Bug 996465 - Add ability to delay running state machine cycles for synchronization between decoding/main and state machine threads. r=cpearce

content/media/MediaDecoderStateMachine.cpp

@@ -2162,6 +2162,9 @@ MediaDecoderStateMachine::SeekCompleted()
   // Try to decode another frame to detect if we're at the end...
   DECODER_LOG(PR_LOG_DEBUG, "Seek completed, mCurrentFrameTime=%lld", mCurrentFrameTime);
 
+  // Prevent changes in playback position before 'seeked' is fired for we
+  // expect currentTime equals seek target in 'seeked' callback.
+  mScheduler->FreezeScheduling();
   {
     ReentrantMonitorAutoExit exitMon(mDecoder->GetReentrantMonitor());
     NS_DispatchToMainThread(stopEvent, NS_DISPATCH_SYNC);
@@ -2173,6 +2176,7 @@ MediaDecoderStateMachine::SeekCompleted()
   mQuickBuffering = false;
 
   ScheduleStateMachine();
+  mScheduler->ThawScheduling();
 }
 
 // Runnable to dispose of the decoder and state machine on the main thread.

content/media/MediaDecoderStateMachineScheduler.cpp

@@ -89,8 +89,15 @@ MediaDecoderStateMachineScheduler::Schedule(int64_t aUsecs)
 {
   mMonitor.AssertCurrentThreadIn();
 
-  if (mState == SCHEDULER_STATE_SHUTDOWN) {
+  switch(mState) {
+  case SCHEDULER_STATE_SHUTDOWN:
     return NS_ERROR_FAILURE;
+  case SCHEDULER_STATE_FROZEN:
+    mState = SCHEDULER_STATE_FROZEN_WITH_PENDING_TASK;
+  case SCHEDULER_STATE_FROZEN_WITH_PENDING_TASK:
+    return NS_OK;
+  case SCHEDULER_STATE_NONE:
+    break;
   }
 
   aUsecs = std::max<int64_t>(aUsecs, 0);
@@ -161,6 +168,9 @@ void
 MediaDecoderStateMachineScheduler::ScheduleAndShutdown()
 {
   mMonitor.AssertCurrentThreadIn();
+  if (IsFrozen()) {
+    ThawScheduling();
+  }
   // Schedule next cycle to handle SHUTDOWN in state machine thread.
   Schedule();
   // This must be set after calling Schedule()
@@ -191,4 +201,33 @@ MediaDecoderStateMachineScheduler::ResetTimer()
   mTimeout = TimeStamp();
 }
 
+void MediaDecoderStateMachineScheduler::FreezeScheduling()
+{
+  mMonitor.AssertCurrentThreadIn();
+  if (mState == SCHEDULER_STATE_SHUTDOWN) {
+    return;
+  }
+  MOZ_ASSERT(mState == SCHEDULER_STATE_NONE);
+  mState = !IsScheduled() ? SCHEDULER_STATE_FROZEN :
+                            SCHEDULER_STATE_FROZEN_WITH_PENDING_TASK;
+  // Nullify pending timer task if any.
+  ++mTimerId;
+  mTimeout = TimeStamp();
+}
+
+void MediaDecoderStateMachineScheduler::ThawScheduling()
+{
+  mMonitor.AssertCurrentThreadIn();
+  if (mState == SCHEDULER_STATE_SHUTDOWN) {
+    return;
+  }
+  // We should be in frozen state and no pending timer task.
+  MOZ_ASSERT(IsFrozen() && !IsScheduled());
+  bool pendingTask = mState == SCHEDULER_STATE_FROZEN_WITH_PENDING_TASK;
+  mState = SCHEDULER_STATE_NONE;
+  if (pendingTask) {
+    Schedule();
+  }
+}
+
 } // namespace mozilla

content/media/MediaDecoderStateMachineScheduler.h

@@ -21,6 +21,8 @@ class ReentrantMonitor;
 class MediaDecoderStateMachineScheduler {
   enum State {
     SCHEDULER_STATE_NONE,
+    SCHEDULER_STATE_FROZEN,
+    SCHEDULER_STATE_FROZEN_WITH_PENDING_TASK,
     SCHEDULER_STATE_SHUTDOWN
   };
 public:
@@ -32,6 +34,8 @@ public:
   nsresult Schedule(int64_t aUsecs = 0);
   void ScheduleAndShutdown();
   nsresult TimeoutExpired(int aTimerId);
+  void FreezeScheduling();
+  void ThawScheduling();
 
   bool OnStateMachineThread() const;
   bool IsScheduled() const;
@@ -44,6 +48,11 @@ public:
     return mEventTarget;
   }
 
+  bool IsFrozen() const {
+    return mState == SCHEDULER_STATE_FROZEN ||
+           mState == SCHEDULER_STATE_FROZEN_WITH_PENDING_TASK;
+  }
+
 private:
   void ResetTimer();