self.std).poll_write(cx, buf)
     }
 
-    fn poll_flush(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
-        blocking_io(|| (&mut self.std).flush())
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.std).poll_flush(cx)
     }
 
-    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
-        Poll::Ready(Ok(()))
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.std).poll_shutdown(cx)
     }
 }

tokio-fs/src/symlink_metadata.rs

@@ -13,5 +13,6 @@ pub async fn symlink_metadata<P>(path: P) -> io::Result<Metadata>
 where
     P: AsRef<Path> + Send + 'static,
 {
-    asyncify(|| std::fs::symlink_metadata(&path)).await
+    let path = path.as_ref().to_owned();
+    asyncify(|| std::fs::symlink_metadata(path)).await
 }

tokio-fs/src/write.rs

@@ -1,6 +1,4 @@
-use crate::File;
-
-use tokio_io::AsyncWriteExt;
+use crate::asyncify;
 
 use std::{io, path::Path};
 
@@ -23,8 +21,8 @@ pub async fn write<P, C: AsRef<[u8]> + Unpin>(path: P, contents: C) -> io::Resul
 where
     P: AsRef<Path> + Send + Unpin + 'static,
 {
-    let mut file = File::create(path).await?;
-    file.write_all(contents.as_ref()).await?;
+    let path = path.as_ref().to_owned();
+    let contents = contents.as_ref().to_owned();
 
-    Ok(())
+    asyncify(move || std::fs::write(path, contents)).await
 }

tokio-fs/tests/dir.rs

@@ -1,83 +1,69 @@
 #![warn(rust_2018_idioms)]
 
+use tokio::fs;
+use tokio_test::assert_ok;
+
 use futures_util::future;
 use futures_util::try_stream::TryStreamExt;
-use std::fs;
 use std::sync::{Arc, Mutex};
 use tempfile::tempdir;
-use tokio_fs::*;
 
-mod pool;
-
-#[test]
-fn create() {
+#[tokio::test]
+async fn create_dir() {
     let base_dir = tempdir().unwrap();
     let new_dir = base_dir.path().join("foo");
     let new_dir_2 = new_dir.clone();
 
-    pool::run(async move {
-        create_dir(new_dir).await?;
-        Ok(())
-    });
+    assert_ok!(fs::create_dir(new_dir).await);
 
     assert!(new_dir_2.is_dir());
 }
 
-#[test]
-fn create_all() {
+#[tokio::test]
+async fn create_all() {
     let base_dir = tempdir().unwrap();
     let new_dir = base_dir.path().join("foo").join("bar");
     let new_dir_2 = new_dir.clone();
 
-    pool::run(async move {
-        create_dir_all(new_dir).await?;
-        Ok(())
-    });
-
+    assert_ok!(fs::create_dir_all(new_dir).await);
     assert!(new_dir_2.is_dir());
 }
 
-#[test]
-fn remove() {
+#[tokio::test]
+async fn remove() {
     let base_dir = tempdir().unwrap();
     let new_dir = base_dir.path().join("foo");
     let new_dir_2 = new_dir.clone();
 
-    fs::create_dir(new_dir.clone()).unwrap();
-
-    pool::run(async move {
-        remove_dir(new_dir).await?;
-        Ok(())
-    });
+    std::fs::create_dir(new_dir.clone()).unwrap();
 
+    assert_ok!(fs::remove_dir(new_dir).await);
     assert!(!new_dir_2.exists());
 }
 
-#[test]
-fn read() {
+#[tokio::test]
+async fn read() {
     let base_dir = tempdir().unwrap();
 
     let p = base_dir.path();
-    fs::create_dir(p.join("aa")).unwrap();
-    fs::create_dir(p.join("bb")).unwrap();
-    fs::create_dir(p.join("cc")).unwrap();
+    std::fs::create_dir(p.join("aa")).unwrap();
+    std::fs::create_dir(p.join("bb")).unwrap();
+    std::fs::create_dir(p.join("cc")).unwrap();
 
     let files = Arc::new(Mutex::new(Vec::new()));
 
     let f = files.clone();
     let p = p.to_path_buf();
 
