io: use intrusive wait list for I/O driver (#2828)

This refactors I/O registration in a few ways:

- Cleans up the cached readiness in `PollEvented`. This cache used to
  be helpful when readiness was a linked list of `*mut Node`s in
  `Registration`. Previous refactors have turned `Registration` into just
  an `AtomicUsize` holding the current readiness, so the cache is just
  extra work and complexity. Gone.
- Polling the `Registration` for readiness now gives a `ReadyEvent`,
  which includes the driver tick. This event must be passed back into
  `clear_readiness`, so that the readiness is only cleared from `Registration`
  if the tick hasn't changed. Previously, it was possible to clear the
  readiness even though another thread had *just* polled the driver and
  found the socket ready again.
- Registration now also contains an `async fn readiness`, which stores
  wakers in an instrusive linked list. This allows an unbounded number
  of tasks to register for readiness (previously, only 1 per direction (read
  and write)). By using the intrusive linked list, there is no concern of
  leaking the storage of the wakers, since they are stored inside the `async fn`
  and released when the future is dropped.
- Registration retains a `poll_readiness(Direction)` method, to support
  `AsyncRead` and `AsyncWrite`. They aren't able to use `async fn`s, and
  so there are 2 reserved slots for those methods.
- IO types where it makes sense to have multiple tasks waiting on them
  now take advantage of this new `async fn readiness`, such as `UdpSocket`
  and `UnixDatagram`.

Additionally, this makes the `io-driver` "feature" internal-only (no longer
documented, not part of public API), and adds a second internal-only
feature, `io-readiness`, to group together linked list part of registration
that is only used by some of the IO types.

After a bit of discussion, changing stream-based transports (like
`TcpStream`) to have `async fn read(&self)` is punted, since that
is likely too easy of a footgun to activate.

Refs: #2779, #2728

.github/workflows/ci.yml

@@ -150,11 +150,11 @@ jobs:
         run: cargo install cargo-hack
 
       - name: check --each-feature
-        run: cargo hack check --all --each-feature -Z avoid-dev-deps
+        run: cargo hack check --all --each-feature --skip io-driver,io-readiness -Z avoid-dev-deps
 
       # Try with unstable feature flags
       - name: check --each-feature --unstable
-        run: cargo hack check --all --each-feature -Z avoid-dev-deps
+        run: cargo hack check --all --each-feature --skip io-driver,io-readiness -Z avoid-dev-deps
         env:
           RUSTFLAGS: --cfg tokio_unstable -Dwarnings
 

examples/connect.rs

@@ -96,7 +96,6 @@ mod udp {
     use std::error::Error;
     use std::io;
     use std::net::SocketAddr;
-    use tokio::net::udp::{RecvHalf, SendHalf};
     use tokio::net::UdpSocket;
 
     pub async fn connect(
@@ -114,16 +113,15 @@ mod udp {
 
         let socket = UdpSocket::bind(&bind_addr).await?;
         socket.connect(addr).await?;
-        let (mut r, mut w) = socket.split();
 
-        future::try_join(send(stdin, &mut w), recv(stdout, &mut r)).await?;
+        future::try_join(send(stdin, &socket), recv(stdout, &socket)).await?;
 
         Ok(())
     }
 
     async fn send(
         mut stdin: impl Stream<Item = Result<Bytes, io::Error>> + Unpin,
-        writer: &mut SendHalf,
+        writer: &UdpSocket,
     ) -> Result<(), io::Error> {
         while let Some(item) = stdin.next().await {
             let buf = item?;
@@ -135,7 +133,7 @@ mod udp {
 
     async fn recv(
         mut stdout: impl Sink<Bytes, Error = io::Error> + Unpin,
-        reader: &mut RecvHalf,
+        reader: &UdpSocket,
     ) -> Result<(), io::Error> {
         loop {
             let mut buf = vec![0; 1024];

examples/echo-udp.rs

@@ -26,7 +26,7 @@ struct Server {
 impl Server {
     async fn run(self) -> Result<(), io::Error> {
         let Server {
-            mut socket,
+            socket,
             mut buf,
             mut to_send,
         } = self;

examples/udp-client.rs

@@ -55,7 +55,7 @@ async fn main() -> Result<(), Box<dyn Error>> {
     }
     .parse()?;
 
-    let mut socket = UdpSocket::bind(local_addr).await?;
+    let socket = UdpSocket::bind(local_addr).await?;
     const MAX_DATAGRAM_SIZE: usize = 65_507;
     socket.connect(&remote_addr).await?;
     let data = get_stdin_data()?;

examples/udp-codec.rs

@@ -1,3 +1,8 @@
+fn main() {}
+
+// Disabled while future of UdpFramed is decided on.
+// See https://github.com/tokio-rs/tokio/issues/2830
+/*
 //! This example leverages `BytesCodec` to create a UDP client and server which
 //! speak a custom protocol.
 //!
@@ -78,3 +83,4 @@ async fn pong(socket: &mut UdpFramed<BytesCodec>) -> Result<(), io::Error> {
 
     Ok(())
 }
+*/

tokio-util/Cargo.toml

@@ -25,11 +25,10 @@ publish = false
 default = []
 
 # Shorthand for enabling everything
-full = ["codec", "udp", "compat", "io"]
+full = ["codec", "compat", "io"]
 
 compat = ["futures-io",]
 codec = ["tokio/stream"]
-udp = ["tokio/udp"]
 io = []
 
 [dependencies]

tokio-util/src/cfg.rs

@@ -18,6 +18,7 @@ macro_rules! cfg_compat {
     }
 }
 
+/*
 macro_rules! cfg_udp {
     ($($item:item)*) => {
         $(
@@ -27,6 +28,7 @@ macro_rules! cfg_udp {
         )*
     }
 }
+*/
 
 macro_rules! cfg_io {
     ($($item:item)*) => {

tokio-util/src/lib.rs

@@ -30,9 +30,14 @@ cfg_codec! {
     pub mod codec;
 }
 
+/*
+Disabled due to removal of poll_ functions on UdpSocket.
+
+See https://github.com/tokio-rs/tokio/issues/2830
 cfg_udp! {
     pub mod udp;
 }
+*/
 
 cfg_compat! {
     pub mod compat;

tokio-util/tests/udp.rs

@@ -1,3 +1,4 @@
+/*
 #![warn(rust_2018_idioms)]
 
 use tokio::{net::UdpSocket, stream::StreamExt};
@@ -100,3 +101,4 @@ async fn send_framed_lines_codec() -> std::io::Result<()> {
 
     Ok(())
 }
+*/

tokio/Cargo.toml

@@ -33,7 +33,6 @@ full = [
   "blocking",
   "dns",
   "fs",
-  "io-driver",
   "io-util",
   "io-std",
   "macros",
@@ -51,7 +50,8 @@ full = [
 blocking = ["rt-core"]
 dns = ["rt-core"]
 fs = ["rt-core", "io-util"]
-io-driver = ["mio", "lazy_static"]
+io-driver = ["mio", "lazy_static"] # internal only
+io-readiness = [] # internal only
 io-util = ["memchr"]
 # stdin, stdout, stderr
 io-std = ["rt-core"]
@@ -85,8 +85,8 @@ sync = ["fnv"]
 test-util = []
 tcp = ["io-driver", "iovec"]
 time = ["slab"]
-udp = ["io-driver"]
+udp = ["io-driver", "io-readiness"]
-uds = ["io-driver", "mio-uds", "libc"]
+uds = ["io-driver", "io-readiness", "mio-uds", "libc"]
 
 [dependencies]
 tokio-macros = { version = "0.3.0", path = "../tokio-macros", optional = true }

tokio/src/io/driver/mod.rs

@@ -12,14 +12,13 @@ use mio::event::Evented;
 use std::fmt;
 use std::io;
 use std::sync::{Arc, Weak};
-use std::task::Waker;
 use std::time::Duration;
 
 /// I/O driver, backed by Mio
 pub(crate) struct Driver {
     /// Tracks the number of times `turn` is called. It is safe for this to wrap
     /// as it is mostly used to determine when to call `compact()`
-    tick: u16,
+    tick: u8,
 
     /// Reuse the `mio::Events` value across calls to poll.
     events: Option<mio::Events>,
@@ -40,6 +39,11 @@ pub(crate) struct Handle {
     inner: Weak<Inner>,
 }
 
+pub(crate) struct ReadyEvent {
+    tick: u8,
+    readiness: mio::Ready,
+}
+
 pub(super) struct Inner {
     /// The underlying system event queue.
     io: mio::Poll,
@@ -57,6 +61,11 @@ pub(super) enum Direction {
     Write,
 }
 
+enum Tick {
+    Set(u8),
+    Clear(u8),
+}
+
 // TODO: Don't use a fake token. Instead, reserve a slot entry for the wakeup
 // token.
 const TOKEN_WAKEUP: mio::Token = mio::Token(1 << 31);
@@ -122,11 +131,11 @@ impl Driver {
 
     fn turn(&mut self, max_wait: Option<Duration>) -> io::Result<()> {
         // How often to call `compact()` on the resource slab
-        const COMPACT_INTERVAL: u16 = 256;
+        const COMPACT_INTERVAL: u8 = 255;
 
         self.tick = self.tick.wrapping_add(1);
 
-        if self.tick % COMPACT_INTERVAL == 0 {
+        if self.tick == COMPACT_INTERVAL {
             self.resources.compact();
         }
 
@@ -160,9 +169,6 @@ impl Driver {
     }
 
     fn dispatch(&mut self, token: mio::Token, ready: mio::Ready) {
-        let mut rd = None;
-        let mut wr = None;
-
         let addr = slab::Address::from_usize(ADDRESS.unpack(token.0));
 
         let io = match self.resources.get(addr) {
@@ -170,29 +176,15 @@ impl Driver {
             None => return,
         };
 
-        if io
+        let set = io.set_readiness(Some(token.0), Tick::Set(self.tick), |curr| {
-            .set_readiness(Some(token.0), |curr| curr | ready.as_usize())
+            curr | ready.as_usize()
-            .is_err()
+        });
-        {
+        if set.is_err() {
             // token no longer valid!
             return;
         }
 
-        if ready.is_writable() || platform::is_hup(ready) || platform::is_error(ready) {
+        io.wake(ready);
-            wr = io.writer.take_waker();
-        }
-
-        if !(ready & (!mio::Ready::writable())).is_empty() {
-            rd = io.reader.take_waker();
-        }
-
-        if let Some(w) = rd {
-            w.wake();
-        }
-
-        if let Some(w) = wr {
-            w.wake();
-        }
     }
 }
 
@@ -202,8 +194,7 @@ impl Drop for Driver {
             // 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.
-            io.reader.wake();
+            io.wake(mio::Ready::all());
-            io.writer.wake();
         })
     }
 }
@@ -310,16 +301,6 @@ impl Inner {
     pub(super) fn deregister_source(&self, source: &dyn Evented) -> io::Result<()> {
         self.io.deregister(source)
     }
-
-    /// Registers interest in the I/O resource associated with `token`.
-    pub(super) fn register(&self, io: &slab::Ref<ScheduledIo>, dir: Direction, w: Waker) {
-        let waker = match dir {
-            Direction::Read => &io.reader,
-            Direction::Write => &io.writer,
-        };
-
-        waker.register(w);
-    }
 }
 
 impl Direction {

tokio/src/io/driver/scheduled_io.rs

@@ -1,8 +1,21 @@
-use crate::loom::future::AtomicWaker;
+use super::{platform, Direction, ReadyEvent, Tick};
 use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::Mutex;
+use crate::util::bit;
 use crate::util::slab::Entry;
 
 use std::sync::atomic::Ordering::{AcqRel, Acquire, Release};
+use std::task::{Context, Poll, Waker};
+
+cfg_io_readiness! {
+    use crate::util::linked_list::{self, LinkedList};
+
+    use std::cell::UnsafeCell;
+    use std::future::Future;
+    use std::marker::PhantomPinned;
+    use std::pin::Pin;
+    use std::ptr::NonNull;
+}
 
 /// Stored in the I/O driver resource slab.
 #[derive(Debug)]
@@ -10,19 +23,84 @@ pub(crate) struct ScheduledIo {
     /// Packs the resource's readiness with the resource's generation.
     readiness: AtomicUsize,
 
-    /// Task waiting on read readiness
+    waiters: Mutex<Waiters>,
-    pub(crate) reader: AtomicWaker,
-
-    /// Task waiting on write readiness
-    pub(crate) writer: AtomicWaker,
 }
 
+#[cfg(feature = "io-readiness")]
+type WaitList = LinkedList<Waiter, <Waiter as linked_list::Link>::Target>;
+
+#[derive(Debug, Default)]
+struct Waiters {
+    #[cfg(feature = "io-readiness")]
+    /// List of all current waiters
+    list: WaitList,
+
+    /// Waker used for AsyncRead
+    reader: Option<Waker>,
+
+    /// Waker used for AsyncWrite
+    writer: Option<Waker>,
+}
+
+cfg_io_readiness! {
+    #[derive(Debug)]
+    struct Waiter {
+        pointers: linked_list::Pointers<Waiter>,
+
+        /// The waker for this task
+        waker: Option<Waker>,
+
+        /// The interest this waiter is waiting on
+        interest: mio::Ready,
+
+        is_ready: bool,
+
+        /// Should never be `!Unpin`
+        _p: PhantomPinned,
+    }
+
+    /// Future returned by `readiness()`
+    struct Readiness<'a> {
+        scheduled_io: &'a ScheduledIo,
+
+        state: State,
+
+        /// Entry in the waiter `LinkedList`.
+        waiter: UnsafeCell<Waiter>,
+    }
+
+    enum State {
+        Init,
+        Waiting,
+        Done,
+    }
+}
+
+// The `ScheduledIo::readiness` (`AtomicUsize`) is packed full of goodness.
+//
+// | reserved | generation |  driver tick | readinesss |
+// |----------+------------+--------------+------------|
+// |   1 bit  |   7 bits   +    8 bits    +   16 bits  |
+
+const READINESS: bit::Pack = bit::Pack::least_significant(16);
+
+const TICK: bit::Pack = READINESS.then(8);
+
+const GENERATION: bit::Pack = TICK.then(7);
+
+#[test]
+fn test_generations_assert_same() {
+    assert_eq!(super::GENERATION, GENERATION);
+}
+
+// ===== impl ScheduledIo =====
+
 impl Entry for ScheduledIo {
     fn reset(&self) {
         let state = self.readiness.load(Acquire);
 
