android中Sensor 工作流程

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转自http://www.apkbus.com/forum.php?mod=viewthread&tid=2740

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,....);

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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 on

SensorChanged 和 onAccuracyChanged 方法

public void onSensorChanged(int sensor, float[] values)
public void onAccuracyChanged(int sensor, int accuracy)

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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(...);
...
}

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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
...
}

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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) {
...
}
}

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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

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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();
...
}

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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));

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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 {
...
}

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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);
}

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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;
}

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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();
}

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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();
}
}

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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);
}

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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();

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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 },
};

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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
}

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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;

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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 },
};

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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;
}

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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;

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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:pen_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);
};

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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);
}

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