content: Add task queue manager

base/task/task_queue_manager.h

Index: base/task/task_queue_manager.h
diff --git a/base/task/task_queue_manager.h b/base/task/task_queue_manager.h
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+// 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 BASE_TASK_TASK_QUEUE_MANAGER_H_
+#define BASE_TASK_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"
+
+namespace base {
+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 BASE_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<SingleThreadTaskRunner> main_task_runner,
+                   TaskQueueSelector* selector);
+  ~TaskQueueManager();
+
+  // Returns the task runner which targets the queue selected by |queue_index|.
+  scoped_refptr<SingleThreadTaskRunner> TaskRunnerForQueue(size_t queue_index);
+
+  // 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|. 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 are any 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 PollQueue(size_t queue_index);
+
+ private:
+  class TaskRunner : public SingleThreadTaskRunner {
+   public:
+    TaskRunner(TaskQueueManager* task_queue_manager, size_t queue_index);
+
+    // SingleThreadTaskRunner implementation.
+    virtual bool RunsTasksOnCurrentThread() const override;
+    virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
+                                 const Closure& task,
+                                 TimeDelta delay) override;
+    virtual bool PostNonNestableDelayedTask(
+        const tracked_objects::Location& from_here,
+        const Closure& task,
+        TimeDelta delay) override;
+
+   private:
+    virtual ~TaskRunner();
+
+    TaskQueueManager* task_queue_manager_;
+    const size_t queue_index_;
+  };
+  friend class 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 PendingTask& pending_task);
+
+  // Post a task to call DoWork() on the main task runner.
+  void ScheduleWork();
+
+  // Use the selector to choose a pending task and run it.
+  void DoWork();
+
+  // Reloads the work queue identified by |queue_index| and returns true if
+  // it ended up having tasks. The work queue must be empty when this function
+  // is called.
+  bool ReloadWorkQueue(size_t queue_index);
+
+  // Returns true if any work queue is non-empty.
+  bool ReloadWorkQueues();
+
+  // 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 Closure& task,
+                       TimeDelta delay);
+  bool PostNonNestableDelayedTask(size_t queue_index,
+                                  const tracked_objects::Location& from_here,
+                                  const Closure& task,
+                                  TimeDelta delay);
+  struct InternalTaskQueue {
+    InternalTaskQueue();
+    ~InternalTaskQueue();
+
+    scoped_refptr<TaskRunner> task_runner;
+
+    Lock incoming_queue_lock;
+    TaskQueue incoming_queue;
+
+    bool auto_pump;
+    TaskQueue work_queue;
+  };
+
+  InternalTaskQueue* Queue(size_t queue_index) const;
+  void PumpQueueLocked(InternalTaskQueue* queue);
+
+  ScopedVector<InternalTaskQueue> queues_;
+  AtomicSequenceNumber task_sequence_num_;
+  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  // BASE_TASK_TASK_QUEUE_MANAGER_H_