Merge 141851

Source/WebCore/Modules/webaudio/AudioBufferSourceNode.cpp

 /*
  * 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 83 matching lines @@
     }
 
     // The audio thread can't block on this lock, so we call tryLock() instead.
     MutexTryLocker tryLocker(m_processLock);
     if (tryLocker.locked()) {
         if (!buffer()) {
             outputBus->zero();
             return;
         }
 
+        // After calling setBuffer() with a buffer having a different number of channels, there can in rare cases be a slight delay
+        // before the output bus is updated to the new number of channels because of use of tryLocks() in the context's updating system.
+        // In this case, if the the buffer has just been changed and we're not quite ready yet, then just output silence.
+        if (numberOfChannels() != buffer()->numberOfChannels()) {
+            outputBus->zero();
+            return;
+        }
+
         size_t quantumFrameOffset;
         size_t bufferFramesToProcess;
 
         updateSchedulingInfo(framesToProcess,
                              outputBus,
                              quantumFrameOffset,
                              bufferFramesToProcess);
                              
         if (!bufferFramesToProcess) {
             outputBus->zero();
@@ skipping 34 matching lines @@
 
         finish();
         return true;
     }
     return false;
 }
 
 bool AudioBufferSourceNode::renderFromBuffer(AudioBus* bus, unsigned destinationFrameOffset, size_t numberOfFrames)
 {
     ASSERT(context()->isAudioThread());
-    
+
     // Basic sanity checking
     ASSERT(bus);
     ASSERT(buffer());
     if (!bus || !buffer())
         return false;
 
     unsigned numberOfChannels = this->numberOfChannels();
     unsigned busNumberOfChannels = bus->numberOfChannels();
 
     bool channelCountGood = numberOfChannels && numberOfChannels == busNumberOfChannels;
@@ skipping 326 matching lines @@
 void AudioBufferSourceNode::finish()
 {
     clearPannerNode();
     ASSERT(!m_pannerNode);
     AudioScheduledSourceNode::finish();
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)