-    pool::run(async move {
-        let read_dir_fut = read_dir(p).await?;
-        read_dir_fut
-            .try_for_each(move |e| {
-                let s = e.file_name().to_str().unwrap().to_string();
-                f.lock().unwrap().push(s);
-                future::ok(())
-            })
-            .await?;
-        Ok(())
-    });
+    let read_dir_fut = fs::read_dir(p).await.unwrap();
+    read_dir_fut
+        .try_for_each(move |e| {
+            let s = e.file_name().to_str().unwrap().to_string();
+            f.lock().unwrap().push(s);
+            future::ok(())
+        })
+        .await
+        .unwrap();
 
     let mut files = files.lock().unwrap();
     files.sort(); // because the order is not guaranteed

tokio-fs/tests/file.rs

@@ -1,12 +1,54 @@
 #![warn(rust_2018_idioms)]
 
+use tokio::fs::File;
+use tokio::prelude::*;
+
+use std::io::prelude::*;
+use tempfile::NamedTempFile;
+
+/*
 use rand::{distributions, thread_rng, Rng};
 use std::fs;
 use std::io::SeekFrom;
 use tempfile::Builder as TmpBuilder;
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio_fs::*;
+*/
 
+const HELLO: &[u8] = b"hello world...";
+
+#[tokio::test]
+async fn basic_read() {
+    let mut tempfile = tempfile();
+    tempfile.write_all(HELLO).unwrap();
+
+    let mut file = File::open(tempfile.path()).await.unwrap();
+
+    let mut buf = [0; 1024];
+    let n = file.read(&mut buf).await.unwrap();
+
+    assert_eq!(n, HELLO.len());
+    assert_eq!(&buf[..n], HELLO);
+}
+
+#[tokio::test]
+async fn basic_write() {
+    let tempfile = tempfile();
+
+    let mut file = File::create(tempfile.path()).await.unwrap();
+
+    file.write_all(HELLO).await.unwrap();
+    file.flush().await.unwrap();
+
+    let file = std::fs::read(tempfile.path()).unwrap();
+    assert_eq!(file, HELLO);
+}
+
+fn tempfile() -> NamedTempFile {
+    NamedTempFile::new().unwrap()
+}
+
+/*
 mod pool;
 