-        let generation = super::GENERATION.unpack(state);
+        let generation = GENERATION.unpack(state);
-        let next = super::GENERATION.pack_lossy(generation + 1, 0);
+        let next = GENERATION.pack_lossy(generation + 1, 0);
 
         self.readiness.store(next, Release);
     }
@@ -32,15 +110,14 @@ impl Default for ScheduledIo {
     fn default() -> ScheduledIo {
         ScheduledIo {
             readiness: AtomicUsize::new(0),
-            reader: AtomicWaker::new(),
+            waiters: Mutex::new(Default::default()),
-            writer: AtomicWaker::new(),
         }
     }
 }
 
 impl ScheduledIo {
     pub(crate) fn generation(&self) -> usize {
-        super::GENERATION.unpack(self.readiness.load(Acquire))
+        GENERATION.unpack(self.readiness.load(Acquire))
     }
 
     /// Sets the readiness on this `ScheduledIo` by invoking the given closure on
@@ -48,6 +125,8 @@ impl ScheduledIo {
     ///
     /// # Arguments
     /// - `token`: the token for this `ScheduledIo`.
+    /// - `tick`: whether setting the tick or trying to clear readiness for a
+    ///    specific tick.
     /// - `f`: a closure returning a new readiness value given the previous
     ///   readiness.
     ///
@@ -57,51 +136,330 @@ impl ScheduledIo {
     /// generation, then the corresponding IO resource has been removed and
     /// replaced with a new resource. In that case, this method returns `Err`.
     /// Otherwise, this returns the previous readiness.
-    pub(crate) fn set_readiness(
+    pub(super) fn set_readiness(
         &self,
         token: Option<usize>,
+        tick: Tick,
         f: impl Fn(usize) -> usize,
     ) -> Result<usize, ()> {
         let mut current = self.readiness.load(Acquire);
 
         loop {
-            let current_generation = super::GENERATION.unpack(current);
+            let current_generation = GENERATION.unpack(current);
 
             if let Some(token) = token {
                 // Check that the generation for this access is still the
                 // current one.
-                if super::GENERATION.unpack(token) != current_generation {
+                if GENERATION.unpack(token) != current_generation {
                     return Err(());
                 }
             }
 
-            // Mask out the generation bits so that the modifying function
+            // Mask out the tick/generation bits so that the modifying
-            // doesn't see them.
+            // function doesn't see them.
             let current_readiness = current & mio::Ready::all().as_usize();
-            let new = f(current_readiness);
+            let mut new = f(current_readiness);
 
             debug_assert!(
-                new <= super::ADDRESS.max_value(),
+                new <= READINESS.max_value(),
-                "new readiness value would overwrite generation bits!"
+                "new readiness value would overwrite tick/generation bits!"
             );
 
-            match self.readiness.compare_exchange(
+            match tick {
-                current,
+                Tick::Set(t) => {
-                super::GENERATION.pack(current_generation, new),
+                    new = TICK.pack(t as usize, new);
-                AcqRel,
+                }
-                Acquire,
+                Tick::Clear(t) => {
-            ) {
+                    if TICK.unpack(current) as u8 != t {
+                        // Trying to clear readiness with an old event!
+                        return Err(());
+                    }
+                    new = TICK.pack(t as usize, new);
+                }
+            }
+
+            new = GENERATION.pack(current_generation, new);
+
+            match self
+                .readiness
+                .compare_exchange(current, new, AcqRel, Acquire)
+            {
                 Ok(_) => return Ok(current),
                 // we lost the race, retry!
                 Err(actual) => current = actual,
             }
         }
     }
+
+    pub(super) fn wake(&self, ready: mio::Ready) {
+        let mut waiters = self.waiters.lock().unwrap();
+
+        // check for AsyncRead slot
+        if !(ready & (!mio::Ready::writable())).is_empty() {
+            if let Some(waker) = waiters.reader.take() {
+                waker.wake();
+            }
+        }
+
+        // check for AsyncWrite slot
+        if ready.is_writable() || platform::is_hup(ready) || platform::is_error(ready) {
+            if let Some(waker) = waiters.writer.take() {
+                waker.wake();
+            }
+        }
+
+        #[cfg(feature = "io-readiness")]
+        {
+            // check list of waiters
+            for waiter in waiters
+                .list
+                .drain_filter(|w| !(w.interest & ready).is_empty())
+            {
+                let waiter = unsafe { &mut *waiter.as_ptr() };
+                if let Some(waker) = waiter.waker.take() {
+                    waiter.is_ready = true;
+                    waker.wake();
+                }
+            }
+        }
+    }
+
+    /// Poll version of checking readiness for a certain direction.
+    ///
+    /// These are to support `AsyncRead` and `AsyncWrite` polling methods,
+    /// which cannot use the `async fn` version. This uses reserved reader
+    /// and writer slots.
+    pub(in crate::io) fn poll_readiness(
+        &self,
+        cx: &mut Context<'_>,
+        direction: Direction,
+    ) -> Poll<ReadyEvent> {
+        let curr = self.readiness.load(Acquire);
+
+        let ready = direction.mask() & mio::Ready::from_usize(READINESS.unpack(curr));
+
+        if ready.is_empty() {
+            // Update the task info
+            let mut waiters = self.waiters.lock().unwrap();
+            let slot = match direction {
+                Direction::Read => &mut waiters.reader,
+                Direction::Write => &mut waiters.writer,
+            };
+            *slot = Some(cx.waker().clone());
+
+            // Try again, in case the readiness was changed while we were
+            // taking the waiters lock
+            let curr = self.readiness.load(Acquire);
+            let ready = direction.mask() & mio::Ready::from_usize(READINESS.unpack(curr));
+            if ready.is_empty() {
+                Poll::Pending
+            } else {
+                Poll::Ready(ReadyEvent {
+                    tick: TICK.unpack(curr) as u8,
+                    readiness: ready,
+                })
+            }
+        } else {
+            Poll::Ready(ReadyEvent {
+                tick: TICK.unpack(curr) as u8,
+                readiness: ready,
+            })
+        }
+    }
+
+    pub(crate) fn clear_readiness(&self, event: ReadyEvent) {
+        // This consumes the current readiness state **except** for HUP and
+        // error. HUP and error are excluded because a) they are final states
+        // and never transition out and b) both the read AND the write
+        // directions need to be able to obvserve these states.
+        //
+        // # Platform-specific behavior
+        //
+        // HUP and error readiness are platform-specific. On epoll platforms,
+        // HUP has specific conditions that must be met by both peers of a
+        // connection in order to be triggered.
+        //
+        // On epoll platforms, `EPOLLERR` is signaled through
+        // `UnixReady::error()` and is important to be observable by both read
+        // AND write. A specific case that `EPOLLERR` occurs is when the read
+        // end of a pipe is closed. When this occurs, a peer blocked by
+        // writing to the pipe should be notified.
+        let mask_no_hup = (event.readiness - platform::hup() - platform::error()).as_usize();
+
+        // result isn't important
+        let _ = self.set_readiness(None, Tick::Clear(event.tick), |curr| curr & (!mask_no_hup));
+    }
 }
 
 impl Drop for ScheduledIo {
     fn drop(&mut self) {
-        self.writer.wake();
+        self.wake(mio::Ready::all());
-        self.reader.wake();
     }
 }
+
+unsafe impl Send for ScheduledIo {}
+unsafe impl Sync for ScheduledIo {}
+
+cfg_io_readiness! {
+    impl ScheduledIo {
+        /// An async version of `poll_readiness` which uses a linked list of wakers
+        pub(crate) async fn readiness(&self, interest: mio::Ready) -> ReadyEvent {
+            self.readiness_fut(interest).await
+        }
+
+        // This is in a separate function so that the borrow checker doesn't think
+        // we are borrowing the `UnsafeCell` possibly over await boundaries.
+        //
+        // Go figure.
+        fn readiness_fut(&self, interest: mio::Ready) -> Readiness<'_> {
+            Readiness {
+                scheduled_io: self,
+                state: State::Init,
+                waiter: UnsafeCell::new(Waiter {
+                    pointers: linked_list::Pointers::new(),
+                    waker: None,
+                    is_ready: false,
+                    interest,
+                    _p: PhantomPinned,
+                }),
+            }
+        }
+    }
+
+    unsafe impl linked_list::Link for Waiter {
+        type Handle = NonNull<Waiter>;
+        type Target = Waiter;
+
+        fn as_raw(handle: &NonNull<Waiter>) -> NonNull<Waiter> {
+            *handle
+        }
+
+        unsafe fn from_raw(ptr: NonNull<Waiter>) -> NonNull<Waiter> {
+            ptr
+        }
+
+        unsafe fn pointers(mut target: NonNull<Waiter>) -> NonNull<linked_list::Pointers<Waiter>> {
+            NonNull::from(&mut target.as_mut().pointers)
+        }
+    }
+
+    // ===== impl Readiness =====
+
+    impl Future for Readiness<'_> {
+        type Output = ReadyEvent;
+
+        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            use std::sync::atomic::Ordering::SeqCst;
+
+            let (scheduled_io, state, waiter) = unsafe {
+                let me = self.get_unchecked_mut();
+                (&me.scheduled_io, &mut me.state, &me.waiter)
+            };
+
+            loop {
+                match *state {
+                    State::Init => {
+                        // Optimistically check existing readiness
+                        let curr = scheduled_io.readiness.load(SeqCst);
+                        let readiness = mio::Ready::from_usize(READINESS.unpack(curr));
+
+                        // Safety: `waiter.interest` never changes
+                        let interest = unsafe { (*waiter.get()).interest };
+
+                        if readiness.contains(interest) {
+                            // Currently ready!
+                            let tick = TICK.unpack(curr) as u8;
+                            *state = State::Done;
+                            return Poll::Ready(ReadyEvent { readiness, tick });
+                        }
+
+                        // Wasn't ready, take the lock (and check again while locked).
+                        let mut waiters = scheduled_io.waiters.lock().unwrap();
+
+                        let curr = scheduled_io.readiness.load(SeqCst);
+                        let readiness = mio::Ready::from_usize(READINESS.unpack(curr));
+
+                        if readiness.contains(interest) {
+                            // Currently ready!
+                            let tick = TICK.unpack(curr) as u8;
+                            *state = State::Done;
+                            return Poll::Ready(ReadyEvent { readiness, tick });
+                        }
+
+                        // Not ready even after locked, insert into list...
+
+                        // Safety: called while locked
+                        unsafe {
+                            (*waiter.get()).waker = Some(cx.waker().clone());
+                        }
+
+                        // Insert the waiter into the linked list
+                        //
+                        // safety: pointers from `UnsafeCell` are never null.
+                        waiters
+                            .list
+                            .push_front(unsafe { NonNull::new_unchecked(waiter.get()) });
+                        *state = State::Waiting;
+                    }
+                    State::Waiting => {
+                        // Currently in the "Waiting" state, implying the caller has
+                        // a waiter stored in the waiter list (guarded by
+                        // `notify.waiters`). In order to access the waker fields,
+                        // we must hold the lock.
+
+                        let waiters = scheduled_io.waiters.lock().unwrap();
+
+                        // Safety: called while locked
+                        let w = unsafe { &mut *waiter.get() };
+
+                        if w.is_ready {
+                            // Our waker has been notified.
+                            *state = State::Done;
+                        } else {
+                            // Update the waker, if necessary.
+                            if !w.waker.as_ref().unwrap().will_wake(cx.waker()) {
+                                w.waker = Some(cx.waker().clone());
+                            }
+
+                            return Poll::Pending;
+                        }
+
+                        // Explicit drop of the lock to indicate the scope that the
+                        // lock is held. Because holding the lock is required to
+                        // ensure safe access to fields not held within the lock, it
+                        // is helpful to visualize the scope of the critical
+                        // section.
+                        drop(waiters);
+                    }
+                    State::Done => {
+                        let tick = TICK.unpack(scheduled_io.readiness.load(Acquire)) as u8;
+
+                        // Safety: State::Done means it is no longer shared
+                        let w = unsafe { &mut *waiter.get() };
+
+                        return Poll::Ready(ReadyEvent {
+                            tick,
+                            readiness: w.interest,
+                        });
+                    }
+                }
+            }
+        }
+    }
+
+    impl Drop for Readiness<'_> {
+        fn drop(&mut self) {
+            let mut waiters = self.scheduled_io.waiters.lock().unwrap();
+
+            // Safety: `waiter` is only ever stored in `waiters`
+            unsafe {
+                waiters
+                    .list
+                    .remove(NonNull::new_unchecked(self.waiter.get()))
+            };
+        }
+    }
+
+    unsafe impl Send for Readiness<'_> {}
+    unsafe impl Sync for Readiness<'_> {}
+}

tokio/src/io/mod.rs

@@ -207,10 +207,10 @@ cfg_io_driver! {
     pub(crate) mod driver;
 
     mod poll_evented;
-    pub use poll_evented::PollEvented;
+    #[cfg(not(loom))]
+    pub(crate) use poll_evented::PollEvented;
 
     mod registration;
-    pub use registration::Registration;
 }
 
 cfg_io_std! {

tokio/src/io/poll_evented.rs

@@ -1,13 +1,12 @@
-use crate::io::driver::platform;
+use crate::io::driver::{Direction, Handle, ReadyEvent};
-use crate::io::{AsyncRead, AsyncWrite, ReadBuf, Registration};
+use crate::io::registration::Registration;
+use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
 
 use mio::event::Evented;
 use std::fmt;
 use std::io::{self, Read, Write};
 use std::marker::Unpin;
 use std::pin::Pin;
-use std::sync::atomic::AtomicUsize;
-use std::sync::atomic::Ordering::Relaxed;
 use std::task::{Context, Poll};
 
 cfg_io_driver! {
@@ -53,37 +52,6 @@ cfg_io_driver! {
     /// [`TcpListener`] implements poll_accept by using [`poll_read_ready`] and
     /// [`clear_read_ready`].
     ///
-    /// ```rust
-    /// use tokio::io::PollEvented;
-    ///
-    /// use futures::ready;
-    /// use mio::Ready;
-    /// use mio::net::{TcpStream, TcpListener};
-    /// use std::io;
-    /// use std::task::{Context, Poll};
-    ///
-    /// struct MyListener {
-    ///     poll_evented: PollEvented<TcpListener>,
-    /// }
-    ///
-    /// impl MyListener {
-    ///     pub fn poll_accept(&mut self, cx: &mut Context<'_>) -> Poll<Result<TcpStream, io::Error>> {
-    ///         let ready = Ready::readable();
-    ///
-    ///         ready!(self.poll_evented.poll_read_ready(cx, ready))?;
-    ///
-    ///         match self.poll_evented.get_ref().accept() {
-    ///             Ok((socket, _)) => Poll::Ready(Ok(socket)),
-    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-    ///                 self.poll_evented.clear_read_ready(cx, ready)?;
-    ///                 Poll::Pending
-    ///             }
-    ///             Err(e) => Poll::Ready(Err(e)),
-    ///         }
-    ///     }
-    /// }
-    /// ```
-    ///
     /// ## Platform-specific events
     ///
     /// `PollEvented` also allows receiving platform-specific `mio::Ready` events.
@@ -101,66 +69,14 @@ cfg_io_driver! {
     /// [`clear_write_ready`]: method@Self::clear_write_ready
     /// [`poll_read_ready`]: method@Self::poll_read_ready
     /// [`poll_write_ready`]: method@Self::poll_write_ready
-    pub struct PollEvented<E: Evented> {
+    pub(crate) struct PollEvented<E: Evented> {
         io: Option<E>,
-        inner: Inner,
+        registration: Registration,
     }
 }
 
