Android sensor flow

Sensor 工作流程
                                                           --by once
JAVA 程序
我们使用 sensor 接口一般只要注册一下 SensorListener 像下面这样
**************************************************************
ApiDemo:
     mGraphView = new GraphView(this);
     mSensorManager.registerListener(mGraphView,....);
**************************************************************
这里的 listener 是因为 sensor 状态变化要产生变化的控件
然后在控件里重载 onSensorChanged 和 onAccuracyChanged 方法
public void onSensorChanged(int sensor, float[] values)
public void onAccuracyChanged(int sensor, int accuracy)
SensorManager
Sensor 主体代码和流程在 frameworks/base/core/java/android/hardware/SensorManager.java 里面
1.registerListener 其实是调用 registerLegacyListener:
public boolean registerListener(SensorListener listener, int sensors, int rate) {
...
  result = registerLegacyListener(...);
...
}
2. registerLegacyListener 其实就是构造一个 LegacyListener 对象并将其加入 HashMap 中去
private boolean registerLegacyListener(int legacyType, int type,
                 SensorListener listener, int sensors, int rate)
{
...
     legacyListener = new LegacyListener(listener);
     mLegacyListenersMap.put(listener, legacyListener); //private HashMap<SensorListener,
LegacyListener> mLegacyListenersMap
...
}
3. LegacyListener 做了 2 件事 一个是调用我们重载的那 2 个接口 还有一个就是将 sensor 的
数据刷到我们的设备显示界面上去
private class LegacyListener implements SensorEventListener {
...
LegacyListener(SensorListener target) {
                 mTarget = target;
                 mSensors = 0;
}
public void onSensorChanged(SensorEvent event) {
...
mapSensorDataToWindow();
mTarget.onSensorChanged(...);//private SensorListener mTarget;
...
 }
 public void onAccuracyChanged(Sensor sensor, int accuracy) {
 ...
 }
 }
代码最后是一些 native 方法:
     private static native void nativeClassInit();//SensorManager 构造函数里调用
     private static native int sensors_module_init();//SensorManager 构造函数里调用
     private static native int sensors_module_get_next_sensor(Sensor sensor, int
next);//SensorManager 构造函数里调用
      // Used within this module from outside SensorManager, don't make private
      static native int sensors_data_init();//SensorThread 构造里调用
      static native int sensors_data_uninit();//SensorThread 析构里调用
      static native int sensors_data_open(FileDescriptor fd); //SensorThread 的 run()循环调用
      static native int sensors_data_close();//SensorThread 的 run()循环调用
      static native int sensors_data_poll(float[] values, int[] status, long[] timestamp);//SensorThread
的 run()循环调用
SensorManager 与 IsensorService 的关系
SensorManager 调用 IsensorService 其实只是调用了 service 的方法来控制 thread 是 Lock
 void startLocked(ISensorService service) {
 ...
     ParcelFileDescriptor fd = service.getDataChanel();
 ...
 }
或者打开
 mSensorService.enableSensor(l, name, handle, delay);
IsensorService 的实例是这么获得的
 mSensorService = ISensorService.Stub.asInterface(
                       ServiceManager.getService(Context.SENSOR_SERVICE));
IsensorService 是通过 aidl 定义的
 interface ISensorService
 {
       ParcelFileDescriptor getDataChanel();
       boolean enableSensor(IBinder listener, String name, int sensor, int enable);
 }
SensorService
frameworks/base/services/java/com/android/server/SensorService.java
 class SensorService extends ISensorService.Stub {
 ...
 }
service 最终被 manager 调到走的是 android 的标准流程我们不 care,我们想知道的其实就是
enableSensor 的实现
首先,得有电
 if (enable == SENSOR_DISABLE) {
                  mBatteryStats.noteStopSensor(uid, sensor);
             } else {
                  mBatteryStats.noteStartSensor(uid, sensor);
 }
看是不是能打开 sensor
 if (enable!=SENSOR_DISABLE && !_sensors_control_activate(sensor, true)) {
                       Log.w(TAG, "could not enable sensor " + sensor);
                       return false;
                  }
如果 sensor 打开了 我们要监听状态还要对外面报告状态变化
 if (l == null && enable!=SENSOR_DISABLE) {
                       l = new Listener(binder);
                       binder.linkToDeath(l, 0);
                       mListeners.add(l);
                       mListeners.notify();
                  }
如果 sensor 被关闭了 我们要取消监听并且告诉外面关闭了传感
     if (enable != SENSOR_DISABLE) {
                       l.addSensor(sensor, enable);
                  } else {
                       l.removeSensor(sensor);
                       deactivateIfUnused(sensor);
                       if (l.mSensors == 0) {
                             mListeners.remove(l);
                             binder.unlinkToDeath(l, 0);
                             mListeners.notify();
                       }
                  }
另外还有一些唤醒和设置延迟的动作
 if (mListeners.size() == 0) {
                       _sensors_control_wake();
                  }
   if (minDelay >= 0) {
                       _sensors_control_set_delay(minDelay);
                  }
从上面可以看出来 对于底层而言只要知道上层怎么调用传感的接口就好 所以最关心的还是
我标绿的 native 方法 上层的传感流程其实比较简单 就是标准的 service 管理和 notify 流程
      private static native int _sensors_control_init();
       private static native ParcelFileDescriptor _sensors_control_open();
       private static native boolean _sensors_control_activate(int sensor, boolean activate);
       private static native int _sensors_control_set_delay(int ms);
       private static native int _sensors_control_wake();
native 方法
1. manager 部分
frameworks/base/core/jni/android_hardware_SensorManager.cpp
先看一眼它的方法注册
 static JNINativeMethod gMethods[] = {