 #[test]
@@ -154,3 +196,4 @@ fn clone() {
 
     assert_eq!(dst, b"clone successful")
 }
+*/

tokio-fs/tests/file_mocked.rs

@@ -0,0 +1,736 @@
+#![warn(rust_2018_idioms)]
+
+mod sys {
+    mod file;
+    pub(crate) mod pool;
+
+    pub(crate) use self::file::File;
+    pub(crate) use self::pool::{run, Blocking};
+}
+use sys::pool::{self, asyncify};
+
+#[allow(warnings)]
+#[path = "../src/file.rs"]
+mod file;
+use file::File;
+
+#[allow(warnings)]
+#[path = "../src/blocking.rs"]
+mod blocking;
+
+use tokio::prelude::*;
+use tokio_test::{assert_pending, assert_ready, assert_ready_err, assert_ready_ok, task};
+
+use std::io::SeekFrom;
+
+const HELLO: &[u8] = b"hello world...";
+const FOO: &[u8] = b"foo bar baz...";
+
+#[test]
+fn open_read() {
+    let (mock, file) = sys::File::mock();
+    mock.read(HELLO);
+
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 1024];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_eq!(0, pool::len());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, mock.remaining());
+    assert_eq!(1, pool::len());
+
+    pool::run_one();
+
+    assert_eq!(0, mock.remaining());
+    assert!(t.is_woken());
+
+    let n = assert_ready_ok!(t.poll());
+    assert_eq!(n, HELLO.len());
+    assert_eq!(&buf[..n], HELLO);
+}
+
+#[test]
+fn read_twice_before_dispatch() {
+    let (mock, file) = sys::File::mock();
+    mock.read(HELLO);
+
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 1024];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_pending!(t.poll());
+    assert_pending!(t.poll());
+
+    assert_eq!(pool::len(), 1);
+    pool::run_one();
+
+    assert!(t.is_woken());
+
+    let n = assert_ready_ok!(t.poll());
+    assert_eq!(&buf[..n], HELLO);
+}
+
+#[test]
+fn read_with_smaller_buf() {
+    let (mock, file) = sys::File::mock();
+    mock.read(HELLO);
+
+    let mut file = File::from_std(file);
+
+    {
+        let mut buf = [0; 32];
+        let mut t = task::spawn(file.read(&mut buf));
+        assert_pending!(t.poll());
+    }
+
+    pool::run_one();
+
+    {
+        let mut buf = [0; 4];
+        let mut t = task::spawn(file.read(&mut buf));
+        let n = assert_ready_ok!(t.poll());
+        assert_eq!(n, 4);
+        assert_eq!(&buf[..], &HELLO[..n]);
+    }
+
+    // Calling again immediately succeeds with the rest of the buffer
+    let mut buf = [0; 32];
+    let mut t = task::spawn(file.read(&mut buf));
+    let n = assert_ready_ok!(t.poll());
+    assert_eq!(n, 10);
+    assert_eq!(&buf[..n], &HELLO[4..]);
+
+    assert_eq!(0, pool::len());
+}
+
+#[test]
+fn read_with_bigger_buf() {
+    let (mock, file) = sys::File::mock();
+    mock.read(&HELLO[..4]).read(&HELLO[4..]);
+
+    let mut file = File::from_std(file);
+
+    {
+        let mut buf = [0; 4];
+        let mut t = task::spawn(file.read(&mut buf));
+        assert_pending!(t.poll());
+    }
+
+    pool::run_one();
+
+    {
+        let mut buf = [0; 32];
+        let mut t = task::spawn(file.read(&mut buf));
+        let n = assert_ready_ok!(t.poll());
+        assert_eq!(n, 4);
+        assert_eq!(&buf[..n], &HELLO[..n]);
+    }
+
+    // Calling again immediately succeeds with the rest of the buffer
+    let mut buf = [0; 32];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+
+    let n = assert_ready_ok!(t.poll());
+    assert_eq!(n, 10);
+    assert_eq!(&buf[..n], &HELLO[4..]);
+
+    assert_eq!(0, pool::len());
+}
+
+#[test]
+fn read_err_then_read_success() {
+    let (mock, file) = sys::File::mock();
+    mock.read_err().read(&HELLO);
+
+    let mut file = File::from_std(file);
+
+    {
+        let mut buf = [0; 32];
+        let mut t = task::spawn(file.read(&mut buf));
+        assert_pending!(t.poll());
+
+        pool::run_one();
+
+        assert_ready_err!(t.poll());
+    }
+
+    {
+        let mut buf = [0; 32];
+        let mut t = task::spawn(file.read(&mut buf));
+        assert_pending!(t.poll());
+
+        pool::run_one();
+
+        let n = assert_ready_ok!(t.poll());
+
+        assert_eq!(n, HELLO.len());
+        assert_eq!(&buf[..n], HELLO);
+    }
+}
+
+#[test]
+fn open_write() {
+    let (mock, file) = sys::File::mock();
+    mock.write(HELLO);
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+
+    assert_eq!(0, pool::len());
+    assert_ready_ok!(t.poll());
+
+    assert_eq!(1, mock.remaining());
+    assert_eq!(1, pool::len());
+
+    pool::run_one();
+
