TaskScheduler [11] Support ExecutionMode::SINGLE_THREADED.

base/task_scheduler/scheduler_thread_pool.h

Index: base/task_scheduler/scheduler_thread_pool.h
diff --git a/base/task_scheduler/scheduler_thread_pool.h b/base/task_scheduler/scheduler_thread_pool.h
index 6cbf6f47411c2b590c7a9d085775b9146273881e..0c7e650eb1f9b83ecef4c3b4cbb5b64eaa4950dc 100644
--- a/base/task_scheduler/scheduler_thread_pool.h
+++ b/base/task_scheduler/scheduler_thread_pool.h
@@ -8,6 +8,7 @@
 #include <stddef.h>
 
 #include <memory>
+#include <unordered_map>
 #include <vector>
 
 #include "base/base_export.h"
@@ -36,8 +37,8 @@ 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
@@ -46,11 +47,11 @@ class BASE_EXPORT SchedulerThreadPool : public SchedulerThreadPoolInterface {
   ~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,
@@ -78,14 +79,17 @@ class BASE_EXPORT SchedulerThreadPool : public SchedulerThreadPoolInterface {
   // 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;
@@ -103,17 +107,31 @@ class BASE_EXPORT SchedulerThreadPool : public SchedulerThreadPoolInterface {
   // 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