TaskScheduler: Atomic operations in TaskTracker

base/task_scheduler/task_tracker.h

Index: base/task_scheduler/task_tracker.h
diff --git a/base/task_scheduler/task_tracker.h b/base/task_scheduler/task_tracker.h
index 795ae4937058d0a8f24719b9ae0edfa3641e0b5f..b0bce5d50f0277e59ab105b0f2f3cdd08191ce1f 100644
--- a/base/task_scheduler/task_tracker.h
+++ b/base/task_scheduler/task_tracker.h
@@ -54,6 +54,8 @@ class BASE_EXPORT TaskTracker {
   }
 
  private:
+  class State;
+
   // Called before WillPostTask() informs the tracing system that a task has
   // been posted. Updates |num_tasks_blocking_shutdown_| if necessary and
   // returns true if the current shutdown state allows the task to be posted.
@@ -69,16 +71,22 @@ class BASE_EXPORT TaskTracker {
   // necessary.
   void AfterRunTask(TaskShutdownBehavior shutdown_behavior);
 
-  // Synchronizes access to all members.
+  // Called when the number of tasks blocking shutdown becomes zero after
+  // shutdown has started.
+  void OnNumTasksBlockingShutdownIsZero();

[robliao, 2016/05/27 22:16:14]

Alternately
OnBlockingShutdownTasksComplete

[fdoray, 2016/05/30 15:48:05]

Done.

+
+  // Number of tasks blocking shutdown and boolean indicating whether shutdown
+  // has started.
+  const std::unique_ptr<State> state_;
+
+  // Synchronizes access to all members below.
   mutable SchedulerLock lock_;
 
-  // Condition variable signaled when |num_tasks_blocking_shutdown_| reaches
-  // zero while shutdown is in progress. Null if shutdown isn't in progress.
+  // Condition variable signaled when the number of tasks blocking shutdown
+  // reaches zero while shutdown is in progress. Null if shutdown isn't in
+  // progress.
   std::unique_ptr<ConditionVariable> shutdown_cv_;
 
-  // Number of tasks blocking shutdown.
-  size_t num_tasks_blocking_shutdown_ = 0;
-
   // Number of BLOCK_SHUTDOWN tasks posted during shutdown.
   HistogramBase::Sample num_block_shutdown_tasks_posted_during_shutdown_ = 0;