android中Sensor工作流程(5)

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);