From cdc2162522bb8611701113144f48e91b29337464 Mon Sep 17 00:00:00 2001
From: Randell Jesup <rjesup@jesup.org>
Date: Sun, 28 Sep 2014 12:07:24 -0400
Subject: [PATCH] Bug 1072780: patch 1 - clean up CurrentDriver() use
 off-MSG-thread; fix InCallback() r=roc

---
 content/media/GraphDriver.cpp        |  7 ++++++-
 content/media/MediaStreamGraph.cpp   | 22 ++++++++++++----------
 content/media/MediaStreamGraphImpl.h | 13 +++++++++++++
 3 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/content/media/GraphDriver.cpp b/content/media/GraphDriver.cpp
index 3e77d9d19124..4d3818a703dd 100644
--- a/content/media/GraphDriver.cpp
+++ b/content/media/GraphDriver.cpp
@@ -767,7 +767,12 @@ AudioCallbackDriver::DataCallback(AudioDataValue* aBuffer, long aFrames)
     return aFrames;
   }
 
-  DebugOnly<AutoInCallback> aic(AutoInCallback(this));
+#ifdef DEBUG
+  // DebugOnly<> doesn't work here... it forces an initialization that will cause
+  // mInCallback to be set back to false before we exit the statement.  Do it by
+  // hand instead.
+  AutoInCallback aic(this);
+#endif
 
   if (mStateComputedTime == 0) {
     MonitorAutoLock mon(mGraphImpl->GetMonitor());
diff --git a/content/media/MediaStreamGraph.cpp b/content/media/MediaStreamGraph.cpp
index 62faa6cb3b84..70284302c3d6 100644
--- a/content/media/MediaStreamGraph.cpp
+++ b/content/media/MediaStreamGraph.cpp
@@ -1651,11 +1651,12 @@ MediaStreamGraphImpl::RunInStableState(bool aSourceIsMSG)
         // Note that we need to put messages into its queue before reviving it,
         // or it might exit immediately.
         {
-          MonitorAutoUnlock unlock(mMonitor);
           LIFECYCLE_LOG("Reviving a graph (%p) ! %s\n",
               this, CurrentDriver()->AsAudioCallbackDriver() ? "AudioDriver" :
                                                                "SystemDriver");
-          CurrentDriver()->Revive();
+          nsRefPtr<GraphDriver> driver = CurrentDriver();
+          MonitorAutoUnlock unlock(mMonitor);
+          driver->Revive();
         }
       }
     }
@@ -1671,12 +1672,13 @@ MediaStreamGraphImpl::RunInStableState(bool aSourceIsMSG)
       {
         // We should exit the monitor for now, because starting a stream might
         // take locks, and we don't want to deadlock.
-        MonitorAutoUnlock unlock(mMonitor);
         LIFECYCLE_LOG("Starting a graph (%p) ! %s\n",
                       this,
                       CurrentDriver()->AsAudioCallbackDriver() ? "AudioDriver" :
                                                                  "SystemDriver");
-        CurrentDriver()->Start();
+        nsRefPtr<GraphDriver> driver = CurrentDriver();
+        MonitorAutoUnlock unlock(mMonitor);
+        driver->Start();
       }
     }
 
@@ -2258,7 +2260,7 @@ SourceMediaStream::SetPullEnabled(bool aEnabled)
   MutexAutoLock lock(mMutex);
   mPullEnabled = aEnabled;
   if (mPullEnabled && GraphImpl()) {
-    GraphImpl()->CurrentDriver()->EnsureNextIteration();
+    GraphImpl()->EnsureNextIteration();
   }
 }
 
@@ -2278,7 +2280,7 @@ SourceMediaStream::AddTrack(TrackID aID, TrackRate aRate, TrackTicks aStart,
   data->mData = aSegment;
   data->mHaveEnough = false;
   if (auto graph = GraphImpl()) {
-    graph->CurrentDriver()->EnsureNextIteration();
+    graph->EnsureNextIteration();
   }
 }
 
@@ -2340,7 +2342,7 @@ SourceMediaStream::AppendToTrack(TrackID aID, MediaSegment* aSegment, MediaSegme
       NotifyDirectConsumers(track, aRawSegment ? aRawSegment : aSegment);
       track->mData->AppendFrom(aSegment); // note: aSegment is now dead
       appended = true;
-      GraphImpl()->CurrentDriver()->EnsureNextIteration();
+      GraphImpl()->EnsureNextIteration();
     } else {
       aSegment->Clear();
     }
@@ -2464,7 +2466,7 @@ SourceMediaStream::EndTrack(TrackID aID)
     }
   }
   if (auto graph = GraphImpl()) {
-    graph->CurrentDriver()->EnsureNextIteration();
+    graph->EnsureNextIteration();
   }
 }
 
@@ -2475,7 +2477,7 @@ SourceMediaStream::AdvanceKnownTracksTime(StreamTime aKnownTime)
   MOZ_ASSERT(aKnownTime >= mUpdateKnownTracksTime);
   mUpdateKnownTracksTime = aKnownTime;
   if (auto graph = GraphImpl()) {
-    graph->CurrentDriver()->EnsureNextIteration();
+    graph->EnsureNextIteration();
   }
 }
 
@@ -2485,7 +2487,7 @@ SourceMediaStream::FinishWithLockHeld()
   mMutex.AssertCurrentThreadOwns();
   mUpdateFinished = true;
   if (auto graph = GraphImpl()) {
-    graph->CurrentDriver()->EnsureNextIteration();
+    graph->EnsureNextIteration();
   }
 }
 
diff --git a/content/media/MediaStreamGraphImpl.h b/content/media/MediaStreamGraphImpl.h
index ff8c34d5cd61..afc408012d2b 100644
--- a/content/media/MediaStreamGraphImpl.h
+++ b/content/media/MediaStreamGraphImpl.h
@@ -414,6 +414,9 @@ public:
   void PausedIndefinitly();
   void ResumedFromPaused();
 
+  /**
+   * Not safe to call off the MediaStreamGraph thread unless monitor is held!
+   */
   GraphDriver* CurrentDriver() {
     return mDriver;
   }
@@ -432,6 +435,16 @@ public:
     return mMonitor;
   }
 
+  /**
+   * Must implement here to avoid dangerous data races around CurrentDriver() -
+   * we don't want stuff off MSG thread using "graph->CurrentDriver()->EnsureNextIteration()"
+   * because CurrentDriver may change (and it's a TSAN data race)
+   */
+  void EnsureNextIteration() {
+    MonitorAutoLock mon(mMonitor);
+    CurrentDriver()->EnsureNextIterationLocked();
+  }
+
   // Data members
   //
   /**