Revert of 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