Bug 1181204 - Prevent use of the decoder outside the reader's taskqueue. r=cpearce

This fix a potential race when the decoder could be shutting down on the reader's taskqueue while the MediaDecoderStateMachine thread attempts to read it.

--HG--
extra : amend_source : d8a7ac55539c22f69d965299010a20b34c8a4c58
extra : transplant_source : %F6%D2z%A2%40%D1%CE%8BX%FB%9E%CA%2B%ABa%7D%F9%7Fl%BF

dom/media/MediaFormatReader.cpp

@@ -1024,6 +1024,10 @@ MediaFormatReader::Update(TrackType aTrack)
     needOutput = true;
     if (!decoder.mOutput.IsEmpty()) {
       // We have a decoded sample ready to be returned.
+      if (aTrack == TrackType::kVideoTrack) {
+        mVideo.mIsHardwareAccelerated =
+          mVideo.mDecoder && mVideo.mDecoder->IsHardwareAccelerated();
+      }
       nsRefPtr<MediaData> output = decoder.mOutput[0];
       decoder.mOutput.RemoveElementAt(0);
       decoder.mSizeOfQueue -= 1;
@@ -1504,7 +1508,7 @@ MediaFormatReader::SetSharedDecoderManager(SharedDecoderManager* aManager)
 bool
 MediaFormatReader::VideoIsHardwareAccelerated() const
 {
-  return mVideo.mDecoder && mVideo.mDecoder->IsHardwareAccelerated();
+  return mVideo.mIsHardwareAccelerated;
 }
 
 void

dom/media/MediaFormatReader.h

@@ -203,6 +203,7 @@ private:
       , mNumSamplesInput(0)
       , mNumSamplesOutput(0)
       , mSizeOfQueue(0)
+      , mIsHardwareAccelerated(false)
       , mLastStreamSourceID(UINT32_MAX)
     {}
 
@@ -294,6 +295,9 @@ private:
 
     // Used by the MDSM for logging purposes.
     Atomic<size_t> mSizeOfQueue;
+    // Used by the MDSM to determine if video decoding is hardware accelerated.
+    // This value is updated after a frame is successfully decoded.
+    Atomic<bool> mIsHardwareAccelerated;
     // Sample format monitoring.
     uint32_t mLastStreamSourceID;
     Maybe<uint32_t> mNextStreamSourceID;