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      1 // Copyright 2011 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 CC_SCHEDULER_DELAY_BASED_TIME_SOURCE_H_
      6 #define CC_SCHEDULER_DELAY_BASED_TIME_SOURCE_H_
      7 
      8 #include "base/memory/weak_ptr.h"
      9 #include "cc/base/cc_export.h"
     10 #include "cc/scheduler/time_source.h"
     11 
     12 namespace base { class SingleThreadTaskRunner; }
     13 
     14 namespace cc {
     15 
     16 // This timer implements a time source that achieves the specified interval
     17 // in face of millisecond-precision delayed callbacks and random queueing
     18 // delays.
     19 class CC_EXPORT DelayBasedTimeSource : public TimeSource {
     20  public:
     21   static scoped_refptr<DelayBasedTimeSource> Create(
     22       base::TimeDelta interval, base::SingleThreadTaskRunner* task_runner);
     23 
     24   virtual void SetClient(TimeSourceClient* client) OVERRIDE;
     25 
     26   // TimeSource implementation
     27   virtual void SetTimebaseAndInterval(base::TimeTicks timebase,
     28                                       base::TimeDelta interval) OVERRIDE;
     29 
     30   virtual void SetActive(bool active) OVERRIDE;
     31   virtual bool Active() const OVERRIDE;
     32 
     33   // Get the last and next tick times. nextTimeTime() returns null when
     34   // inactive.
     35   virtual base::TimeTicks LastTickTime() OVERRIDE;
     36   virtual base::TimeTicks NextTickTime() OVERRIDE;
     37 
     38   // Virtual for testing.
     39   virtual base::TimeTicks Now() const;
     40 
     41  protected:
     42   DelayBasedTimeSource(base::TimeDelta interval,
     43                        base::SingleThreadTaskRunner* task_runner);
     44   virtual ~DelayBasedTimeSource();
     45 
     46   base::TimeTicks NextTickTarget(base::TimeTicks now);
     47   void PostNextTickTask(base::TimeTicks now);
     48   void OnTimerFired();
     49 
     50   enum State {
     51     STATE_INACTIVE,
     52     STATE_STARTING,
     53     STATE_ACTIVE,
     54   };
     55 
     56   struct Parameters {
     57     Parameters(base::TimeDelta interval, base::TimeTicks tick_target)
     58         : interval(interval), tick_target(tick_target) {}
     59     base::TimeDelta interval;
     60     base::TimeTicks tick_target;
     61   };
     62 
     63   TimeSourceClient* client_;
     64   bool has_tick_target_;
     65   base::TimeTicks last_tick_time_;
     66 
     67   // current_parameters_ should only be written by PostNextTickTask.
     68   // next_parameters_ will take effect on the next call to PostNextTickTask.
     69   // Maintaining a pending set of parameters allows NextTickTime() to always
     70   // reflect the actual time we expect OnTimerFired to be called.
     71   Parameters current_parameters_;
     72   Parameters next_parameters_;
     73 
     74   State state_;
     75 
     76   base::SingleThreadTaskRunner* task_runner_;
     77   base::WeakPtrFactory<DelayBasedTimeSource> weak_factory_;
     78 
     79  private:
     80   DISALLOW_COPY_AND_ASSIGN(DelayBasedTimeSource);
     81 };
     82 
     83 }  // namespace cc
     84 
     85 #endif  // CC_SCHEDULER_DELAY_BASED_TIME_SOURCE_H_
     86