[sensors](CrOS/Linux) Implement Sensor device manager for sensors

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/memory/ref_counted.h"
+#include "device/generic_sensor/generic_sensor_export.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}
+
+namespace device {
+
+class PlatformSensorLinux;
+class PlatformSensorConfiguration;
+struct SensorInfoLinux;
+
+// A generic reader class that can be implemented with two different strategies:
+// polling and on trigger.
+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,
+      PlatformSensorLinux* sensor,
+      scoped_refptr<base::SingleThreadTaskRunner> polling_thread_task_runner);
+
+  virtual ~SensorReader();
+
+  // Starts fetching data based on strategy this reader has chosen.
+  // Only polling strategy is supported at the moment. Thread safe.
+  virtual bool StartFetchingData(
+      const PlatformSensorConfiguration& configuration) = 0;
+
+  // Stops fetching data. Thread safe.
+  virtual void StopFetchingData() = 0;
+
+ protected:
+  SensorReader(PlatformSensorLinux* sensor,
+               scoped_refptr<base::SingleThreadTaskRunner> polling_task_runner);
+
+  // Notifies |sensor_| about an error.
+  void NotifyReadError();
+
+  // Non-owned pointer to a sensor that created this reader.
+  PlatformSensorLinux* sensor_;
+
+  // A task runner that is used to poll data.
+  scoped_refptr<base::SingleThreadTaskRunner> polling_task_runner_;
+
+  // A task runner that belongs to a thread this reader is created on.
+  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_