Handle loops in audio graph better for PannerNodes

Source/modules/webaudio/PannerNode.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 67 matching lines @@
     uninitialize();
 }
 
 void PannerNode::pullInputs(size_t framesToProcess)
 {
     // We override pullInputs(), so we can detect new AudioSourceNodes which have connected to us when new connections are made.
     // These AudioSourceNodes need to be made aware of our existence in order to handle doppler shift pitch changes.
     if (m_connectionCount != context()->connectionCount()) {
         m_connectionCount = context()->connectionCount();
 
-        // Recursively go through all nodes connected to us.
-        notifyAudioSourcesConnectedToNode(this);
+        // A map for keeping track if we have visited a node or not. This prevents feedback loops
+        // from recursing infinitely. See crbug.com/331446.
+        HashMap<AudioNode*, bool> visitedNodes;
+
+        // Recursively go through all nodes connected to us
+        notifyAudioSourcesConnectedToNode(this, visitedNodes);
     }
 
     AudioNode::pullInputs(framesToProcess);
 }
 
 void PannerNode::process(size_t framesToProcess)
 {
     AudioBus* destination = output(0)->bus();
 
     if (!isInitialized() || !input(0)->isConnected() || !m_panner.get()) {
@@ skipping 279 matching lines @@
     m_distanceGain->setValue(static_cast<float>(distanceGain));
 
     // FIXME: could optimize by caching coneGain
     double coneGain = m_coneEffect.gain(m_position, m_orientation, listenerPosition);
 
     m_coneGain->setValue(static_cast<float>(coneGain));
 
     return float(distanceGain * coneGain);
 }
 
-void PannerNode::notifyAudioSourcesConnectedToNode(AudioNode* node)
+void PannerNode::notifyAudioSourcesConnectedToNode(AudioNode* node, HashMap<AudioNode*, bool>& visitedNodes)
 {
     ASSERT(node);
     if (!node)
         return;
 
     // First check if this node is an AudioBufferSourceNode. If so, let it know about us so that doppler shift pitch can be taken into account.
     if (node->nodeType() == NodeTypeAudioBufferSource) {
         AudioBufferSourceNode* bufferSourceNode = static_cast<AudioBufferSourceNode*>(node);
         bufferSourceNode->setPannerNode(this);
     } else {
         // Go through all inputs to this node.
         for (unsigned i = 0; i < node->numberOfInputs(); ++i) {
             AudioNodeInput* input = node->input(i);
 
             // For each input, go through all of its connections, looking for AudioBufferSourceNodes.
             for (unsigned j = 0; j < input->numberOfRenderingConnections(); ++j) {
                 AudioNodeOutput* connectedOutput = input->renderingOutput(j);
                 AudioNode* connectedNode = connectedOutput->node();
-                notifyAudioSourcesConnectedToNode(connectedNode); // recurse
+                HashMap<AudioNode*, bool>::iterator iterator = visitedNodes.find(connectedNode);
+
+                // If we've seen this node already, we don't need to process it again. Otherwise,
+                // mark it as visited and recurse through the node looking for sources.
+                if (iterator == visitedNodes.end()) {
+                    visitedNodes.set(connectedNode, true);
+                    notifyAudioSourcesConnectedToNode(connectedNode, visitedNodes); // recurse
+                }
             }
         }
     }
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)