use a time.Timer for read deadlines

receive_stream.go

@@ -44,7 +44,8 @@ type receiveStream struct {
 	resetRemotely     bool // set when HandleRstStreamFrame() is called
 
 	readChan      chan struct{}
-	readDeadline time.Time
+	deadline      time.Time
+	deadlineTimer *time.Timer // initialized by SetReadDeadline()
 
 	flowController flowcontrol.StreamFlowController
 	version        protocol.VersionNumber
@@ -120,8 +121,7 @@ func (s *receiveStream) readImpl(p []byte) (bool /*stream completed */, int, err
 				return false, bytesRead, s.resetRemotelyErr
 			}
 
-			deadline := s.readDeadline
-			if !deadline.IsZero() && !time.Now().Before(deadline) {
+			if !s.deadline.IsZero() && !time.Now().Before(s.deadline) {
 				return false, bytesRead, errDeadline
 			}
 
@@ -130,12 +130,12 @@ func (s *receiveStream) readImpl(p []byte) (bool /*stream completed */, int, err
 			}
 
 			s.mutex.Unlock()
-			if deadline.IsZero() {
+			if s.deadline.IsZero() {
 				<-s.readChan
 			} else {
 				select {
 				case <-s.readChan:
-				case <-time.After(time.Until(deadline)):
+				case <-s.deadlineTimer.C:
 				}
 			}
 			s.mutex.Lock()
@@ -272,13 +272,22 @@ func (s *receiveStream) onClose(offset protocol.ByteCount) {
 
 func (s *receiveStream) SetReadDeadline(t time.Time) error {
 	s.mutex.Lock()
-	oldDeadline := s.readDeadline
-	s.readDeadline = t
-	s.mutex.Unlock()
-	// if the new deadline is before the currently set deadline, wake up Read()
-	if t.Before(oldDeadline) {
+	defer s.mutex.Unlock()
+	s.deadline = t
+	if s.deadline.IsZero() { // skip if there's no deadline to set
 		s.signalRead()
+		return nil
 	}
+	// Lazily initialize the deadline timer.
+	if s.deadlineTimer == nil {
+		s.deadlineTimer = time.NewTimer(time.Until(t))
+		return nil
+	}
+	// reset the timer to the new deadline
+	if !s.deadlineTimer.Stop() {
+		<-s.deadlineTimer.C
+	}
+	s.deadlineTimer.Reset(time.Until(t))
 	return nil
 }
 

receive_stream_test.go

@@ -243,6 +243,20 @@ var _ = Describe("Receive Stream", func() {
 				Expect(n).To(BeZero())
 			})
 
+			It("unblocks when the deadline is changed to the past", func() {
+				str.SetReadDeadline(time.Now().Add(time.Hour))
+				done := make(chan struct{})
+				go func() {
+					defer GinkgoRecover()
+					_, err := str.Read(make([]byte, 6))
+					Expect(err).To(MatchError(errDeadline))
+					close(done)
+				}()
+				Consistently(done).ShouldNot(BeClosed())
+				str.SetReadDeadline(time.Now().Add(-time.Hour))
+				Eventually(done).Should(BeClosed())
+			})
+
 			It("unblocks after the deadline", func() {
 				deadline := time.Now().Add(scaleDuration(50 * time.Millisecond))
 				str.SetReadDeadline(deadline)