       {"nativeClassInit", "()V",          (void*)nativeClassInit },
       {"sensors_module_init","()I",          (void*)sensors_module_init },
       {"sensors_module_get_next_sensor","(Landroid/hardware/Sensor;I)I",
                                                           (void*)sensors_module_get_next_sensor },
       {"sensors_data_init", "()I",         (void*)sensors_data_init },
       {"sensors_data_uninit", "()I",        (void*)sensors_data_uninit },
       {"sensors_data_open", "(Ljava/io/FileDescriptor;)I", (void*)sensors_data_open },
       {"sensors_data_close", "()I",         (void*)sensors_data_close },
       {"sensors_data_poll", "([F[I[J)I", (void*)sensors_data_poll },
 };
小贴一个例子作为代表
 static jint
 sensors_data_open(JNIEnv *env, jclass clazz, jobject fdo)
 {
       jclass FileDescriptor = env->FindClass("java/io/FileDescriptor");
       jfieldID offset = env->GetFieldID(FileDescriptor, "descriptor", "I");
       int fd = env->GetIntField(fdo, offset);
       return sSensorDevice->data_open(sSensorDevice, fd); // doesn't take ownership of fd
 }
调用到最后其实都是用的 sSensorDevice 的方法
 /*
   * The method below are not thread-safe and not intended to be
   */
 static sensors_data_device_t* sSensorDevice = 0;
2.service 部分
frameworks/base/services/jni/com_android_server_SensorService.cpp
先看一眼它的方法注册
 static JNINativeMethod gMethods[] = {
       {"_sensors_control_init", "()I", (void*) android_init },
       {"_sensors_control_open", "()Landroid/os/ParcelFileDescriptor;", (void*) android_open },
       {"_sensors_control_activate", "(IZ)Z", (void*) android_activate },
      {"_sensors_control_wake", "()I", (void*) android_data_wake },
      {"_sensors_control_set_delay","(I)I", (void*) android_set_delay },
};
然后上面的那些方法我就不一一贴了 给出一个例子 其实这么实现的
static jboolean
android_activate(JNIEnv *env, jclass clazz, jint sensor, jboolean activate)
{
      int active = sSensorDevice->activate(sSensorDevice, sensor, activate);
      return (active<0) ? false : true;
}
所以最后调用的其实都是 sSensorDevice 的方法 其他的几个也是这样 sSensorDevice 是这个
(不是线程安全的)
/*
  * The method below are not thread-safe and not intended to be
  */
static sensors_control_device_t* sSensorDevice = 0;
3.继续追 终于到了硬件层了 最后一切的方法其实就在这里了
hardware/libhardware/include/hardware/sensor.h
struct sensors_control_device_t {
      struct hw_device_t common;
      /**
        * Returns the fd which will be the parameter to
        * sensors_data_device_t::open_data().
        * The caller takes ownership of this fd. This is intended to be
        * passed cross processes.
        *
        * @return a fd if successful, < 0 on error
        */
      int (*open_data_source)(struct sensors_control_device_t *dev);
      /** Activate/deactivate one sensor.
        *
        * @param handle is the handle of the sensor to change.
        * @param enabled set to 1 to enable, or 0 to disable the sensor.
        *
        * @return 0 on success, negative errno code otherwise
        */
      int (*activate)(struct sensors_control_device_t *dev,
                 int handle, int enabled);
      /**
       * Set the delay between sensor events in ms
       *
       * @return 0 if successful, < 0 on error
       */
     int (*set_delay)(struct sensors_control_device_t *dev, int32_t ms);
     /**
       * Causes sensors_data_device_t.poll() to return -EWOULDBLOCK immediately.
       */
     int (*wake)(struct sensors_control_device_t *dev);
};
struct sensors_data_device_t {
     struct hw_device_t common;
     /**
       * Prepare to read sensor data.
       *
       * This routine does NOT take ownership of the fd
       * and must not close it. Typically this routine would
       * use a duplicate of the fd parameter.
       *
       * @param fd from sensors_control_open.
       *
       * @return 0 if successful, < 0 on error
       */
     int (*data_open)(struct sensors_data_device_t *dev, int fd);
     /**
       * Caller has completed using the sensor data.
       * The caller will not be blocked in sensors_data_poll
       * when this routine is called.
       *
       * @return 0 if successful, < 0 on error
       */
     int (*data_close)(struct sensors_data_device_t *dev);
     /**
       * Return sensor data for one of the enabled sensors.
       *
       * @return sensor handle for the returned data, 0x7FFFFFFF when
       * sensors_control_device_t.wake() is called and -errno on error
       *
        */
      int (*poll)(struct sensors_data_device_t *dev,
                 sensors_data_t* data);
};
最后一组函数
/** convenience API for opening and closing a device */
static inline int sensors_control_open(const struct hw_module_t* module,
            struct sensors_control_device_t** device) {
      return module->methods->open(module,
                 SENSORS_HARDWARE_CONTROL, (struct hw_device_t**)device);
}
static inline int sensors_control_close(struct sensors_control_device_t* device) {
      return device->common.close(&device->common);
}
static inline int sensors_data_open(const struct hw_module_t* module,
            struct sensors_data_device_t** device) {
      return module->methods->open(module,
                 SENSORS_HARDWARE_DATA, (struct hw_device_t**)device);
}
static inline int sensors_data_close(struct sensors_data_device_t* device) {
      return device->common.close(&device->common);
}