TaskScheduler: Always remove SchedulerWorker from idle stack on wake up.

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 96 matching lines @@
                               io_restriction,
                           const TimeDelta& suggested_reclaim_time,
                           TaskTracker* task_tracker,
                           DelayedTaskManager* delayed_task_manager);
 
   bool Initialize(
       ThreadPriority priority_hint,
       size_t max_threads,
       const ReEnqueueSequenceCallback& re_enqueue_sequence_callback);
 
+  // Wakes up |worker|.
+  void WakeUpWorker(SchedulerWorker* worker);
+
   // Wakes up the last worker from this worker pool to go idle, if any.
   void WakeUpOneWorker();
 
   // Adds |worker| to |idle_workers_stack_|.
   void AddToIdleWorkersStack(SchedulerWorker* worker);
 
   // Peeks from |idle_workers_stack_|.
   const SchedulerWorker* PeekAtIdleWorkersStack() const;
 
   // Removes |worker| from |idle_workers_stack_|.
@@ skipping 25 matching lines @@
   // Suggested reclaim time for workers.
   const TimeDelta suggested_reclaim_time_;
 
   // Synchronizes access to |idle_workers_stack_| and
   // |idle_workers_stack_cv_for_testing_|. 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.
+  // 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_;
 
   // Signaled once JoinForTesting() has returned.
   WaitableEvent join_for_testing_returned_;
 
   // Indicates to the delegates that workers are not permitted to detach their
   // threads.
@@ skipping 23 matching lines @@
   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_