update timer scheduler to use crossbeam

components/constellation/constellation.rs

@@ -110,7 +110,7 @@ use canvas_traits::canvas::CanvasMsg;
 use compositing::compositor_thread::CompositorProxy;
 use compositing::compositor_thread::Msg as ToCompositorMsg;
 use compositing::SendableFrameTree;
-use crossbeam_channel::{unbounded, Receiver, Sender};
+use crossbeam_channel::{after, never, unbounded, Receiver, Sender};
 use devtools_traits::{ChromeToDevtoolsControlMsg, DevtoolsControlMsg};
 use embedder_traits::{Cursor, EmbedderMsg, EmbedderProxy, EventLoopWaker};
 use euclid::{default::Size2D as UntypedSize2D, Scale, Size2D};
@@ -329,10 +329,15 @@ pub struct Constellation<Message, LTF, STF> {
     /// memory profiler thread.
     mem_profiler_chan: mem::ProfilerChan,
 
-    /// A channel for the constellation to send messages to the
-    /// timer thread.
+    /// A channel for a pipeline to schedule timer events.
     scheduler_chan: IpcSender<TimerSchedulerMsg>,
 
+    /// The receiver to which the IPC requests from scheduler_chan will be forwarded.
+    scheduler_receiver: Receiver<Result<TimerSchedulerMsg, IpcError>>,
+
+    /// The logic and data behing scheduling timer events.
+    timer_scheduler: TimerScheduler,
+
     /// A single WebRender document the constellation operates on.
     webrender_document: webrender_api::DocumentId,
 
@@ -686,6 +691,12 @@ where
                     ipc_namespace_receiver,
                 );
 
+                let (scheduler_chan, ipc_scheduler_receiver) =
+                    ipc::channel().expect("ipc channel failure");
+                let scheduler_receiver = route_ipc_receiver_to_new_mpsc_receiver_preserving_errors(
+                    ipc_scheduler_receiver,
+                );
+
                 let (background_hang_monitor_sender, ipc_bhm_receiver) =
                     ipc::channel().expect("ipc channel failure");
                 let background_hang_monitor_receiver =
@@ -765,7 +776,9 @@ where
                     },
                     phantom: PhantomData,
                     webdriver: WebDriverData::new(),
-                    scheduler_chan: TimerScheduler::start(),
+                    timer_scheduler: TimerScheduler::new(),
+                    scheduler_chan,
+                    scheduler_receiver,
                     document_states: HashMap::new(),
                     webrender_document: state.webrender_document,
                     webrender_api_sender: state.webrender_api_sender,
@@ -1179,8 +1192,16 @@ where
             Layout(FromLayoutMsg),
             NetworkListener((PipelineId, FetchResponseMsg)),
             FromSWManager(SWManagerMsg),
+            Timer(TimerSchedulerMsg),
         }
 
+        // A timeout corresponding to the earliest scheduled timer event, if any.
+        let scheduler_timeout = self
+            .timer_scheduler
+            .check_timers()
+            .map(|timeout| after(timeout))
+            .unwrap_or(never());
+
         // Get one incoming request.
         // This is one of the few places where the compositor is
         // allowed to panic. If one of the receiver.recv() calls
@@ -1216,6 +1237,14 @@ where
             recv(self.swmanager_receiver) -> msg => {
                 msg.expect("Unexpected panic channel panic in constellation").map(Request::FromSWManager)
             }
+            recv(self.scheduler_receiver) -> msg => {
+                msg.expect("Unexpected panic channel panic in constellation").map(Request::Timer)
+            }
+            recv(scheduler_timeout) -> _ => {
+                // Note: by returning, we go back to the top,
+                // where check_timers will be called.
+                return;
+            },
         };
 
         let request = match request {
@@ -1243,6 +1272,9 @@ where
             Request::FromSWManager(message) => {
                 self.handle_request_from_swmanager(message);
             },
+            Request::Timer(message) => {
+                self.timer_scheduler.handle_timer_request(message);
+            },
         }
     }
 
@@ -1859,11 +1891,6 @@ where
             }
         }
 
-        debug!("Exiting timer scheduler.");
-        if let Err(e) = self.scheduler_chan.send(TimerSchedulerMsg::Exit) {
-            warn!("Exit timer scheduler failed ({})", e);
-        }
-
         debug!("Exiting font cache thread.");
         self.font_cache_thread.exit();
 

components/constellation/timer_scheduler.rs

@@ -2,15 +2,12 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use crossbeam_channel::{self, TryRecvError};
-use ipc_channel::ipc::{self, IpcSender};
 use script_traits::{TimerEvent, TimerEventRequest, TimerSchedulerMsg};
 use std::cmp::{self, Ord};
 use std::collections::BinaryHeap;
-use std::thread;
 use std::time::{Duration, Instant};
 
