content/renderer/device_sensors/device_sensor_event_pump.h

   1 // Copyright 2014 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 CONTENT_RENDERER_DEVICE_SENSORS_DEVICE_SENSOR_EVENT_PUMP_H_
   6 #define CONTENT_RENDERER_DEVICE_SENSORS_DEVICE_SENSOR_EVENT_PUMP_H_
   7
   8 #include "base/memory/shared_memory.h"
   9 #include "base/time/time.h"
  10 #include "base/timer/timer.h"
  11 #include "content/public/renderer/platform_event_observer.h"
  12
  13 namespace content {
  14
  15 template <typename ListenerType>
  16 class CONTENT_EXPORT DeviceSensorEventPump
  17     : NON_EXPORTED_BASE(public PlatformEventObserver<ListenerType>) {
  18  public:
  19   // Default rate for firing events.
  20   static const int kDefaultPumpFrequencyHz = 60;
  21   static const int kDefaultPumpDelayMicroseconds =
  22       base::Time::kMicrosecondsPerSecond / kDefaultPumpFrequencyHz;
  23
  24   // PlatformEventObserver
  25   void Start(blink::WebPlatformEventListener* listener) override {
  26     DVLOG(2) << "requested start";
  27
  28     if (state_ != STOPPED)
  29       return;
  30
  31     DCHECK(!timer_.IsRunning());
  32
  33     PlatformEventObserver<ListenerType>::Start(listener);
  34     state_ = PENDING_START;
  35   }
  36
  37   void Stop() override {
  38     DVLOG(2) << "stop";
  39
  40     if (state_ == STOPPED)
  41       return;
  42
  43     DCHECK((state_ == PENDING_START && !timer_.IsRunning()) ||
  44         (state_ == RUNNING && timer_.IsRunning()));
  45
  46     if (timer_.IsRunning())
  47       timer_.Stop();
  48     PlatformEventObserver<ListenerType>::Stop();
  49     state_ = STOPPED;
  50   }
  51
  52  protected:
  53   explicit DeviceSensorEventPump(RenderThread* thread)
  54       : PlatformEventObserver<ListenerType>(thread),
  55         pump_delay_microseconds_(kDefaultPumpDelayMicroseconds),
  56         state_(STOPPED) {}
  57
  58   ~DeviceSensorEventPump() override {
  59     PlatformEventObserver<ListenerType>::StopIfObserving();
  60   }
  61
  62   // The pump is a tri-state automaton with allowed transitions as follows:
  63   // STOPPED -> PENDING_START
  64   // PENDING_START -> RUNNING
  65   // PENDING_START -> STOPPED
  66   // RUNNING -> STOPPED
  67   enum PumpState {
  68       STOPPED,
  69       RUNNING,
  70       PENDING_START
  71   };
  72
  73   void OnDidStart(base::SharedMemoryHandle handle) {
  74     DVLOG(2) << "did start sensor event pump";
  75
  76     if (state_ != PENDING_START)
  77       return;
  78
  79     DCHECK(!timer_.IsRunning());
  80
  81     if (InitializeReader(handle)) {
  82       timer_.Start(FROM_HERE,
  83                    base::TimeDelta::FromMicroseconds(pump_delay_microseconds_),
  84                    this,
  85                    &DeviceSensorEventPump::FireEvent);
  86       state_ = RUNNING;
  87     }
  88   }
  89
  90   virtual void FireEvent() = 0;
  91   virtual bool InitializeReader(base::SharedMemoryHandle handle) = 0;
  92
  93   int pump_delay_microseconds_;
  94   PumpState state_;
  95   base::RepeatingTimer<DeviceSensorEventPump> timer_;
  96
  97   DISALLOW_COPY_AND_ASSIGN(DeviceSensorEventPump);
  98 };
  99
 100 }  // namespace content
 101
 102 #endif  // CONTENT_RENDERER_DEVICE_SENSORS_DEVICE_SENSOR_EVENT_PUMP_H_