-struct Inner {
-    registration: Registration,
-
-    /// Currently visible read readiness
-    read_readiness: AtomicUsize,
-
-    /// Currently visible write readiness
-    write_readiness: AtomicUsize,
-}
-
 // ===== impl PollEvented =====
 
-macro_rules! poll_ready {
-    ($me:expr, $mask:expr, $cache:ident, $take:ident, $poll:expr) => {{
-        // Load cached & encoded readiness.
-        let mut cached = $me.inner.$cache.load(Relaxed);
-        let mask = $mask | platform::hup() | platform::error();
-
-        // See if the current readiness matches any bits.
-        let mut ret = mio::Ready::from_usize(cached) & $mask;
-
-        if ret.is_empty() {
-            // Readiness does not match, consume the registration's readiness
-            // stream. This happens in a loop to ensure that the stream gets
-            // drained.
-            loop {
-                let ready = match $poll? {
-                    Poll::Ready(v) => v,
-                    Poll::Pending => return Poll::Pending,
-                };
-                cached |= ready.as_usize();
-
-                // Update the cache store
-                $me.inner.$cache.store(cached, Relaxed);
-
-                ret |= ready & mask;
-
-                if !ret.is_empty() {
-                    return Poll::Ready(Ok(ret));
-                }
-            }
-        } else {
-            // Check what's new with the registration stream. This will not
-            // request to be notified
-            if let Some(ready) = $me.inner.registration.$take()? {
-                cached |= ready.as_usize();
-                $me.inner.$cache.store(cached, Relaxed);
-            }
-
-            Poll::Ready(Ok(mio::Ready::from_usize(cached)))
-        }
-    }};
-}
-
 impl<E> PollEvented<E>
 where
     E: Evented,
@@ -174,7 +90,8 @@ where
     /// 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.
-    pub fn new(io: E) -> io::Result<Self> {
+    #[cfg_attr(feature = "signal", allow(unused))]
+    pub(crate) fn new(io: E) -> io::Result<Self> {
         PollEvented::new_with_ready(io, mio::Ready::all())
     }
 
@@ -202,27 +119,39 @@ where
     /// 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.
-    pub fn new_with_ready(io: E, ready: mio::Ready) -> io::Result<Self> {
+    #[cfg_attr(feature = "signal", allow(unused))]
-        let registration = Registration::new_with_ready(&io, ready)?;
+    pub(crate) fn new_with_ready(io: E, ready: mio::Ready) -> io::Result<Self> {
+        Self::new_with_ready_and_handle(io, ready, Handle::current())
+    }
+
+    pub(crate) fn new_with_ready_and_handle(
+        io: E,
+        ready: mio::Ready,
+        handle: Handle,
+    ) -> io::Result<Self> {
+        let registration = Registration::new_with_ready_and_handle(&io, ready, handle)?;
         Ok(Self {
             io: Some(io),
-            inner: Inner {
+            registration,
-                registration,
-                read_readiness: AtomicUsize::new(0),
-                write_readiness: AtomicUsize::new(0),
-            },
         })
     }
 
     /// Returns a shared reference to the underlying I/O object this readiness
     /// stream is wrapping.
-    pub fn get_ref(&self) -> &E {
+    #[cfg(any(
+        feature = "process",
+        feature = "tcp",
+        feature = "udp",
+        feature = "uds",
+        feature = "signal"
+    ))]
+    pub(crate) fn get_ref(&self) -> &E {
         self.io.as_ref().unwrap()
     }
 
     /// Returns a mutable reference to the underlying I/O object this readiness
     /// stream is wrapping.
-    pub fn get_mut(&mut self) -> &mut E {
+    pub(crate) fn get_mut(&mut self) -> &mut E {
         self.io.as_mut().unwrap()
     }
 
@@ -234,12 +163,17 @@ where
     /// Note that deregistering does not guarantee that the I/O resource can be
     /// registered with a different reactor. Some I/O resource types can only be
     /// associated with a single reactor instance for their lifetime.
-    pub fn into_inner(mut self) -> io::Result<E> {
+    #[cfg(any(feature = "tcp", feature = "udp", feature = "uds"))]
+    pub(crate) fn into_inner(mut self) -> io::Result<E> {
         let io = self.io.take().unwrap();
-        self.inner.registration.deregister(&io)?;
+        self.registration.deregister(&io)?;
         Ok(io)
     }
 
+    pub(crate) fn clear_readiness(&self, event: ReadyEvent) {
+        self.registration.clear_readiness(event);
+    }
+
     /// Checks the I/O resource's read readiness state.
     ///
     /// The mask argument allows specifying what readiness to notify on. This
@@ -266,51 +200,8 @@ where
     ///
     /// This method may not be called concurrently. It takes `&self` to allow
     /// calling it concurrently with `poll_write_ready`.
-    pub fn poll_read_ready(
+    pub(crate) fn poll_read_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<ReadyEvent>> {
-        &self,
+        self.registration.poll_readiness(cx, Direction::Read)
-        cx: &mut Context<'_>,
-        mask: mio::Ready,
-    ) -> Poll<io::Result<mio::Ready>> {
-        assert!(!mask.is_writable(), "cannot poll for write readiness");
-        poll_ready!(
-            self,
-            mask,
-            read_readiness,
-            take_read_ready,
-            self.inner.registration.poll_read_ready(cx)
-        )
-    }
-
-    /// Clears the I/O resource's read readiness state and registers the current
-    /// task to be notified once a read readiness event is received.
-    ///
-    /// After calling this function, `poll_read_ready` will return
-    /// `Poll::Pending` until a new read readiness event has been received.
-    ///
-    /// The `mask` argument specifies the readiness bits to clear. This may not
-    /// include `writable` or `hup`.
-    ///
-    /// # Panics
-    ///
-    /// This function panics if:
-    ///
-    /// * `ready` includes writable or HUP
-    /// * called from outside of a task context.
-    pub fn clear_read_ready(&self, cx: &mut Context<'_>, ready: mio::Ready) -> io::Result<()> {
-        // Cannot clear write readiness
-        assert!(!ready.is_writable(), "cannot clear write readiness");
-        assert!(!platform::is_hup(ready), "cannot clear HUP readiness");
-
-        self.inner
-            .read_readiness
-            .fetch_and(!ready.as_usize(), Relaxed);
-
-        if self.poll_read_ready(cx, ready)?.is_ready() {
-            // Notify the current task
-            cx.waker().wake_by_ref();
-        }
-
-        Ok(())
     }
 
     /// Checks the I/O resource's write readiness state.
@@ -337,41 +228,35 @@ where
     ///
     /// This method may not be called concurrently. It takes `&self` to allow
     /// calling it concurrently with `poll_read_ready`.
-    pub fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<mio::Ready>> {
+    pub(crate) fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<ReadyEvent>> {
-        poll_ready!(
+        self.registration.poll_readiness(cx, Direction::Write)
-            self,
-            mio::Ready::writable(),
-            write_readiness,
-            take_write_ready,
-            self.inner.registration.poll_write_ready(cx)
-        )
     }
+}
 
-    /// Resets the I/O resource's write readiness state and registers the current
+cfg_io_readiness! {
-    /// task to be notified once a write readiness event is received.
+    impl<E> PollEvented<E>
-    ///
+    where
-    /// This only clears writable readiness. HUP (on platforms that support HUP)
+        E: Evented,
-    /// cannot be cleared as it is a final state.
+    {
-    ///
+        pub(crate) async fn readiness(&self, interest: mio::Ready) -> io::Result<ReadyEvent> {
-    /// After calling this function, `poll_write_ready(Ready::writable())` will
+            self.registration.readiness(interest).await
-    /// return `NotReady` until a new write readiness event has been received.
-    ///
-    /// # Panics
-    ///
-    /// This function will panic if called from outside of a task context.
-    pub fn clear_write_ready(&self, cx: &mut Context<'_>) -> io::Result<()> {
-        let ready = mio::Ready::writable();
-
-        self.inner
-            .write_readiness
-            .fetch_and(!ready.as_usize(), Relaxed);
-
-        if self.poll_write_ready(cx)?.is_ready() {
-            // Notify the current task
-            cx.waker().wake_by_ref();
         }
 
-        Ok(())
+        pub(crate) async fn async_io<F, R>(&self, interest: mio::Ready, mut op: F) -> io::Result<R>
+        where
+            F: FnMut(&E) -> io::Result<R>,
+        {
+            loop {
+                let event = self.readiness(interest).await?;
+
+                match op(self.get_ref()) {
+                    Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+                        self.clear_readiness(event);
+                    }
+                    x => return x,
+                }
+            }
+        }
     }
 }
 
@@ -386,20 +271,22 @@ where
         cx: &mut Context<'_>,
         buf: &mut ReadBuf<'_>,
     ) -> Poll<io::Result<()>> {
-        ready!(self.poll_read_ready(cx, mio::Ready::readable()))?;
+        loop {
+            let ev = ready!(self.poll_read_ready(cx))?;
 
-        // We can't assume the `Read` won't look at the read buffer,
+            // We can't assume the `Read` won't look at the read buffer,
-        // so we have to force initialization here.
+            // so we have to force initialization here.
-        let r = (*self).get_mut().read(buf.initialize_unfilled());
+            let r = (*self).get_mut().read(buf.initialize_unfilled());
 
-        if is_wouldblock(&r) {
+            if is_wouldblock(&r) {
-            self.clear_read_ready(cx, mio::Ready::readable())?;
+                self.clear_readiness(ev);
-            return Poll::Pending;
+                continue;
+            }
+
+            return Poll::Ready(r.map(|n| {
+                buf.add_filled(n);
+            }));
         }
-
-        Poll::Ready(r.map(|n| {
-            buf.add_filled(n);
-        }))
     }
 }
 
@@ -412,29 +299,33 @@ where
         cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<io::Result<usize>> {
-        ready!(self.poll_write_ready(cx))?;
+        loop {
+            let ev = ready!(self.poll_write_ready(cx))?;
 
-        let r = (*self).get_mut().write(buf);
+            let r = (*self).get_mut().write(buf);
 
-        if is_wouldblock(&r) {
+            if is_wouldblock(&r) {
-            self.clear_write_ready(cx)?;
+                self.clear_readiness(ev);
-            return Poll::Pending;
+                continue;
+            }
+
+            return Poll::Ready(r);
         }
-
-        Poll::Ready(r)
     }
 
     fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        ready!(self.poll_write_ready(cx))?;
+        loop {
+            let ev = ready!(self.poll_write_ready(cx))?;
 
-        let r = (*self).get_mut().flush();
+            let r = (*self).get_mut().flush();
 
-        if is_wouldblock(&r) {
+            if is_wouldblock(&r) {
-            self.clear_write_ready(cx)?;
+                self.clear_readiness(ev);
-            return Poll::Pending;
+                continue;
+            }
+
+            return Poll::Ready(r);
         }
-
-        Poll::Ready(r)
     }
 
     fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
@@ -459,7 +350,7 @@ impl<E: Evented> Drop for PollEvented<E> {
     fn drop(&mut self) {
         if let Some(io) = self.io.take() {
             // Ignore errors
-            let _ = self.inner.registration.deregister(&io);
+            let _ = self.registration.deregister(&io);
         }
     }
 }

tokio/src/io/registration.rs

@@ -1,4 +1,4 @@
-use crate::io::driver::{platform, Direction, Handle, ScheduledIo};
+use crate::io::driver::{Direction, Handle, ReadyEvent, ScheduledIo};
 use crate::util::slab;
 
 use mio::{self, Evented};
@@ -38,7 +38,7 @@ cfg_io_driver! {
     /// [`poll_read_ready`]: method@Self::poll_read_ready`
     /// [`poll_write_ready`]: method@Self::poll_write_ready`
     #[derive(Debug)]
-    pub struct Registration {
+    pub(crate) struct Registration {
         /// Handle to the associated driver.
         handle: Handle,
 
@@ -53,28 +53,6 @@ unsafe impl Sync for Registration {}
 // ===== impl Registration =====
 
 impl Registration {
-    /// Registers the I/O resource with the default reactor.
-    ///
-    /// # Return
-    ///
-    /// - `Ok` if the registration happened successfully
-    /// - `Err` if an error was encountered during registration
-    ///
-    ///
-    /// # Panics
-    ///
-    /// This function panics if thread-local runtime is not set.
-    ///
-    /// 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.
-    pub fn new<T>(io: &T) -> io::Result<Registration>
-    where
-        T: Evented,
-    {
-        Registration::new_with_ready(io, mio::Ready::all())
-    }
-
     /// Registers the I/O resource with the default reactor, for a specific `mio::Ready` state.
     /// `new_with_ready` 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
@@ -96,23 +74,6 @@ impl Registration {
     ///
     /// - `Ok` if the registration happened successfully
     /// - `Err` if an error was encountered during registration
-    ///
-    ///
-    /// # Panics
-    ///
-    /// This function panics if thread-local runtime is not set.
-    ///
-    /// 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.
-    pub fn new_with_ready<T>(io: &T, ready: mio::Ready) -> io::Result<Registration>
-    where
-        T: Evented,
-    {
-        Self::new_with_ready_and_handle(io, ready, Handle::current())
-    }
-
-    /// Same as `new_with_ready` but also accepts an explicit handle.
     pub(crate) fn new_with_ready_and_handle<T>(
         io: &T,
         ready: mio::Ready,
@@ -149,7 +110,7 @@ impl Registration {
     /// no longer result in notifications getting sent for this registration.
     ///
     /// `Err` is returned if an error is encountered.
-    pub fn deregister<T>(&mut self, io: &T) -> io::Result<()>
+    pub(super) fn deregister<T>(&mut self, io: &T) -> io::Result<()>
     where
         T: Evented,
     {
@@ -160,192 +121,36 @@ impl Registration {
         inner.deregister_source(io)
     }
 
