[Sensors] Improvements in shared buffer managing

device/generic_sensor/platform_sensor.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_H_
 #define DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_H_
 
 #include <list>
 #include <map>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
+#include "device/generic_sensor/public/cpp/sensor_reading.h"
 #include "device/generic_sensor/public/interfaces/sensor.mojom.h"
 #include "mojo/public/cpp/system/buffer.h"
 
 namespace device {
 
 class PlatformSensorProvider;
 class PlatformSensorConfiguration;
 
 // Base class for the sensors provided by the platform. Concrete instances of
 // this class are created by platform specific PlatformSensorProvider.
@@ skipping 24 matching lines @@
   void AddClient(Client*);
   void RemoveClient(Client*);
 
  protected:
   virtual ~PlatformSensor();
   PlatformSensor(mojom::SensorType type,
                  mojo::ScopedSharedBufferMapping mapping,
                  PlatformSensorProvider* provider);
 
   using ConfigMap = std::map<Client*, std::list<PlatformSensorConfiguration>>;
+  using ReadingBuffer = SensorReadingSharedBuffer;
 
   virtual bool UpdateSensorInternal(const ConfigMap& configurations);
   virtual bool StartSensor(
       const PlatformSensorConfiguration& configuration) = 0;
   virtual void StopSensor() = 0;
   virtual bool CheckSensorConfiguration(
       const PlatformSensorConfiguration& configuration) = 0;
 
+  // Updates shared buffer with new sensor reading data.
+  // Note: this method is thread-safe.
+  void UpdateSensorReading(const SensorReading& reading, bool notify_clients);
+
   void NotifySensorReadingChanged();
   void NotifySensorError();
 
-  mojo::ScopedSharedBufferMapping shared_buffer_mapping_;
-
   // For testing purposes.
   const ConfigMap& config_map() const { return config_map_; }
 
+  // Task runner that is used by mojo objects for the IPC.
+  // If platfrom sensor events are processed on a different
+  // thread, notifications are forwarded to |task_runner_|.
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
  private:
   friend class base::RefCountedThreadSafe<PlatformSensor>;
-
+  mojo::ScopedSharedBufferMapping shared_buffer_mapping_;

[Ken Rockot(use gerrit already), 2016/10/10 19:12:43]

This must be const if you want UpdateSensorReading to be thread-safe.

Otherwise there's nothing to stop subclasses (or even PlatformSensor itself)
from accidentally modifying it and creating data races in UpdateSensorReading.

   mojom::SensorType type_;
   base::ObserverList<Client, true> clients_;
   ConfigMap config_map_;
   PlatformSensorProvider* provider_;
   base::WeakPtrFactory<PlatformSensor> weak_factory_;
   DISALLOW_COPY_AND_ASSIGN(PlatformSensor);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_H_