webaudio/blink/ReverbConvolver.cpp

/*
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#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