Implement poll-based backend

Introduces a new backend for UNIX using the level triggered poll() syscall instead of epoll or kqueue. This support is crucial for embedded systems like the esp32 family but also for alternative operating systems like Haiku. This diff does not introduce any new platform support targets itself but provides the core technical implementation necessary to support these other targets. Future PRs will introduce specific platform support however due to reasons outlined in #1602 (many thanks for this initial effort BTW!) it is not possible to automate tests for those platforms. We will instead rely on the fact that Linux can serve as a proxy to prove that the mio code is working nominally. Note that only Linux has a sufficiently complex implementation to pass all tests. This is due to SIGRDHUP missing on other platforms and is required for about a dozen or so tests that check is_read_closed().
tokio-rs · Jul 31, 2023 · d070937 · d070937
1 parent f20ec94
commit d070937
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diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -31,6 +31,18 @@ jobs:
       run: cargo test --all-features
     - name: Tests release build
       run: cargo test --release --all-features
+  TestPoll:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    env:
+      RUSTFLAGS="--cfg mio_unsupported_force_poll_poll"
+    steps:
+    - uses: actions/checkout@v3
+    - uses: dtolnay/rust-toolchain@stable
+    - name: Tests
+      run: cargo test --all-features
+    - name: Tests release build
+      run: cargo test --release --all-features
   MinimalVersions:
     runs-on: ${{ matrix.os }}
     timeout-minutes: 10
@@ -133,6 +145,7 @@ jobs:
     runs-on: ubuntu-latest
     needs:
       - Test
+      - TestPoll
       - MinimalVersions
       - MSRV
       - Nightly

diff --git a/src/io_source.rs b/src/io_source.rs
@@ -142,9 +142,7 @@ where
     ) -> io::Result<()> {
         #[cfg(debug_assertions)]
         self.selector_id.associate(registry)?;
-        registry
-            .selector()
-            .register(self.inner.as_raw_fd(), token, interests)
+        self.state.register(registry, token, interests, self.inner.as_raw_fd())
     }
 
     fn reregister(
@@ -155,15 +153,13 @@ where
     ) -> io::Result<()> {
         #[cfg(debug_assertions)]
         self.selector_id.check_association(registry)?;
-        registry
-            .selector()
-            .reregister(self.inner.as_raw_fd(), token, interests)
+        self.state.reregister(registry, token, interests, self.inner.as_raw_fd())
     }
 
     fn deregister(&mut self, registry: &Registry) -> io::Result<()> {
         #[cfg(debug_assertions)]
         self.selector_id.remove_association(registry)?;
-        registry.selector().deregister(self.inner.as_raw_fd())
+        self.state.deregister(registry, self.inner.as_raw_fd())
     }
 }
 

diff --git a/src/poll.rs b/src/poll.rs
@@ -1,5 +1,5 @@
 use crate::{event, sys, Events, Interest, Token};
-#[cfg(unix)]
+#[cfg(all(unix, not(mio_unsupported_force_poll_poll)))]
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::time::Duration;
 use std::{fmt, io};
@@ -411,7 +411,7 @@ impl Poll {
     }
 }
 
-#[cfg(unix)]
+#[cfg(all(unix, not(mio_unsupported_force_poll_poll)))]
 impl AsRawFd for Poll {
     fn as_raw_fd(&self) -> RawFd {
         self.registry.as_raw_fd()
@@ -696,15 +696,18 @@ impl fmt::Debug for Registry {
     }
 }
 
-#[cfg(unix)]
+#[cfg(all(unix, not(mio_unsupported_force_poll_poll)))]
 impl AsRawFd for Registry {
     fn as_raw_fd(&self) -> RawFd {
         self.selector.as_raw_fd()
     }
 }
 
 cfg_os_poll! {
-    #[cfg(unix)]
+    #[cfg(all(
+        unix,
+        not(mio_unsupported_force_poll_poll)
+    ))]
     #[test]
     pub fn as_raw_fd() {
         let poll = Poll::new().unwrap();

diff --git a/src/sys/unix/mod.rs b/src/sys/unix/mod.rs
@@ -33,25 +33,65 @@ cfg_os_poll! {
     }
 
     cfg_io_source! {
-        use std::io;
-
         // Both `kqueue` and `epoll` don't need to hold any user space state.
-        pub(crate) struct IoSourceState;
+        #[cfg(not(mio_unsupported_force_poll_poll))]
+        mod stateless_io_source {
+            use std::io;
+            use std::os::unix::io::RawFd;
+            use crate::Registry;
+            use crate::Token;
+            use crate::Interest;
 
