TaskScheduler: Atomic operations in TaskTracker

base/task_scheduler/task_tracker.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_TASK_SCHEDULER_TASK_TRACKER_H_
 #define BASE_TASK_SCHEDULER_TASK_TRACKER_H_
 
 #include <memory>
 
 #include "base/base_export.h"
@@ skipping 36 matching lines @@
   // Returns true while shutdown is in progress (i.e. Shutdown() has been called
   // but hasn't returned).
   bool IsShuttingDownForTesting() const;
 
   bool shutdown_completed() const {
     AutoSchedulerLock auto_lock(lock_);
     return shutdown_completed_;
   }
 
  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.
   bool BeforePostTask(TaskShutdownBehavior shutdown_behavior);
 
   // Called before a task with |shutdown_behavior| is run by RunTask(). Updates
   // |num_tasks_blocking_shutdown_| if necessary and returns true if the current
   // shutdown state allows the task to be run.
   bool BeforeRunTask(TaskShutdownBehavior shutdown_behavior);
 
   // Called after a task with |shutdown_behavior| has been run by RunTask().
   // Updates |num_tasks_blocking_shutdown_| and signals |shutdown_cv_| if
   // 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;
 
   // True once Shutdown() has returned. No new task can be scheduled after this.
   bool shutdown_completed_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(TaskTracker);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_TASK_TRACKER_H_