Implement an eventfd-based ping source for Linux.

This separates and reorganises the underlying mechanics for the ping source,
and implements an eventfd-based ping for Linux.

CHANGELOG.md

@@ -20,6 +20,7 @@
   associated event callback.
 - **Breaking:** The minimum supported Rust version is now 1.53.0
 - Introduce `EventLoop::try_new_high_precision()` for sub-millisecond accuracy in the event loop
+- The `PingSource` event source now uses an `eventfd` instead of a pipe on Linux.
 
 ## 0.9.2 -- 2021-12-27
 

src/sources/ping.rs

@@ -4,64 +4,39 @@
 //! [`Ping::ping`](Ping#method.ping) method is called. If the event source is pinged multiple times
 //! between a single dispatching, it'll only generate one event.
 //!
-//! This event loop is a simple way of waking up the event loop from an other part of your program
+//! This event source is a simple way of waking up the event loop from an other part of your program
 //! (and is what backs the [`LoopSignal`](crate::LoopSignal)). It can also be used as a building
 //! block to construct event sources whose source of event is not file descriptor, but rather an
 //! userspace source (like an other thread).
 
-use std::{os::unix::io::RawFd, sync::Arc};
+use nix::unistd::close;
+use std::os::unix::io::RawFd;
 
-use nix::{
-    fcntl::OFlag,
-    unistd::{close, read, write},
-};
+// The ping source has platform-dependent implementations provided by modules
+// under this one. These modules should expose:
+// - a make_ping() function
+// - a Ping type
+// - a PingSource type
+//
+// See eg. the pipe implementation for these items' specific requirements.
 
-use super::generic::Generic;
-use crate::{EventSource, Interest, Mode, Poll, PostAction, Readiness, Token, TokenFactory};
+#[cfg(target_os = "linux")]
+mod eventfd;
+#[cfg(target_os = "linux")]
+use eventfd as platform;
+
+#[cfg(not(target_os = "linux"))]
+mod pipe;
+#[cfg(not(target_os = "linux"))]
+use pipe as platform;
 
 /// Create a new ping event source
 ///
 /// you are given a [`Ping`] instance, which can be cloned and used to ping the
 /// event loop, and a [`PingSource`], which you can insert in your event loop to
 /// receive the pings.
 pub fn make_ping() -> std::io::Result<(Ping, PingSource)> {
-    #[cfg(not(target_os = "macos"))]
-    let (read, write) = {
-        use nix::unistd::pipe2;
-
-        pipe2(OFlag::O_CLOEXEC | OFlag::O_NONBLOCK)?
-    };
-
-    // macOS does not have pipe2, but we can emulate the behavior of pipe2 by setting the flags after calling pipe.
-    #[cfg(target_os = "macos")]
-    let (read, write) = {
-        use nix::{
-            fcntl::{fcntl, FcntlArg},
-            unistd::pipe,
-        };
-
-        let (read, write) = pipe()?;
-
-        let read_flags = OFlag::from_bits_truncate(fcntl(read, FcntlArg::F_GETFD)?)
-            | OFlag::O_CLOEXEC
-            | OFlag::O_NONBLOCK;
-        let write_flags = OFlag::from_bits_truncate(fcntl(write, FcntlArg::F_GETFD)?)
-            | OFlag::O_CLOEXEC
-            | OFlag::O_NONBLOCK;
-
-        fcntl(read, FcntlArg::F_SETFL(read_flags))?;
-        fcntl(write, FcntlArg::F_SETFL(write_flags))?;
-
-        (read, write)
-    };
-
-    let source = PingSource {
-        pipe: Generic::new(read, Interest::READ, Mode::Level),
-    };
-    let ping = Ping {
-        pipe: Arc::new(CloseOnDrop(write)),
-    };
-    Ok((ping, source))
+    platform::make_ping()
 }
 
