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WebRtcVideoCapturer: Getting rid of the |critical_section_stopping_| lock and all of its critical sections.

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This avoids a deadlock in WebRtcVideoCapturer.
The deadlock could occur because OnIncomingFrame() has the |critical_section_stopping_| lock, which could block a Stop() on the |start_thread_|. When OnIncomingFrame() then tries to do synchronous invoke on |start_thread_| (before releasing said lock) we have a deadlock.

BUG=4670
R=magjed@webrtc.org, tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/47259004

Cr-Commit-Position: refs/heads/master@{#9294}
This commit is contained in:
Henrik Boström
2015-05-27 10:11:34 +02:00
parent c065cc797d
commit cbe408aa11
2 changed files with 68 additions and 62 deletions
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122
talk/media/webrtc/webrtcvideocapturer.cc
View File

@ -129,17 +129,19 @@ static bool FormatToCapability(const VideoFormat& format,
WebRtcVideoCapturer::WebRtcVideoCapturer()
: factory_(new WebRtcVcmFactory),
module_(NULL),
module_(nullptr),
captured_frames_(0),
start_thread_(nullptr) {
start_thread_(nullptr),
async_invoker_(nullptr) {
set_frame_factory(new WebRtcVideoFrameFactory());
}
WebRtcVideoCapturer::WebRtcVideoCapturer(WebRtcVcmFactoryInterface* factory)
: factory_(factory),
module_(NULL),
module_(nullptr),
captured_frames_(0),
start_thread_(nullptr) {
start_thread_(nullptr),
async_invoker_(nullptr) {
set_frame_factory(new WebRtcVideoFrameFactory());
}
@ -281,16 +283,17 @@ CaptureState WebRtcVideoCapturer::Start(const VideoFormat& capture_format) {
LOG(LS_ERROR) << "The capturer has not been initialized";
return CS_NO_DEVICE;
}
rtc::CritScope cs(&critical_section_stopping_);
if (IsRunning()) {
if (start_thread_) {
LOG(LS_ERROR) << "The capturer is already running";
DCHECK(start_thread_->IsCurrent())
<< "Trying to start capturer on different threads";
return CS_FAILED;
}
DCHECK(!start_thread_);
start_thread_ = rtc::Thread::Current();
DCHECK(!async_invoker_);
async_invoker_.reset(new rtc::AsyncInvoker());
captured_frames_ = 0;
SetCaptureFormat(&capture_format);
@ -300,44 +303,50 @@ CaptureState WebRtcVideoCapturer::Start(const VideoFormat& capture_format) {
return CS_FAILED;
}
std::string camera_id(GetId());
uint32 start = rtc::Time();
module_->RegisterCaptureDataCallback(*this);
if (module_->StartCapture(cap) != 0) {
LOG(LS_ERROR) << "Camera '" << camera_id << "' failed to start";
LOG(LS_ERROR) << "Camera '" << GetId() << "' failed to start";
module_->DeRegisterCaptureDataCallback();
async_invoker_.reset();
SetCaptureFormat(nullptr);
start_thread_ = nullptr;
return CS_FAILED;
}
LOG(LS_INFO) << "Camera '" << camera_id << "' started with format "
LOG(LS_INFO) << "Camera '" << GetId() << "' started with format "
<< capture_format.ToString() << ", elapsed time "
<< rtc::TimeSince(start) << " ms";
captured_frames_ = 0;
SetCaptureState(CS_RUNNING);
return CS_STARTING;
}
// Critical section blocks Stop from shutting down during callbacks from capture
// thread to OnIncomingCapturedFrame. Note that the crit is try-locked in
// OnFrameCaptured, as the lock ordering between this and the system component
// controlling the camera is reversed: system frame -> OnIncomingCapturedFrame;
// Stop -> system stop camera).
void WebRtcVideoCapturer::Stop() {
rtc::CritScope cs(&critical_section_stopping_);
if (IsRunning()) {
DCHECK(start_thread_);
rtc::Thread::Current()->Clear(this);
module_->StopCapture();
module_->DeRegisterCaptureDataCallback();
// TODO(juberti): Determine if the VCM exposes any drop stats we can use.
double drop_ratio = 0.0;
std::string camera_id(GetId());
LOG(LS_INFO) << "Camera '" << camera_id << "' stopped after capturing "
<< captured_frames_ << " frames and dropping "
<< drop_ratio << "%";
if (!start_thread_) {
LOG(LS_ERROR) << "The capturer is already stopped";
return;
}
DCHECK(start_thread_);
DCHECK(start_thread_->IsCurrent());
DCHECK(async_invoker_);
if (IsRunning()) {
// The module is responsible for OnIncomingCapturedFrame being called, if
// we stop it we will get no further callbacks.
module_->StopCapture();
}
module_->DeRegisterCaptureDataCallback();
// TODO(juberti): Determine if the VCM exposes any drop stats we can use.
double drop_ratio = 0.0;
LOG(LS_INFO) << "Camera '" << GetId() << "' stopped after capturing "
<< captured_frames_ << " frames and dropping "
<< drop_ratio << "%";
// Clear any pending async invokes (that OnIncomingCapturedFrame may have
// caused).
async_invoker_.reset();
SetCaptureFormat(NULL);
start_thread_ = nullptr;
}
@ -362,37 +371,22 @@ bool WebRtcVideoCapturer::GetPreferredFourccs(
void WebRtcVideoCapturer::OnIncomingCapturedFrame(
const int32_t id,
const webrtc::I420VideoFrame& sample) {
// This would be a normal CritScope, except that it's possible that:
// (1) whatever system component producing this frame has taken a lock, and
// (2) Stop() probably calls back into that system component, which may take
// the same lock. Due to the reversed order, we have to try-lock in order to
// avoid a potential deadlock. Besides, if we can't enter because we're
// stopping, we may as well drop the frame.
rtc::TryCritScope cs(&critical_section_stopping_);
if (!cs.locked() || !IsRunning()) {
// Capturer has been stopped or is in the process of stopping.
return;
}
++captured_frames_;
// Log the size and pixel aspect ratio of the first captured frame.
if (1 == captured_frames_) {
LOG(LS_INFO) << "Captured frame size "
<< sample.width() << "x" << sample.height()
<< ". Expected format " << GetCaptureFormat()->ToString();
}
// This can only happen between Start() and Stop().
DCHECK(start_thread_);
DCHECK(async_invoker_);
if (start_thread_->IsCurrent()) {
SignalFrameCapturedOnStartThread(&sample);
SignalFrameCapturedOnStartThread(sample);
} else {
// This currently happens on with at least VideoCaptureModuleV4L2 and
// possibly other implementations of WebRTC's VideoCaptureModule.
// In order to maintain the threading contract with the upper layers and
// consistency with other capturers such as in Chrome, we need to do a
// thread hop.
start_thread_->Invoke<void>(
// Note that Stop() can cause the async invoke call to be cancelled.
async_invoker_->AsyncInvoke<void>(start_thread_,
// Note that this results in a shallow copying of the frame.
rtc::Bind(&WebRtcVideoCapturer::SignalFrameCapturedOnStartThread,
this, &sample));
this, sample));
}
}
@ -402,18 +396,30 @@ void WebRtcVideoCapturer::OnCaptureDelayChanged(const int32_t id,
}
void WebRtcVideoCapturer::SignalFrameCapturedOnStartThread(
const webrtc::I420VideoFrame* frame) {
const webrtc::I420VideoFrame frame) {
// This can only happen between Start() and Stop().
DCHECK(start_thread_);
DCHECK(start_thread_->IsCurrent());
DCHECK(async_invoker_);
++captured_frames_;
// Log the size and pixel aspect ratio of the first captured frame.
if (1 == captured_frames_) {
LOG(LS_INFO) << "Captured frame size "
<< frame.width() << "x" << frame.height()
<< ". Expected format " << GetCaptureFormat()->ToString();
}
// Signal down stream components on captured frame.
// The CapturedFrame class doesn't support planes. We have to ExtractBuffer
// to one block for it.
size_t length =
webrtc::CalcBufferSize(webrtc::kI420, frame->width(), frame->height());
webrtc::CalcBufferSize(webrtc::kI420, frame.width(), frame.height());
capture_buffer_.resize(length);
// TODO(magjed): Refactor the WebRtcCapturedFrame to avoid memory copy or
// take over ownership of the buffer held by |frame| if that's possible.
webrtc::ExtractBuffer(*frame, length, &capture_buffer_[0]);
WebRtcCapturedFrame webrtc_frame(*frame, &capture_buffer_[0], length);
webrtc::ExtractBuffer(frame, length, &capture_buffer_[0]);
WebRtcCapturedFrame webrtc_frame(frame, &capture_buffer_[0], length);
SignalFrameCaptured(this, &webrtc_frame);
}