+    assert_eq!(0, mock.remaining());
+    assert!(!t.is_woken());
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn flush_while_idle() {
+    let (_mock, file) = sys::File::mock();
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn read_with_buffer_larger_than_max() {
+    // Chunks
+    let a = 16 * 1024;
+    let b = a * 2;
+    let c = a * 3;
+    let d = a * 4;
+
+    assert_eq!(d / 1024, 64);
+
+    let mut data = vec![];
+    for i in 0..(d - 1) {
+        data.push((i % 151) as u8);
+    }
+
+    let (mock, file) = sys::File::mock();
+    mock.read(&data[0..a])
+        .read(&data[a..b])
+        .read(&data[b..c])
+        .read(&data[c..]);
+
+    let mut file = File::from_std(file);
+
+    let mut actual = vec![0; d];
+    let mut pos = 0;
+
+    while pos < data.len() {
+        let mut t = task::spawn(file.read(&mut actual[pos..]));
+
+        assert_pending!(t.poll());
+        pool::run_one();
+        assert!(t.is_woken());
+
+        let n = assert_ready_ok!(t.poll());
+        assert!(n <= a);
+
+        pos += n;
+    }
+
+    assert_eq!(mock.remaining(), 0);
+    assert_eq!(data, &actual[..data.len()]);
+}
+
+#[test]
+fn write_with_buffer_larger_than_max() {
+    // Chunks
+    let a = 16 * 1024;
+    let b = a * 2;
+    let c = a * 3;
+    let d = a * 4;
+
+    assert_eq!(d / 1024, 64);
+
+    let mut data = vec![];
+    for i in 0..(d - 1) {
+        data.push((i % 151) as u8);
+    }
+
+    let (mock, file) = sys::File::mock();
+    mock.write(&data[0..a])
+        .write(&data[a..b])
+        .write(&data[b..c])
+        .write(&data[c..]);
+
+    let mut file = File::from_std(file);
+
+    let mut rem = &data[..];
+
+    let mut first = true;
+
+    while !rem.is_empty() {
+        let mut t = task::spawn(file.write(rem));
+
+        if !first {
+            assert_pending!(t.poll());
+            pool::run_one();
+            assert!(t.is_woken());
+        }
+
+        first = false;
+
+        let n = assert_ready_ok!(t.poll());
+
+        rem = &rem[n..];
+    }
+
+    pool::run_one();
+
+    assert_eq!(mock.remaining(), 0);
+}
+
+#[test]
+fn write_twice_before_dispatch() {
+    let (mock, file) = sys::File::mock();
+    mock.write(HELLO).write(FOO);
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_pending!(t.poll());
+
+    assert_eq!(pool::len(), 1);
+    pool::run_one();
+
+    assert!(t.is_woken());
+
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.flush());
+    assert_pending!(t.poll());
+
+    assert_eq!(pool::len(), 1);
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn incomplete_read_followed_by_write() {
+    let (mock, file) = sys::File::mock();
+    mock.read(HELLO)
+        .seek_current_ok(-(HELLO.len() as i64), 0)
+        .write(FOO);
+
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 32];
+
+    let mut t = task::spawn(file.read(&mut buf));
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_ok!(t.poll());
+
+    assert_eq!(pool::len(), 1);
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn incomplete_partial_read_followed_by_write() {
+    let (mock, file) = sys::File::mock();
+    mock.read(HELLO).seek_current_ok(-10, 0).write(FOO);
+
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 32];
+    let mut t = task::spawn(file.read(&mut buf));
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    let mut buf = [0; 4];
+    let mut t = task::spawn(file.read(&mut buf));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_ok!(t.poll());
+
+    assert_eq!(pool::len(), 1);
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn incomplete_read_followed_by_flush() {
+    let (mock, file) = sys::File::mock();
+    mock.read(HELLO)
+        .seek_current_ok(-(HELLO.len() as i64), 0)
+        .write(FOO);
+
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 32];
+
+    let mut t = task::spawn(file.read(&mut buf));
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_ok!(t.poll());
+
+    pool::run_one();
+}
+
+#[test]
+fn incomplete_flush_followed_by_write() {
+    let (mock, file) = sys::File::mock();
+    mock.write(HELLO).write(FOO);
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+    let n = assert_ready_ok!(t.poll());
+    assert_eq!(n, HELLO.len());
+
+    let mut t = task::spawn(file.flush());
+    assert_pending!(t.poll());
+
+    // TODO: Move under write
+    pool::run_one();
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_ok!(t.poll());
