SensorService启动分析

首先看下sensor的一个整体大概架构图：

4.0中sensor是以一个service 的方式启动的

在base\cmds\sensorservice\main_sensorservice.cpp

#include <binder/BinderService.h>#include <SensorService.h>using namespace android;int main(int argc, char** argv) {    SensorService::publishAndJoinThreadPool();    return 0;}    static void publishAndJoinThreadPool(bool allowIsolated = false) {        sp<IServiceManager> sm(defaultServiceManager());        sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated);        ProcessState::self()->startThreadPool();        IPCThreadState::self()->joinThreadPool();}

主要是new了一个service并添加到ServiceManager，然后启动线程池

在add service的过程中会调用SensorService的onFirstRef

void SensorService::onFirstRef(){    ALOGD("nuSensorService starting...");    SensorDevice& dev(SensorDevice::getInstance());//获取sensorSevice实例    if (dev.initCheck() == NO_ERROR) {        sensor_t const* list;        ssize_t count = dev.getSensorList(&list);//获取sensorSevice列表        if (count > 0) {            ssize_t orientationIndex = -1;            bool hasGyro = false;            uint32_t virtualSensorsNeeds =                    (1<<SENSOR_TYPE_GRAVITY) |                    (1<<SENSOR_TYPE_LINEAR_ACCELERATION) |                    (1<<SENSOR_TYPE_ROTATION_VECTOR);            mLastEventSeen.setCapacity(count);            for (ssize_t i=0 ; i<count ; i++) {                registerSensor( new HardwareSensor(list[i]) );//注册各个sensor                switch (list[i].type) {                    case SENSOR_TYPE_ORIENTATION:                        orientationIndex = i;                        break;                    case SENSOR_TYPE_GYROSCOPE:                        hasGyro = true;                        break;                    case SENSOR_TYPE_GRAVITY:                    case SENSOR_TYPE_LINEAR_ACCELERATION:                    case SENSOR_TYPE_ROTATION_VECTOR:                        virtualSensorsNeeds &= ~(1<<list[i].type);                        break;                }            }            // it's safe to instantiate the SensorFusion object here            // (it wants to be instantiated after h/w sensors have been            // registered)            const SensorFusion& fusion(SensorFusion::getInstance());            if (hasGyro) {//如果有陀螺仪传感器，则虚拟的旋转矢量、重力、线性加速度、方向传感器                // Always instantiate Android's virtual sensors. Since they are                // instantiated behind sensors from the HAL, they won't                // interfere with applications, unless they looks specifically                // for them (by name).                registerVirtualSensor( new RotationVectorSensor() );                registerVirtualSensor( new GravitySensor(list, count) );                registerVirtualSensor( new LinearAccelerationSensor(list, count) );                // these are optional                registerVirtualSensor( new OrientationSensor() );                registerVirtualSensor( new CorrectedGyroSensor(list, count) );                // virtual debugging sensors...                char value[PROPERTY_VALUE_MAX];                property_get("debug.sensors", value, "0");                if (atoi(value)) {                    registerVirtualSensor( new GyroDriftSensor() );                }            }            // build the sensor list returned to users            mUserSensorList = mSensorList;            if (hasGyro &&                    (virtualSensorsNeeds & (1<<SENSOR_TYPE_ROTATION_VECTOR))) {                // if we have the fancy sensor fusion, and it's not provided by the                // HAL, use our own (fused) orientation sensor by removing the                // HAL supplied one form the user list.                /*if (orientationIndex >= 0) {                    mUserSensorList.removeItemsAt(orientationIndex);                }*/            }            run("SensorService", PRIORITY_URGENT_DISPLAY);//启动线程            mInitCheck = NO_ERROR;        }    }}

onFirstRef主要做了下面三件事:

1构造SensorDevice 

SensorDevice::SensorDevice()    :  mSensorDevice(0),       mSensorModule(0){    status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,            (hw_module_t const**)&mSensorModule);//获取sensor模块    ALOGE_IF(err, "couldn't load %s module (%s)",            SENSORS_HARDWARE_MODULE_ID, strerror(-err));    if (mSensorModule) {        err = sensors_open(&mSensorModule->common, &mSensorDevice);//打开sensor设备        ALOGE_IF(err, "couldn't open device for module %s (%s)",                SENSORS_HARDWARE_MODULE_ID, strerror(-err));        if (mSensorDevice) {            sensor_t const* list;            ssize_t count = mSensorModule->get_sensors_list(mSensorModule, &list);//获取sensor列表            mActivationCount.setCapacity(count);            Info model;            for (size_t i=0 ; i<size_t(count) ; i++) {                mActivationCount.add(list[i].handle, model);                mSensorDevice->activate(mSensorDevice, list[i].handle, 0);            }        }    }}

2、获取到sensor之后 ，就是注册sensor，开始注册的都是HardwareSensor类型的sensor

void SensorService::registerSensor(SensorInterface* s){    sensors_event_t event;    memset(&event, 0, sizeof(event));    const Sensor sensor(s->getSensor());    // add to the sensor list (returned to clients)    mSensorList.add(sensor);    // add to our handle->SensorInterface mapping    mSensorMap.add(sensor.getHandle(), s);    // create an entry in the mLastEventSeen array    mLastEventSeen.add(sensor.getHandle(), event);}