-    /// Polls for events on the I/O resource's read readiness stream.
+    pub(super) fn clear_readiness(&self, event: ReadyEvent) {
-    ///
+        self.shared.clear_readiness(event);
-    /// If the I/O resource receives a new read readiness event since the last
-    /// call to `poll_read_ready`, it is returned. If it has not, the current
-    /// task is notified once a new event is received.
-    ///
-    /// All events except `HUP` are [edge-triggered]. Once `HUP` is returned,
-    /// the function will always return `Ready(HUP)`. This should be treated as
-    /// the end of the readiness stream.
-    ///
-    /// # Return value
-    ///
-    /// There are several possible return values:
-    ///
-    /// * `Poll::Ready(Ok(readiness))` means that the I/O resource has received
-    ///   a new readiness event. The readiness value is included.
-    ///
-    /// * `Poll::Pending` means that no new readiness events have been received
-    ///   since the last call to `poll_read_ready`.
-    ///
-    /// * `Poll::Ready(Err(err))` means that the registration has encountered an
-    ///   error. This could represent a permanent internal error for example.
-    ///
-    /// [edge-triggered]: struct@mio::Poll#edge-triggered-and-level-triggered
-    ///
-    /// # Panics
-    ///
-    /// This function will panic if called from outside of a task context.
-    pub fn poll_read_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<mio::Ready>> {
-        // Keep track of task budget
-        let coop = ready!(crate::coop::poll_proceed(cx));
-
-        let v = self.poll_ready(Direction::Read, Some(cx)).map_err(|e| {
-            coop.made_progress();
-            e
-        })?;
-        match v {
-            Some(v) => {
-                coop.made_progress();
-                Poll::Ready(Ok(v))
-            }
-            None => Poll::Pending,
-        }
-    }
-
-    /// Consume any pending read readiness event.
-    ///
-    /// This function is identical to [`poll_read_ready`] **except** that it
-    /// will not notify the current task when a new event is received. As such,
-    /// it is safe to call this function from outside of a task context.
-    ///
-    /// [`poll_read_ready`]: method@Self::poll_read_ready
-    pub fn take_read_ready(&self) -> io::Result<Option<mio::Ready>> {
-        self.poll_ready(Direction::Read, None)
-    }
-
-    /// Polls for events on the I/O resource's write readiness stream.
-    ///
-    /// If the I/O resource receives a new write readiness event since the last
-    /// call to `poll_write_ready`, it is returned. If it has not, the current
-    /// task is notified once a new event is received.
-    ///
-    /// All events except `HUP` are [edge-triggered]. Once `HUP` is returned,
-    /// the function will always return `Ready(HUP)`. This should be treated as
-    /// the end of the readiness stream.
-    ///
-    /// # Return value
-    ///
-    /// There are several possible return values:
-    ///
-    /// * `Poll::Ready(Ok(readiness))` means that the I/O resource has received
-    ///   a new readiness event. The readiness value is included.
-    ///
-    /// * `Poll::Pending` means that no new readiness events have been received
-    ///   since the last call to `poll_write_ready`.
-    ///
-    /// * `Poll::Ready(Err(err))` means that the registration has encountered an
-    ///   error. This could represent a permanent internal error for example.
-    ///
-    /// [edge-triggered]: struct@mio::Poll#edge-triggered-and-level-triggered
-    ///
-    /// # Panics
-    ///
-    /// This function will panic if called from outside of a task context.
-    pub fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<mio::Ready>> {
-        // Keep track of task budget
-        let coop = ready!(crate::coop::poll_proceed(cx));
-
-        let v = self.poll_ready(Direction::Write, Some(cx)).map_err(|e| {
-            coop.made_progress();
-            e
-        })?;
-        match v {
-            Some(v) => {
-                coop.made_progress();
-                Poll::Ready(Ok(v))
-            }
-            None => Poll::Pending,
-        }
-    }
-
-    /// Consumes any pending write readiness event.
-    ///
-    /// This function is identical to [`poll_write_ready`] **except** that it
-    /// will not notify the current task when a new event is received. As such,
-    /// it is safe to call this function from outside of a task context.
-    ///
-    /// [`poll_write_ready`]: method@Self::poll_write_ready
-    pub fn take_write_ready(&self) -> io::Result<Option<mio::Ready>> {
-        self.poll_ready(Direction::Write, None)
     }
 
     /// Polls for events on the I/O resource's `direction` readiness stream.
     ///
     /// If called with a task context, notify the task when a new event is
     /// received.
-    fn poll_ready(
+    pub(super) fn poll_readiness(
         &self,
+        cx: &mut Context<'_>,
         direction: Direction,
-        cx: Option<&mut Context<'_>>,
+    ) -> Poll<io::Result<ReadyEvent>> {
-    ) -> io::Result<Option<mio::Ready>> {
+        if self.handle.inner().is_none() {
-        let inner = match self.handle.inner() {
+            return Poll::Ready(Err(io::Error::new(io::ErrorKind::Other, "reactor gone")));
-            Some(inner) => inner,
-            None => return Err(io::Error::new(io::ErrorKind::Other, "reactor gone")),
-        };
-
-        // If the task should be notified about new events, ensure that it has
-        // been registered
-        if let Some(ref cx) = cx {
-            inner.register(&self.shared, direction, cx.waker().clone())
         }
 
-        let mask = direction.mask();
+        // Keep track of task budget
-        let mask_no_hup = (mask - platform::hup() - platform::error()).as_usize();
+        let coop = ready!(crate::coop::poll_proceed(cx));
-
+        let ev = ready!(self.shared.poll_readiness(cx, direction));
-        // This consumes the current readiness state **except** for HUP and
+        coop.made_progress();
-        // error. HUP and error are excluded because a) they are final states
+        Poll::Ready(Ok(ev))
-        // and never transitition out and b) both the read AND the write
-        // directions need to be able to obvserve these states.
-        //
-        // # Platform-specific behavior
-        //
-        // HUP and error readiness are platform-specific. On epoll platforms,
-        // HUP has specific conditions that must be met by both peers of a
-        // connection in order to be triggered.
-        //
-        // On epoll platforms, `EPOLLERR` is signaled through
-        // `UnixReady::error()` and is important to be observable by both read
-        // AND write. A specific case that `EPOLLERR` occurs is when the read
-        // end of a pipe is closed. When this occurs, a peer blocked by
-        // writing to the pipe should be notified.
-        let curr_ready = self
-            .shared
-            .set_readiness(None, |curr| curr & (!mask_no_hup))
-            .unwrap_or_else(|_| unreachable!());
-
-        let mut ready = mask & mio::Ready::from_usize(curr_ready);
-
-        if ready.is_empty() {
-            if let Some(cx) = cx {
-                // Update the task info
-                match direction {
-                    Direction::Read => self.shared.reader.register_by_ref(cx.waker()),
-                    Direction::Write => self.shared.writer.register_by_ref(cx.waker()),
-                }
-
-                // Try again
-                let curr_ready = self
-                    .shared
-                    .set_readiness(None, |curr| curr & (!mask_no_hup))
-                    .unwrap();
-                ready = mask & mio::Ready::from_usize(curr_ready);
-            }
-        }
-
-        if ready.is_empty() {
-            Ok(None)
-        } else {
-            Ok(Some(ready))
-        }
     }
 }
 
-impl Drop for Registration {
+cfg_io_readiness! {
-    fn drop(&mut self) {
+    impl Registration {
-        drop(self.shared.reader.take_waker());
+        pub(super) async fn readiness(&self, interest: mio::Ready) -> io::Result<ReadyEvent> {
-        drop(self.shared.writer.take_waker());
+            // TODO: does this need to return a `Result`?
+            Ok(self.shared.readiness(interest).await)
+        }
     }
 }

tokio/src/lib.rs

@@ -77,7 +77,6 @@
 //! - `rt-core`: Enables `tokio::spawn` and the basic (single-threaded) scheduler.
 //! - `rt-threaded`: Enables the heavier, multi-threaded, work-stealing scheduler.
 //! - `rt-util`: Enables non-scheduler utilities.
-//! - `io-driver`: Enables the `mio` based IO driver.
 //! - `io-util`: Enables the IO based `Ext` traits.
 //! - `io-std`: Enable `Stdout`, `Stdin` and `Stderr` types.
 //! - `net`: Enables `tokio::net` types such as `TcpStream`, `UnixStream` and `UdpSocket`.
@@ -269,8 +268,7 @@
 //! the [`AsyncRead`], [`AsyncWrite`], and [`AsyncBufRead`] traits. In addition,
 //! when the "io-util" feature flag is enabled, it also provides combinators and
 //! functions for working with these traits, forming as an asynchronous
-//! counterpart to [`std::io`]. When the "io-driver" feature flag is enabled, it
+//! counterpart to [`std::io`].
-//! also provides utilities for library authors implementing I/O resources.
 //!
 //! Tokio also includes APIs for performing various kinds of I/O and interacting
 //! with the operating system asynchronously. These include:

tokio/src/macros/cfg.rs

@@ -129,7 +129,6 @@ macro_rules! cfg_io_driver {
     ($($item:item)*) => {
         $(
             #[cfg(feature = "io-driver")]
-            #[cfg_attr(docsrs, doc(cfg(feature = "io-driver")))]
             $item
         )*
     }
@@ -144,6 +143,15 @@ macro_rules! cfg_not_io_driver {
     }
 }
 
+macro_rules! cfg_io_readiness {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "io-readiness")]
+            $item
+        )*
+    }
+}
+
 macro_rules! cfg_io_std {
     ($($item:item)*) => {
         $(

tokio/src/net/tcp/listener.rs

@@ -205,15 +205,16 @@ impl TcpListener {
         &mut self,
         cx: &mut Context<'_>,
     ) -> Poll<io::Result<(net::TcpStream, SocketAddr)>> {
-        ready!(self.io.poll_read_ready(cx, mio::Ready::readable()))?;
+        loop {
+            let ev = ready!(self.io.poll_read_ready(cx))?;
 
-        match self.io.get_ref().accept_std() {
+            match self.io.get_ref().accept_std() {
-            Ok(pair) => Poll::Ready(Ok(pair)),
+                Ok(pair) => return Poll::Ready(Ok(pair)),
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_read_ready(cx, mio::Ready::readable())?;
+                    self.io.clear_readiness(ev);
-                Poll::Pending
+                }
+                Err(e) => return Poll::Ready(Err(e)),
             }
-            Err(e) => Poll::Ready(Err(e)),
         }
     }
 
@@ -411,11 +412,6 @@ impl TryFrom<TcpListener> for mio::net::TcpListener {
     type Error = io::Error;
 
     /// Consumes value, returning the mio I/O object.
-    ///
-    /// See [`PollEvented::into_inner`] for more details about
-    /// resource deregistration that happens during the call.
-    ///
-    /// [`PollEvented::into_inner`]: crate::io::PollEvented::into_inner
     fn try_from(value: TcpListener) -> Result<Self, Self::Error> {
         value.io.into_inner()
     }

tokio/src/net/tcp/stream.rs

@@ -299,15 +299,16 @@ impl TcpStream {
         cx: &mut Context<'_>,
         buf: &mut [u8],
     ) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_read_ready(cx, mio::Ready::readable()))?;
+        loop {
+            let ev = ready!(self.io.poll_read_ready(cx))?;
 
-        match self.io.get_ref().peek(buf) {
+            match self.io.get_ref().peek(buf) {
-            Ok(ret) => Poll::Ready(Ok(ret)),
+                Ok(ret) => return Poll::Ready(Ok(ret)),
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_read_ready(cx, mio::Ready::readable())?;
+                    self.io.clear_readiness(ev);
-                Poll::Pending
+                }
+                Err(e) => return Poll::Ready(Err(e)),
             }
-            Err(e) => Poll::Ready(Err(e)),
         }
     }
 
@@ -703,26 +704,28 @@ impl TcpStream {
         cx: &mut Context<'_>,
         buf: &mut ReadBuf<'_>,
     ) -> Poll<io::Result<()>> {
-        ready!(self.io.poll_read_ready(cx, mio::Ready::readable()))?;
+        loop {
+            let ev = ready!(self.io.poll_read_ready(cx))?;
 
-        // Safety: `TcpStream::read` will not peak at the maybe uinitialized bytes.
+            // Safety: `TcpStream::read` will not peek at the maybe uinitialized bytes.
-        let b =
+            let b = unsafe {
-            unsafe { &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };
+                &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8])
-        match self.io.get_ref().read(b) {
+            };
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+            match self.io.get_ref().read(b) {
-                self.io.clear_read_ready(cx, mio::Ready::readable())?;
+                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                Poll::Pending
+                    self.io.clear_readiness(ev);
-            }
-            Ok(n) => {
-                // Safety: We trust `TcpStream::read` to have filled up `n` bytes
-                // in the buffer.
-                unsafe {
-                    buf.assume_init(n);
                 }
-                buf.add_filled(n);
+                Ok(n) => {
-                Poll::Ready(Ok(()))
+                    // Safety: We trust `TcpStream::read` to have filled up `n` bytes
+                    // in the buffer.
+                    unsafe {
+                        buf.assume_init(n);
+                    }
+                    buf.add_filled(n);
+                    return Poll::Ready(Ok(()));
+                }
+                Err(e) => return Poll::Ready(Err(e)),
             }
-            Err(e) => Poll::Ready(Err(e)),
         }
     }
 
@@ -731,14 +734,15 @@ impl TcpStream {
         cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_write_ready(cx))?;
+        loop {
+            let ev = ready!(self.io.poll_write_ready(cx))?;
 
-        match self.io.get_ref().write(buf) {
+            match self.io.get_ref().write(buf) {
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_write_ready(cx)?;
+                    self.io.clear_readiness(ev);
-                Poll::Pending
+                }
+                x => return Poll::Ready(x),
             }
-            x => Poll::Ready(x),
         }
     }
 
@@ -749,99 +753,100 @@ impl TcpStream {
     ) -> Poll<io::Result<usize>> {
         use std::io::IoSlice;
 
-        ready!(self.io.poll_write_ready(cx))?;
+        loop {
+            let ev = ready!(self.io.poll_write_ready(cx))?;
 