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn read_err() {
+    let (mock, file) = sys::File::mock();
+    mock.read_err();
+
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 1024];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_pending!(t.poll());
+
+    pool::run_one();
+    assert!(t.is_woken());
+
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn write_write_err() {
+    let (mock, file) = sys::File::mock();
+    mock.write_err();
+
+    let mut file = 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.write(FOO));
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn write_read_write_err() {
+    let (mock, file) = sys::File::mock();
+    mock.write_err().read(HELLO);
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    pool::run_one();
+
+    let mut buf = [0; 1024];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn write_read_flush_err() {
+    let (mock, file) = sys::File::mock();
+    mock.write_err().read(HELLO);
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    pool::run_one();
+
+    let mut buf = [0; 1024];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn write_seek_write_err() {
+    let (mock, file) = sys::File::mock();
+    mock.write_err().seek_start_ok(0);
+
+    let mut file = 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_pending!(t.poll());
+    }
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn write_seek_flush_err() {
+    let (mock, file) = sys::File::mock();
+    mock.write_err().seek_start_ok(0);
+
+    let mut file = 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_pending!(t.poll());
+    }
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn sync_all_ordered_after_write() {
+    let (mock, file) = sys::File::mock();
+    mock.write(HELLO).sync_all();
+
+    let mut file = File::from_std(file);
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.sync_all());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn sync_all_err_ordered_after_write() {
+    let (mock, file) = sys::File::mock();
+    mock.write(HELLO).sync_all_err();
+
+    let mut file = File::from_std(file);
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.sync_all());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn sync_data_ordered_after_write() {
+    let (mock, file) = sys::File::mock();
+    mock.write(HELLO).sync_data();
+
+    let mut file = File::from_std(file);
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.sync_data());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn sync_data_err_ordered_after_write() {
+    let (mock, file) = sys::File::mock();
+    mock.write(HELLO).sync_data_err();
+
+    let mut file = File::from_std(file);
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.sync_data());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn open_set_len_ok() {
+    let (mock, file) = sys::File::mock();
+    mock.set_len(123);
+
+    let mut file = File::from_std(file);
+    let mut t = task::spawn(file.set_len(123));
+
+    assert_pending!(t.poll());
+    assert_eq!(1, mock.remaining());
+
+    pool::run_one();
+    assert_eq!(0, mock.remaining());
+
+    assert!(t.is_woken());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn open_set_len_err() {
+    let (mock, file) = sys::File::mock();
+    mock.set_len_err(123);
+
+    let mut file = File::from_std(file);
+    let mut t = task::spawn(file.set_len(123));
+
+    assert_pending!(t.poll());
+    assert_eq!(1, mock.remaining());
+
+    pool::run_one();
+    assert_eq!(0, mock.remaining());
+
+    assert!(t.is_woken());
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn partial_read_set_len_ok() {
+    let (mock, file) = sys::File::mock();
+    mock.read(HELLO)
+        .seek_current_ok(-14, 0)
+        .set_len(123)
+        .read(FOO);
+
+    let mut buf = [0; 32];
+    let mut file = File::from_std(file);
+
+    {
+        let mut t = task::spawn(file.read(&mut buf));
+        assert_pending!(t.poll());
+    }
+
+    pool::run_one();
+
+    {
+        let mut t = task::spawn(file.set_len(123));
+
+        assert_pending!(t.poll());
+        pool::run_one();
+        assert_ready_ok!(t.poll());
+    }
+
+    let mut t = task::spawn(file.read(&mut buf));
+    assert_pending!(t.poll());
+    pool::run_one();
+    let n = assert_ready_ok!(t.poll());
+
+    assert_eq!(n, FOO.len());
+    assert_eq!(&buf[..n], FOO);
+}

