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use lock-free pipe for local audio in device callback

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This commit is contained in:
Zach Pomerantz 2017-01-21 19:10:34 -05:00
parent 72f8fa49f9
commit 061668cba4
3 changed files with 20 additions and 2 deletions
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13
libraries/audio-client/src/AudioClient.cpp
View file

@ -190,6 +190,9 @@ AudioClient::AudioClient() :
_inputGate(),
_positionGetter(DEFAULT_POSITION_GETTER),
_orientationGetter(DEFAULT_ORIENTATION_GETTER) {
// avoid putting a lock in the device callback
assert(_localSamplesAvailable.is_lock_free());
// deprecate legacy settings
{
Setting::Handle<int>::Deprecated("maxFramesOverDesired", InboundAudioStream::MAX_FRAMES_OVER_DESIRED);
@ -1105,7 +1108,8 @@ void AudioClient::prepareLocalAudioInjectors() {
int bufferCapacity = _localInjectorsStream.getSampleCapacity();
if (_localToOutputResampler) {
// avoid overwriting the buffer
// avoid overwriting the buffer,
// instead of failing on writes because the buffer is used as a lock-free pipe
bufferCapacity -=
_localToOutputResampler->getMaxOutput(AudioConstants::NETWORK_FRAME_SAMPLES_PER_CHANNEL) *
AudioConstants::STEREO;
@ -1115,9 +1119,10 @@ void AudioClient::prepareLocalAudioInjectors() {
int samplesNeeded = std::numeric_limits<int>::max();
while (samplesNeeded > 0) {
// lock for every write to avoid locking out the device callback
// this lock is intentional - the buffer is only lock-free in its use in the device callback
Lock lock(_localAudioMutex);
samplesNeeded = bufferCapacity - _localInjectorsStream.samplesAvailable();
samplesNeeded = bufferCapacity - _localSamplesAvailable.load(std::memory_order_relaxed);
if (samplesNeeded <= 0) {
break;
}
@ -1149,6 +1154,7 @@ void AudioClient::prepareLocalAudioInjectors() {
AudioConstants::NETWORK_FRAME_SAMPLES_STEREO);
}
_localSamplesAvailable.fetch_add(samples, std::memory_order_release);
samplesNeeded -= samples;
}
}
@ -1452,6 +1458,7 @@ bool AudioClient::switchOutputToAudioDevice(const QAudioDeviceInfo& outputDevice
bool supportedFormat = false;
Lock lock(_localAudioMutex);
_localSamplesAvailable.exchange(0, std::memory_order_release);
// cleanup any previously initialized device
if (_audioOutput) {
@ -1666,7 +1673,9 @@ qint64 AudioClient::AudioOutputIODevice::readData(char * data, qint64 maxSize) {
{
Lock lock(_audio->_localAudioMutex);
bool append = networkSamplesPopped > 0;
samplesRequested = std::min(samplesRequested, _audio->_localSamplesAvailable.load(std::memory_order_acquire));
if ((injectorSamplesPopped = _localInjectorsStream.appendSamples(mixBuffer, samplesRequested, append)) > 0) {
_audio->_localSamplesAvailable.fetch_sub(injectorSamplesPopped, std::memory_order_release);
qCDebug(audiostream, "Read %d samples from injectors (%d available, %d requested)", injectorSamplesPopped, _localInjectorsStream.samplesAvailable(), samplesRequested);
}
}

3
libraries/audio-client/src/AudioClient.h
View file

@ -280,6 +280,9 @@ private:
QIODevice* _loopbackOutputDevice;
AudioRingBuffer _inputRingBuffer;
LocalInjectorsStream _localInjectorsStream;
// In order to use _localInjectorsStream as a lock-free pipe,
// use it with a single producer/consumer, and track available samples
std::atomic<int> _localSamplesAvailable { 0 };
MixedProcessedAudioStream _receivedAudioStream;
bool _isStereoInput;

6
libraries/audio/src/AudioRingBuffer.h
View file

@ -45,6 +45,12 @@ public:
// FIXME: discards any data in the buffer
void resizeForFrameSize(int numFrameSamples);
// Reading and writing to the buffer uses minimal shared data, such that
// in cases that avoid overwriting the buffer, a single producer/consumer
// may use this as a lock-free pipe (see audio-client/src/AudioClient.cpp).
// IMPORTANT: Avoid changes to the implementation that touch shared data unless you can
// maintain this behavior.
/// Read up to maxSamples into destination (will only read up to samplesAvailable())
/// Returns number of read samples
int readSamples(Sample* destination, int maxSamples);