Sensor注册流程

一.概要

       我们在android中经常会注册sensor然后监听sensor的数据来做一些特殊的功能，但是之前一直没有关注过整个注册的流程，本文将会告诉你高通855平台中sensor的整个完整的注册流程是什么样子的，先大概总结一下：

APP进程创建一个SensorEventQueue，等待接收system_server发送过来的数据
system_server进程会保存app端的SensorEventQueue，有一个线程会循环的读取android.hardware.sensors@1.0-service进程发送过来的消息，当有消息来到时会往APP端的SensorEventQueue中发送sensor 数据，
android.hardware.sensors@1.0-service进程会初始化一个socket和子系统通信，并且创建一个线程一直等待BP发送上来的数据，当接收到数据时会发给system_server。
注册流程图参考绿色部分

二.APP进程注册：

sensorEventListener = new MySensorEventListener(); //获取方向传感器 Sensor orientationSensor = sensorManager.getDefaultSensor(Sensor.TYPE_ORIENTATION);// NO.1 获取sensor sensorManager.registerListener(sensorEventListener, orientationSensor, SensorManager.SENSOR_DELAY_NORMAL); // NO.2注册sensor   private final class MySensorEventListener implements SensorEventListener {     //可以得到传感器实时测量出来的变化值     @Override     public void onSensorChanged(SensorEvent event)     {         //得到方向的值         if(event.sensor.getType()==Sensor.TYPE_ORIENTATION)         {             float x = event.values[SensorManager.DATA_X];             float y = event.values[SensorManager.DATA_Y];             float z = event.values[SensorManager.DATA_Z];             orientationView.setText("Orientation: " + x + ", " + y + ", " + z);         }     }     //重写变化     @Override     public void onAccuracyChanged(Sensor sensor, int accuracy)     {     } }

首先我们先写一个SensorEventListener，之后sensor有数据之后会回调onSensorChanged/onAccuracyChanged，先不管怎么回调的，先看看注册过程
NO.1获取对应type的sensor

public Sensor getDefaultSensor(int type) {     // TODO: need to be smarter, for now, just return the 1st sensor     // NO.1.1 这里是从所有的sensor中获得对应type的sensor.     List l = getSensorList(type);     boolean wakeUpSensor = false;     // For the following sensor types, return a wake-up sensor. These types are by default     // defined as wake-up sensors. For the rest of the SDK defined sensor types return a     // non_wake-up version.     if (type == Sensor.TYPE_PROXIMITY || type == Sensor.TYPE_SIGNIFICANT_MOTION ||             type == Sensor.TYPE_TILT_DETECTOR || type == Sensor.TYPE_WAKE_GESTURE ||             type == Sensor.TYPE_GLANCE_GESTURE || type == Sensor.TYPE_PICK_UP_GESTURE ||             type == Sensor.TYPE_WRIST_TILT_GESTURE || type == Sensor.TYPE_DYNAMIC_SENSOR_META) {         wakeUpSensor = true;     }           // NO.1.2 一般sensor有一个wakeup sensor,一个non wakeup sensor     for (Sensor sensor : l) {         if (sensor.isWakeUpSensor() == wakeUpSensor) return sensor;     }     return null; }

NO.1.1 这里是从所有的sensor中获得对应type的sensor.

public List getSensorList(int type) {     // cache the returned lists the first time     List list;     // 获取所有sensor     final List fullList = getFullSensorList();     synchronized (mSensorListByType) {         // 看看缓存里有没有要组成的sensor,如果有的话直接返回         list = mSensorListByType.get(type);         if (list == null) {             if (type == Sensor.TYPE_ALL) {                 list = fullList;             } else {                 list = new ArrayList();                 // 遍历所有sensor,找到对应type的sensor                 for (Sensor i : fullList) {                     if (i.getType() == type)                         list.add(i);                 }             }             list = Collections.unmodifiableList(list);             // 存入缓存             mSensorListByType.append(type, list);         }     }     return list; }

 

// NO.1.2 一般sensor有一个wakeup sensor,一个non wakeup sensor，我们返回wakeup sensor。
若是注册Non-Wakeup的sensor的话，在系统suspend时，不会有任何数据上报.若是注册Wakeup的sensor的话，系统会被wakelock住，根本睡不下去，这时系统功耗非常高
 

