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Elimiteted race condition in the AudioMixer.

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The mixer allocates an audio frame for each added data source. This
audio frame was deallocated when a source was removed from the
mixer. Source removal could happen during the mixing, and the existing
locking scheme (and the Clang thread checker) was not sufficient to
prevent a data race.

After this change, the mixer doesn't release its lock until it is
finished with the sources' Audio frames. Since multi-threaded access to
the mixer only happens when a source is added or removed, we believe
that this change wouldn't have any noticeable performance impact.

NOTRY=True

BUG=webrtc:6346

Review-Url: https://codereview.webrtc.org/2439283002
Cr-Commit-Position: refs/heads/master@{#14744}
This commit is contained in:
aleloi
2016-10-24 06:56:56 -07:00
committed by Commit bot
parent 2206c959f1
commit 1655e45d85
2 changed files with 16 additions and 16 deletions
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30
webrtc/modules/audio_mixer/audio_mixer_impl.cc
View File

@ -200,23 +200,23 @@ void AudioMixerImpl::Mix(int sample_rate,
{
rtc::CritScope lock(&crit_);
mix_list = GetAudioFromSources();
for (const auto& frame : mix_list) {
RemixFrame(number_of_channels, frame);
}
audio_frame_for_mixing->UpdateFrame(
-1, time_stamp_, NULL, 0, OutputFrequency(), AudioFrame::kNormalSpeech,
AudioFrame::kVadPassive, number_of_channels);
time_stamp_ += static_cast<uint32_t>(sample_size_);
use_limiter_ = mix_list.size() > 1;
// We only use the limiter if we're actually mixing multiple streams.
MixFromList(audio_frame_for_mixing, mix_list, use_limiter_);
}
for (const auto& frame : mix_list) {
RemixFrame(number_of_channels, frame);
}
audio_frame_for_mixing->UpdateFrame(
-1, time_stamp_, NULL, 0, OutputFrequency(), AudioFrame::kNormalSpeech,
AudioFrame::kVadPassive, number_of_channels);
time_stamp_ += static_cast<uint32_t>(sample_size_);
use_limiter_ = mix_list.size() > 1;
// We only use the limiter if we're actually mixing multiple streams.
MixFromList(audio_frame_for_mixing, mix_list, use_limiter_);
if (audio_frame_for_mixing->samples_per_channel_ == 0) {
// Nothing was mixed, set the audio samples to silence.
audio_frame_for_mixing->samples_per_channel_ = sample_size_;

2
webrtc/modules/audio_mixer/audio_mixer_impl.h
View File

@ -57,7 +57,7 @@ class AudioMixerImpl : public AudioMixer {
void Mix(int sample_rate_hz,
size_t number_of_channels,
AudioFrame* audio_frame_for_mixing) override;
AudioFrame* audio_frame_for_mixing) override LOCKS_EXCLUDED(crit_);
// Returns true if the source was mixed last round. Returns
// false and logs an error if the source was never added to the