Refactor IO registration using intrusive linked list

.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 -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 -Z avoid-dev-deps
         env:
           RUSTFLAGS: --cfg tokio_unstable
 

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/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();
         }
 
@@ -160,39 +169,22 @@ 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) {
             Some(io) => io,
             None => return,
         };
 
-        if io
-            .set_readiness(Some(token.0), |curr| curr | ready.as_usize())
-            .is_err()
-        {
+        let set = io.set_readiness(Some(token.0), Tick::Set(self.tick), |curr| {
+            curr | ready.as_usize()
+        });
+        if set.is_err() {
             // token no longer valid!
             return;
         }
 
-        if ready.is_writable() || platform::is_hup(ready) || platform::is_error(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();
-        }
+        io.wake(ready);
     }
 }
 
@@ -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.writer.wake();
+            io.wake(mio::Ready::all());
         })
     }
 }
@@ -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 {