Avoid threading races on TraceSamplingThread's members.

base/debug/trace_event_impl.cc

Index: base/debug/trace_event_impl.cc
diff --git a/base/debug/trace_event_impl.cc b/base/debug/trace_event_impl.cc
index 9ee9fc802be105ea979576ec239c6275c467a7fc..71b5fbf6a243268120dfde53272cc2639eacb023 100644
--- a/base/debug/trace_event_impl.cc
+++ b/base/debug/trace_event_impl.cc
@@ -716,6 +716,7 @@ class TraceSamplingThread : public PlatformThread::Delegate {
                                      const char** category,
                                      const char** name);
   std::vector<TraceBucketData> sample_buckets_;
+  Lock lock_;
   bool thread_running_;
   scoped_ptr<CancellationFlag> cancellation_flag_;
   scoped_ptr<WaitableEvent> waitable_event_for_testing_;
@@ -724,6 +725,7 @@ class TraceSamplingThread : public PlatformThread::Delegate {
 
 TraceSamplingThread::TraceSamplingThread()
     : thread_running_(false) {
+  AutoLock lock(lock_);
   cancellation_flag_.reset(new CancellationFlag);
 }
 
@@ -734,10 +736,14 @@ void TraceSamplingThread::ThreadMain() {
   PlatformThread::SetName("Sampling Thread");
   thread_running_ = true;
   const int kSamplingFrequencyMicroseconds = 1000;
-  while (!cancellation_flag_->IsSet()) {
+  while (true) {
     PlatformThread::Sleep(
         TimeDelta::FromMicroseconds(kSamplingFrequencyMicroseconds));
     GetSamples();
+
+    AutoLock lock(lock_);
+    if (cancellation_flag_->IsSet())
+        break;

[Alexander Potapenko, 2013/10/09 06:55:32]

Nit: please fix the indentation

[haraken, 2013/10/09 07:05:07]

Done.

     if (waitable_event_for_testing_.get())
       waitable_event_for_testing_->Signal();
   }
@@ -784,11 +790,13 @@ void TraceSamplingThread::ExtractCategoryAndName(const char* combined,
 }
 
 void TraceSamplingThread::Stop() {
+  AutoLock lock(lock_);
   cancellation_flag_->Set();
 }
 
 void TraceSamplingThread::InstallWaitableEventForSamplingTesting(
     WaitableEvent* waitable_event) {
+  AutoLock lock(lock_);
   waitable_event_for_testing_.reset(waitable_event);
 }