device/generic_sensor/platform_sensor_reader_linux.h

// Copyright 2016 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 DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_READER_LINUX_H_
#define DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_READER_LINUX_H_

#include "base/callback.h"
#include "base/memory/ref_counted.h"
#include "base/memory/weak_ptr.h"
#include "base/threading/thread_checker.h"
#include "device/generic_sensor/generic_sensor_export.h"

namespace base {
class SingleThreadTaskRunner;
}

namespace device {

class PlatformSensorConfiguration;
class PlatformSensorLinux;
struct SensorInfoLinux;

// A generic reader class that can be implemented with two different strategies:
// polling and on trigger. All methods are not thread-safe and must be called
// on a polling thread that allows I/O.
class SensorReader {
 public:
  // Creates a new instance of SensorReader. At the moment, only polling
  // reader is supported.
  static std::unique_ptr<SensorReader> Create(
      const SensorInfoLinux* sensor_device,
      base::WeakPtr<PlatformSensorLinux> sensor,
      scoped_refptr<base::SingleThreadTaskRunner> task_runner);

  virtual ~SensorReader();

  // Starts fetching data based on strategy this reader has chosen.
  // Only polling strategy is supported at the moment.
  virtual void StartFetchingData(
      const PlatformSensorConfiguration& configuration) = 0;

  // Stops fetching data.
  virtual void StopFetchingData() = 0;

 protected:
  SensorReader(base::WeakPtr<PlatformSensorLinux> sensor,
               scoped_refptr<base::SingleThreadTaskRunner> task_runner);

  // Notifies |sensor_| about an error.
  void NotifyReadError();

  // In builds with DCHECK enabled checks that methods of this
  // and derived classes are called on a right thread.
  base::ThreadChecker thread_checker_;

  // A sensor that this reader is owned by and notifies about errors and
  // readings to.
  base::WeakPtr<PlatformSensorLinux> sensor_;

  // A task runner that is used to report about new readings and errors
  // to a |sensor_|.
  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;

  // Indicates if reading is active.
  bool is_reading_active_;

  DISALLOW_COPY_AND_ASSIGN(SensorReader);
};

}  // namespace device

#endif  // DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_READER_LINUX_H_