Add comments to vectors/hash sets of raw pointers to on-heap objects used in webaudio/

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 258 matching lines @@
     void derefNode(AudioNode*);
 
     // When the context goes away, there might still be some sources which haven't finished playing.
     // Make sure to dereference them here.
     void derefUnfinishedSourceNodes();
 
     RefPtrWillBeMember<AudioDestinationNode> m_destinationNode;
     RefPtrWillBeMember<AudioListener> m_listener;
 
     // Only accessed in the audio thread.
+    // Oilpan: Since items are added to the vector by the audio thread (not registered to Oilpan),
+    // we cannot use a HeapVector.
     Vector<AudioNode*> m_finishedNodes;
 
     // List of source nodes. This is either accessed when the graph lock is
     // held, or on the main thread when the audio thread has finished.
     // This RefPtr is connection reference. We must call AudioNode::
     // makeConnection() after ref(), and call AudioNode::breakConnection()
     // before deref().
     // Oilpan: This Vector holds connection references. We must call
     // AudioNode::makeConnection when we add an AudioNode to this, and must call
     // AudioNode::breakConnection() when we remove an AudioNode from this.
@@ skipping 21 matching lines @@
     // The purpose of m_liveAudioSummingJunctions is to remove a dying
     // AudioSummingJunction from m_dirtySummingJunctions. However we put all of
     // AudioSummingJunction objects to m_liveAudioSummingJunctions to avoid
     // concurrent access to m_liveAudioSummingJunctions.
     HeapHashMap<WeakMember<AudioSummingJunction>, OwnPtr<AudioSummingJunctionDisposer> > m_liveAudioSummingJunctions;
 #else
     // Accumulate nodes which need to be deleted here.
     // This is copied to m_nodesToDelete at the end of a render cycle in handlePostRenderTasks(), where we're assured of a stable graph
     // state which will have no references to any of the nodes in m_nodesToDelete once the context lock is released
     // (when handlePostRenderTasks() has completed).
+    // Oilpan: Since items are added to the vector by the audio thread (not registered to Oilpan),
+    // we cannot use a HeapVector.
     Vector<AudioNode*> m_nodesMarkedForDeletion;
 
     // They will be scheduled for deletion (on the main thread) at the end of a render cycle (in realtime thread).
+    // Oilpan: Since items are added to the vector by the audio thread (not registered to Oilpan),
+    // we cannot use a HeapVector.
     Vector<AudioNode*> m_nodesToDelete;
     bool m_isDeletionScheduled;
 #endif
 
     // These two HashSet must be accessed only when the graph lock is held.
     // Oilpan: These HashSet should be HeapHashSet<WeakMember<AudioNodeOutput>>
     // ideally. But it's difficult to lock them correctly during GC.
+    // Oilpan: Since items are added to these hash sets by the audio thread (not registered to Oilpan),
+    // we cannot use HeapHashSets.
     HashSet<AudioSummingJunction*> m_dirtySummingJunctions;
     HashSet<AudioNodeOutput*> m_dirtyAudioNodeOutputs;
     void handleDirtyAudioSummingJunctions();
     void handleDirtyAudioNodeOutputs();
 
     // For the sake of thread safety, we maintain a seperate Vector of automatic pull nodes for rendering in m_renderingAutomaticPullNodes.
     // It will be copied from m_automaticPullNodes by updateAutomaticPullNodes() at the very start or end of the rendering quantum.
+    // Oilpan: Since items are added to the vector/hash set by the audio thread (not registered to Oilpan),
+    // we cannot use a HeapVector/HeapHashSet.
     HashSet<AudioNode*> m_automaticPullNodes;
     Vector<AudioNode*> m_renderingAutomaticPullNodes;
     // m_automaticPullNodesNeedUpdating keeps track if m_automaticPullNodes is modified.
     bool m_automaticPullNodesNeedUpdating;
     void updateAutomaticPullNodes();
 
     unsigned m_connectionCount;
 
     // Graph locking.
     Mutex m_contextGraphMutex;
     volatile ThreadIdentifier m_audioThread;
     volatile ThreadIdentifier m_graphOwnerThread; // if the lock is held then this is the thread which owns it, otherwise == UndefinedThreadIdentifier
 
     // Only accessed in the audio thread.
+    // Oilpan: Since items are added to these vectors by the audio thread (not registered to Oilpan),
+    // we cannot use HeapVectors.
     Vector<AudioNode*> m_deferredBreakConnectionList;
     Vector<AudioNode*> m_deferredFinishDerefList;
 
     RefPtrWillBeMember<AudioBuffer> m_renderTarget;
 
     bool m_isOfflineContext;
 
     AsyncAudioDecoder m_audioDecoder;
 
     // This is considering 32 is large enough for multiple channels audio.
     // It is somewhat arbitrary and could be increased if necessary.
     enum { MaxNumberOfChannels = 32 };
 };
 
 } // namespace blink
 
 #endif // AudioContext_h