temperature_sensor_monitor.h

// Copyright 2015 The Chromium OS 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 THERMALD_TEMPERATURE_SENSOR_MONITOR_H_
#define THERMALD_TEMPERATURE_SENSOR_MONITOR_H_

#include <map>
#include <memory>
#include <string>

#include "base/callback.h"
#include "base/callback_list.h"
#include "base/macros.h"
#include "base/memory/weak_ptr.h"
#include "base/time/time.h"
#include "base/timer/timer.h"

#include "thermald/temperature_monitor_interface.h"
#include "thermald/temperature_sensor_interface.h"

namespace thermald {

// Periodically reads a temperature sensor at a configurable rate and
// provides an interface to subscribe for notification upon temperature
// changes.
//
// Subscribers are only notified about changes in the temperature, not every
// time the sensor is read. The monitoring of the sensors is only performed
// when at least one subscription is active.
//
// The TemperatureSensorMonitor is based on the libbase event model. A
// TemperatureSensorMonitor instance must not be used in multiple threads
// of execution.
class TemperatureSensorMonitor : public TemperatureMonitorInterface {
 public:
  // Does not take ownership of the sensor.
  TemperatureSensorMonitor(TemperatureSensorInterface *sensor,
                           base::TimeDelta sample_period);
  virtual ~TemperatureSensorMonitor();

  std::string name() const;

#if BASE_VER < 860220
  std::unique_ptr<TemperatureMonitorInterface::Subscription>
#else
  base::CallbackListSubscription
#endif
  Subscribe(const TemperatureMonitorCallback &cb);

 private:
  friend class TemperatureSensorMonitorTest;

  void StartSampling();
  void StopSampling();

  // Invoked whenever a subscriber is removed.
  void OnSubscriberRemoved();

  // Read the temperature sensor and reports changes to all subscribers.
  void ReadAndReportTemperature();

  // Report the current/latest temperature to a new subscriber.
  void ReportInitialTemperature(const TemperatureMonitorCallback &cb,
                                int temperature);

  TemperatureSensorInterface *sensor_;
  const base::TimeDelta sample_period_;

  base::WeakPtrFactory<TemperatureSensorMonitor> weak_ptr_factory_;

  base::CallbackList<void(int)> subscribers_;
  int prev_temperature_;
  bool sensor_was_operational_;

  // Timer for periodic sampling.
  //
  // The Timer class is used instead of RepeatingTimer to facilitate testing
  // through injection of a MockTimer.
  std::unique_ptr<base::RepeatingTimer> timer_;

  DISALLOW_COPY_AND_ASSIGN(TemperatureSensorMonitor);
};

}  // namespace thermald

#endif  // THERMALD_TEMPERATURE_SENSOR_MONITOR_H_