tokio-fs/tests/link.rs

@@ -1,35 +1,30 @@
 #![warn(rust_2018_idioms)]
 
-use std::fs;
+use tokio::fs;
+
 use std::io::prelude::*;
 use std::io::BufReader;
 use tempfile::tempdir;
-use tokio_fs::*;
 
-mod pool;
-
-#[test]
-fn test_hard_link() {
+#[tokio::test]
+async fn test_hard_link() {
     let dir = tempdir().unwrap();
     let src = dir.path().join("src.txt");
     let dst = dir.path().join("dst.txt");
 
     {
-        let mut file = fs::File::create(&src).unwrap();
+        let mut file = std::fs::File::create(&src).unwrap();
         file.write_all(b"hello").unwrap();
     }
 
     let dst_2 = dst.clone();
 
-    pool::run(async move {
-        assert!(hard_link(src, dst_2.clone()).await.is_ok());
-        Ok(())
-    });
+    assert!(fs::hard_link(src, dst_2.clone()).await.is_ok());
 
     let mut content = String::new();
 
     {
-        let file = fs::File::open(dst).unwrap();
+        let file = std::fs::File::open(dst).unwrap();
         let mut reader = BufReader::new(file);
         reader.read_to_string(&mut content).unwrap();
     }
@@ -38,43 +33,37 @@ fn test_hard_link() {
 }
 
 #[cfg(unix)]
-#[test]
-fn test_symlink() {
+#[tokio::test]
+async fn test_symlink() {
     let dir = tempdir().unwrap();
     let src = dir.path().join("src.txt");
     let dst = dir.path().join("dst.txt");
 
     {
-        let mut file = fs::File::create(&src).unwrap();
+        let mut file = std::fs::File::create(&src).unwrap();
         file.write_all(b"hello").unwrap();
     }
 
     let src_2 = src.clone();
     let dst_2 = dst.clone();
 
-    pool::run(async move {
-        assert!(os::unix::symlink(src_2.clone(), dst_2.clone())
-            .await
-            .is_ok());
-        Ok(())
-    });
+    assert!(fs::os::unix::symlink(src_2.clone(), dst_2.clone())
+        .await
+        .is_ok());
 
     let mut content = String::new();
 
     {
-        let file = fs::File::open(dst.clone()).unwrap();
+        let file = std::fs::File::open(dst.clone()).unwrap();
         let mut reader = BufReader::new(file);
         reader.read_to_string(&mut content).unwrap();
     }
 
     assert!(content == "hello");
 
-    pool::run(async move {
-        let read = read_link(dst.clone()).await.unwrap();
-        assert!(read == src);
+    let read = fs::read_link(dst.clone()).await.unwrap();
+    assert!(read == src);
 
-        let symlink_meta = symlink_metadata(dst.clone()).await.unwrap();
-        assert!(symlink_meta.file_type().is_symlink());
-        Ok(())
-    });
+    let symlink_meta = fs::symlink_metadata(dst.clone()).await.unwrap();
+    assert!(symlink_meta.file_type().is_symlink());
 }

tokio-fs/tests/pool/mod.rs

@@ -1,18 +0,0 @@
-use tokio_executor::threadpool::Builder;
-
-use std::future::Future;
-use std::io;
-use std::sync::mpsc;
-
-pub fn run<F>(f: F)
-where
-    F: Future<Output = io::Result<()>> + Send + 'static,
-{
-    let pool = Builder::new().pool_size(1).build();
-    let (tx, rx) = mpsc::channel();
-    pool.spawn(async move {
-        f.await.unwrap();
-        tx.send(()).unwrap();
-    });
-    rx.recv().unwrap()
-}

