TaskScheduler [11] Support ExecutionMode::SINGLE_THREADED.

base/task_scheduler/scheduler_thread_pool.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_THREAD_POOL_H_
 #define BASE_TASK_SCHEDULER_SCHEDULER_THREAD_POOL_H_
 
 #include <stddef.h>
 
 #include <memory>
+#include <unordered_map>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/condition_variable.h"
 #include "base/task_runner.h"
 #include "base/task_scheduler/priority_queue.h"
 #include "base/task_scheduler/scheduler_lock.h"
 #include "base/task_scheduler/scheduler_thread_pool_interface.h"
 #include "base/task_scheduler/scheduler_unique_stack.h"
 #include "base/task_scheduler/scheduler_worker_thread.h"
 #include "base/task_scheduler/sequence.h"
 #include "base/task_scheduler/task.h"
 #include "base/task_scheduler/task_traits.h"
 #include "base/threading/platform_thread.h"
 
 namespace base {
 namespace internal {
 
 class DelayedTaskManager;
 struct SequenceSortKey;
 class TaskTracker;
 
 // A pool of threads that run Tasks. This class is thread-safe.
 class BASE_EXPORT SchedulerThreadPool : public SchedulerThreadPoolInterface {
  public:
-  // Callback invoked when a Sequence isn't empty after a worker thread pops a
-  // Task from it.
+  // Callback invoked when a non-single-threaded Sequence isn't empty after a
+  // worker thread pops a Task from it.
   using EnqueueSequenceCallback = Callback<void(scoped_refptr<Sequence>)>;
 
   // Destroying a SchedulerThreadPool returned by CreateThreadPool() is not
   // allowed in production; it is always leaked. In tests, it can only be
   // destroyed after JoinForTesting() has returned.
   ~SchedulerThreadPool() override;
 
   // Creates a SchedulerThreadPool with up to |max_threads| threads of priority
-  // |thread_priority|. |enqueue_sequence_callback| will be invoked after a
-  // thread of this thread pool tries to run a Task. |task_tracker| is used to
-  // handle shutdown behavior of Tasks. |delayed_task_manager| handles Tasks
-  // posted with a delay. Returns nullptr on failure to create a thread pool
-  // with at least one thread.
+  // |thread_priority|. |enqueue_sequence_callback| will be invoked when a non-
+  // single-threaded Sequence isn't empty after a worker thread pops a Task from
+  // it. |task_tracker| is used to handle shutdown behavior of Tasks.
+  // |delayed_task_manager| handles Tasks posted with a delay. Returns nullptr
+  // on failure to create a thread pool with at least one thread.
   static std::unique_ptr<SchedulerThreadPool> CreateThreadPool(
       ThreadPriority thread_priority,
       size_t max_threads,
       const EnqueueSequenceCallback& enqueue_sequence_callback,
       TaskTracker* task_tracker,
       DelayedTaskManager* delayed_task_manager);
 
   // Returns a TaskRunner whose PostTask invocations will result in scheduling
   // Tasks with |traits| and |execution_mode| in this thread pool.
   scoped_refptr<TaskRunner> CreateTaskRunnerWithTraits(
       const TaskTraits& traits,
       ExecutionMode execution_mode);
 
   // Inserts |sequence| into this thread pool's shared priority queue with
   // |sequence_sort_key|. Must only be called from a worker thread to put
   // |sequence| back into a PriorityQueue after running a Task from it. The
   // worker thread doesn't have to belong to this thread pool.
   void EnqueueSequence(scoped_refptr<Sequence> sequence,
                        const SequenceSortKey& sequence_sort_key);
 
   // Waits until all threads are idle.
   void WaitForAllWorkerThreadsIdleForTesting();
 
   // Joins all threads of this thread pool. Tasks that are already running are
   // allowed to complete their execution. This can only be called once.
   void JoinForTesting();
 