注册sensor比较简单，主要是添加到几个list和map中。

还有一个registerVirtualSensor，注册虚拟的sensor

void SensorService::registerVirtualSensor(SensorInterface* s){    registerSensor(s);    mVirtualSensorList.add( s );}

调用registerSensor并添加到mVirtualSensorList链表。

3、run启动threadLoop线程

bool SensorService::threadLoop(){    ALOGD("nuSensorService thread starting...");    const size_t numEventMax = 16;    const size_t minBufferSize = numEventMax + numEventMax * mVirtualSensorList.size();    sensors_event_t buffer[minBufferSize];    sensors_event_t scratch[minBufferSize];    SensorDevice& device(SensorDevice::getInstance());    const size_t vcount = mVirtualSensorList.size();    ssize_t count;    do {        count = device.poll(buffer, numEventMax);//查看sensor上是否有数据到来        if (count<0) {            ALOGE("sensor poll failed (%s)", strerror(-count));            break;        }        recordLastValue(buffer, count);//记录每个sensor的最后一次事件        // handle virtual sensors        if (count && vcount) {            sensors_event_t const * const event = buffer;            const DefaultKeyedVector<int, SensorInterface*> virtualSensors(                    getActiveVirtualSensors());//获取虚拟的sensor            const size_t activeVirtualSensorCount = virtualSensors.size();            if (activeVirtualSensorCount) {                size_t k = 0;                SensorFusion& fusion(SensorFusion::getInstance());                if (fusion.isEnabled()) {//融合传感器使能，则调用它的process对根据event数据对SensorFusion里面的一些变量进行设置，                                            //后面调用其相应的sensor process的时候会用到                    for (size_t i=0 ; i<size_t(count) ; i++) {                        fusion.process(event[i]);                    }                }                for (size_t i=0 ; i<size_t(count) && k<minBufferSize ; i++) {                    for (size_t j=0 ; j<activeVirtualSensorCount ; j++) {                        if (count + k >= minBufferSize) {                            ALOGE("buffer too small to hold all events: "                                    "count=%u, k=%u, size=%u",                                    count, k, minBufferSize);                            break;                        }                        sensors_event_t out;                        SensorInterface* si = virtualSensors.valueAt(j);                        if (si->process(&out, event[i])) {//调用模拟sensor的process处理，输出一个event,添加到buffer                            buffer[count + k] = out;                            k++;                        }                    }                }                if (k) {                    // record the last synthesized values                    recordLastValue(&buffer[count], k);//重新记录每个sensor的最后一次事件                    count += k;                    // sort the buffer by time-stamps                    sortEventBuffer(buffer, count);                }            }        }        // send our events to clients...        const SortedVector< wp<SensorEventConnection> > activeConnections(                getActiveConnections());        size_t numConnections = activeConnections.size();        for (size_t i=0 ; i<numConnections ; i++) {            sp<SensorEventConnection> connection(                    activeConnections[i].promote());            if (connection != 0) {                connection->sendEvents(buffer, count, scratch);//把收到的数据传上去            }        }    } while (count >= 0 || Thread::exitPending());    ALOGW("Exiting SensorService::threadLoop => aborting...");    abort();    return false;}

代码中大概注释了各个比较关键地方的函数意义，主要是收到数据后，查看下如果有虚拟的sensor：

1、             如果使能了SensorFusion，调用它的process对数据进行处理(这里应该是每种类型sensor一次poll最多只会上报一次)，处理过程中会设置相应的一些成员变量值

2、             两个for循环，对所有的event,针对所有的已使能的virtual sensor调用它的process,这里面会用到一些前面第一步设置的一些值，根据输入的event输出一个event并添加到buffer.

数据处理完成后，获取所有活动的连接，并把数据发给它。看一下sendEvents

status_t SensorService::SensorEventConnection::sendEvents(        sensors_event_t const* buffer, size_t numEvents,        sensors_event_t* scratch){    // filter out events not for this connection    size_t count = 0;    if (scratch) {        Mutex::Autolock _l(mConnectionLock);        size_t i=0;        while (i<numEvents) {            const int32_t curr = buffer[i].sensor;            if (mSensorInfo.indexOf(curr) >= 0) {//检查在该连接里面是否存在这个sensor,存在则添加到scratch里面                do {                    scratch[count++] = buffer[i++];                } while ((i<numEvents) && (buffer[i].sensor == curr));            } else {                i++;            }        }    } else {        scratch = const_cast<sensors_event_t *>(buffer);        count = numEvents;    }    // NOTE: ASensorEvent and sensors_event_t are the same type    ssize_t size = SensorEventQueue::write(mChannel,//将数据写到一个通道            reinterpret_cast<ASensorEvent const*>(scratch), count);    if (size == -EAGAIN) {        // the destination doesn't accept events anymore, it's probably        // full. For now, we just drop the events on the floor.        //ALOGW("dropping %d events on the floor", count);        return size;    }    return size < 0 ? status_t(size) : status_t(NO_ERROR);}

这样sensorservice就启动起来了