content: Add task queue manager

content/renderer/scheduler/task_queue_manager.h

+// Copyright 2014 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 CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_
+#define CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_
+
+#include "base/atomic_sequence_num.h"
+#include "base/debug/task_annotator.h"
+#include "base/macros.h"
+#include "base/memory/scoped_vector.h"
+#include "base/memory/weak_ptr.h"
+#include "base/pending_task.h"
+#include "base/single_thread_task_runner.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/thread_checker.h"
+#include "content/common/content_export.h"
+
+namespace content {
+namespace internal {
+class TaskRunner;
+struct TaskQueue;
+}
+class TaskQueueSelector;
+
+// The task queue manager provides N task queues and a selector interface for
+// choosing which task queue to service next. Each task queue consists of two
+// sub queues:
+//
+// 1. Incoming task queue. Tasks that are posted get immediately appended here.
+//    When a task is appended into an empty incoming queue, the task manager
+//    work function (DoWork) is scheduled to run on the main task runner.
+//
+// 2. Work queue. If a work queue is empty when DoWork() is entered, tasks from
+//    the incoming task queue (if any) are moved here. The work queues are
+//    registered with the selector as input to the scheduling decision.
+//
+class CONTENT_EXPORT TaskQueueManager {
+ public:
+  // Create a task queue manager with |task_queue_count| task queues.
+  // |main_task_runner| identifies the thread on which where the tasks are
+  // eventually run. |selector| is used to choose which task queue to service.
+  // It should outlive this class.
+  TaskQueueManager(size_t task_queue_count,
+                   scoped_refptr<base::SingleThreadTaskRunner> main_task_runner,
+                   TaskQueueSelector* selector);
+  ~TaskQueueManager();
+
+  // Returns the task runner which targets the queue selected by |queue_index|.
+  scoped_refptr<base::SingleThreadTaskRunner> TaskRunnerForQueue(
+      size_t queue_index) const;
+
+  // If |auto_pump| is false, tasks posted to the given incoming queue will not
+  // be automatically scheduled for execution or transferred to the work queue.
+  // Instead, the selector should call PumpQueue() when necessary to bring in
+  // new tasks for execution.
+  void SetAutoPump(size_t queue_index, bool auto_pump);
+
+  // Reloads new tasks from the incoming queue for |queue_index| into the work
+  // queue, regardless of whether the work queue is empty or not. After this,
+  // this function ensures that the tasks in the work queue, if any, are
+  // scheduled for execution.
+  //
+  // This function only needs to be called if automatic pumping is disabled
+  // for |queue_index|. See |SetQueueAutoPump|. By default automatic pumping is
+  // enabled for all queues.
+  void PumpQueue(size_t queue_index);
+
+  // Returns true if there no tasks in either the work or incoming task queue
+  // identified by |queue_index|. Note that this function involves taking a
+  // lock, so calling it has some overhead.
+  bool IsQueueEmpty(size_t queue_index);
+
+ private:
+  friend class internal::TaskRunner;
+
+  // Adds a task at the end of the incoming task queue for |queue_index| and
+  // schedules a call to DoWork() if the incoming queue was empty and automatic
+  // pumping is enabled. Can be called on an arbitrary thread.
+  void EnqueueTask(size_t queue_index, const base::PendingTask& pending_task);
+
+  // Post a task to call DoWork() on the main task runner.
+  void PostDoWorkOnMainRunner();
+
+  // Use the selector to choose a pending task and run it.
+  void DoWork();
+
+  // Reloads any empty work queues which have automatic pumping enabled.
+  // Returns true if any work queue has tasks after doing this.
+  bool UpdateWorkQueues();
+
+  // Runs a single task from the work queue designated by |queue_index|. The
+  // queue must not be empty.
+  void RunTaskFromWorkQueue(size_t queue_index);
+
+  bool RunsTasksOnCurrentThread() const;
+  bool PostDelayedTask(size_t queue_index,
+                       const tracked_objects::Location& from_here,
+                       const base::Closure& task,
+                       base::TimeDelta delay);
+  bool PostNonNestableDelayedTask(size_t queue_index,
+                                  const tracked_objects::Location& from_here,
+                                  const base::Closure& task,
+                                  base::TimeDelta delay);
+  internal::TaskQueue* Queue(size_t queue_index) const;

[jar (doing other things), 2014/10/29 21:14:07]

I found this declaration, and its use, but didn't see its implementation.  Where
is it?  (I doesn't even show in the unified diff for the patch).

[Sami, 2014/10/30 10:43:00]

It's at line 113 of task_queue_manager.cc in this patch set.

+  void PumpQueueLocked(internal::TaskQueue* queue);
+
+  ScopedVector<internal::TaskQueue> queues_;
+  base::AtomicSequenceNumber task_sequence_num_;
+  base::debug::TaskAnnotator task_annotator_;
+
+  base::ThreadChecker main_thread_checker_;
+  scoped_refptr<base::SingleThreadTaskRunner> main_task_runner_;
+  TaskQueueSelector* selector_;
+
+  base::WeakPtrFactory<TaskQueueManager> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(TaskQueueManager);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_