TaskScheduler [11] Support ExecutionMode::SINGLE_THREADED.

base/task_scheduler/scheduler_worker_thread.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_THREAD_H_
 #define BASE_TASK_SCHEDULER_SCHEDULER_WORKER_THREAD_H_
 
 #include <memory>
 
 #include "base/base_export.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/single_thread_task_runner.h"
 #include "base/synchronization/waitable_event.h"
+#include "base/task_scheduler/priority_queue.h"
 #include "base/task_scheduler/scheduler_lock.h"
+#include "base/task_scheduler/scheduler_task_executor.h"
 #include "base/task_scheduler/sequence.h"
 #include "base/threading/platform_thread.h"
 
 namespace base {
 namespace internal {
 
+class DelayedTaskManager;
 class TaskTracker;
 
 // A thread that runs Tasks from Sequences returned by a delegate.
 //
 // A SchedulerWorkerThread starts out sleeping. It is woken up by a call to
 // WakeUp(). After a wake-up, a SchedulerWorkerThread runs Tasks from Sequences
 // returned by the GetWork() method of its delegate as long as it doesn't return
 // nullptr. It also periodically checks with its TaskTracker whether shutdown
 // has completed and exits when it has.
 //
 // This class is thread-safe.
-class BASE_EXPORT SchedulerWorkerThread : public PlatformThread::Delegate {
+class BASE_EXPORT SchedulerWorkerThread : public PlatformThread::Delegate,
+                                          public SchedulerTaskExecutor {
  public:
   // Delegate interface for SchedulerWorkerThread. The methods are always called
   // from the thread managed by the SchedulerWorkerThread instance.
   class Delegate {
    public:
     virtual ~Delegate() = default;
 
     // Called when the main function of the SchedulerWorkerThread enters.
     virtual void OnMainEntry() = 0;
 
     // Called by |worker_thread| to get a Sequence from which to run a Task.
+    // Sets |is_single_threaded_sequence| to true if the returned Sequence comes
+    // from |single_threaded_priority_queue|.
     virtual scoped_refptr<Sequence> GetWork(
-        SchedulerWorkerThread* worker_thread) = 0;
+        SchedulerWorkerThread* worker_thread,
+        PriorityQueue* single_threaded_priority_queue,
+        bool* is_single_threaded_sequence) = 0;

[gab, 2016/04/18 18:04:02]

I don't think the Delegate needs to know that this PQ is "single_threaded".

How about "PQ* alternate_priority_queue" and "bool
*alternate_priority_queue_used" with comment above changed to:

// |alternate_priority_queue| will be considered as an alternate source of work.
|alternate_priority_queue_used| is set to true if the returned Sequence was
selected from it.

[fdoray, 2016/04/18 19:04:50]

Done.

 
-    // Called when |sequence| isn't empty after the SchedulerWorkerThread pops a
-    // Task from it. |sequence| is the last Sequence returned by GetWork().
+    // Called when a non-single-threaded Sequence returned by GetWork() isn't

[gab, 2016/04/18 18:04:02]

Idem: re-word without enforcing "single-threaded"

[fdoray, 2016/04/18 19:04:50]

Done.

+    // empty after the SchedulerWorkerThread pops a Task from it.
     virtual void EnqueueSequence(scoped_refptr<Sequence> sequence) = 0;
   };
 
   // Creates a SchedulerWorkerThread with priority |thread_priority| that runs
-  // Tasks from Sequences returned by |delegate|. |task_tracker| is used to
-  // handle shutdown behavior of Tasks. Returns nullptr if creating the
-  // underlying platform thread fails.
+  // Tasks from Sequences returned by |delegate|. |task_tracker| handles
+  // shutdown behavior of Tasks. |delayed_task_manager| handles Tasks posted
+  // with a delay. |predecessor_priority_queue| is a PriorityQueue for which a
+  // thread is allowed to have an active Transaction when its creates a

[gab, 2016/04/18 18:04:02]

s/its creates/it creates/

but also "it" doesn't create the Transaction in practice, GetWork() does, so
it's more "|predecessor_priority_queue| is a PriorityQueue whose transactions
may overlap this thread's PriorityQueue's transactions"

[fdoray, 2016/04/18 19:04:50]

Done.

+  // Transaction for this worker thread's single-threaded PriorityQueue. Returns
+  // nullptr if creating the underlying platform thread fails.
   static std::unique_ptr<SchedulerWorkerThread> CreateSchedulerWorkerThread(
       ThreadPriority thread_priority,
       Delegate* delegate,
-      TaskTracker* task_tracker);
+      TaskTracker* task_tracker,
+      DelayedTaskManager* delayed_task_manager,
+      const PriorityQueue* predecessor_priority_queue);
 
   // Destroying a SchedulerWorkerThread in production is not allowed; it is
   // always leaked. In tests, it can only be destroyed after JoinForTesting()
   // has returned.
   ~SchedulerWorkerThread() override;
 
+  // Returns a SingleThreadTaskRunner whose PostTask invocations will result in
+  // scheduling Tasks with |traits| on this worker thread.
+  scoped_refptr<SingleThreadTaskRunner> CreateTaskRunnerWithTraits(
+      const TaskTraits& traits);
+
   // Wakes up this SchedulerWorkerThread if it wasn't already awake. After this
   // is called, this SchedulerWorkerThread will run Tasks from Sequences
   // returned by the GetWork() method of its delegate until it returns nullptr.
   void WakeUp();
 
   // Joins this SchedulerWorkerThread. If a Task is already running, it will be
   // allowed to complete its execution. This can only be called once.
   void JoinForTesting();
 
+  // SchedulerTaskExecutor:
+  void PostTaskWithSequence(std::unique_ptr<Task> task,
+                            scoped_refptr<Sequence> sequence) override;
+
  private:
   SchedulerWorkerThread(ThreadPriority thread_priority,
                         Delegate* delegate,
-                        TaskTracker* task_tracker);
+                        TaskTracker* task_tracker,
+                        DelayedTaskManager* delayed_task_manager,
+                        const PriorityQueue* predecessor_priority_queue);
 
   // PlatformThread::Delegate:
   void ThreadMain() override;
 
   bool ShouldExitForTesting() const;
 
   // Platform thread managed by this SchedulerWorkerThread.
   PlatformThreadHandle thread_handle_;
 
   // Event signaled to wake up this SchedulerWorkerThread.
   WaitableEvent wake_up_event_;
 
+  // PriorityQueue for Tasks/Sequences posted through SingleThreadTaskRunners
+  // returned by CreateTaskRunnerWithTraits.
+  PriorityQueue single_threaded_priority_queue_;
+
   Delegate* const delegate_;
   TaskTracker* const task_tracker_;
+  DelayedTaskManager* const delayed_task_manager_;
 
   // Synchronizes access to |should_exit_for_testing_|.
   mutable SchedulerLock should_exit_for_testing_lock_;
 
   // True once JoinForTesting() has been called.
   bool should_exit_for_testing_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(SchedulerWorkerThread);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_SCHEDULER_WORKER_THREAD_H_