scheduler: Add a base directory

components/scheduler/child/task_queue_selector.h

-// Copyright 2015 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 COMPONENTS_SCHEDULER_CHILD_TASK_QUEUE_SELECTOR_H_
-#define COMPONENTS_SCHEDULER_CHILD_TASK_QUEUE_SELECTOR_H_
-
-#include <set>
-
-#include "base/compiler_specific.h"
-#include "base/pending_task.h"
-#include "base/threading/thread_checker.h"
-#include "components/scheduler/child/task_queue_sets.h"
-#include "components/scheduler/scheduler_export.h"
-
-namespace scheduler {
-namespace internal {
-
-// TaskQueueSelector is used by the SchedulerHelper to enable prioritization
-// of particular task queues.
-class SCHEDULER_EXPORT TaskQueueSelector {
- public:
-  TaskQueueSelector();
-  ~TaskQueueSelector();
-
-  // Set the priority of |queue| to |priority|.
-  void SetQueuePriority(internal::TaskQueueImpl* queue,
-                        TaskQueue::QueuePriority priority);
-
-  // Whether |queue| is enabled.
-  bool IsQueueEnabled(const internal::TaskQueueImpl* queue) const;
-
-  // Called to register a queue that can be selected. This function is called
-  // on the main thread.
-  void AddQueue(internal::TaskQueueImpl* queue);
-
-  // The specified work will no longer be considered for selection. This
-  // function is called on the main thread.
-  void RemoveQueue(internal::TaskQueueImpl* queue);
-
-  // Called to choose the work queue from which the next task should be taken
-  // and run. Return true if |out_queue| indicates the queue to service or
-  // false to avoid running any task.
-  //
-  // This function is called on the main thread.
-  bool SelectQueueToService(internal::TaskQueueImpl** out_queue);
-
-  // Serialize the selector state for tracing.
-  void AsValueInto(base::trace_event::TracedValue* state) const;
-
-  class SCHEDULER_EXPORT Observer {
-   public:
-    virtual ~Observer() {}
-
-    // Called when |queue| transitions from disabled to enabled.
-    virtual void OnTaskQueueEnabled(internal::TaskQueueImpl* queue) = 0;
-  };
-
-  // Called once to set the Observer. This function is called
-  // on the main thread. If |observer| is null, then no callbacks will occur.
-  void SetTaskQueueSelectorObserver(Observer* observer);
-
-  TaskQueueSets* GetTaskQueueSets() { return &task_queue_sets_; }
-
-  // Returns true if all the enabled work queues are empty. Returns false
-  // otherwise.
-  bool EnabledWorkQueuesEmpty() const;
-
- private:
-  // Returns the priority which is next after |priority|.
-  static TaskQueue::QueuePriority NextPriority(
-      TaskQueue::QueuePriority priority);
-
-  // Return true if |out_queue| contains the queue with the oldest pending task
-  // from the set of queues of |priority|, or false if all queues of that
-  // priority are empty.
-  bool ChooseOldestWithPriority(TaskQueue::QueuePriority priority,
-                                internal::TaskQueueImpl** out_queue) const;
-
-  // Called whenever the selector chooses a task queue for execution with the
-  // priority |priority|.
-  void DidSelectQueueWithPriority(TaskQueue::QueuePriority priority);
-
-  // Number of high priority tasks which can be run before a normal priority
-  // task should be selected to prevent starvation.
-  // TODO(rmcilroy): Check if this is a good value.
-  static const size_t kMaxStarvationTasks = 5;
-
-  base::ThreadChecker main_thread_checker_;
-  TaskQueueSets task_queue_sets_;
-
-  size_t starvation_count_;
-  Observer* task_queue_selector_observer_;  // NOT OWNED
-  DISALLOW_COPY_AND_ASSIGN(TaskQueueSelector);
-};
-
-}  // namespace internal
-}  // namespace scheduler
-
-#endif  // COMPONENTS_SCHEDULER_CHILD_TASK_QUEUE_SELECTOR_H