tokio-fs/tests/sys/file.rs

@@ -0,0 +1,265 @@
+use std::collections::VecDeque;
+use std::fmt;
+use std::fs::{Metadata, Permissions};
+use std::io;
+use std::io::prelude::*;
+use std::io::SeekFrom;
+use std::path::PathBuf;
+use std::sync::{Arc, Mutex};
+
+pub struct File {
+    shared: Arc<Mutex<Shared>>,
+}
+
+pub struct Handle {
+    shared: Arc<Mutex<Shared>>,
+}
+
+struct Shared {
+    calls: VecDeque<Call>,
+}
+
+#[derive(Debug)]
+enum Call {
+    Read(io::Result<Vec<u8>>),
+    Write(io::Result<Vec<u8>>),
+    Seek(SeekFrom, io::Result<u64>),
+    SyncAll(io::Result<()>),
+    SyncData(io::Result<()>),
+    SetLen(u64, io::Result<()>),
+}
+
+impl Handle {
+    pub fn read(&self, data: &[u8]) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls.push_back(Call::Read(Ok(data.to_owned())));
+        self
+    }
+
+    pub fn read_err(&self) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls
+            .push_back(Call::Read(Err(io::ErrorKind::Other.into())));
+        self
+    }
+
+    pub fn write(&self, data: &[u8]) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls.push_back(Call::Write(Ok(data.to_owned())));
+        self
+    }
+
+    pub fn write_err(&self) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls
+            .push_back(Call::Write(Err(io::ErrorKind::Other.into())));
+        self
+    }
+
+    pub fn seek_start_ok(&self, offset: u64) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls
+            .push_back(Call::Seek(SeekFrom::Start(offset), Ok(offset)));
+        self
+    }
+
+    pub fn seek_current_ok(&self, offset: i64, ret: u64) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls
+            .push_back(Call::Seek(SeekFrom::Current(offset), Ok(ret)));
+        self
+    }
+
+    pub fn sync_all(&self) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls.push_back(Call::SyncAll(Ok(())));
+        self
+    }
+
+    pub fn sync_all_err(&self) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls
+            .push_back(Call::SyncAll(Err(io::ErrorKind::Other.into())));
+        self
+    }
+
+    pub fn sync_data(&self) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls.push_back(Call::SyncData(Ok(())));
+        self
+    }
+
+    pub fn sync_data_err(&self) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls
+            .push_back(Call::SyncData(Err(io::ErrorKind::Other.into())));
+        self
+    }
+
+    pub fn set_len(&self, size: u64) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls.push_back(Call::SetLen(size, Ok(())));
+        self
+    }
+
+    pub fn set_len_err(&self, size: u64) -> &Self {
+        let mut s = self.shared.lock().unwrap();
+        s.calls
+            .push_back(Call::SetLen(size, Err(io::ErrorKind::Other.into())));
+        self
+    }
+
+    pub fn remaining(&self) -> usize {
+        let s = self.shared.lock().unwrap();
+        s.calls.len()
+    }
+}
+
+impl Drop for Handle {
+    fn drop(&mut self) {
+        if !std::thread::panicking() {
+            let s = self.shared.lock().unwrap();
+            assert_eq!(0, s.calls.len());
+        }
+    }
+}
+
+impl File {
+    pub fn open(_: PathBuf) -> io::Result<File> {
+        unimplemented!();
+    }
+
+    pub fn create(_: PathBuf) -> io::Result<File> {
+        unimplemented!();
+    }
+
+    pub fn mock() -> (Handle, File) {
+        let shared = Arc::new(Mutex::new(Shared {
+            calls: VecDeque::new(),
+        }));
+
+        let handle = Handle {
+            shared: shared.clone(),
+        };
+        let file = File { shared };
+
+        (handle, file)
+    }
+
+    pub fn sync_all(&self) -> io::Result<()> {
+        use self::Call::*;
+
+        let mut s = self.shared.lock().unwrap();
+
+        match s.calls.pop_front() {
+            Some(SyncAll(ret)) => ret,
+            Some(op) => panic!("expected next call to be {:?}; was sync_all", op),
+            None => panic!("did not expect call"),
+        }
+    }
+
+    pub fn sync_data(&self) -> io::Result<()> {
+        use self::Call::*;
+
+        let mut s = self.shared.lock().unwrap();
+
+        match s.calls.pop_front() {
+            Some(SyncData(ret)) => ret,
+            Some(op) => panic!("expected next call to be {:?}; was sync_all", op),
+            None => panic!("did not expect call"),
+        }
+    }
+
+    pub fn set_len(&self, size: u64) -> io::Result<()> {
+        use self::Call::*;
+
+        let mut s = self.shared.lock().unwrap();
+
+        match s.calls.pop_front() {
+            Some(SetLen(arg, ret)) => {
+                assert_eq!(arg, size);
+                ret
+            }
+            Some(op) => panic!("expected next call to be {:?}; was sync_all", op),
+            None => panic!("did not expect call"),
+        }
+    }
+
+    pub fn metadata(&self) -> io::Result<Metadata> {
+        unimplemented!();
+    }
+
+    pub fn set_permissions(&self, _perm: Permissions) -> io::Result<()> {
+        unimplemented!();
+    }
+
+    pub fn try_clone(&self) -> io::Result<Self> {
+        unimplemented!();
+    }
+}
+
+impl Read for &'_ File {
+    fn read(&mut self, dst: &mut [u8]) -> io::Result<usize> {
+        use self::Call::*;
+
+        let mut s = self.shared.lock().unwrap();
+
+        match s.calls.pop_front() {
+            Some(Read(Ok(data))) => {
+                assert!(dst.len() >= data.len());
+                assert!(dst.len() <= 16 * 1024, "actual = {}", dst.len()); // max buffer
+
+                &mut dst[..data.len()].copy_from_slice(&data);
+                Ok(data.len())
+            }
+            Some(Read(Err(e))) => Err(e),
+            Some(op) => panic!("expected next call to be {:?}; was a read", op),
+            None => panic!("did not expect call"),
+        }
+    }
+}
+
+impl Write for &'_ File {
+    fn write(&mut self, src: &[u8]) -> io::Result<usize> {
+        use self::Call::*;
+
+        let mut s = self.shared.lock().unwrap();
+
+        match s.calls.pop_front() {
+            Some(Write(Ok(data))) => {
+                assert_eq!(src, &data[..]);
+                Ok(src.len())
+            }
+            Some(Write(Err(e))) => Err(e),
+            Some(op) => panic!("expected next call to be {:?}; was write", op),
+            None => panic!("did not expect call"),
+        }
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}
+
+impl Seek for &'_ File {
+    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
+        use self::Call::*;
+
+        let mut s = self.shared.lock().unwrap();
+
+        match s.calls.pop_front() {
+            Some(Seek(expect, res)) => {
+                assert_eq!(expect, pos);
+                res
+            }
+            Some(op) => panic!("expected call {:?}; was `seek`", op),
+            None => panic!("did not expect call; was `seek`"),
+        }
+    }
+}
+
+impl fmt::Debug for File {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("mock::File").finish()
+    }
+}

