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diff --git a/Source/WebCore/webaudio/AudioGainNode.cpp b/Source/WebCore/webaudio/AudioGainNode.cpp
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+++ b/Source/WebCore/webaudio/AudioGainNode.cpp
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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.
+ */
+
+#include "config.h"
+
+#if ENABLE(WEB_AUDIO)
+
+#include "AudioGainNode.h"
+
+#include "AudioBus.h"
+#include "AudioNodeInput.h"
+#include "AudioNodeOutput.h"
+
+namespace WebCore {
+
+AudioGainNode::AudioGainNode(AudioContext* context, double sampleRate)
+    : AudioNode(context, sampleRate)
+    , m_lastGain(1.0)
+{
+    m_gain = AudioGain::create("gain", 1.0, 0.0, 1.0);
+
+    addInput(adoptPtr(new AudioNodeInput(this)));
+    addOutput(adoptPtr(new AudioNodeOutput(this, 1)));
+    
+    setType(NodeTypeGain);
+    
+    initialize();
+}
+
+void AudioGainNode::process(size_t /*framesToProcess*/)
+{
+    // FIXME: there is a nice optimization to avoid processing here, and let the gain change
+    // happen in the summing junction input of the AudioNode we're connected to.
+    // Then we can avoid all of the following:
+
+    AudioBus* outputBus = output(0)->bus();
+    ASSERT(outputBus);
+
+    // The realtime thread can't block on this lock, so we call tryLock() instead.
+    if (m_processLock.tryLock()) {
+        if (!isInitialized() || !input(0)->isConnected())
+            outputBus->zero();
+        else {
+            AudioBus* inputBus = input(0)->bus();
+
+            // Apply the gain with de-zippering into the output bus.
+            outputBus->copyWithGainFrom(*inputBus, &m_lastGain, gain()->value());
+        }
+
+        m_processLock.unlock();
+    } else {
+        // Too bad - the tryLock() failed.  We must be in the middle of re-connecting and were already outputting silence anyway...
+        outputBus->zero();
+    }
+}
+
+void AudioGainNode::reset()
+{
+    // Snap directly to desired gain.
+    m_lastGain = gain()->value();
+}
+
+// FIXME: this can go away when we do mixing with gain directly in summing junction of AudioNodeInput
+//
+// As soon as we know the channel count of our input, we can lazily initialize.
+// Sometimes this may be called more than once with different channel counts, in which case we must safely
+// uninitialize and then re-initialize with the new channel count.
+void AudioGainNode::checkNumberOfChannelsForInput(AudioNodeInput* input)
+{
+    ASSERT(input && input == this->input(0));
+    if (input != this->input(0))
+        return;
+        
+    unsigned numberOfChannels = input->numberOfChannels();    
+
+    if (isInitialized() && numberOfChannels != output(0)->numberOfChannels()) {
+        // We're already initialized but the channel count has changed.
+        // We need to be careful since we may be actively processing right now, so synchronize with process().
+        MutexLocker locker(m_processLock);
+        uninitialize();
+    }
+
+    if (!isInitialized()) {
+        // This will propagate the channel count to any nodes connected further downstream in the graph.
+        output(0)->setNumberOfChannels(numberOfChannels);
+        initialize();
+    }
+}
+
+} // namespace WebCore
+
+#endif // ENABLE(WEB_AUDIO)