-        // The `IoVec` (v0.1.x) type can't have a zero-length size, so create
+            // The `IoVec` (v0.1.x) type can't have a zero-length size, so create
-        // a dummy version from a 1-length slice which we'll overwrite with
+            // a dummy version from a 1-length slice which we'll overwrite with
-        // the `bytes_vectored` method.
+            // the `bytes_vectored` method.
-        static S: &[u8] = &[0];
+            static S: &[u8] = &[0];
-        const MAX_BUFS: usize = 64;
+            const MAX_BUFS: usize = 64;
 
-        // IoSlice isn't Copy, so we must expand this manually ;_;
+            // IoSlice isn't Copy, so we must expand this manually ;_;
-        let mut slices: [IoSlice<'_>; MAX_BUFS] = [
+            let mut slices: [IoSlice<'_>; MAX_BUFS] = [
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-            IoSlice::new(S),
+                IoSlice::new(S),
-        ];
+            ];
-        let cnt = buf.bytes_vectored(&mut slices);
+            let cnt = buf.bytes_vectored(&mut slices);
 
-        let iovec = <&IoVec>::from(S);
+            let iovec = <&IoVec>::from(S);
-        let mut vecs = [iovec; MAX_BUFS];
+            let mut vecs = [iovec; MAX_BUFS];
-        for i in 0..cnt {
+            for i in 0..cnt {
-            vecs[i] = (*slices[i]).into();
+                vecs[i] = (*slices[i]).into();
-        }
-
-        match self.io.get_ref().write_bufs(&vecs[..cnt]) {
-            Ok(n) => {
-                buf.advance(n);
-                Poll::Ready(Ok(n))
             }
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+
-                self.io.clear_write_ready(cx)?;
+            match self.io.get_ref().write_bufs(&vecs[..cnt]) {
-                Poll::Pending
+                Ok(n) => {
+                    buf.advance(n);
+                    return Poll::Ready(Ok(n));
+                }
+                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+                    self.io.clear_readiness(ev);
+                }
+                Err(e) => return Poll::Ready(Err(e)),
             }
-            Err(e) => Poll::Ready(Err(e)),
         }
     }
 }
@@ -850,11 +855,6 @@ impl TryFrom<TcpStream> for mio::net::TcpStream {
     type Error = io::Error;
 
     /// Consumes value, returning the mio I/O object.
-    ///
-    /// See [`PollEvented::into_inner`] for more details about
-    /// resource deregistration that happens during the call.
-    ///
-    /// [`PollEvented::into_inner`]: crate::io::PollEvented::into_inner
     fn try_from(value: TcpStream) -> Result<Self, Self::Error> {
         value.io.into_inner()
     }

tokio/src/net/udp/mod.rs

@@ -1,7 +1,3 @@
 //! UDP utility types.
 
 pub(crate) mod socket;
-pub(crate) use socket::UdpSocket;
-
-mod split;
-pub use split::{RecvHalf, ReuniteError, SendHalf};

tokio/src/net/udp/socket.rs

@@ -1,13 +1,10 @@
-use crate::future::poll_fn;
 use crate::io::PollEvented;
-use crate::net::udp::split::{split, RecvHalf, SendHalf};
 use crate::net::ToSocketAddrs;
 
 use std::convert::TryFrom;
 use std::fmt;
 use std::io;
 use std::net::{self, Ipv4Addr, Ipv6Addr, SocketAddr};
-use std::task::{Context, Poll};
 
 cfg_udp! {
     /// A UDP socket
@@ -67,15 +64,7 @@ impl UdpSocket {
     /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
     pub fn from_std(socket: net::UdpSocket) -> io::Result<UdpSocket> {
         let io = mio::net::UdpSocket::from_socket(socket)?;
-        let io = PollEvented::new(io)?;
+        UdpSocket::new(io)
-        Ok(UdpSocket { io })
-    }
-
-    /// Splits the `UdpSocket` into a receive half and a send half. The two parts
-    /// can be used to receive and send datagrams concurrently, even from two
-    /// different tasks.
-    pub fn split(self) -> (RecvHalf, SendHalf) {
-        split(self)
     }
 
     /// Returns the local address that this socket is bound to.
@@ -112,8 +101,10 @@ impl UdpSocket {
     /// will resolve to an error if the socket is not connected.
     ///
     /// [`connect`]: method@Self::connect
-    pub async fn send(&mut self, buf: &[u8]) -> io::Result<usize> {
+    pub async fn send(&self, buf: &[u8]) -> io::Result<usize> {
-        poll_fn(|cx| self.poll_send(cx, buf)).await
+        self.io
+            .async_io(mio::Ready::writable(), |sock| sock.send(buf))
+            .await
     }
 
     /// Try to send data on the socket to the remote address to which it is
@@ -130,29 +121,6 @@ impl UdpSocket {
         self.io.get_ref().send(buf)
     }
 
-    // Poll IO functions that takes `&self` are provided for the split API.
-    //
-    // They are not public because (taken from the doc of `PollEvented`):
-    //
-    // While `PollEvented` is `Sync` (if the underlying I/O type is `Sync`), the
-    // caller must ensure that there are at most two tasks that use a
-    // `PollEvented` instance concurrently. One for reading and one for writing.
-    // While violating this requirement is "safe" from a Rust memory model point
-    // of view, it will result in unexpected behavior in the form of lost
-    // notifications and tasks hanging.
-    #[doc(hidden)]
-    pub fn poll_send(&self, cx: &mut Context<'_>, buf: &[u8]) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_write_ready(cx))?;
-
-        match self.io.get_ref().send(buf) {
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_write_ready(cx)?;
-                Poll::Pending
-            }
-            x => Poll::Ready(x),
-        }
-    }
-
     /// Returns a future that receives a single datagram message on the socket from
     /// the remote address to which it is connected. On success, the future will resolve
     /// to the number of bytes read.
@@ -165,21 +133,10 @@ impl UdpSocket {
     /// will fail if the socket is not connected.
     ///
     /// [`connect`]: method@Self::connect
-    pub async fn recv(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+    pub async fn recv(&self, buf: &mut [u8]) -> io::Result<usize> {
-        poll_fn(|cx| self.poll_recv(cx, buf)).await
+        self.io
-    }
+            .async_io(mio::Ready::readable(), |sock| sock.recv(buf))
-
+            .await
-    #[doc(hidden)]
-    pub fn poll_recv(&self, cx: &mut Context<'_>, buf: &mut [u8]) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_read_ready(cx, mio::Ready::readable()))?;
-
-        match self.io.get_ref().recv(buf) {
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_read_ready(cx, mio::Ready::readable())?;
-                Poll::Pending
-            }
-            x => Poll::Ready(x),
-        }
     }
 
     /// Returns a future that sends data on the socket to the given address.
@@ -187,11 +144,11 @@ impl UdpSocket {
     ///
     /// The future will resolve to an error if the IP version of the socket does
     /// not match that of `target`.
-    pub async fn send_to<A: ToSocketAddrs>(&mut self, buf: &[u8], target: A) -> io::Result<usize> {
+    pub async fn send_to<A: ToSocketAddrs>(&self, buf: &[u8], target: A) -> io::Result<usize> {
         let mut addrs = target.to_socket_addrs().await?;
 
         match addrs.next() {
-            Some(target) => poll_fn(|cx| self.poll_send_to(cx, buf, &target)).await,
+            Some(target) => self.send_to_addr(buf, &target).await,
             None => Err(io::Error::new(
                 io::ErrorKind::InvalidInput,
                 "no addresses to send data to",
@@ -214,23 +171,10 @@ impl UdpSocket {
         self.io.get_ref().send_to(buf, &target)
     }
 
-    // TODO: Public or not?
+    async fn send_to_addr(&self, buf: &[u8], target: &SocketAddr) -> io::Result<usize> {
-    #[doc(hidden)]
+        self.io
-    pub fn poll_send_to(
+            .async_io(mio::Ready::writable(), |sock| sock.send_to(buf, target))
-        &self,
+            .await
-        cx: &mut Context<'_>,
-        buf: &[u8],
-        target: &SocketAddr,
-    ) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_write_ready(cx))?;
-
-        match self.io.get_ref().send_to(buf, target) {
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_write_ready(cx)?;
-                Poll::Pending
-            }
-            x => Poll::Ready(x),
-        }
     }
 
     /// Returns a future that receives a single datagram on the socket. On success,
@@ -239,25 +183,10 @@ impl UdpSocket {
     /// The function must be called with valid byte array `buf` of sufficient size
     /// to hold the message bytes. If a message is too long to fit in the supplied
     /// buffer, excess bytes may be discarded.
-    pub async fn recv_from(&mut self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+    pub async fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
-        poll_fn(|cx| self.poll_recv_from(cx, buf)).await
+        self.io
-    }
+            .async_io(mio::Ready::readable(), |sock| sock.recv_from(buf))
-
+            .await
-    #[doc(hidden)]
-    pub fn poll_recv_from(
-        &self,
-        cx: &mut Context<'_>,
-        buf: &mut [u8],
-    ) -> Poll<Result<(usize, SocketAddr), io::Error>> {
-        ready!(self.io.poll_read_ready(cx, mio::Ready::readable()))?;
-
-        match self.io.get_ref().recv_from(buf) {
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_read_ready(cx, mio::Ready::readable())?;
-                Poll::Pending
-            }
-            x => Poll::Ready(x),
-        }
     }
 
     /// Gets the value of the `SO_BROADCAST` option for this socket.
@@ -399,11 +328,6 @@ impl TryFrom<UdpSocket> for mio::net::UdpSocket {
     type Error = io::Error;
 
     /// Consumes value, returning the mio I/O object.
-    ///
-    /// See [`PollEvented::into_inner`] for more details about
-    /// resource deregistration that happens during the call.
-    ///
-    /// [`PollEvented::into_inner`]: crate::io::PollEvented::into_inner
     fn try_from(value: UdpSocket) -> Result<Self, Self::Error> {
         value.io.into_inner()
     }
@@ -423,7 +347,7 @@ impl TryFrom<net::UdpSocket> for UdpSocket {
 
 impl fmt::Debug for UdpSocket {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.io.get_ref().fmt(f)
+        self.io.fmt(f)
     }
 }
 

tokio/src/net/udp/split.rs

@@ -1,148 +0,0 @@
-//! [`UdpSocket`](crate::net::UdpSocket) split support.
-//!
-//! The [`split`](method@crate::net::UdpSocket::split) method splits a
-//! `UdpSocket` into a receive half and a send half, which can be used to
-//! receive and send datagrams concurrently, even from two different tasks.
-//!
-//! The halves provide access to the underlying socket, implementing
-//! `AsRef<UdpSocket>`. This allows you to call `UdpSocket` methods that takes
-//! `&self`, e.g., to get local address, to get and set socket options, to join
-//! or leave multicast groups, etc.
-//!
-//! The halves can be reunited to the original socket with their `reunite`
-//! methods.
-
-use crate::future::poll_fn;
-use crate::net::udp::UdpSocket;
-
-use std::error::Error;
-use std::fmt;
-use std::io;
-use std::net::SocketAddr;
-use std::sync::Arc;
-
-/// The send half after [`split`](super::UdpSocket::split).
-///
-/// Use [`send_to`](method@Self::send_to) or [`send`](method@Self::send) to send
-/// datagrams.
-#[derive(Debug)]
-pub struct SendHalf(Arc<UdpSocket>);
-
-/// The recv half after [`split`](super::UdpSocket::split).
-///
-/// Use [`recv_from`](method@Self::recv_from) or [`recv`](method@Self::recv) to receive
-/// datagrams.
-#[derive(Debug)]
-pub struct RecvHalf(Arc<UdpSocket>);
-
-pub(crate) fn split(socket: UdpSocket) -> (RecvHalf, SendHalf) {
-    let shared = Arc::new(socket);
-    let send = shared.clone();
-    let recv = shared;
-    (RecvHalf(recv), SendHalf(send))
-}
-
-/// Error indicating that two halves were not from the same socket, and thus could
-/// not be `reunite`d.
-#[derive(Debug)]
-pub struct ReuniteError(pub SendHalf, pub RecvHalf);
-
-impl fmt::Display for ReuniteError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(
-            f,
-            "tried to reunite halves that are not from the same socket"
-        )
-    }
-}
-
-impl Error for ReuniteError {}
-
-fn reunite(s: SendHalf, r: RecvHalf) -> Result<UdpSocket, ReuniteError> {
-    if Arc::ptr_eq(&s.0, &r.0) {
-        drop(r);
-        // Only two instances of the `Arc` are ever created, one for the
-        // receiver and one for the sender, and those `Arc`s are never exposed
-        // externally. And so when we drop one here, the other one must be the
-        // only remaining one.
-        Ok(Arc::try_unwrap(s.0).expect("udp: try_unwrap failed in reunite"))
-    } else {
-        Err(ReuniteError(s, r))
-    }
-}
-
-impl RecvHalf {
-    /// Attempts to put the two "halves" of a `UdpSocket` back together and
-    /// recover the original socket. Succeeds only if the two "halves"
-    /// originated from the same call to `UdpSocket::split`.
-    pub fn reunite(self, other: SendHalf) -> Result<UdpSocket, ReuniteError> {
-        reunite(other, self)
-    }
-
-    /// Returns a future that receives a single datagram on the socket. On success,
-    /// the future resolves to the number of bytes read and the origin.
-    ///
-    /// The function must be called with valid byte array `buf` of sufficient size
-    /// to hold the message bytes. If a message is too long to fit in the supplied
-    /// buffer, excess bytes may be discarded.
-    pub async fn recv_from(&mut self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
-        poll_fn(|cx| self.0.poll_recv_from(cx, buf)).await
-    }
-
-    /// Returns a future that receives a single datagram message on the socket from
-    /// the remote address to which it is connected. On success, the future will resolve
-    /// to the number of bytes read.
-    ///
-    /// The function must be called with valid byte array `buf` of sufficient size to
-    /// hold the message bytes. If a message is too long to fit in the supplied buffer,
-    /// excess bytes may be discarded.
-    ///
-    /// The [`connect`] method will connect this socket to a remote address. The future
-    /// will fail if the socket is not connected.
-    ///
-    /// [`connect`]: super::UdpSocket::connect
-    pub async fn recv(&mut self, buf: &mut [u8]) -> io::Result<usize> {
-        poll_fn(|cx| self.0.poll_recv(cx, buf)).await
-    }
-}
-
-impl SendHalf {
-    /// Attempts to put the two "halves" of a `UdpSocket` back together and
-    /// recover the original socket. Succeeds only if the two "halves"
-    /// originated from the same call to `UdpSocket::split`.
-    pub fn reunite(self, other: RecvHalf) -> Result<UdpSocket, ReuniteError> {
-        reunite(self, other)
-    }
-
-    /// Returns a future that sends data on the socket to the given address.
-    /// On success, the future will resolve to the number of bytes written.
-    ///
-    /// The future will resolve to an error if the IP version of the socket does
-    /// not match that of `target`.
-    pub async fn send_to(&mut self, buf: &[u8], target: &SocketAddr) -> io::Result<usize> {
-        poll_fn(|cx| self.0.poll_send_to(cx, buf, target)).await
-    }
-
-    /// Returns a future that sends data on the socket to the remote address to which it is connected.
-    /// On success, the future will resolve to the number of bytes written.
-    ///
-    /// The [`connect`] method will connect this socket to a remote address. The future
-    /// will resolve to an error if the socket is not connected.
-    ///
-    /// [`connect`]: super::UdpSocket::connect
-    pub async fn send(&mut self, buf: &[u8]) -> io::Result<usize> {
-        poll_fn(|cx| self.0.poll_send(cx, buf)).await
-    }
-}
-
-impl AsRef<UdpSocket> for SendHalf {
-    fn as_ref(&self) -> &UdpSocket {
-        &self.0
-    }
-}
-
-impl AsRef<UdpSocket> for RecvHalf {
-    fn as_ref(&self) -> &UdpSocket {
-        &self.0
-    }
-}