-        impl IoSourceState {
-            pub fn new() -> IoSourceState {
-                IoSourceState
-            }
+            pub(crate) struct IoSourceState;
+
+            impl IoSourceState {
+                pub fn new() -> IoSourceState {
+                    IoSourceState
+                }
+
+                pub fn do_io<T, F, R>(&self, f: F, io: &T) -> io::Result<R>
+                where
+                    F: FnOnce(&T) -> io::Result<R>,
+                {
+                    // We don't hold state, so we can just call the function and
+                    // return.
+                    f(io)
+                }
 
-            pub fn do_io<T, F, R>(&self, f: F, io: &T) -> io::Result<R>
-            where
-                F: FnOnce(&T) -> io::Result<R>,
-            {
-                // We don't hold state, so we can just call the function and
-                // return.
-                f(io)
+                pub fn register(
+                    &mut self,
+                    registry: &Registry,
+                    token: Token,
+                    interests: Interest,
+                    fd: RawFd,
+                ) -> io::Result<()> {
+                    // Pass through, we don't have any state
+                    registry.selector().register(fd, token, interests)
+                }
+
+                pub fn reregister(
+                    &mut self,
+                    registry: &Registry,
+                    token: Token,
+                    interests: Interest,
+                    fd: RawFd,
+                ) -> io::Result<()> {
+                    // Pass through, we don't have any state
+                    registry.selector().reregister(fd, token, interests)
+                }
+
+                pub fn deregister(&mut self, registry: &Registry, fd: RawFd) -> io::Result<()> {
+                    // Pass through, we don't have any state
+                    registry.selector().deregister(fd)
+                }
             }
         }
+
+        #[cfg(not(mio_unsupported_force_poll_poll))]
+        pub(crate) use self::stateless_io_source::IoSourceState;
+
+        #[cfg(mio_unsupported_force_poll_poll)]
+        pub(crate) use self::selector::IoSourceState;
     }
 
     cfg_os_ext! {

diff --git a/src/sys/unix/selector/mod.rs b/src/sys/unix/selector/mod.rs
@@ -1,40 +1,58 @@
-#[cfg(any(
-    target_os = "android",
-    target_os = "illumos",
-    target_os = "linux",
-    target_os = "redox",
+#[cfg(all(
+    not(mio_unsupported_force_poll_poll),
+    any(
+        target_os = "android",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "redox",
+    )
 ))]
 mod epoll;
 
-#[cfg(any(
-    target_os = "android",
-    target_os = "illumos",
-    target_os = "linux",
-    target_os = "redox",
+#[cfg(all(
+    not(mio_unsupported_force_poll_poll),
+    any(
+        target_os = "android",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "redox",
+    )
 ))]
 pub(crate) use self::epoll::{event, Event, Events, Selector};
 
-#[cfg(any(
-    target_os = "dragonfly",
-    target_os = "freebsd",
-    target_os = "ios",
-    target_os = "macos",
-    target_os = "netbsd",
-    target_os = "openbsd",
-    target_os = "tvos",
-    target_os = "watchos",
+#[cfg(mio_unsupported_force_poll_poll)]
+mod poll;
+
+#[cfg(mio_unsupported_force_poll_poll)]
+pub(crate) use self::poll::{event, Event, Events, Selector, IoSourceState};
+
+#[cfg(all(
+    not(mio_unsupported_force_poll_poll),
+    any(
+        target_os = "dragonfly",
+        target_os = "freebsd",
+        target_os = "ios",
+        target_os = "macos",
+        target_os = "netbsd",
+        target_os = "openbsd",
+        target_os = "tvos",
+        target_os = "watchos",
+    )
 ))]
 mod kqueue;
 
-#[cfg(any(
-    target_os = "dragonfly",
-    target_os = "freebsd",
-    target_os = "ios",
-    target_os = "macos",
-    target_os = "netbsd",
-    target_os = "openbsd",
-    target_os = "tvos",
-    target_os = "watchos",
+#[cfg(all(
+    not(mio_unsupported_force_poll_poll),
+    any(
+        target_os = "dragonfly",
+        target_os = "freebsd",
+        target_os = "ios",
+        target_os = "macos",
+        target_os = "netbsd",
+        target_os = "openbsd",
+        target_os = "tvos",
+        target_os = "watchos",
+    ),
 ))]
 pub(crate) use self::kqueue::{event, Event, Events, Selector};