NO.2注册sensor

public boolean registerListener(SensorEventListener listener, Sensor sensor,            int samplingPeriodUs) {        return registerListener(listener, sensor, samplingPeriodUs, null);    }         public boolean registerListener(SensorEventListener listener, Sensor sensor,            int samplingPeriodUs, Handler handler) {        // SensorManager.SENSOR_DELAY_NORMAL默认采样率 200000us        int delay = getDelay(samplingPeriodUs);        return registerListenerImpl(listener, sensor, delay, handler, 0, 0);    } @Override    protected boolean registerListenerImpl(SensorEventListener listener, Sensor sensor,            int delayUs, Handler handler, int maxBatchReportLatencyUs, int reservedFlags) {        android.util.SeempLog.record_sensor_rate(381, sensor, delayUs);        if (listener == null || sensor == null) {            Log.e(TAG, "sensor or listener is null");            return false;        }        // Trigger Sensors should use the requestTriggerSensor call.        // NO2.1如果sensor类型是Sensor.REPORTING_MODE_ONE_SHOT就返回，requestTriggerSensor注册的sensor        if (sensor.getReportingMode() == Sensor.REPORTING_MODE_ONE_SHOT) {            Log.e(TAG, "Trigger Sensors should use the requestTriggerSensor.");            return false;        }        // Sensor.REPORTING_MODE_ONE_SHOT ,判断时间        if (maxBatchReportLatencyUs < 0 || delayUs < 0) {            Log.e(TAG, "maxBatchReportLatencyUs and delayUs should be non-negative");            return false;        }        // 判断Listener数量是否超过超过MAX_LISTENER_COUNT        if (mSensorListeners.size() >= MAX_LISTENER_COUNT) {            throw new IllegalStateException("register failed, "                + "the sensor listeners size has exceeded the maximum limit "                + MAX_LISTENER_COUNT);        }          // Invariants to preserve:        // - one Looper per SensorEventListener        // - one Looper per SensorEventQueue        // We map SensorEventListener to a SensorEventQueue, which holds the looper        synchronized (mSensorListeners) {            // 从缓存里获取listener            SensorEventQueue queue = mSensorListeners.get(listener);            if (queue == null) {                Looper looper = (handler != null) ? handler.getLooper() : mMainLooper;                final String fullClassName =                        listener.getClass().getEnclosingClass() != null                            ? listener.getClass().getEnclosingClass().getName()                            : listener.getClass().getName();                // NO2.2 新建一个SensorEventQueue                queue = new SensorEventQueue(listener, looper, this, fullClassName);                // NO2.3 添加sennsor                if (!queue.addSensor(sensor, delayUs, maxBatchReportLatencyUs)) {                    queue.dispose();                    return false;                }                // 将listener放入缓存                mSensorListeners.put(listener, queue);                return true;            } else {                return queue.addSensor(sensor, delayUs, maxBatchReportLatencyUs);            }        }    }

sensor的模式类型有：
REPORTING_MODE_CONTINUOUS 常用的都是CONTINUOUS类型，例如light,acc,gryo等等
REPORTING_MODE_ON_CHANGE 
REPORTING_MODE_ONE_SHOT 例如：计步
REPORTING_MODE_SPECIAL_TRIGGER

 

NO2.2 新建一个SensorEventQueue

frameworks/base/core/java/android/hardware/SystemSensorManager.java static final class SensorEventQueue extends BaseEventQueue {         private final SensorEventListener mListener;         private final SparseArray mSensorsEvents = new SparseArray();           public SensorEventQueue(SensorEventListener listener, Looper looper,                 SystemSensorManager manager, String packageName) {             // NO2.2.1调用父类方法             super(looper, manager, OPERATING_MODE_NORMAL, packageName);             mListener = listener;         }           @Override         public void addSensorEvent(Sensor sensor) {             SensorEvent t = new SensorEvent(Sensor.getMaxLengthValuesArray(sensor,                     mManager.mTargetSdkLevel));             synchronized (mSensorsEvents) {                 mSensorsEvents.put(sensor.getHandle(), t);             }         }         ......         // Called from native code.         @SuppressWarnings("unused") &nb