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

@@ -1,8 +1,3 @@
 //! Unix datagram types.
 
 pub(crate) mod socket;
-pub(crate) mod split;
-pub(crate) mod split_owned;
-
-pub use split::{RecvHalf, SendHalf};
-pub use split_owned::{OwnedRecvHalf, OwnedSendHalf, ReuniteError};

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

@@ -1,7 +1,4 @@
-use crate::future::poll_fn;
 use crate::io::PollEvented;
-use crate::net::unix::datagram::split::{split, RecvHalf, SendHalf};
-use crate::net::unix::datagram::split_owned::{split_owned, OwnedRecvHalf, OwnedSendHalf};
 
 use std::convert::TryFrom;
 use std::fmt;
@@ -10,7 +7,6 @@ use std::net::Shutdown;
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::os::unix::net::{self, SocketAddr};
 use std::path::Path;
-use std::task::{Context, Poll};
 
 cfg_uds! {
     /// An I/O object representing a Unix datagram socket.
@@ -38,9 +34,9 @@ cfg_uds! {
     ///
     /// // Bind each socket to a filesystem path
     /// let tx_path = tmp.path().join("tx");
-    /// let mut tx = UnixDatagram::bind(&tx_path)?;
+    /// let tx = UnixDatagram::bind(&tx_path)?;
     /// let rx_path = tmp.path().join("rx");
-    /// let mut rx = UnixDatagram::bind(&rx_path)?;
+    /// let rx = UnixDatagram::bind(&rx_path)?;
     ///
     /// let bytes = b"hello world";
     /// tx.send_to(bytes, &rx_path).await?;
@@ -64,7 +60,7 @@ cfg_uds! {
     /// use tokio::net::UnixDatagram;
     ///
     /// // Create the pair of sockets
-    /// let (mut sock1, mut sock2) = UnixDatagram::pair()?;
+    /// let (sock1, sock2) = UnixDatagram::pair()?;
     ///
     /// // Since the sockets are paired, the paired send/recv
     /// // functions can be used
@@ -128,7 +124,7 @@ impl UnixDatagram {
     /// use tokio::net::UnixDatagram;
     ///
     /// // Create the pair of sockets
-    /// let (mut sock1, mut sock2) = UnixDatagram::pair()?;
+    /// let (sock1, sock2) = UnixDatagram::pair()?;
     ///
     /// // Since the sockets are paired, the paired send/recv
     /// // functions can be used
@@ -208,12 +204,12 @@ impl UnixDatagram {
     /// use tempfile::tempdir;
     ///
     /// // Create an unbound socket
-    /// let mut tx = UnixDatagram::unbound()?;
+    /// let tx = UnixDatagram::unbound()?;
     ///
     /// // Create another, bound socket
     /// let tmp = tempdir()?;
     /// let rx_path = tmp.path().join("rx");
-    /// let mut rx = UnixDatagram::bind(&rx_path)?;
+    /// let rx = UnixDatagram::bind(&rx_path)?;
     ///
     /// // Send to the bound socket
     /// let bytes = b"hello world";
@@ -247,12 +243,12 @@ impl UnixDatagram {
     /// use tempfile::tempdir;
     ///
     /// // Create an unbound socket
-    /// let mut tx = UnixDatagram::unbound()?;
+    /// let tx = UnixDatagram::unbound()?;
     ///
     /// // Create another, bound socket
     /// let tmp = tempdir()?;
     /// let rx_path = tmp.path().join("rx");
-    /// let mut rx = UnixDatagram::bind(&rx_path)?;
+    /// let rx = UnixDatagram::bind(&rx_path)?;
     ///
     /// // Connect to the bound socket
     /// tx.connect(&rx_path)?;
@@ -284,7 +280,7 @@ impl UnixDatagram {
     /// use tokio::net::UnixDatagram;
     ///
     /// // Create the pair of sockets
-    /// let (mut sock1, mut sock2) = UnixDatagram::pair()?;
+    /// let (sock1, sock2) = UnixDatagram::pair()?;
     ///
     /// // Since the sockets are paired, the paired send/recv
     /// // functions can be used
@@ -300,8 +296,10 @@ impl UnixDatagram {
     /// # Ok(())
     /// # }
     /// ```
-    pub async fn send(&mut self, buf: &[u8]) -> io::Result<usize> {
+    pub async fn send(&self, buf: &[u8]) -> io::Result<usize> {
-        poll_fn(|cx| self.poll_send_priv(cx, buf)).await
+        self.io
+            .async_io(mio::Ready::writable(), |sock| sock.send(buf))
+            .await
     }
 
     /// Try to send a datagram to the peer without waiting.
@@ -371,32 +369,6 @@ impl UnixDatagram {
         self.io.get_ref().send_to(buf, target)
     }
 
-    // Poll IO functions that takes `&self` are provided for the split API.
-    //
-    // They are not public because (taken from the doc of `PollEvented`):
-    //
-    // While `PollEvented` is `Sync` (if the underlying I/O type is `Sync`), the
-    // caller must ensure that there are at most two tasks that use a
-    // `PollEvented` instance concurrently. One for reading and one for writing.
-    // While violating this requirement is "safe" from a Rust memory model point
-    // of view, it will result in unexpected behavior in the form of lost
-    // notifications and tasks hanging.
-    pub(crate) fn poll_send_priv(
-        &self,
-        cx: &mut Context<'_>,
-        buf: &[u8],
-    ) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_write_ready(cx))?;
-
-        match self.io.get_ref().send(buf) {
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_write_ready(cx)?;
-                Poll::Pending
-            }
-            x => Poll::Ready(x),
-        }
-    }
-
     /// Receives data from the socket.
     ///
     /// # Examples
@@ -407,7 +379,7 @@ impl UnixDatagram {
     /// use tokio::net::UnixDatagram;
     ///
     /// // Create the pair of sockets
-    /// let (mut sock1, mut sock2) = UnixDatagram::pair()?;
+    /// let (sock1, sock2) = UnixDatagram::pair()?;
     ///
     /// // Since the sockets are paired, the paired send/recv
     /// // functions can be used
@@ -423,8 +395,10 @@ impl UnixDatagram {
     /// # Ok(())
     /// # }
     /// ```
-    pub async fn recv(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+    pub async fn recv(&self, buf: &mut [u8]) -> io::Result<usize> {
-        poll_fn(|cx| self.poll_recv_priv(cx, buf)).await
+        self.io
+            .async_io(mio::Ready::readable(), |sock| sock.recv(buf))
+            .await
     }
 
     /// Try to receive a datagram from the peer without waiting.
@@ -455,22 +429,6 @@ impl UnixDatagram {
         self.io.get_ref().recv(buf)
     }
 
-    pub(crate) fn poll_recv_priv(
-        &self,
-        cx: &mut Context<'_>,
-        buf: &mut [u8],
-    ) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_read_ready(cx, mio::Ready::readable()))?;
-
-        match self.io.get_ref().recv(buf) {
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_read_ready(cx, mio::Ready::readable())?;
-                Poll::Pending
-            }
-            x => Poll::Ready(x),
-        }
-    }
-
     /// Sends data on the socket to the specified address.
     ///
     /// # Examples
@@ -487,9 +445,9 @@ impl UnixDatagram {
     ///
     /// // Bind each socket to a filesystem path
     /// let tx_path = tmp.path().join("tx");
-    /// let mut tx = UnixDatagram::bind(&tx_path)?;
+    /// let tx = UnixDatagram::bind(&tx_path)?;
     /// let rx_path = tmp.path().join("rx");
-    /// let mut rx = UnixDatagram::bind(&rx_path)?;
+    /// let rx = UnixDatagram::bind(&rx_path)?;
     ///
     /// let bytes = b"hello world";
     /// tx.send_to(bytes, &rx_path).await?;
@@ -504,28 +462,15 @@ impl UnixDatagram {
     /// # Ok(())
     /// # }
     /// ```
-    pub async fn send_to<P>(&mut self, buf: &[u8], target: P) -> io::Result<usize>
+    pub async fn send_to<P>(&self, buf: &[u8], target: P) -> io::Result<usize>
     where
-        P: AsRef<Path> + Unpin,
+        P: AsRef<Path>,
     {
-        poll_fn(|cx| self.poll_send_to_priv(cx, buf, target.as_ref())).await
+        self.io
-    }
+            .async_io(mio::Ready::writable(), |sock| {
-
+                sock.send_to(buf, target.as_ref())
-    pub(crate) fn poll_send_to_priv(
+            })
-        &self,
+            .await
-        cx: &mut Context<'_>,
-        buf: &[u8],
-        target: &Path,
-    ) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_write_ready(cx))?;
-
-        match self.io.get_ref().send_to(buf, target) {
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_write_ready(cx)?;
-                Poll::Pending
-            }
-            x => Poll::Ready(x),
-        }
     }
 
     /// Receives data from the socket.
@@ -544,9 +489,9 @@ impl UnixDatagram {
     ///
     /// // Bind each socket to a filesystem path
     /// let tx_path = tmp.path().join("tx");
-    /// let mut tx = UnixDatagram::bind(&tx_path)?;
+    /// let tx = UnixDatagram::bind(&tx_path)?;
     /// let rx_path = tmp.path().join("rx");
-    /// let mut rx = UnixDatagram::bind(&rx_path)?;
+    /// let rx = UnixDatagram::bind(&rx_path)?;
     ///
     /// let bytes = b"hello world";
     /// tx.send_to(bytes, &rx_path).await?;
@@ -561,8 +506,10 @@ impl UnixDatagram {
     /// # Ok(())
     /// # }
     /// ```
-    pub async fn recv_from(&mut self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+    pub async fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
-        poll_fn(|cx| self.poll_recv_from_priv(cx, buf)).await
+        self.io
+            .async_io(mio::Ready::readable(), |sock| sock.recv_from(buf))
+            .await
     }
 
     /// Try to receive data from the socket without waiting.
@@ -601,22 +548,6 @@ impl UnixDatagram {
         self.io.get_ref().recv_from(buf)
     }
 
-    pub(crate) fn poll_recv_from_priv(
-        &self,
-        cx: &mut Context<'_>,
-        buf: &mut [u8],
-    ) -> Poll<Result<(usize, SocketAddr), io::Error>> {
-        ready!(self.io.poll_read_ready(cx, mio::Ready::readable()))?;
-
-        match self.io.get_ref().recv_from(buf) {
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_read_ready(cx, mio::Ready::readable())?;
-                Poll::Pending
-            }
-            x => Poll::Ready(x),
-        }
-    }
-
     /// Returns the local address that this socket is bound to.
     ///
     /// # Examples
@@ -748,7 +679,7 @@ impl UnixDatagram {
     /// use std::net::Shutdown;
     ///
     /// // Create an unbound socket
-    /// let (mut socket, other) = UnixDatagram::pair()?;
+    /// let (socket, other) = UnixDatagram::pair()?;
     ///
     /// socket.shutdown(Shutdown::Both)?;
     ///
@@ -768,102 +699,12 @@ impl UnixDatagram {
     pub fn shutdown(&self, how: Shutdown) -> io::Result<()> {
         self.io.get_ref().shutdown(how)
     }
-
-    // These lifetime markers also appear in the generated documentation, and make
-    // it more clear that this is a *borrowed* split.
-    #[allow(clippy::needless_lifetimes)]
-    /// Split a `UnixDatagram` into a receive half and a send half, which can be used
-    /// to receive and send the datagram concurrently.
-    ///
-    /// This method is more efficient than [`into_split`], but the halves cannot
-    /// be moved into independently spawned tasks.
-    ///
-    /// [`into_split`]: fn@crate::net::UnixDatagram::into_split
-    ///
-    /// # Examples
-    /// ```
-    /// # use std::error::Error;
-    /// # #[tokio::main]
-    /// # async fn main() -> Result<(), Box<dyn Error>> {
-    /// use tokio::net::UnixDatagram;
-    ///
-    /// // Create the pair of sockets
-    /// let (mut sock1, mut sock2) = UnixDatagram::pair()?;
-    ///
-    /// // Split sock1
-    /// let (sock1_rx, mut sock1_tx) = sock1.split();
-    ///
-    /// // Since the sockets are paired, the paired send/recv
-    /// // functions can be used
-    /// let bytes = b"hello world";
-    /// sock1_tx.send(bytes).await?;
-    ///
-    /// let mut buff = vec![0u8; 24];
-    /// let size = sock2.recv(&mut buff).await?;
-    ///
-    /// let dgram = &buff[..size];
-    /// assert_eq!(dgram, bytes);
-    ///
-    /// # Ok(())
-    /// # }
-    /// ```
-    pub fn split<'a>(&'a mut self) -> (RecvHalf<'a>, SendHalf<'a>) {
-        split(self)
-    }
-
-    /// Split a `UnixDatagram` into a receive half and a send half, which can be used
-    /// to receive and send the datagram concurrently.
-    ///
-    /// Unlike [`split`], the owned halves can be moved to separate tasks,
-    /// however this comes at the cost of a heap allocation.
-    ///
-    /// **Note:** Dropping the write half will shut down the write half of the
-    /// datagram. This is equivalent to calling [`shutdown(Write)`].
-    ///
-    /// # Examples
-    /// ```
-    /// # use std::error::Error;
-    /// # #[tokio::main]
-    /// # async fn main() -> Result<(), Box<dyn Error>> {
-    /// use tokio::net::UnixDatagram;
-    ///
-    /// // Create the pair of sockets
-    /// let (sock1, mut sock2) = UnixDatagram::pair()?;
-    ///
-    /// // Split sock1
-    /// let (sock1_rx, mut sock1_tx) = sock1.into_split();
-    ///
-    /// // Since the sockets are paired, the paired send/recv
-    /// // functions can be used
-    /// let bytes = b"hello world";
-    /// sock1_tx.send(bytes).await?;
-    ///
-    /// let mut buff = vec![0u8; 24];
-    /// let size = sock2.recv(&mut buff).await?;
-    ///
-    /// let dgram = &buff[..size];
-    /// assert_eq!(dgram, bytes);
-    ///
-    /// # Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`split`]: fn@crate::net::UnixDatagram::split
-    /// [`shutdown(Write)`]:fn@crate::net::UnixDatagram::shutdown
-    pub fn into_split(self) -> (OwnedRecvHalf, OwnedSendHalf) {
-        split_owned(self)
-    }
 }
 
 impl TryFrom<UnixDatagram> for mio_uds::UnixDatagram {
     type Error = io::Error;
 
