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
...
}
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);
}