streams: PushPromise tasks are notified properly (#793)

The push task is a separate task from the recv task, so its state needs
to be tracked separately for waking. I don't know how to be systematic
about ensuring that notify_push is called in all the right places, but
this is an initial attempt.

In order to test this works, we manually utilize FuturesUnordered which
does fine-grained task wake tracking. The added test failed before
making the other changes.

src/proto/streams/prioritize.rs

@@ -839,10 +839,7 @@ impl Prioritize {
                         }),
                         None => {
                             if let Some(reason) = stream.state.get_scheduled_reset() {
-                                let stream_id = stream.id;
-                                stream
-                                    .state
-                                    .set_reset(stream_id, reason, Initiator::Library);
+                                stream.set_reset(reason, Initiator::Library);
 
                                 let frame = frame::Reset::new(stream.id, reason);
                                 Frame::Reset(frame)

src/proto/streams/recv.rs

@@ -296,7 +296,7 @@ impl Recv {
             let is_open = stream.state.ensure_recv_open()?;
 
             if is_open {
-                stream.recv_task = Some(cx.waker().clone());
+                stream.push_task = Some(cx.waker().clone());
                 Poll::Pending
             } else {
                 Poll::Ready(None)
@@ -760,6 +760,7 @@ impl Recv {
             .pending_recv
             .push_back(&mut self.buffer, Event::Headers(Server(req)));
         stream.notify_recv();
+        stream.notify_push();
         Ok(())
     }
 
@@ -814,6 +815,7 @@ impl Recv {
 
         stream.notify_send();
         stream.notify_recv();
+        stream.notify_push();
 
         Ok(())
     }
@@ -826,6 +828,7 @@ impl Recv {
         // If a receiver is waiting, notify it
         stream.notify_send();
         stream.notify_recv();
+        stream.notify_push();
     }
 
     pub fn go_away(&mut self, last_processed_id: StreamId) {
@@ -837,6 +840,7 @@ impl Recv {
         stream.state.recv_eof();
         stream.notify_send();
         stream.notify_recv();
+        stream.notify_push();
     }
 
     pub(super) fn clear_recv_buffer(&mut self, stream: &mut Stream) {

src/proto/streams/send.rs

@@ -206,10 +206,7 @@ impl Send {
         }
 
         // Transition the state to reset no matter what.
-        stream.state.set_reset(stream_id, reason, initiator);
-        // Notify the recv task if it's waiting, because it'll
-        // want to hear about the reset.
-        stream.notify_recv();
+        stream.set_reset(reason, initiator);
 
         // If closed AND the send queue is flushed, then the stream cannot be
         // reset explicitly, either. Implicit resets can still be queued.

src/proto/streams/stream.rs

@@ -1,3 +1,5 @@
+use crate::Reason;
+
 use super::*;
 
 use std::task::{Context, Waker};
@@ -104,6 +106,9 @@ pub(super) struct Stream {
     /// Task tracking receiving frames
     pub recv_task: Option<Waker>,
 
+    /// Task tracking pushed promises.
+    pub push_task: Option<Waker>,
+
     /// The stream's pending push promises
     pub pending_push_promises: store::Queue<NextAccept>,
 
@@ -186,6 +191,7 @@ impl Stream {
             pending_recv: buffer::Deque::new(),
             is_recv: true,
             recv_task: None,
+            push_task: None,
             pending_push_promises: store::Queue::new(),
             content_length: ContentLength::Omitted,
         }
@@ -369,6 +375,20 @@ impl Stream {
             task.wake();
         }
     }
+
+    pub(super) fn notify_push(&mut self) {
+        if let Some(task) = self.push_task.take() {
+            task.wake();
+        }
+    }
+
+    /// Set the stream's state to `Closed` with the given reason and initiator.
+    /// Notify the send and receive tasks, if they exist.
+    pub(super) fn set_reset(&mut self, reason: Reason, initiator: Initiator) {
+        self.state.set_reset(self.id, reason, initiator);
+        self.notify_push();
+        self.notify_recv();
+    }
 }
 
 impl store::Next for NextAccept {

src/proto/streams/streams.rs

@@ -825,7 +825,7 @@ impl Inner {
 
             let parent = &mut self.store.resolve(parent_key);
             parent.pending_push_promises = ppp;
-            parent.notify_recv();
+            parent.notify_push();
         };
 
         Ok(())

tests/h2-tests/tests/push_promise.rs

@@ -1,5 +1,6 @@
-use futures::future::join;
-use futures::{StreamExt, TryStreamExt};
+use std::iter::FromIterator;
+
+use futures::{future::join, FutureExt as _, StreamExt, TryStreamExt};
 use h2_support::prelude::*;
 
 #[tokio::test]
@@ -51,9 +52,15 @@ async fn recv_push_works() {
             let ps: Vec<_> = p.collect().await;
             assert_eq!(1, ps.len())
         };
-
-        h2.drive(join(check_resp_status, check_pushed_response))
-            .await;
+        // Use a FuturesUnordered to poll both tasks but only poll them
+        // if they have been notified.
+        let tasks = futures::stream::FuturesUnordered::from_iter([
+            check_resp_status.boxed(),
+            check_pushed_response.boxed(),
+        ])
+        .collect::<()>();
+
+        h2.drive(tasks).await;
     };
 
     join(mock, h2).await;