[scheduler] Implement time-based cpu throttling.

third_party/WebKit/Source/platform/scheduler/renderer/throttling_helper.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 THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_RENDERER_THROTTLING_HELPER_H_
-#define THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_RENDERER_THROTTLING_HELPER_H_
-
-#include <set>
-
-#include "base/macros.h"
-#include "platform/scheduler/base/cancelable_closure_holder.h"
-#include "platform/scheduler/base/time_domain.h"
-#include "public/platform/WebViewScheduler.h"
-
-namespace blink {
-namespace scheduler {
-
-class RendererSchedulerImpl;
-class ThrottledTimeDomain;
-class WebFrameSchedulerImpl;
-
-// The job of the ThrottlingHelper is to run tasks posted on throttled queues at
-// most once per second. This is done by disabling throttled queues and running
-// a special "heart beat" function |PumpThrottledTasks| which when run
-// temporarily enables throttled queues and inserts a fence to ensure tasks
-// posted from a throttled task run next time the queue is pumped.
-//
-// Of course the ThrottlingHelper isn't the only sub-system that wants to enable
-// or disable queues. E.g. RendererSchedulerImpl also does this for policy
-// reasons.  To prevent the systems from fighting, clients of ThrottlingHelper
-// must use SetQueueEnabled rather than calling the function directly on the
-// queue.
-//
-// There may be more than one system that wishes to throttle a queue (e.g.
-// renderer suspension vs tab level suspension) so the ThrottlingHelper keeps a
-// count of the number of systems that wish a queue to be throttled.
-// See IncreaseThrottleRefCount & DecreaseThrottleRefCount.
-class BLINK_PLATFORM_EXPORT ThrottlingHelper : public TimeDomain::Observer {
- public:
-  ThrottlingHelper(RendererSchedulerImpl* renderer_scheduler,
-                   const char* tracing_category);
-
-  ~ThrottlingHelper() override;
-
-  // TimeDomain::Observer implementation:
-  void OnTimeDomainHasImmediateWork() override;
-  void OnTimeDomainHasDelayedWork() override;
-
-  // The purpose of this method is to make sure throttling doesn't conflict with
-  // enabling/disabling the queue for policy reasons.
-  // If |task_queue| is throttled then the ThrottlingHelper remembers the
-  // |enabled| setting.  In addition if |enabled| is false then the queue is
-  // immediatly disabled.  Otherwise if |task_queue| not throttled then
-  // TaskQueue::SetEnabled(enabled) is called.
-  void SetQueueEnabled(TaskQueue* task_queue, bool enabled);
-
-  // Increments the throttled refcount and causes |task_queue| to be throttled
-  // if its not already throttled.
-  void IncreaseThrottleRefCount(TaskQueue* task_queue);
-
-  // If the refcouint is non-zero it's decremented.  If the throttled refcount
-  // becomes zero then |task_queue| is unthrottled.  If the refcount was already
-  // zero this function does nothing.
-  void DecreaseThrottleRefCount(TaskQueue* task_queue);
-
-  // Removes |task_queue| from |throttled_queues_|.
-  void UnregisterTaskQueue(TaskQueue* task_queue);
-
-  // Returns true if the |task_queue| is throttled.
-  bool IsThrottled(TaskQueue* task_queue) const;
-
-  // Tells the ThrottlingHelper we're using virtual time, which disables all
-  // throttling.
-  void EnableVirtualTime();
-
-  const ThrottledTimeDomain* time_domain() const { return time_domain_.get(); }
-
-  static base::TimeTicks ThrottledRunTime(base::TimeTicks unthrottled_runtime);
-
-  const scoped_refptr<TaskQueue>& task_runner() const { return task_runner_; }
-
- private:
-  struct Metadata {
-    Metadata() : throttling_ref_count(0), enabled(false) {}
-
-    Metadata(size_t ref_count, bool is_enabled)
-        : throttling_ref_count(ref_count), enabled(is_enabled) {}
-
-    size_t throttling_ref_count;
-    bool enabled;
-  };
-  using TaskQueueMap = std::map<TaskQueue*, Metadata>;
-
-  void PumpThrottledTasks();
-
-  // Note |unthrottled_runtime| might be in the past. When this happens we
-  // compute the delay to the next runtime based on now rather than
-  // unthrottled_runtime.
-  void MaybeSchedulePumpThrottledTasksLocked(
-      const tracked_objects::Location& from_here,
-      base::TimeTicks now,
-      base::TimeTicks unthrottled_runtime);
-
-  TaskQueueMap throttled_queues_;
-  base::Closure forward_immediate_work_closure_;
-  scoped_refptr<TaskQueue> task_runner_;
-  RendererSchedulerImpl* renderer_scheduler_;  // NOT OWNED
-  base::TickClock* tick_clock_;                // NOT OWNED
-  const char* tracing_category_;               // NOT OWNED
-  std::unique_ptr<ThrottledTimeDomain> time_domain_;
-
-  CancelableClosureHolder pump_throttled_tasks_closure_;
-  base::TimeTicks pending_pump_throttled_tasks_runtime_;
-  bool virtual_time_;
-
-  base::WeakPtrFactory<ThrottlingHelper> weak_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(ThrottlingHelper);
-};
-
-}  // namespace scheduler
-}  // namespace blink
-
-#endif  // THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_RENDERER_THROTTLING_HELPER_H_