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diff --git a/dom/media/webaudio/blink/ReverbConvolver.cpp b/dom/media/webaudio/blink/ReverbConvolver.cpp
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+++ b/dom/media/webaudio/blink/ReverbConvolver.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.
+ * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
+ *     its contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE 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 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 "ReverbConvolver.h"
+#include "ReverbConvolverStage.h"
+
+using namespace mozilla;
+
+namespace WebCore {
+
+const int InputBufferSize = 8 * 16384;
+
+// We only process the leading portion of the impulse response in the real-time thread.  We don't exceed this length.
+// It turns out then, that the background thread has about 278msec of scheduling slop.
+// Empirically, this has been found to be a good compromise between giving enough time for scheduling slop,
+// while still minimizing the amount of processing done in the primary (high-priority) thread.
+// This was found to be a good value on Mac OS X, and may work well on other platforms as well, assuming
+// the very rough scheduling latencies are similar on these time-scales.  Of course, this code may need to be
+// tuned for individual platforms if this assumption is found to be incorrect.
+const size_t RealtimeFrameLimit = 8192 + 4096 // ~278msec @ 44.1KHz
+                                  - WEBAUDIO_BLOCK_SIZE;
+// First stage will have size MinFFTSize - successive stages will double in
+// size each time until we hit the maximum size.
+const size_t MinFFTSize = 256;
+// If we are using background threads then don't exceed this FFT size for the
+// stages which run in the real-time thread.  This avoids having only one or
+// two large stages (size 16384 or so) at the end which take a lot of time
+// every several processing slices.  This way we amortize the cost over more
+// processing slices.
+const size_t MaxRealtimeFFTSize = 4096;
+
+ReverbConvolver::ReverbConvolver(const float* impulseResponseData,
+                                 size_t impulseResponseLength,
+                                 size_t maxFFTSize,
+                                 size_t convolverRenderPhase,
+                                 bool useBackgroundThreads)
+    : m_impulseResponseLength(impulseResponseLength)
+    , m_accumulationBuffer(impulseResponseLength + WEBAUDIO_BLOCK_SIZE)
+    , m_inputBuffer(InputBufferSize)
+    , m_backgroundThread("ConvolverWorker")
+    , m_backgroundThreadCondition(&m_backgroundThreadLock)
+    , m_useBackgroundThreads(useBackgroundThreads)
+    , m_wantsToExit(false)
+    , m_moreInputBuffered(false)
+{
+    // For the moment, a good way to know if we have real-time constraint is to check if we're using background threads.
+    // Otherwise, assume we're being run from a command-line tool.
+    bool hasRealtimeConstraint = useBackgroundThreads;
+
+    const float* response = impulseResponseData;
+    size_t totalResponseLength = impulseResponseLength;
+
+    // The total latency is zero because the first FFT stage is small enough
+    // to return output in the first block.
+    size_t reverbTotalLatency = 0;
+
+    size_t stageOffset = 0;
+    size_t stagePhase = 0;
+    size_t fftSize = MinFFTSize;
+    while (stageOffset < totalResponseLength) {
+        size_t stageSize = fftSize / 2;
+
+        // For the last stage, it's possible that stageOffset is such that we're straddling the end
+        // of the impulse response buffer (if we use stageSize), so reduce the last stage's length...
+        if (stageSize + stageOffset > totalResponseLength) {
+            stageSize = totalResponseLength - stageOffset;
+            // Use smallest FFT that is large enough to cover the last stage.
+            fftSize = MinFFTSize;
+            while (stageSize * 2 > fftSize) {
+              fftSize *= 2;
+            }
+        }
+
+        // This "staggers" the time when each FFT happens so they don't all happen at the same time
+        int renderPhase = convolverRenderPhase + stagePhase;
+
+        nsAutoPtr<ReverbConvolverStage> stage
+          (new ReverbConvolverStage(response, totalResponseLength,
+                                    reverbTotalLatency, stageOffset, stageSize,
+                                    fftSize, renderPhase,
+                                    &m_accumulationBuffer));
+
+        bool isBackgroundStage = false;
+
+        if (this->useBackgroundThreads() && stageOffset > RealtimeFrameLimit) {
+            m_backgroundStages.AppendElement(stage.forget());
+            isBackgroundStage = true;
+        } else
+            m_stages.AppendElement(stage.forget());
+
+        // Figure out next FFT size
+        fftSize *= 2;
+
+        stageOffset += stageSize;
+
+        if (hasRealtimeConstraint && !isBackgroundStage
+            && fftSize > MaxRealtimeFFTSize) {
+            fftSize = MaxRealtimeFFTSize;
+            // Custom phase positions for all but the first of the realtime
+            // stages of largest size.  These spread out the work of the
+            // larger realtime stages.  None of the FFTs of size 1024, 2048 or
+            // 4096 are performed when processing the same block.  The first
+            // MaxRealtimeFFTSize = 4096 stage, at the end of the doubling,
+            // performs its FFT at block 7.  The FFTs of size 2048 are
+            // performed in blocks 3 + 8 * n and size 1024 at 1 + 4 * n.
+            const uint32_t phaseLookup[] = { 14, 0, 10, 4 };
+            stagePhase = WEBAUDIO_BLOCK_SIZE *
+                phaseLookup[m_stages.Length() % ArrayLength(phaseLookup)];
+        } else if (fftSize > maxFFTSize) {
+            fftSize = maxFFTSize;
+            // A prime offset spreads out FFTs in a way that all
+            // available phase positions will be used if there are sufficient
+            // stages.