     /// Consumes value, returning the mio I/O object.
-    ///
-    /// See [`PollEvented::into_inner`] for more details about
-    /// resource deregistration that happens during the call.
-    ///
-    /// [`PollEvented::into_inner`]: crate::io::PollEvented::into_inner
     fn try_from(value: UnixDatagram) -> Result<Self, Self::Error> {
         value.io.into_inner()
     }

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

@@ -1,68 +0,0 @@
-//! `UnixDatagram` split support.
-//!
-//! A `UnixDatagram` can be split into a `RecvHalf` and a `SendHalf` with the
-//! `UnixDatagram::split` method.
-
-use crate::future::poll_fn;
-use crate::net::UnixDatagram;
-
-use std::io;
-use std::os::unix::net::SocketAddr;
-use std::path::Path;
-
-/// Borrowed receive half of a [`UnixDatagram`], created by [`split`].
-///
-/// [`UnixDatagram`]: UnixDatagram
-/// [`split`]: crate::net::UnixDatagram::split()
-#[derive(Debug)]
-pub struct RecvHalf<'a>(&'a UnixDatagram);
-
-/// Borrowed send half of a [`UnixDatagram`], created by [`split`].
-///
-/// [`UnixDatagram`]: UnixDatagram
-/// [`split`]: crate::net::UnixDatagram::split()
-#[derive(Debug)]
-pub struct SendHalf<'a>(&'a UnixDatagram);
-
-pub(crate) fn split(stream: &mut UnixDatagram) -> (RecvHalf<'_>, SendHalf<'_>) {
-    (RecvHalf(&*stream), SendHalf(&*stream))
-}
-
-impl RecvHalf<'_> {
-    /// Receives data from the socket.
-    pub async fn recv_from(&mut self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
-        poll_fn(|cx| self.0.poll_recv_from_priv(cx, buf)).await
-    }
-
-    /// Receives data from the socket.
-    pub async fn recv(&mut self, buf: &mut [u8]) -> io::Result<usize> {
-        poll_fn(|cx| self.0.poll_recv_priv(cx, buf)).await
-    }
-}
-
-impl SendHalf<'_> {
-    /// Sends data on the socket to the specified address.
-    pub async fn send_to<P>(&mut self, buf: &[u8], target: P) -> io::Result<usize>
-    where
-        P: AsRef<Path> + Unpin,
-    {
-        poll_fn(|cx| self.0.poll_send_to_priv(cx, buf, target.as_ref())).await
-    }
-
-    /// Sends data on the socket to the socket's peer.
-    pub async fn send(&mut self, buf: &[u8]) -> io::Result<usize> {
-        poll_fn(|cx| self.0.poll_send_priv(cx, buf)).await
-    }
-}
-
-impl AsRef<UnixDatagram> for RecvHalf<'_> {
-    fn as_ref(&self) -> &UnixDatagram {
-        self.0
-    }
-}
-
-impl AsRef<UnixDatagram> for SendHalf<'_> {
-    fn as_ref(&self) -> &UnixDatagram {
-        self.0
-    }
-}

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

@@ -1,148 +0,0 @@
-//! `UnixDatagram` owned split support.
-//!
-//! A `UnixDatagram` can be split into an `OwnedSendHalf` and a `OwnedRecvHalf`
-//! with the `UnixDatagram::into_split` method.
-
-use crate::future::poll_fn;
-use crate::net::UnixDatagram;
-
-use std::error::Error;
-use std::net::Shutdown;
-use std::os::unix::net::SocketAddr;
-use std::path::Path;
-use std::sync::Arc;
-use std::{fmt, io};
-
-pub(crate) fn split_owned(socket: UnixDatagram) -> (OwnedRecvHalf, OwnedSendHalf) {
-    let shared = Arc::new(socket);
-    let send = shared.clone();
-    let recv = shared;
-    (
-        OwnedRecvHalf { inner: recv },
-        OwnedSendHalf {
-            inner: send,
-            shutdown_on_drop: true,
-        },
-    )
-}
-
-/// Owned send half of a [`UnixDatagram`], created by [`into_split`].
-///
-/// [`UnixDatagram`]: UnixDatagram
-/// [`into_split`]: UnixDatagram::into_split()
-#[derive(Debug)]
-pub struct OwnedSendHalf {
-    inner: Arc<UnixDatagram>,
-    shutdown_on_drop: bool,
-}
-
-/// Owned receive half of a [`UnixDatagram`], created by [`into_split`].
-///
-/// [`UnixDatagram`]: UnixDatagram
-/// [`into_split`]: UnixDatagram::into_split()
-#[derive(Debug)]
-pub struct OwnedRecvHalf {
-    inner: Arc<UnixDatagram>,
-}
-
-/// Error indicating that two halves were not from the same socket, and thus could
-/// not be `reunite`d.
-#[derive(Debug)]
-pub struct ReuniteError(pub OwnedSendHalf, pub OwnedRecvHalf);
-
-impl fmt::Display for ReuniteError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(
-            f,
-            "tried to reunite halves that are not from the same socket"
-        )
-    }
-}
-
-impl Error for ReuniteError {}
-
-fn reunite(s: OwnedSendHalf, r: OwnedRecvHalf) -> Result<UnixDatagram, ReuniteError> {
-    if Arc::ptr_eq(&s.inner, &r.inner) {
-        s.forget();
-        // Only two instances of the `Arc` are ever created, one for the
-        // receiver and one for the sender, and those `Arc`s are never exposed
-        // externally. And so when we drop one here, the other one must be the
-        // only remaining one.
-        Ok(Arc::try_unwrap(r.inner).expect("UnixDatagram: try_unwrap failed in reunite"))
-    } else {
-        Err(ReuniteError(s, r))
-    }
-}
-
-impl OwnedRecvHalf {
-    /// Attempts to put the two "halves" of a `UnixDatagram` back together and
-    /// recover the original socket. Succeeds only if the two "halves"
-    /// originated from the same call to [`into_split`].
-    ///
-    /// [`into_split`]: UnixDatagram::into_split()
-    pub fn reunite(self, other: OwnedSendHalf) -> Result<UnixDatagram, ReuniteError> {
-        reunite(other, self)
-    }
-
-    /// Receives data from the socket.
-    pub async fn recv_from(&mut self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
-        poll_fn(|cx| self.inner.poll_recv_from_priv(cx, buf)).await
-    }
-
-    /// Receives data from the socket.
-    pub async fn recv(&mut self, buf: &mut [u8]) -> io::Result<usize> {
-        poll_fn(|cx| self.inner.poll_recv_priv(cx, buf)).await
-    }
-}
-
-impl OwnedSendHalf {
-    /// Attempts to put the two "halves" of a `UnixDatagram` back together and
-    /// recover the original socket. Succeeds only if the two "halves"
-    /// originated from the same call to [`into_split`].
-    ///
-    /// [`into_split`]: UnixDatagram::into_split()
-    pub fn reunite(self, other: OwnedRecvHalf) -> Result<UnixDatagram, ReuniteError> {
-        reunite(self, other)
-    }
-
-    /// Sends data on the socket to the specified address.
-    pub async fn send_to<P>(&mut self, buf: &[u8], target: P) -> io::Result<usize>
-    where
-        P: AsRef<Path> + Unpin,
-    {
-        poll_fn(|cx| self.inner.poll_send_to_priv(cx, buf, target.as_ref())).await
-    }
-
-    /// Sends data on the socket to the socket's peer.
-    pub async fn send(&mut self, buf: &[u8]) -> io::Result<usize> {
-        poll_fn(|cx| self.inner.poll_send_priv(cx, buf)).await
-    }
-
-    /// Destroy the send half, but don't close the send half of the stream
-    /// until the receive half is dropped. If the read half has already been
-    /// dropped, this closes the stream.
-    pub fn forget(mut self) {
-        self.shutdown_on_drop = false;
-        drop(self);
-    }
-}
-
-impl Drop for OwnedSendHalf {
-    fn drop(&mut self) {
-        if self.shutdown_on_drop {
-            let _ = self.inner.shutdown(Shutdown::Write);
-        }
-    }
-}
-
-impl AsRef<UnixDatagram> for OwnedSendHalf {
-    fn as_ref(&self) -> &UnixDatagram {
-        &self.inner
-    }
-}
-
-impl AsRef<UnixDatagram> for OwnedRecvHalf {
-    fn as_ref(&self) -> &UnixDatagram {
-        &self.inner
-    }
-}

tokio/src/net/unix/listener.rs

@@ -2,7 +2,6 @@ use crate::future::poll_fn;
 use crate::io::PollEvented;
 use crate::net::unix::{Incoming, UnixStream};
 
-use mio::Ready;
 use std::convert::TryFrom;
 use std::fmt;
 use std::io;
@@ -122,19 +121,19 @@ impl UnixListener {
         &mut self,
         cx: &mut Context<'_>,
     ) -> Poll<io::Result<(net::UnixStream, SocketAddr)>> {
-        ready!(self.io.poll_read_ready(cx, Ready::readable()))?;
+        loop {
+            let ev = ready!(self.io.poll_read_ready(cx))?;
 
-        match self.io.get_ref().accept_std() {
+            match self.io.get_ref().accept_std() {
-            Ok(None) => {
+                Ok(None) => {
-                self.io.clear_read_ready(cx, Ready::readable())?;
+                    self.io.clear_readiness(ev);
-                Poll::Pending
+                }
+                Ok(Some((sock, addr))) => return Ok((sock, addr)).into(),
+                Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
+                    self.io.clear_readiness(ev);
+                }
+                Err(err) => return Err(err).into(),
             }
-            Ok(Some((sock, addr))) => Ok((sock, addr)).into(),
-            Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_read_ready(cx, Ready::readable())?;
-                Poll::Pending
-            }
-            Err(err) => Err(err).into(),
         }
     }
 
@@ -197,11 +196,6 @@ impl TryFrom<UnixListener> for mio_uds::UnixListener {
     type Error = io::Error;
 
     /// Consumes value, returning the mio I/O object.
-    ///
-    /// See [`PollEvented::into_inner`] for more details about
-    /// resource deregistration that happens during the call.
-    ///
-    /// [`PollEvented::into_inner`]: crate::io::PollEvented::into_inner
     fn try_from(value: UnixListener) -> Result<Self, Self::Error> {
         value.io.into_inner()
     }

tokio/src/net/unix/stream.rs

@@ -143,11 +143,6 @@ impl TryFrom<UnixStream> for mio_uds::UnixStream {
     type Error = io::Error;
 
     /// Consumes value, returning the mio I/O object.
-    ///
-    /// See [`PollEvented::into_inner`] for more details about
-    /// resource deregistration that happens during the call.
-    ///
-    /// [`PollEvented::into_inner`]: crate::io::PollEvented::into_inner
     fn try_from(value: UnixStream) -> Result<Self, Self::Error> {
         value.io.into_inner()
     }
@@ -211,26 +206,28 @@ impl UnixStream {
         cx: &mut Context<'_>,
         buf: &mut ReadBuf<'_>,
     ) -> Poll<io::Result<()>> {
-        ready!(self.io.poll_read_ready(cx, mio::Ready::readable()))?;
+        loop {
+            let ev = ready!(self.io.poll_read_ready(cx))?;
 
-        // Safety: `UnixStream::read` will not peak at the maybe uinitialized bytes.
+            // Safety: `UnixStream::read` will not peek at the maybe uinitialized bytes.
-        let b =
+            let b = unsafe {
-            unsafe { &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };
+                &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8])
-        match self.io.get_ref().read(b) {
+            };
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+            match self.io.get_ref().read(b) {
-                self.io.clear_read_ready(cx, mio::Ready::readable())?;
+                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                Poll::Pending
+                    self.io.clear_readiness(ev);
-            }
-            Ok(n) => {
-                // Safety: We trust `UnixStream::read` to have filled up `n` bytes
-                // in the buffer.
-                unsafe {
-                    buf.assume_init(n);
                 }
-                buf.add_filled(n);
+                Ok(n) => {
-                Poll::Ready(Ok(()))
+                    // Safety: We trust `UnixStream::read` to have filled up `n` bytes
+                    // in the buffer.
+                    unsafe {
+                        buf.assume_init(n);
+                    }
+                    buf.add_filled(n);
+                    return Poll::Ready(Ok(()));
+                }
+                Err(e) => return Poll::Ready(Err(e)),
             }
-            Err(e) => Poll::Ready(Err(e)),
         }
     }
 
@@ -239,14 +236,15 @@ impl UnixStream {
         cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_write_ready(cx))?;
+        loop {
+            let ev = ready!(self.io.poll_write_ready(cx))?;
 
-        match self.io.get_ref().write(buf) {
+            match self.io.get_ref().write(buf) {
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_write_ready(cx)?;
+                    self.io.clear_readiness(ev);
-                Poll::Pending
+                }
+                x => return Poll::Ready(x),
             }
-            x => Poll::Ready(x),
         }
     }
 }

tokio/src/signal/unix/driver.rs

@@ -1,13 +1,15 @@
 //! Signal driver
 
 use crate::io::driver::Driver as IoDriver;
-use crate::io::Registration;
+use crate::io::PollEvented;
 use crate::park::Park;
 use crate::runtime::context;
 use crate::signal::registry::globals;
 use mio_uds::UnixStream;
 use std::io::{self, Read};
+use std::ptr;
 use std::sync::{Arc, Weak};
+use std::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
 use std::time::Duration;
 
 /// Responsible for registering wakeups when an OS signal is received, and
@@ -21,11 +23,7 @@ pub(crate) struct Driver {
     park: IoDriver,
 
