scheduler: Move the Blink scheduler into Blink

components/scheduler/base/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_BASE_TASK_QUEUE_SELECTOR_H_
-#define COMPONENTS_SCHEDULER_BASE_TASK_QUEUE_SELECTOR_H_
-
-#include <stddef.h>
-
-#include <set>
-
-#include "base/compiler_specific.h"
-#include "base/macros.h"
-#include "base/pending_task.h"
-#include "base/threading/thread_checker.h"
-#include "components/scheduler/base/work_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();
-
-  // 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);
-
-  // Make |queue| eligible for selection. This function is called on the main
-  // thread. Must only be called if |queue| is disabled.
-  void EnableQueue(internal::TaskQueueImpl* queue);
-
-  // Disable selection from |queue|. If task blocking is enabled for the queue,
-  // Observer::OnTriedToSelectBlockedWorkQueue will be emitted if the
-  // SelectWorkQueueToService tries to select this disabled queue for execution.
-  // Must only be called if |queue| is enabled.
-  void DisableQueue(internal::TaskQueueImpl* queue);
-
-  // Called get or set the priority of |queue|.
-  void SetQueuePriority(internal::TaskQueueImpl* queue,
-                        TaskQueue::QueuePriority priority);
-
-  // Called to choose the work queue from which the next task should be taken
-  // and run. Return true if |out_work_queue| indicates the queue to service or
-  // false to avoid running any task.
-  //
-  // This function is called on the main thread.
-  bool SelectWorkQueueToService(WorkQueue** out_work_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 when the selector tried to select a task from a disabled work
-    // queue. See TaskQueue::Spec::SetShouldReportWhenExecutionBlocked. A single
-    // call to SelectWorkQueueToService will only result in up to one
-    // blocking notification even if multiple disabled queues could have been
-    // selected.
-    virtual void OnTriedToSelectBlockedWorkQueue(
-        internal::WorkQueue* work_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);
-
-  // Returns true if all the enabled work queues are empty. Returns false
-  // otherwise.
-  bool EnabledWorkQueuesEmpty() const;
-
- protected:
-  class SCHEDULER_EXPORT PrioritizingSelector {
-   public:
-    PrioritizingSelector(TaskQueueSelector* task_queue_selector,
-                         const char* name);
-
-    void ChangeSetIndex(internal::TaskQueueImpl* queue,
-                        TaskQueue::QueuePriority priority);
-    void AddQueue(internal::TaskQueueImpl* queue,
-                  TaskQueue::QueuePriority priority);
-    void RemoveQueue(internal::TaskQueueImpl* queue);
-
-    bool SelectWorkQueueToService(TaskQueue::QueuePriority max_priority,
-                                  WorkQueue** out_work_queue,
-                                  bool* out_chose_delayed_over_immediate);
-
-    WorkQueueSets* delayed_work_queue_sets() {
-      return &delayed_work_queue_sets_;
-    }
-    WorkQueueSets* immediate_work_queue_sets() {
-      return &immediate_work_queue_sets_;
-    }
-
-    const WorkQueueSets* delayed_work_queue_sets() const {
-      return &delayed_work_queue_sets_;
-    }
-    const WorkQueueSets* immediate_work_queue_sets() const {
-      return &immediate_work_queue_sets_;
-    }
-
-    bool ChooseOldestWithPriority(TaskQueue::QueuePriority priority,
-                                  bool* out_chose_delayed_over_immediate,
-                                  WorkQueue** out_work_queue) const;
-
-#if DCHECK_IS_ON() || !defined(NDEBUG)
-    bool CheckContainsQueueForTest(const internal::TaskQueueImpl* queue) const;
-#endif
-
-   private:
-    bool ChooseOldestImmediateTaskWithPriority(
-        TaskQueue::QueuePriority priority,
-        WorkQueue** out_work_queue) const;
-
-    bool ChooseOldestDelayedTaskWithPriority(TaskQueue::QueuePriority priority,
-                                             WorkQueue** out_work_queue) const;
-
-    // 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. In addition |out_chose_delayed_over_immediate| is set
-    // to true iff we chose a delayed work queue in favour of an immediate work
-    // queue.
-    bool ChooseOldestImmediateOrDelayedTaskWithPriority(
-        TaskQueue::QueuePriority priority,
-        bool* out_chose_delayed_over_immediate,
-        WorkQueue** out_work_queue) const;
-
-    const TaskQueueSelector* task_queue_selector_;
-    WorkQueueSets delayed_work_queue_sets_;
-    WorkQueueSets immediate_work_queue_sets_;
-
-    DISALLOW_COPY_AND_ASSIGN(PrioritizingSelector);
-  };
-
-  // 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. In addition |out_chose_delayed_over_immediate| is set
-  // to true iff we chose a delayed work queue in favour of an immediate work
-  // queue.  This method will force select an immediate task if those are being
-  // starved by delayed tasks.
-  void SetImmediateStarvationCountForTest(size_t immediate_starvation_count);
-
-  PrioritizingSelector* enabled_selector_for_test() {
-    return &enabled_selector_;
-  }
-
- private:
-  // Returns the priority which is next after |priority|.
-  static TaskQueue::QueuePriority NextPriority(
-      TaskQueue::QueuePriority priority);
-
-  bool SelectWorkQueueToServiceInternal(WorkQueue** out_work_queue);
-
-  // Called whenever the selector chooses a task queue for execution with the
-  // priority |priority|.
-  void DidSelectQueueWithPriority(TaskQueue::QueuePriority priority,
-                                  bool chose_delayed_over_immediate);
-
-  // No enabled queue could be selected, check if we could have chosen a
-  // disabled (blocked) work queue instead.
-  void TrySelectingBlockedQueue();
-
-  // Check if we could have chosen a disabled (blocked) work queue instead.
-  // |chosen_enabled_queue| is the enabled queue that got chosen.
-  void TrySelectingBlockedQueueOverEnabledQueue(
-      const WorkQueue& chosen_enabled_queue);
-
-  // 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 kMaxHighPriorityStarvationTasks = 5;
-
-  // Maximum number of delayed tasks tasks which can be run while there's a
-  // waiting non-delayed task.
-  static const size_t kMaxDelayedStarvationTasks = 3;
-
- private:
-  base::ThreadChecker main_thread_checker_;
-
-  PrioritizingSelector enabled_selector_;
-  PrioritizingSelector blocked_selector_;
-  size_t immediate_starvation_count_;
-  size_t high_priority_starvation_count_;
-  size_t num_blocked_queues_to_report_;
-
-  Observer* task_queue_selector_observer_;  // NOT OWNED
-  DISALLOW_COPY_AND_ASSIGN(TaskQueueSelector);
-};
-
-}  // namespace internal
-}  // namespace scheduler
-
-#endif  // COMPONENTS_SCHEDULER_BASE_TASK_QUEUE_SELECTOR_H