Bug 1299515 - Signal SetPullEnabled with a message. r=padenot

With the added invariant that NotifyPull() needs a MediaStreamListener present
to not underrun, we need SetPullEnabled() and AddListener() to stay in sync by
using the same signaling mechanism.

MozReview-Commit-ID: 49KWdiTOG98

--HG--
extra : rebase_source : d0ad44d7ce431aa792c4908f96baf0c0920dbe90

dom/media/MediaManager.cpp

@@ -1289,7 +1289,8 @@ public:
     RefPtr<GetUserMediaStreamRunnable> self = this;
     MediaManager::PostTask(NewTaskFrom([self, domStream, callback]() mutable {
       MOZ_ASSERT(MediaManager::IsInMediaThread());
-      SourceMediaStream* source = self->mSourceListener->GetSourceStream();
+      RefPtr<SourceMediaStream> source =
+        self->mSourceListener->GetSourceStream();
 
       RefPtr<MediaMgrError> error = nullptr;
       if (self->mAudioDevice) {
@@ -1334,7 +1335,6 @@ public:
       // Start() queued the tracks to be added synchronously to avoid races
       source->FinishAddTracks();
 
-      source->SetPullEnabled(true);
       source->AdvanceKnownTracksTime(STREAM_TIME_MAX);
 
       LOG(("started all sources"));
@@ -1342,7 +1342,9 @@ public:
       // onTracksAvailableCallback must be added to domStream on the main thread.
       uint64_t windowID = self->mWindowID;
       NS_DispatchToMainThread(NS_NewRunnableFunction("MediaManager::NotifyChromeOfStart",
-                                                     [domStream, callback, windowID]() mutable {
+                                                     [source, domStream, callback, windowID]() mutable {
+        source->SetPullEnabled(true);
+
         MediaManager* manager = MediaManager::GetIfExists();
         if (!manager) {
           return;

dom/media/MediaStreamGraph.cpp

@@ -2730,11 +2730,22 @@ SourceMediaStream::DestroyImpl()
 void
 SourceMediaStream::SetPullEnabled(bool aEnabled)
 {
-  MutexAutoLock lock(mMutex);
-  mPullEnabled = aEnabled;
-  if (mPullEnabled && GraphImpl()) {
-    GraphImpl()->EnsureNextIteration();
-  }
+  class Message : public ControlMessage {
+  public:
+    Message(SourceMediaStream* aStream, bool aEnabled)
+      : ControlMessage(nullptr)
+      , mStream(aStream)
+      , mEnabled(aEnabled)
+    {}
+    void Run() override
+    {
+      MutexAutoLock lock(mStream->mMutex);
+      mStream->mPullEnabled = mEnabled;
+    }
+    SourceMediaStream* mStream;
+    bool mEnabled;
+  };
+  GraphImpl()->AppendMessage(MakeUnique<Message>(this, aEnabled));
 }
 
 bool

dom/media/MediaStreamGraph.h

@@ -676,7 +676,16 @@ public:
 
   SourceMediaStream* AsSourceStream() override { return this; }
 
-  // Media graph thread only
+  // Main thread only
+
+  /**
+   * Enable or disable pulling. When pulling is enabled, NotifyPull
+   * gets called on MediaStreamListeners for this stream during the
+   * MediaStreamGraph control loop. Pulling is initially disabled.
+   * Due to unavoidable race conditions, after a call to SetPullEnabled(false)
+   * it is still possible for a NotifyPull to occur.
+   */
+  void SetPullEnabled(bool aEnabled);
 
   // Users of audio inputs go through the stream so it can track when the
   // last stream referencing an input goes away, so it can close the cubeb
@@ -687,18 +696,10 @@ public:
   // Note: also implied when Destroy() happens
   void CloseAudioInput();
 
+  // MediaStreamGraph thread only
   void DestroyImpl() override;
 
   // Call these on any thread.
-  /**
-   * Enable or disable pulling. When pulling is enabled, NotifyPull
-   * gets called on MediaStreamListeners for this stream during the
-   * MediaStreamGraph control loop. Pulling is initially disabled.
-   * Due to unavoidable race conditions, after a call to SetPullEnabled(false)
-   * it is still possible for a NotifyPull to occur.
-   */
-  void SetPullEnabled(bool aEnabled);
-
   /**
    * Call all MediaStreamListeners to request new data via the NotifyPull API
    * (if enabled).