Implement Android shared memory data fetcher for Device Motion.

content/browser/device_orientation/data_fetcher_impl_android.h

 // Copyright (c) 2012 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 CHROME_BROWSER_DEVICE_ORIENTATION_DATA_FETCHER_IMPL_ANDROID_H_
 #define CHROME_BROWSER_DEVICE_ORIENTATION_DATA_FETCHER_IMPL_ANDROID_H_
 
 #include "base/android/scoped_java_ref.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/synchronization/lock.h"
 #include "content/browser/device_orientation/data_fetcher.h"
 #include "content/browser/device_orientation/device_data.h"
+#include "content/common/device_motion_hardware_buffer.h"
+
+template<typename T> struct DefaultSingletonTraits;

[bulach, 2013/07/12 14:00:41]

I don't quite understand why the Leaky version wouldn't compile?

[timvolodine, 2013/07/12 15:22:18]

If I change this to Leaky the below friend declaration gives an error that it is
not defined. If I put Leaky in the friend declaration, the compiler will
complain that the destructor/constructor of fetcher is protected. I think this
is because Leaky is a subclass of Default, so Default needs to be friend of
fetcher to have access to constructor/destructor of fetcher.

In chromium some files just include singleton.h in the header to avoid this
template<> declaration.

 
 namespace content {
-
 class Orientation;
 
 // Android implementation of DeviceOrientation API.
 
 // Android's SensorManager has a push API, whereas Chrome wants to pull data.
 // To fit them together, we store incoming sensor events in a 1-element buffer.
 // SensorManager calls SetOrientation() which pushes a new value (discarding the
 // previous value if any). Chrome calls GetDeviceData() which reads the most
 // recent value. Repeated calls to GetDeviceData() will return the same value.
 
-class DataFetcherImplAndroid : public DataFetcher {
+// TODO(timvolodine): Move this class implementation to
+// data_fetcher_shared_memory_android.cc, once Device Orientation switches to
+// shared memory implementation.

[bulach, 2013/07/12 14:00:41]

would this be the case? I think this class will remain as is to bridge from
C/C++ to java, right?

[timvolodine, 2013/07/12 15:22:18]

yes, but the class can be simplified once device orientation switches to shared
memory approach. I've added a comment to reflect that.

+class DataFetcherImplAndroid {
  public:
-  // Must be called at startup, before Create().
+  // Must be called at startup, before GetInstance().
   static void Init(JNIEnv* env);
 
-  // Factory function. We'll listen for events for the lifetime of this object.
-  // Returns NULL on error.
-  static DataFetcher* Create();
-
-  virtual ~DataFetcherImplAndroid();
+  // Needs to be thread-safe, because accessed from different threads.
+  static DataFetcherImplAndroid* GetInstance();
 
   // Called from Java via JNI.
   void GotOrientation(JNIEnv*, jobject,
                       double alpha, double beta, double gamma);
   void GotAcceleration(JNIEnv*, jobject,
                        double x, double y, double z);
   void GotAccelerationIncludingGravity(JNIEnv*, jobject,
                                        double x, double y, double z);
   void GotRotationRate(JNIEnv*, jobject,
                        double alpha, double beta, double gamma);
 
   // Implementation of DataFetcher.
   virtual const DeviceData* GetDeviceData(DeviceData::Type type) OVERRIDE;
 
- private:
-  DataFetcherImplAndroid();
-  const Orientation* GetOrientation();
-
   // Wrappers for JNI methods.
   // TODO(timvolodine): move the DeviceData::Type enum to the service class
   // once it is implemented.

[bulach, 2013/07/12 14:00:41]

I think 52-54 can be dropped? :)

[timvolodine, 2013/07/12 15:22:18]

Done.

-  bool Start(DeviceData::Type event_type, int rate_in_milliseconds);
-  void Stop(DeviceData::Type event_type);
+  virtual bool Start(DeviceData::Type event_type);
+  virtual void Stop(DeviceData::Type event_type);
+
+  // Shared memory related methods.
+  virtual bool NeedsPolling();
+  virtual bool FetchDeviceMotionDataIntoBuffer();
+  virtual bool StartFetchingDeviceMotionData(
+      DeviceMotionHardwareBuffer* buffer);
+  virtual void StopFetchingDeviceMotionData();

[bulach, 2013/07/12 14:00:41]

hmm... is "NeedsPolling()" necessary, since this class is no longer an
interface? also, make all of these non-virtual?

[timvolodine, 2013/07/12 15:22:18]

Done.

+
+ protected:
+  DataFetcherImplAndroid();
+  virtual ~DataFetcherImplAndroid();
+
+  const Orientation* GetOrientation();
 
   virtual int GetNumberActiveDeviceMotionSensors();
+  void CheckBufferReadyToRead();
+  void SetBufferReadyStatus(bool ready);
+  void ClearInternalBuffers();
 
+ private:
+  friend struct DefaultSingletonTraits<DataFetcherImplAndroid>;
+
+  enum {
+    RECEIVED_MOTION_DATA_ACCELERATION = 0,
+    RECEIVED_MOTION_DATA_ACCELERATION_INCL_GRAVITY = 1,
+    RECEIVED_MOTION_DATA_ROTATION_RATE = 2,
+    RECEIVED_MOTION_DATA_MAX = 3,
+  };
   // Value returned by GetDeviceData.
   scoped_refptr<Orientation> current_orientation_;
 
   // 1-element buffer, written by GotOrientation, read by GetDeviceData.
   base::Lock next_orientation_lock_;
   scoped_refptr<Orientation> next_orientation_;
 
   // The Java provider of orientation info.
   base::android::ScopedJavaGlobalRef<jobject> device_orientation_;
+  int number_active_device_motion_sensors_;
+  int received_motion_data_[RECEIVED_MOTION_DATA_MAX];
+  DeviceMotionHardwareBuffer* device_motion_buffer_;
+  bool is_buffer_ready_;
 
   DISALLOW_COPY_AND_ASSIGN(DataFetcherImplAndroid);
 };
 
 }  // namespace content
 
 #endif  // CHROME_BROWSER_DEVICE_ORIENTATION_DATA_FETCHER_IMPL_ANDROID_H_