Separate the create and start phases in SchedulerSingleThreadTaskRunnerManager.

base/task_scheduler/scheduler_worker_pool_impl.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_SCHEDULER_WORKER_POOL_IMPL_H_
 #define BASE_TASK_SCHEDULER_SCHEDULER_WORKER_POOL_IMPL_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 129 matching lines @@
 
   const std::string name_;
   const ThreadPriority priority_hint_;
   const ReEnqueueSequenceCallback re_enqueue_sequence_callback_;
 
   // PriorityQueue from which all threads of this worker pool get work.
   PriorityQueue shared_priority_queue_;
 
   // All workers owned by this worker pool. Initialized by Start() within the
   // scope of |idle_workers_stack_lock_|. Never modified afterwards (i.e. can be
-  // read without synchronization once |workers_created_.IsSignaled()|).
+  // read without synchronization once |workers_created_.IsSet()|).
   std::vector<scoped_refptr<SchedulerWorker>> workers_;
 
   // Suggested reclaim time for workers. Initialized by Start(). Never modified
   // afterwards (i.e. can be read without synchronization once
-  // |workers_created_.IsSignaled()|).
+  // |workers_created_.IsSet()|).
   TimeDelta suggested_reclaim_time_;
 
   // Synchronizes access to |idle_workers_stack_|,
   // |idle_workers_stack_cv_for_testing_| and |num_wake_ups_before_start_|. Has
   // |shared_priority_queue_|'s lock as its predecessor so that a worker can be
   // pushed to |idle_workers_stack_| within the scope of a Transaction (more
   // details in GetWork()).
   mutable SchedulerLock idle_workers_stack_lock_;
 
   // Stack of idle workers. Initially, all workers are on this stack. A worker
   // is removed from the stack before its WakeUp() function is called and when
   // it receives work from GetWork() (a worker calls GetWork() when its sleep
   // timeout expires, even if its WakeUp() method hasn't been called). A worker
   // is pushed on this stack when it receives nullptr from GetWork().
   SchedulerWorkerStack idle_workers_stack_;
 
   // Signaled when all workers become idle.
   std::unique_ptr<ConditionVariable> idle_workers_stack_cv_for_testing_;
 
-  // Number of wake ups that occurred before Start().
+  // Number of wake ups that occurred before Start(). Never modified after
+  // Start() (i.e. can be read without synchronization once
+  // |workers_created_.IsSet()|).
   int num_wake_ups_before_start_ = 0;
 
   // Signaled once JoinForTesting() has returned.
   WaitableEvent join_for_testing_returned_;
 
   // Indicates to the delegates that workers are not permitted to detach their
   // threads.
   AtomicFlag worker_detachment_disallowed_;
 
 #if DCHECK_IS_ON()
-  // Signaled when all workers have been created.
-  mutable WaitableEvent workers_created_;
+  // Set when all workers have been created.
+  AtomicFlag workers_created_;
 #endif
 
   // TaskScheduler.DetachDuration.[worker pool name] histogram. Intentionally
   // leaked.
   HistogramBase* const detach_duration_histogram_;
 
   // TaskScheduler.NumTasksBeforeDetach.[worker pool name] histogram.
   // Intentionally leaked.
   HistogramBase* const num_tasks_before_detach_histogram_;
 
   // TaskScheduler.NumTasksBetweenWaits.[worker pool name] histogram.
   // Intentionally leaked.
   HistogramBase* const num_tasks_between_waits_histogram_;
 
   TaskTracker* const task_tracker_;
   DelayedTaskManager* const delayed_task_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(SchedulerWorkerPoolImpl);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_SCHEDULER_WORKER_POOL_IMPL_H_