Access current frame counter carefully and remove m_cachedSampleFrame.

Source/modules/webaudio/AudioContext.h

 /*
  * Copyright (C) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 90 matching lines @@
 
     bool isInitialized() const { return m_isInitialized; }
     bool isOfflineContext() { return m_isOfflineContext; }
 
     // Document notification
     virtual void stop() override final;
     virtual bool hasPendingActivity() const override;
 
     AudioDestinationNode* destination() { return m_destinationNode.get(); }
 
-    // currentSampleFrame() and currentTime() can be called from both the main
-    // thread and the audio thread. Note that, however, they return the cached
-    // value instead of actual current ones when they are accessed from the main
-    // thread. See: crbug.com/431874
-    size_t currentSampleFrame() const;
-    double currentTime() const;
+    size_t currentSampleFrame() const
+    {
+        return m_destinationNode ? m_destinationNode->audioDestinationHandler().currentSampleFrame() : 0;

[Ken Russell (switch to Gerrit), 2015/05/21 20:45:16]

Is it safe to access the destination node's AudioDestinationHandler from the
main thread? The previous code only accessed it from the audio thread.

[Raymond Toy, 2015/05/21 21:19:06]

I believe this is safe. The purpose of the handler is to implement the guts of
the node and the audio node (which encapsulates the JS object) is just a thin
wrapper to the handler.

+tkent to verify.

[tkent, 2015/05/22 00:47:12]

Yes, it's ok to touch handlers from the main thread if we correctly avoid races.

+    }
+
+    double currentTime() const
+    {
+        return m_destinationNode ? m_destinationNode->audioDestinationHandler().currentTime() : 0;
+    }
 
     float sampleRate() const { return m_destinationNode ? m_destinationNode->handler().sampleRate() : 0; }
 
     String state() const;
     AudioContextState contextState() const { return m_contextState; }
 
     AudioBuffer* createBuffer(unsigned numberOfChannels, size_t numberOfFrames, float sampleRate, ExceptionState&);
 
     // Asynchronous audio file data decoding.
     void decodeAudioData(DOMArrayBuffer*, AudioBufferCallback*, AudioBufferCallback*, ExceptionState&);
@@ skipping 177 matching lines @@
 
     // The state of the AudioContext.
     AudioContextState m_contextState;
     void setContextState(AudioContextState);
 
     AsyncAudioDecoder m_audioDecoder;
 
     // The Promise that is returned by close();
     RefPtrWillBeMember<ScriptPromiseResolver> m_closeResolver;
 
-    // Follows the destination's currentSampleFrame, but might be slightly behind due to locking.
-    size_t m_cachedSampleFrame;
-
     // Tries to handle AudioBufferSourceNodes that were started but became disconnected or was never
     // connected. Because these never get pulled anymore, they will stay around forever. So if we
     // can, try to stop them so they can be collected.
     void handleStoppableSourceNodes();
 
     // This is considering 32 is large enough for multiple channels audio.
     // It is somewhat arbitrary and could be increased if necessary.
     enum { MaxNumberOfChannels = 32 };
 
     unsigned m_contextId;
 };
 
 } // namespace blink
 
 #endif // AudioContext_h