 /// The ping event source
@@ -70,122 +45,35 @@ pub fn make_ping() -> std::io::Result<(Ping, PingSource)> {
 ///
 /// If you use it directly, it will automatically remove itself from the event loop
 /// once all [`Ping`] instances are dropped.
-#[derive(Debug)]
-pub struct PingSource {
-    pipe: Generic<RawFd>,
-}
-
-impl EventSource for PingSource {
-    type Event = ();
-    type Metadata = ();
-    type Ret = ();
-    type Error = PingError;
-
-    fn process_events<C>(
-        &mut self,
-        readiness: Readiness,
-        token: Token,
-        mut callback: C,
-    ) -> Result<PostAction, Self::Error>
-    where
-        C: FnMut(Self::Event, &mut Self::Metadata) -> Self::Ret,
-    {
-        self.pipe
-            .process_events(readiness, token, |_, &mut fd| {
-                let mut buf = [0u8; 32];
-                let mut read_something = false;
-                let mut action = PostAction::Continue;
-                loop {
-                    match read(fd, &mut buf) {
-                        Ok(0) => {
-                            // The other end of the pipe was closed, mark ourselved to for removal
-                            action = PostAction::Remove;
-                            break;
-                        }
-                        Ok(_) => read_something = true,
-
-                        Err(e) => {
-                            let e: std::io::Error = e.into();
-
-                            if e.kind() == std::io::ErrorKind::WouldBlock {
-                                // nothing more to read
-                                break;
-                            } else {
-                                // propagate error
-                                return Err(e);
-                            }
-                        }
-                    }
-                }
-                if read_something {
-                    callback((), &mut ());
-                }
-                Ok(action)
-            })
-            .map_err(|e| PingError(e.into()))
-    }
-
-    fn register(&mut self, poll: &mut Poll, token_factory: &mut TokenFactory) -> crate::Result<()> {
-        self.pipe.register(poll, token_factory)
-    }
-
-    fn reregister(
-        &mut self,
-        poll: &mut Poll,
-        token_factory: &mut TokenFactory,
-    ) -> crate::Result<()> {
-        self.pipe.reregister(poll, token_factory)
-    }
-
-    fn unregister(&mut self, poll: &mut Poll) -> crate::Result<()> {
-        self.pipe.unregister(poll)
-    }
-}
-
-impl Drop for PingSource {
-    fn drop(&mut self) {
-        if let Err(e) = close(self.pipe.file) {
-            log::warn!("[calloop] Failed to close read ping: {:?}", e);
-        }
-    }
-}
+pub type Ping = platform::Ping;
 
 /// The Ping handle
 ///
 /// This handle can be cloned and sent accross threads. It can be used to
 /// send pings to the `PingSource`.
-#[derive(Clone, Debug)]
-pub struct Ping {
-    pipe: Arc<CloseOnDrop>,
-}
+pub type PingSource = platform::PingSource;
 
-impl Ping {
-    /// Send a ping to the `PingSource`
-    pub fn ping(&self) {
-        if let Err(e) = write(self.pipe.0, &[0u8]) {
-            log::warn!("[calloop] Failed to write a ping: {:?}", e);
-        }
-    }
-}
+/// An error arising from processing events for a ping.
+#[derive(thiserror::Error, Debug)]
+#[error(transparent)]
+pub struct PingError(Box<dyn std::error::Error + Sync + Send>);
 
 #[derive(Debug)]
 struct CloseOnDrop(RawFd);
 
 impl Drop for CloseOnDrop {
     fn drop(&mut self) {
         if let Err(e) = close(self.0) {
-            log::warn!("[calloop] Failed to close write ping: {:?}", e);
+            log::warn!("[calloop] Failed to close ping fd: {:?}", e);
         }
     }
 }
 
-/// An error arising from processing events for a ping.
-#[derive(thiserror::Error, Debug)]
-#[error(transparent)]
-pub struct PingError(Box<dyn std::error::Error + Sync + Send>);
-
 #[cfg(test)]
 mod tests {
+    use crate::transient::TransientSource;
+    use std::time::Duration;
+
     use super::*;
 