-  // Posts |task| to be executed as part of |sequence|.  Returns true if |task|
-  // is posted.
+  // Posts |task| to be executed as part of |sequence|. |task| will run on
+  // |worker_thread| if specified; otherwise it can run on a any thread owned by

[danakj, 2016/04/27 18:28:43]

"on any"

[fdoray, 2016/04/27 19:17:04]

n/a with latest patch set

+  // this pool. Returns true if |task| is posted.
   bool PostTaskWithSequence(std::unique_ptr<Task> task,
-                            scoped_refptr<Sequence> sequence);
+                            scoped_refptr<Sequence> sequence,
+                            SchedulerWorkerThread* worker_thread);
 
   // SchedulerThreadPoolInterface:
   void PostTaskWithSequenceNow(std::unique_ptr<Task> task,
-                               scoped_refptr<Sequence> sequence) override;
+                               scoped_refptr<Sequence> sequence,
+                               SchedulerWorkerThread* worker_thread) override;
 
  private:
   class SchedulerWorkerThreadDelegateImpl;
 
   SchedulerThreadPool(TaskTracker* task_tracker,
                       DelayedTaskManager* delayed_task_manager);
 
   bool Initialize(ThreadPriority thread_priority,
                   size_t max_threads,
                   const EnqueueSequenceCallback& enqueue_sequence_callback);
 
   // Wakes up the last thread from this thread pool to go idle, if any.
   void WakeUpOneThread();
 
   // Adds |worker_thread| to |idle_worker_threads_stack_|.
   void AddToIdleWorkerThreadsStack(SchedulerWorkerThread* worker_thread);
 
+  // Removes |worker_thread| from |idle_worker_threads_stack_|.
+  void RemoveFromIdleWorkerThreadsStack(SchedulerWorkerThread* worker_thread);
+
   // Pops one idle worker thread from |idle_worker_thread_stack_| and returns
   // it. Returns nullptr if |idle_worker_thread_stack_| is empty.
   SchedulerWorkerThread* PopOneIdleWorkerThread();
 
-  // PriorityQueue from which all threads of this thread pool get work.
-  PriorityQueue shared_priority_queue_;
-
   // All worker threads owned by this thread pool. Only modified during
   // initialization of the thread pool.
   std::vector<std::unique_ptr<SchedulerWorkerThread>> worker_threads_;
 
+  // Synchronizes access to |next_worker_thread_index_|.
+  SchedulerLock next_worker_thread_index_lock_;
+
+  // Index of the worker thread that will be assigned to the next single-
+  // threaded TaskRunner returned by this pool.
+  size_t next_worker_thread_index_ = 0;
+
+  // PriorityQueue from which all threads of this thread pool get work.
+  PriorityQueue shared_priority_queue_;
+
+  // Single-threaded PriorityQueues.
+  std::unordered_map<SchedulerWorkerThread*, std::unique_ptr<PriorityQueue>>
+      single_threaded_priority_queues_;
+
   // Synchronizes access to |idle_worker_threads_stack_| and
   // |idle_worker_threads_stack_cv_for_testing_|. Has |shared_priority_queue_|'s
   // lock as its predecessor so that a thread can be pushed to
   // |idle_worker_threads_stack_| within the scope of a Transaction (more
   // details in GetWork()).
   SchedulerLock idle_worker_threads_stack_lock_;
 
   // Stack of idle worker threads.
   SchedulerUniqueStack<SchedulerWorkerThread*> idle_worker_threads_stack_;
 
   // Signaled when all worker threads become idle.
   std::unique_ptr<ConditionVariable> idle_worker_threads_stack_cv_for_testing_;
 
   // Signaled once JoinForTesting() has returned.
   WaitableEvent join_for_testing_returned_;
 
   TaskTracker* const task_tracker_;
   DelayedTaskManager* const delayed_task_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(SchedulerThreadPool);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_SCHEDULER_THREAD_POOL_H_