tokio-fs/tests/sys/pool.rs

@@ -0,0 +1,66 @@
+use tokio_sync::oneshot;
+
+use std::cell::RefCell;
+use std::collections::VecDeque;
+use std::future::Future;
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+thread_local! {
+    static QUEUE: RefCell<VecDeque<Box<dyn FnOnce() + Send>>> = RefCell::new(VecDeque::new())
+}
+
+#[derive(Debug)]
+pub(crate) struct Blocking<T> {
+    rx: oneshot::Receiver<T>,
+}
+
+pub(crate) fn run<F, R>(f: F) -> Blocking<R>
+where
+    F: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
+{
+    let (tx, rx) = oneshot::channel();
+    let task = Box::new(move || {
+        let _ = tx.send(f());
+    });
+
+    QUEUE.with(|cell| cell.borrow_mut().push_back(task));
+
+    Blocking { rx }
+}
+
+impl<T> Future for Blocking<T> {
+    type Output = T;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        use std::task::Poll::*;
+
+        match Pin::new(&mut self.rx).poll(cx) {
+            Ready(Ok(v)) => Ready(v),
+            Ready(Err(e)) => panic!("error = {:?}", e),
+            Pending => Pending,
+        }
+    }
+}
+
+pub(crate) async fn asyncify<F, T>(f: F) -> io::Result<T>
+where
+    F: FnOnce() -> io::Result<T> + Send + 'static,
+    T: Send + 'static,
+{
+    run(f).await
+}
+
+pub(crate) fn len() -> usize {
+    QUEUE.with(|cell| cell.borrow().len())
+}
+
+pub(crate) fn run_one() {
+    let task = QUEUE
+        .with(|cell| cell.borrow_mut().pop_front())
+        .expect("expected task to run, but none ready");
+
+    task();
+}