     #[test]
@@ -241,4 +129,162 @@ mod tests {
             .unwrap();
         assert!(now.elapsed() >= std::time::Duration::from_millis(100));
     }
+
+    #[test]
+    fn ping_removed() {
+        // This keeps track of whether the event fired.
+        let mut dispatched = false;
+
+        let mut event_loop = crate::EventLoop::<bool>::try_new().unwrap();
+
+        let (sender, source) = make_ping().unwrap();
+        let wrapper = TransientSource::from(source);
+
+        // Check that the source starts off in the wrapper.
+        assert!(!matches!(wrapper, TransientSource::None));
+
+        // Put the source in the loop.
+
+        let dispatcher =
+            crate::Dispatcher::new(wrapper, |(), &mut (), dispatched| *dispatched = true);
+
+        let token = event_loop
+            .handle()
+            .register_dispatcher(dispatcher.clone())
+            .unwrap();
+
+        // Drop the sender and check that it's actually removed.
+        drop(sender);
+
+        // There should be no event, but the loop still needs to wake up to
+        // process the close event (just like in the ping_closed() test).
+        event_loop
+            .dispatch(Duration::ZERO, &mut dispatched)
+            .unwrap();
+        assert!(!dispatched);
+
+        // Pull the source wrapper out.
+
+        event_loop.handle().remove(token);
+        let wrapper = dispatcher.into_source_inner();
+
+        // Check that the inner source is now gone.
+        assert!(matches!(wrapper, TransientSource::None));
+    }
+
+    #[test]
+    fn ping_fired_and_removed() {
+        // This is like ping_removed() with the single difference that we fire a
+        // ping and drop it between two successive dispatches of the loop.
+
+        // This keeps track of whether the event fired.
+        let mut dispatched = false;
+
+        let mut event_loop = crate::EventLoop::<bool>::try_new().unwrap();
+
+        let (sender, source) = make_ping().unwrap();
+        let wrapper = TransientSource::from(source);
+
+        // Check that the source starts off in the wrapper.
+        assert!(!matches!(wrapper, TransientSource::None));
+
+        // Put the source in the loop.
+
+        let dispatcher =
+            crate::Dispatcher::new(wrapper, |(), &mut (), dispatched| *dispatched = true);
+
+        let token = event_loop
+            .handle()
+            .register_dispatcher(dispatcher.clone())
+            .unwrap();
+
+        // Send a ping AND drop the sender and check that it's actually removed.
+        sender.ping();
+        drop(sender);
+
+        // There should be an event, but the source should be removed from the
+        // loop immediately after.
+        event_loop
+            .dispatch(Duration::ZERO, &mut dispatched)
+            .unwrap();
+        assert!(dispatched);
+
+        // Pull the source wrapper out.
+
+        event_loop.handle().remove(token);
+        let wrapper = dispatcher.into_source_inner();
+
+        // Check that the inner source is now gone.
+        assert!(matches!(wrapper, TransientSource::None));
+    }
+
+    #[test]
+    fn ping_multiple_senders() {
+        // This is like ping_removed() but for testing the behaviour of multiple
+        // senders.
+
+        // This keeps track of whether the event fired.
+        let mut dispatched = false;
+
+        let mut event_loop = crate::EventLoop::<bool>::try_new().unwrap();
+
+        let (sender0, source) = make_ping().unwrap();
+        let wrapper = TransientSource::from(source);
+        let sender1 = sender0.clone();
+        let sender2 = sender1.clone();
+
+        // Check that the source starts off in the wrapper.
+        assert!(!matches!(wrapper, TransientSource::None));
+
+        // Put the source in the loop.
+
+        let dispatcher =
+            crate::Dispatcher::new(wrapper, |(), &mut (), dispatched| *dispatched = true);
+
+        let token = event_loop
+            .handle()
+            .register_dispatcher(dispatcher.clone())
+            .unwrap();
+
+        // Send a ping AND drop the sender and check that it's actually removed.
+        sender0.ping();
+        drop(sender0);
+
+        // There should be an event, and the source should remain in the loop.
+        event_loop
+            .dispatch(Duration::ZERO, &mut dispatched)
+            .unwrap();
+        assert!(dispatched);
+
+        // Now test that the clones still work. Drop after the dispatch loop
+        // instead of before, this time.
+        dispatched = false;
+
+        sender1.ping();
+
+        event_loop
+            .dispatch(Duration::ZERO, &mut dispatched)
+            .unwrap();
+        assert!(dispatched);
+
+        // Finally, drop all of them without sending anything.
+
+        dispatched = false;
+
+        drop(sender1);
+        drop(sender2);
+
+        event_loop
+            .dispatch(Duration::ZERO, &mut dispatched)
+            .unwrap();
+        assert!(!dispatched);
+
+        // Pull the source wrapper out.
+
+        event_loop.handle().remove(token);
+        let wrapper = dispatcher.into_source_inner();
+
+        // Check that the inner source is now gone.
+        assert!(matches!(wrapper, TransientSource::None));
+    }
 }