8
talk/media/webrtc/webrtcvideocapturer.h
View File

@ -35,8 +35,9 @@
#include "talk/media/base/videocapturer.h"
#include "talk/media/webrtc/webrtcvideoframe.h"
#include "webrtc/base/criticalsection.h"
#include "webrtc/base/asyncinvoker.h"
#include "webrtc/base/messagehandler.h"
#include "webrtc/base/scoped_ptr.h"
#include "webrtc/common_video/libyuv/include/webrtc_libyuv.h"
#include "webrtc/modules/video_capture/include/video_capture.h"
@ -91,7 +92,7 @@ class WebRtcVideoCapturer : public VideoCapturer,
// directly from OnIncomingCapturedFrame.
// TODO(tommi): Remove this workaround when we've updated the WebRTC capturers
// to follow the same contract.
void SignalFrameCapturedOnStartThread(const webrtc::I420VideoFrame* frame);
void SignalFrameCapturedOnStartThread(const webrtc::I420VideoFrame frame);
rtc::scoped_ptr<WebRtcVcmFactoryInterface> factory_;
webrtc::VideoCaptureModule* module_;
@ -99,8 +100,7 @@ class WebRtcVideoCapturer : public VideoCapturer,
std::vector<uint8_t> capture_buffer_;
rtc::Thread* start_thread_; // Set in Start(), unset in Stop();
// Critical section to avoid Stop during an OnIncomingCapturedFrame callback.
rtc::CriticalSection critical_section_stopping_;
rtc::scoped_ptr<rtc::AsyncInvoker> async_invoker_;
};
struct WebRtcCapturedFrame : public CapturedFrame {