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diff --git a/WebCore/webaudio/AudioNodeInput.h b/WebCore/webaudio/AudioNodeInput.h
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+/*
+ * 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
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef AudioNodeInput_h
+#define AudioNodeInput_h
+
+#include "AudioBus.h"
+#include "AudioNode.h"
+#include <wtf/HashSet.h>
+#include <wtf/Vector.h>
+
+namespace WebCore {
+
+class AudioNode;
+class AudioNodeOutput;
+
+// An AudioNodeInput represents an input to an AudioNode and can be connected from one or more AudioNodeOutputs.
+// In the case of multiple connections, the input will act as a unity-gain summing junction, mixing all the outputs.
+// The number of channels of the input's bus is the maximum of the number of channels of all its connections.
+
+class AudioNodeInput {
+public:
+    AudioNodeInput(AudioNode*);
+
+    // Can be called from any thread.
+    AudioNode* node() const { return m_node; }
+    AudioContext* context() { return m_node->context(); }
+
+    // Must be called with the context's graph lock.
+    void connect(AudioNodeOutput*);
+    void disconnect(AudioNodeOutput*);
+
+    // disable() will take the output out of the active connections list and set aside in a disabled list.
+    // enable() will put the output back into the active connections list.
+    // Must be called with the context's graph lock.
+    void enable(AudioNodeOutput*);
+    void disable(AudioNodeOutput*);
+
+    // pull() processes all of the AudioNodes connected to us.
+    // In the case of multiple connections it sums the result into an internal summing bus.
+    // In the single connection case, it allows in-place processing where possible using inPlaceBus.
+    // It returns the bus which it rendered into, returning inPlaceBus if in-place processing was performed.
+    // Called from context's audio thread.
+    AudioBus* pull(AudioBus* inPlaceBus, size_t framesToProcess);
+
+    // bus() contains the rendered audio after pull() has been called for each time quantum.
+    // Called from context's audio thread.
+    AudioBus* bus();
+    
+    // This copies m_outputs to m_renderingOutputs.  Please see comments for these lists below.
+    // This must be called when we own the context's graph lock in the audio thread at the very start or end of the render quantum.
+    void updateRenderingState();
+
+    // Rendering code accesses its version of the current connections here.
+    unsigned numberOfRenderingConnections() const { return m_renderingOutputs.size(); }
+    AudioNodeOutput* renderingOutput(unsigned i) { return m_renderingOutputs[i]; }
+    const AudioNodeOutput* renderingOutput(unsigned i) const { return m_renderingOutputs[i]; }
+    bool isConnected() const { return numberOfRenderingConnections() > 0; }
+
+    // The number of channels of the connection with the largest number of channels.
+    unsigned numberOfChannels() const;        
+    
+private:
+    AudioNode* m_node;
+
+    // m_outputs contains the AudioNodeOutputs representing current connections which are not disabled.
+    // The rendering code should never use this directly, but instead uses m_renderingOutputs.
+    HashSet<AudioNodeOutput*> m_outputs;
+
+    // numberOfConnections() should never be called from the audio rendering thread.
+    // Instead numberOfRenderingConnections() and renderingOutput() should be used.
+    unsigned numberOfConnections() const { return m_outputs.size(); }
+
+    // This must be called whenever we modify m_outputs.
+    void changedOutputs();
+    
+    // m_renderingOutputs is a copy of m_outputs which will never be modified during the graph rendering on the audio thread.
+    // This is the list which is used by the rendering code.
+    // Whenever m_outputs is modified, the context is told so it can later update m_renderingOutputs from m_outputs at a safe time.
+    // Most of the time, m_renderingOutputs is identical to m_outputs.
+    Vector<AudioNodeOutput*> m_renderingOutputs;
+
+    // m_renderingStateNeedUpdating keeps track if m_outputs is modified.
+    bool m_renderingStateNeedUpdating;
+
+    // The number of channels of the rendering connection with the largest number of channels.
+    unsigned numberOfRenderingChannels();
+
+    // m_disabledOutputs contains the AudioNodeOutputs which are disabled (will not be processed) by the audio graph rendering.
+    // But, from JavaScript's perspective, these outputs are still connected to us.
+    // Generally, these represent disabled connections from "notes" which have finished playing but are not yet garbage collected.
+    HashSet<AudioNodeOutput*> m_disabledOutputs;
+
+    // Called from context's audio thread.
+    AudioBus* internalSummingBus();
+    void sumAllConnections(AudioBus* summingBus, size_t framesToProcess);
+
+    OwnPtr<AudioBus> m_monoSummingBus;
+    OwnPtr<AudioBus> m_stereoSummingBus;
+};
+
+} // namespace WebCore
+
+#endif // AudioNodeInput_h