components/scheduler/child/task_queue_selector.h

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef COMPONENTS_SCHEDULER_CHILD_TASK_QUEUE_SELECTOR_H_
   6 #define COMPONENTS_SCHEDULER_CHILD_TASK_QUEUE_SELECTOR_H_
   7
   8 #include <set>
   9
  10 #include "base/compiler_specific.h"
  11 #include "base/pending_task.h"
  12 #include "base/threading/thread_checker.h"
  13 #include "components/scheduler/child/task_queue_sets.h"
  14 #include "components/scheduler/scheduler_export.h"
  15
  16 namespace scheduler {
  17 namespace internal {
  18
  19 // TaskQueueSelector is used by the SchedulerHelper to enable prioritization
  20 // of particular task queues.
  21 class SCHEDULER_EXPORT TaskQueueSelector {
  22  public:
  23   TaskQueueSelector();
  24   ~TaskQueueSelector();
  25
  26   // Set the priority of |queue| to |priority|.
  27   void SetQueuePriority(internal::TaskQueueImpl* queue,
  28                         TaskQueue::QueuePriority priority);
  29
  30   // Whether |queue| is enabled.
  31   bool IsQueueEnabled(const internal::TaskQueueImpl* queue) const;
  32
  33   // Called to register a queue that can be selected. This function is called
  34   // on the main thread.
  35   void AddQueue(internal::TaskQueueImpl* queue);
  36
  37   // The specified work will no longer be considered for selection. This
  38   // function is called on the main thread.
  39   void RemoveQueue(internal::TaskQueueImpl* queue);
  40
  41   // Called to choose the work queue from which the next task should be taken
  42   // and run. Return true if |out_queue| indicates the queue to service or
  43   // false to avoid running any task.
  44   //
  45   // This function is called on the main thread.
  46   bool SelectQueueToService(internal::TaskQueueImpl** out_queue);
  47
  48   // Serialize the selector state for tracing.
  49   void AsValueInto(base::trace_event::TracedValue* state) const;
  50
  51   class SCHEDULER_EXPORT Observer {
  52    public:
  53     virtual ~Observer() {}
  54
  55     // Called when |queue| transitions from disabled to enabled.
  56     virtual void OnTaskQueueEnabled(internal::TaskQueueImpl* queue) = 0;
  57   };
  58
  59   // Called once to set the Observer. This function is called
  60   // on the main thread. If |observer| is null, then no callbacks will occur.
  61   void SetTaskQueueSelectorObserver(Observer* observer);
  62
  63   TaskQueueSets* GetTaskQueueSets() { return &task_queue_sets_; }
  64
  65   // Returns true if all the enabled work queues are empty. Returns false
  66   // otherwise.
  67   bool EnabledWorkQueuesEmpty() const;
  68
  69  private:
  70   // Returns the priority which is next after |priority|.
  71   static TaskQueue::QueuePriority NextPriority(
  72       TaskQueue::QueuePriority priority);
  73
  74   // Return true if |out_queue| contains the queue with the oldest pending task
  75   // from the set of queues of |priority|, or false if all queues of that
  76   // priority are empty.
  77   bool ChooseOldestWithPriority(TaskQueue::QueuePriority priority,
  78                                 internal::TaskQueueImpl** out_queue) const;
  79
  80   // Called whenever the selector chooses a task queue for execution with the
  81   // priority |priority|.
  82   void DidSelectQueueWithPriority(TaskQueue::QueuePriority priority);
  83
  84   // Number of high priority tasks which can be run before a normal priority
  85   // task should be selected to prevent starvation.
  86   // TODO(rmcilroy): Check if this is a good value.
  87   static const size_t kMaxStarvationTasks = 5;
  88
  89   base::ThreadChecker main_thread_checker_;
  90   TaskQueueSets task_queue_sets_;
  91
  92   size_t starvation_count_;
  93   Observer* task_queue_selector_observer_;  // NOT OWNED
  94   DISALLOW_COPY_AND_ASSIGN(TaskQueueSelector);
  95 };
  96
  97 }  // namespace internal
  98 }  // namespace scheduler
  99
 100 #endif  // COMPONENTS_SCHEDULER_CHILD_TASK_QUEUE_SELECTOR_H