-pub struct TimerScheduler;
+pub struct TimerScheduler(BinaryHeap<ScheduledEvent>);
 
 struct ScheduledEvent {
     request: TimerEventRequest,
@@ -37,93 +34,40 @@ impl PartialEq for ScheduledEvent {
 }
 
 impl TimerScheduler {
-    pub fn start() -> IpcSender<TimerSchedulerMsg> {
-        let (req_ipc_sender, req_ipc_receiver) = ipc::channel().expect("Channel creation failed.");
-        let (req_sender, req_receiver) = crossbeam_channel::bounded(1);
-
-        // We could do this much more directly with recv_timeout
-        // (https://github.com/rust-lang/rfcs/issues/962).
-
-        // util::thread doesn't give us access to the JoinHandle, which we need for park/unpark,
-        // so we use the builder directly.
-        let timeout_thread = thread::Builder::new()
-            .name(String::from("TimerScheduler"))
-            .spawn(move || {
-                // We maintain a priority queue of future events, sorted by due time.
-                let mut scheduled_events = BinaryHeap::<ScheduledEvent>::new();
-                loop {
-                    let now = Instant::now();
-                    // Dispatch any events whose due time is past
-                    loop {
-                        match scheduled_events.peek() {
-                            // Dispatch the event if its due time is past
-                            Some(event) if event.for_time <= now => {
-                                let TimerEventRequest(ref sender, source, id, _) = event.request;
-                                let _ = sender.send(TimerEvent(source, id));
-                            },
-                            // Otherwise, we're done dispatching events
-                            _ => break,
-                        }
-                        // Remove the event from the priority queue
-                        // (Note this only executes when the first event has been dispatched
-                        scheduled_events.pop();
-                    }
-                    // Look to see if there are any incoming events
-                    match req_receiver.try_recv() {
-                        // If there is an event, add it to the priority queue
-                        Ok(TimerSchedulerMsg::Request(req)) => {
-                            let TimerEventRequest(_, _, _, delay) = req;
-                            let schedule = Instant::now() + Duration::from_millis(delay.get());
-                            let event = ScheduledEvent {
-                                request: req,
-                                for_time: schedule,
-                            };
-                            scheduled_events.push(event);
-                        },
-                        // If there is no incoming event, park the thread,
-                        // it will either be unparked when a new event arrives,
-                        // or by a timeout.
-                        Err(TryRecvError::Empty) => match scheduled_events.peek() {
-                            None => thread::park(),
-                            Some(event) => thread::park_timeout(event.for_time - now),
-                        },
-                        // If the channel is closed or we are shutting down, we are done.
-                        Ok(TimerSchedulerMsg::Exit) | Err(TryRecvError::Disconnected) => break,
-                    }
-                }
-                // This thread can terminate if the req_ipc_sender is dropped.
-                warn!("TimerScheduler thread terminated.");
-            })
-            .expect("Thread creation failed.")
-            .thread()
-            .clone();
+    pub fn new() -> Self {
+        TimerScheduler(BinaryHeap::<ScheduledEvent>::new())
+    }
 
-        // A proxy that just routes incoming IPC requests over the MPSC channel to the timeout thread,
-        // and unparks the timeout thread each time. Note that if unpark is called while the timeout
-        // thread isn't parked, this causes the next call to thread::park by the timeout thread
-        // not to block. This means that the timeout thread won't park when there is a request
-        // waiting in the MPSC channel buffer.
-        thread::Builder::new()
-            .name(String::from("TimerProxy"))
-            .spawn(move || {
-                while let Ok(req) = req_ipc_receiver.recv() {
-                    let mut shutting_down = false;
-                    match req {
-                        TimerSchedulerMsg::Exit => shutting_down = true,
-                        _ => {},
-                    }
-                    let _ = req_sender.send(req);
-                    timeout_thread.unpark();
-                    if shutting_down {
-                        break;
-                    }
-                }
-                // This thread can terminate if the req_ipc_sender is dropped.
-                warn!("TimerProxy thread terminated.");
-            })
-            .expect("Thread creation failed.");
+    /// Dispatch any events whose due time is past,
+    /// and return a timeout corresponding to the earliest scheduled event, if any.
+    pub fn check_timers(&mut self) -> Option<Duration> {
+        let now = Instant::now();
+        loop {
+            match self.0.peek() {
+                // Dispatch the event if its due time is past
+                Some(event) if event.for_time <= now => {
+                    let TimerEventRequest(ref sender, source, id, _) = event.request;
+                    let _ = sender.send(TimerEvent(source, id));
+                },
+                // Do not schedule a timeout.
+                None => return None,
+                // Schedule a timeout for the earliest event.
+                Some(event) => return Some(event.for_time - now),
+            }
+            // Remove the event from the priority queue
+            // (Note this only executes when the first event has been dispatched).
+            self.0.pop();
+        }
+    }
 
-        // Return the IPC sender
-        req_ipc_sender
+    /// Handle an incoming timer request.
+    pub fn handle_timer_request(&mut self, request: TimerSchedulerMsg) {
+        let TimerEventRequest(_, _, _, delay) = request.0;
+        let schedule = Instant::now() + Duration::from_millis(delay.get());
+        let event = ScheduledEvent {
+            request: request.0,
+            for_time: schedule,
+        };
+        self.0.push(event);
     }
 }

components/script/timers.rs

@@ -285,7 +285,7 @@ impl OneshotTimers {
                 delay,
             );
             self.scheduler_chan
-                .send(TimerSchedulerMsg::Request(request))
+                .send(TimerSchedulerMsg(request))
                 .unwrap();
         }
     }

components/script_traits/lib.rs

@@ -556,14 +556,9 @@ pub struct TimerEventRequest(
     pub MsDuration,
 );
 
-/// Type of messages that can be sent to the timer scheduler.
+/// The message used to send a request to the timer scheduler.
 #[derive(Debug, Deserialize, Serialize)]
-pub enum TimerSchedulerMsg {
-    /// Message to schedule a new timer event.
-    Request(TimerEventRequest),
-    /// Message to exit the timer scheduler.
-    Exit,
-}
+pub struct TimerSchedulerMsg(pub TimerEventRequest);
 
 /// Notifies the script thread to fire due timers.
 /// `TimerSource` must be `FromWindow` when dispatched to `ScriptThread` and