+            stagePhase += 5 * WEBAUDIO_BLOCK_SIZE;
+        } else if (stageSize > WEBAUDIO_BLOCK_SIZE) {
+            // As the stages are doubling in size, the next FFT will occur
+            // mid-way between FFTs for this stage.
+            stagePhase = stageSize - WEBAUDIO_BLOCK_SIZE;
+        }
+    }
+
+    // Start up background thread
+    // FIXME: would be better to up the thread priority here.  It doesn't need to be real-time, but higher than the default...
+    if (this->useBackgroundThreads() && m_backgroundStages.Length() > 0) {
+        if (!m_backgroundThread.Start()) {
+          NS_WARNING("Cannot start convolver thread.");
+          return;
+        }
+        m_backgroundThread.message_loop()->PostTask(NewNonOwningRunnableMethod(this,
+									       &ReverbConvolver::backgroundThreadEntry));
+    }
+}
+
+ReverbConvolver::~ReverbConvolver()
+{
+    // Wait for background thread to stop
+    if (useBackgroundThreads() && m_backgroundThread.IsRunning()) {
+        m_wantsToExit = true;
+
+        // Wake up thread so it can return
+        {
+            AutoLock locker(m_backgroundThreadLock);
+            m_moreInputBuffered = true;
+            m_backgroundThreadCondition.Signal();
+        }
+
+        m_backgroundThread.Stop();
+    }
+}
+
+size_t ReverbConvolver::sizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
+{
+    size_t amount = aMallocSizeOf(this);
+    amount += m_stages.ShallowSizeOfExcludingThis(aMallocSizeOf);
+    for (size_t i = 0; i < m_stages.Length(); i++) {
+        if (m_stages[i]) {
+            amount += m_stages[i]->sizeOfIncludingThis(aMallocSizeOf);
+        }
+    }
+
+    amount += m_backgroundStages.ShallowSizeOfExcludingThis(aMallocSizeOf);
+    for (size_t i = 0; i < m_backgroundStages.Length(); i++) {
+        if (m_backgroundStages[i]) {
+            amount += m_backgroundStages[i]->sizeOfIncludingThis(aMallocSizeOf);
+        }
+    }
+
+    // NB: The buffer sizes are static, so even though they might be accessed
+    //     in another thread it's safe to measure them.
+    amount += m_accumulationBuffer.sizeOfExcludingThis(aMallocSizeOf);
+    amount += m_inputBuffer.sizeOfExcludingThis(aMallocSizeOf);
+
+    // Possible future measurements:
+    // - m_backgroundThread
+    // - m_backgroundThreadLock
+    // - m_backgroundThreadCondition
+    return amount;
+}
+
+void ReverbConvolver::backgroundThreadEntry()
+{
+    while (!m_wantsToExit) {
+        // Wait for realtime thread to give us more input
+        m_moreInputBuffered = false;
+        {
+            AutoLock locker(m_backgroundThreadLock);
+            while (!m_moreInputBuffered && !m_wantsToExit)
+                m_backgroundThreadCondition.Wait();
+        }
+
+        // Process all of the stages until their read indices reach the input buffer's write index
+        int writeIndex = m_inputBuffer.writeIndex();
+
+        // Even though it doesn't seem like every stage needs to maintain its own version of readIndex 
+        // we do this in case we want to run in more than one background thread.
+        int readIndex;
+
+        while ((readIndex = m_backgroundStages[0]->inputReadIndex()) != writeIndex) { // FIXME: do better to detect buffer overrun...
+            // Accumulate contributions from each stage
+            for (size_t i = 0; i < m_backgroundStages.Length(); ++i)
+                m_backgroundStages[i]->processInBackground(this);
+        }
+    }
+}
+
+void ReverbConvolver::process(const float* sourceChannelData,
+                              float* destinationChannelData)
+{
+    const float* source = sourceChannelData;
+    float* destination = destinationChannelData;
+    bool isDataSafe = source && destination;
+    MOZ_ASSERT(isDataSafe);
+    if (!isDataSafe)
+        return;
+
+    // Feed input buffer (read by all threads)
+    m_inputBuffer.write(source, WEBAUDIO_BLOCK_SIZE);
+
+    // Accumulate contributions from each stage
+    for (size_t i = 0; i < m_stages.Length(); ++i)
+        m_stages[i]->process(source);
+
+    // Finally read from accumulation buffer
+    m_accumulationBuffer.readAndClear(destination, WEBAUDIO_BLOCK_SIZE);
+
+    // Now that we've buffered more input, wake up our background thread.
+
+    // Not using a MutexLocker looks strange, but we use a tryLock() instead because this is run on the real-time
+    // thread where it is a disaster for the lock to be contended (causes audio glitching).  It's OK if we fail to
+    // signal from time to time, since we'll get to it the next time we're called.  We're called repeatedly
+    // and frequently (around every 3ms).  The background thread is processing well into the future and has a considerable amount of 
+    // leeway here...
+    if (m_backgroundThreadLock.Try()) {
+        m_moreInputBuffered = true;
+        m_backgroundThreadCondition.Signal();
+        m_backgroundThreadLock.Release();
+    }
+}
+
+} // namespace WebCore