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Implement store as an explicit atomic operation.

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Using explicit atomic operations permits TSan to understand them and
prevents false positives.

Downgrading the atomic Load to acquire semantics. This reduces the
number of memory barriers inserted from two down to one at most.

Also renaming Load/Store to AcquireLoad/ReleaseStore.

BUG=chromium:512382
R=dvyukov@chromium.org, glider@chromium.org
TBR=tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1246073002

Cr-Commit-Position: refs/heads/master@{#9613}
This commit is contained in:
pbos
2015-07-22 08:34:59 -07:00
committed by Commit bot
parent 085856cd35
commit 235c35f292
4 changed files with 13 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
webrtc/base/atomicops.h
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@ -31,10 +31,10 @@ class AtomicOps {
static int Decrement(volatile int* i) {
return ::InterlockedDecrement(reinterpret_cast<volatile LONG*>(i));
}
static int Load(volatile const int* i) {
static int AcquireLoad(volatile const int* i) {
return *i;
}
static void Store(volatile int* i, int value) {
static void ReleaseStore(volatile int* i, int value) {
*i = value;
}
static int CompareAndSwap(volatile int* i, int old_value, int new_value) {
@ -49,13 +49,11 @@ class AtomicOps {
static int Decrement(volatile int* i) {
return __sync_sub_and_fetch(i, 1);
}
static int Load(volatile const int* i) {
// Adding 0 is a no-op, so const_cast is fine.
return __sync_add_and_fetch(const_cast<volatile int*>(i), 0);
static int AcquireLoad(volatile const int* i) {
return __atomic_load_n(i, __ATOMIC_ACQUIRE);
}
static void Store(volatile int* i, int value) {
__sync_synchronize();
*i = value;
static void ReleaseStore(volatile int* i, int value) {
__atomic_store_n(i, value, __ATOMIC_RELEASE);
}
static int CompareAndSwap(volatile int* i, int old_value, int new_value) {
return __sync_val_compare_and_swap(i, old_value, new_value);

6
webrtc/base/refcount.h
View File

@ -96,11 +96,11 @@ class RefCountedObject : public T {
}
virtual int AddRef() {
return rtc::AtomicOps::Increment(&ref_count_);
return AtomicOps::Increment(&ref_count_);
}
virtual int Release() {
int count = rtc::AtomicOps::Decrement(&ref_count_);
int count = AtomicOps::Decrement(&ref_count_);
if (!count) {
delete this;
}
@ -114,7 +114,7 @@ class RefCountedObject : public T {
// barrier needed for the owning thread to act on the object, knowing that it
// has exclusive access to the object.
virtual bool HasOneRef() const {
return rtc::AtomicOps::Load(&ref_count_) == 1;
return AtomicOps::AcquireLoad(&ref_count_) == 1;
}
protected:

4
webrtc/system_wrappers/source/trace_impl.cc
View File

@ -542,12 +542,12 @@ int32_t Trace::TraceFile(char file_name[FileWrapper::kMaxFileNameSize]) {
// static
void Trace::set_level_filter(int filter) {
rtc::AtomicOps::Store(&level_filter_, filter);
rtc::AtomicOps::ReleaseStore(&level_filter_, filter);
}
// static
int Trace::level_filter() {
return rtc::AtomicOps::Load(&level_filter_);
return rtc::AtomicOps::AcquireLoad(&level_filter_);
}
// static

4
webrtc/video/video_capture_input.cc
View File

@ -63,7 +63,7 @@ VideoCaptureInput::~VideoCaptureInput() {
module_process_thread_->DeRegisterModule(overuse_detector_.get());
// Stop the thread.
rtc::AtomicOps::Increment(&stop_);
rtc::AtomicOps::ReleaseStore(&stop_, 1);
capture_event_.Set();
// Stop the camera input.
@ -128,7 +128,7 @@ bool VideoCaptureInput::CaptureProcess() {
static const int kThreadWaitTimeMs = 100;
int64_t capture_time = -1;
if (capture_event_.Wait(kThreadWaitTimeMs) == kEventSignaled) {
if (rtc::AtomicOps::Load(&stop_))
if (rtc::AtomicOps::AcquireLoad(&stop_))
return false;
int64_t encode_start_time = -1;