     /// A pipe for receiving wake events from the signal handler
-    receiver: UnixStream,
+    receiver: PollEvented<UnixStream>,
-
-    /// The actual registraiton for `receiver` when active.
-    /// Lazily bound at the first signal registration.
-    registration: Registration,
 
     /// Shared state
     inner: Arc<Inner>,
@@ -58,13 +56,12 @@ impl Driver {
         // either, since we can't compare Handles or assume they will always
         // point to the exact same reactor.
         let receiver = globals().receiver.try_clone()?;
-        let registration =
+        let receiver =
-            Registration::new_with_ready_and_handle(&receiver, mio::Ready::all(), park.handle())?;
+            PollEvented::new_with_ready_and_handle(receiver, mio::Ready::all(), park.handle())?;
 
         Ok(Self {
             park,
             receiver,
-            registration,
             inner: Arc::new(Inner(())),
         })
     }
@@ -79,17 +76,23 @@ impl Driver {
 
     fn process(&self) {
         // Check if the pipe is ready to read and therefore has "woken" us up
-        match self.registration.take_read_ready() {
+        //
-            Ok(Some(ready)) => assert!(ready.is_readable()),
+        // To do so, we will `poll_read_ready` with a noop waker, since we don't
-            Ok(None) => return, // No wake has arrived, bail
+        // need to actually be notified when read ready...
-            Err(e) => panic!("reactor gone: {}", e),
+        let waker = unsafe { Waker::from_raw(RawWaker::new(ptr::null(), &NOOP_WAKER_VTABLE)) };
-        }
+        let mut cx = Context::from_waker(&waker);
+
+        let ev = match self.receiver.poll_read_ready(&mut cx) {
+            Poll::Ready(Ok(ev)) => ev,
+            Poll::Ready(Err(e)) => panic!("reactor gone: {}", e),
+            Poll::Pending => return, // No wake has arrived, bail
+        };
 
         // Drain the pipe completely so we can receive a new readiness event
         // if another signal has come in.
         let mut buf = [0; 128];
         loop {
-            match (&self.receiver).read(&mut buf) {
+            match self.receiver.get_ref().read(&mut buf) {
                 Ok(0) => panic!("EOF on self-pipe"),
                 Ok(_) => continue, // Keep reading
                 Err(e) if e.kind() == io::ErrorKind::WouldBlock => break,
@@ -97,11 +100,21 @@ impl Driver {
             }
         }
 
+        self.receiver.clear_readiness(ev);
+
         // Broadcast any signals which were received
         globals().broadcast();
     }
 }
 
+const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop);
+
+unsafe fn noop_clone(_data: *const ()) -> RawWaker {
+    RawWaker::new(ptr::null(), &NOOP_WAKER_VTABLE)
+}
+
+unsafe fn noop(_data: *const ()) {}
+
 // ===== impl Park for Driver =====
 
 impl Park for Driver {

tokio/src/sync/task/atomic_waker.rs

@@ -141,13 +141,12 @@ impl AtomicWaker {
         }
     }
 
+    /*
     /// Registers the current waker to be notified on calls to `wake`.
-    ///
-    /// This is the same as calling `register_task` with `task::current()`.
-    #[cfg(feature = "io-driver")]
     pub(crate) fn register(&self, waker: Waker) {
         self.do_register(waker);
     }
+    */
 
     /// Registers the provided waker to be notified on calls to `wake`.
     ///

tokio/src/util/bit.rs

@@ -1,6 +1,6 @@
 use std::fmt;
 
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, PartialEq)]
 pub(crate) struct Pack {
     mask: usize,
     shift: u32,

tokio/src/util/linked_list.rs

@@ -106,6 +106,7 @@ impl<L: Link> LinkedList<L, L::Target> {
 
     /// Removes the last element from a list and returns it, or None if it is
     /// empty.
+    #[cfg_attr(any(feature = "udp", feature = "uds"), allow(unused))]
     pub(crate) fn pop_back(&mut self) -> Option<L::Handle> {
         unsafe {
             let last = self.tail?;
@@ -125,6 +126,7 @@ impl<L: Link> LinkedList<L, L::Target> {
     }
 
     /// Returns whether the linked list doesn not contain any node
+    #[cfg_attr(any(feature = "udp", feature = "uds"), allow(unused))]
     pub(crate) fn is_empty(&self) -> bool {
         if self.head.is_some() {
             return false;
@@ -180,6 +182,12 @@ impl<L: Link> fmt::Debug for LinkedList<L, L::Target> {
     }
 }
 
+impl<L: Link> Default for LinkedList<L, L::Target> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 cfg_sync! {
     impl<L: Link> LinkedList<L, L::Target> {
         pub(crate) fn last(&self) -> Option<&L::Target> {
@@ -222,6 +230,52 @@ cfg_rt_threaded! {
     }
 }
 
+// ===== impl DrainFilter =====
+
+cfg_io_readiness! {
+    pub(crate) struct DrainFilter<'a, T: Link, F> {
+        list: &'a mut LinkedList<T, T::Target>,
+        filter: F,
+        curr: Option<NonNull<T::Target>>,
+    }
+
+    impl<T: Link> LinkedList<T, T::Target> {
+        pub(crate) fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F>
+        where
+            F: FnMut(&mut T::Target) -> bool,
+        {
+            let curr = self.head;
+            DrainFilter {
+                curr,
+                filter,
+                list: self,
+            }
+        }
+    }
+
+    impl<'a, T, F> Iterator for DrainFilter<'a, T, F>
+    where
+        T: Link,
+        F: FnMut(&mut T::Target) -> bool,
+    {
+        type Item = T::Handle;
+
+        fn next(&mut self) -> Option<Self::Item> {
+            while let Some(curr) = self.curr {
+                // safety: the pointer references data contained by the list
+                self.curr = unsafe { T::pointers(curr).as_ref() }.next;
+
+                // safety: the value is still owned by the linked list.
+                if (self.filter)(unsafe { &mut *curr.as_ptr() }) {
+                    return unsafe { self.list.remove(curr) };
+                }
+            }
+
+            None
+        }
+    }
+}
+
 // ===== impl Pointers =====
 
 impl<T> Pointers<T> {

tokio/src/util/mod.rs

@@ -3,7 +3,7 @@ cfg_io_driver! {
     pub(crate) mod slab;
 }
 
-#[cfg(any(feature = "sync", feature = "rt-core"))]
+#[cfg(any(feature = "io-readiness", feature = "sync", feature = "rt-core"))]
 pub(crate) mod linked_list;
 
 #[cfg(any(feature = "rt-threaded", feature = "macros", feature = "stream"))]

tokio/src/util/slab.rs

@@ -141,6 +141,8 @@ unsafe impl<T: Sync> Sync for Page<T> {}
 unsafe impl<T: Sync> Send for Page<T> {}
 unsafe impl<T: Sync> Sync for CachedPage<T> {}
 unsafe impl<T: Sync> Send for CachedPage<T> {}
+unsafe impl<T: Sync> Sync for Ref<T> {}
+unsafe impl<T: Sync> Send for Ref<T> {}
 
 /// A slot in the slab. Contains slot-specific metadata.
 ///

tokio/tests/async_send_sync.rs

@@ -172,10 +172,6 @@ async_assert_fn!(tokio::net::UdpSocket::send(_, &[u8]): Send & Sync);
 async_assert_fn!(tokio::net::UdpSocket::recv(_, &mut [u8]): Send & Sync);
 async_assert_fn!(tokio::net::UdpSocket::send_to(_, &[u8], SocketAddr): Send & Sync);
 async_assert_fn!(tokio::net::UdpSocket::recv_from(_, &mut [u8]): Send & Sync);
-async_assert_fn!(tokio::net::udp::RecvHalf::recv(_, &mut [u8]): Send & Sync);
-async_assert_fn!(tokio::net::udp::RecvHalf::recv_from(_, &mut [u8]): Send & Sync);
-async_assert_fn!(tokio::net::udp::SendHalf::send(_, &[u8]): Send & Sync);
-async_assert_fn!(tokio::net::udp::SendHalf::send_to(_, &[u8], &SocketAddr): Send & Sync);
 
 #[cfg(unix)]
 mod unix_datagram {

tokio/tests/rt_common.rs

@@ -827,6 +827,7 @@ rt_test! {
     #[test]
     fn io_notify_while_shutting_down() {
         use std::net::Ipv6Addr;
+        use std::sync::Arc;
 
         for _ in 1..10 {
             let runtime = rt();
@@ -834,7 +835,8 @@ rt_test! {
             runtime.block_on(async {
                 let socket = UdpSocket::bind((Ipv6Addr::LOCALHOST, 0)).await.unwrap();
                 let addr = socket.local_addr().unwrap();
-                let (mut recv_half, mut send_half) = socket.split();
+                let send_half = Arc::new(socket);
+                let recv_half = send_half.clone();
 
                 tokio::spawn(async move {
                     let mut buf = [0];

tokio/tests/udp.rs

@@ -1,6 +1,7 @@
 #![warn(rust_2018_idioms)]
 #![cfg(feature = "full")]
 
+use std::sync::Arc;
 use tokio::net::UdpSocket;
 
 const MSG: &[u8] = b"hello";
@@ -8,8 +9,8 @@ const MSG_LEN: usize = MSG.len();
 
 #[tokio::test]
 async fn send_recv() -> std::io::Result<()> {
-    let mut sender = UdpSocket::bind("127.0.0.1:0").await?;
+    let sender = UdpSocket::bind("127.0.0.1:0").await?;
-    let mut receiver = UdpSocket::bind("127.0.0.1:0").await?;
+    let receiver = UdpSocket::bind("127.0.0.1:0").await?;
 
     sender.connect(receiver.local_addr()?).await?;
     receiver.connect(sender.local_addr()?).await?;
@@ -25,8 +26,8 @@ async fn send_recv() -> std::io::Result<()> {
 
 #[tokio::test]
 async fn send_to_recv_from() -> std::io::Result<()> {
-    let mut sender = UdpSocket::bind("127.0.0.1:0").await?;
+    let sender = UdpSocket::bind("127.0.0.1:0").await?;
-    let mut receiver = UdpSocket::bind("127.0.0.1:0").await?;
+    let receiver = UdpSocket::bind("127.0.0.1:0").await?;
 
     let receiver_addr = receiver.local_addr()?;
     sender.send_to(MSG, &receiver_addr).await?;
@@ -42,9 +43,10 @@ async fn send_to_recv_from() -> std::io::Result<()> {
 #[tokio::test]
 async fn split() -> std::io::Result<()> {
     let socket = UdpSocket::bind("127.0.0.1:0").await?;
-    let (mut r, mut s) = socket.split();
+    let s = Arc::new(socket);
+    let r = s.clone();
 
-    let addr = s.as_ref().local_addr()?;
+    let addr = s.local_addr()?;
     tokio::spawn(async move {
         s.send_to(MSG, &addr).await.unwrap();
     });
@@ -54,24 +56,6 @@ async fn split() -> std::io::Result<()> {
     Ok(())
 }
 
-#[tokio::test]
-async fn reunite() -> std::io::Result<()> {
-    let socket = UdpSocket::bind("127.0.0.1:0").await?;
-    let (s, r) = socket.split();
-    assert!(s.reunite(r).is_ok());
-    Ok(())
-}
-
-#[tokio::test]
-async fn reunite_error() -> std::io::Result<()> {
-    let socket = UdpSocket::bind("127.0.0.1:0").await?;
-    let socket1 = UdpSocket::bind("127.0.0.1:0").await?;
-    let (s, _) = socket.split();
-    let (_, r1) = socket1.split();
-    assert!(s.reunite(r1).is_err());
-    Ok(())
-}
-
 // # Note
 //
 // This test is purposely written such that each time `sender` sends data on
@@ -86,7 +70,7 @@ async fn try_send_spawn() {
     const MSG2_LEN: usize = MSG2.len();
 
     let sender = UdpSocket::bind("127.0.0.1:0").await.unwrap();
-    let mut receiver = UdpSocket::bind("127.0.0.1:0").await.unwrap();
+    let receiver = UdpSocket::bind("127.0.0.1:0").await.unwrap();
 
     receiver
         .connect(sender.local_addr().unwrap())

tokio/tests/uds_datagram.rs

@@ -6,8 +6,9 @@ use tokio::net::UnixDatagram;
 use tokio::try_join;
 
 use std::io;
+use std::sync::Arc;
 
-async fn echo_server(mut socket: UnixDatagram) -> io::Result<()> {
+async fn echo_server(socket: UnixDatagram) -> io::Result<()> {
     let mut recv_buf = vec![0u8; 1024];
     loop {
         let (len, peer_addr) = socket.recv_from(&mut recv_buf[..]).await?;
@@ -32,7 +33,7 @@ async fn echo() -> io::Result<()> {
     });
 
     {
-        let mut socket = UnixDatagram::bind(&client_path).unwrap();
+        let socket = UnixDatagram::bind(&client_path).unwrap();
         socket.connect(server_path)?;
         socket.send(b"ECHO").await?;
         let mut recv_buf = [0u8; 16];
@@ -87,8 +88,8 @@ async fn try_send_recv_never_block() -> io::Result<()> {
 async fn split() -> std::io::Result<()> {
     let dir = tempfile::tempdir().unwrap();
     let path = dir.path().join("split.sock");
-    let socket = UnixDatagram::bind(path.clone())?;
+    let s = Arc::new(UnixDatagram::bind(path.clone())?);
-    let (mut r, mut s) = socket.into_split();
+    let r = s.clone();
 
     let msg = b"hello";
     let ((), ()) = try_join! {
@@ -106,28 +107,3 @@ async fn split() -> std::io::Result<()> {
 
     Ok(())
 }
-
-#[tokio::test]
-async fn reunite() -> std::io::Result<()> {
-    let dir = tempfile::tempdir().unwrap();
-    let path = dir.path().join("reunite.sock");
-    let socket = UnixDatagram::bind(path)?;
-    let (s, r) = socket.into_split();
-    assert!(s.reunite(r).is_ok());
-    Ok(())
-}
-
-#[tokio::test]
-async fn reunite_error() -> std::io::Result<()> {
-    let dir = tempfile::tempdir().unwrap();
-    let path = dir.path().join("reunit.sock");
-    let dir = tempfile::tempdir().unwrap();
-    let path1 = dir.path().join("reunit.sock");
-    let socket = UnixDatagram::bind(path)?;
-    let socket1 = UnixDatagram::bind(path1)?;
-
-    let (s, _) = socket.into_split();
-    let (_, r1) = socket1.into_split();
-    assert!(s.reunite(r1).is_err());
-    Ok(())
-}