Android应用开发之Android Framework SensorService 分析-职坐标

Android应用开发之Android Framework SensorService 分析

凌雪 2018-10-24 来源：网络阅读 1688 评论 0

摘要：本文将带你了解Android应用开发之Android Framework SensorService 分析，希望本文对大家学Android有所帮助。

本文将带你了解Android应用开发之Android Framework SensorService 分析，希望本文对大家学Android有所帮助。

Android Framework SensorService 分析
1 SensorService 的启动
1.1 SensorService:onFirsrRef()
SensorService 运行在 system_server 里边，在
android/frameworks/base/services/core/jni/com_android_server_SystemServer.cpp
通过实例化一个 SensorService 对象启动，如下:
?1234567891. static void android_server_SystemServer_startSensorService(JNIEnv* /* env */, jobject /* clazz */){2. char propBuf[PROPERTY_VALUE_MAX];3. property_get("system_init.startsensorservice", propBuf, "1");4. if (strcmp(propBuf, "1") == 0) {5. SensorService::instantiate();6. }7.8. }
SensorService 继承关系为：

该 instantiate()方法为 BinderService 的方法，如下：
?12345671. static void instantiate() { publish(); }2. static status_t publish(bool allowIsolated = false) {3. sp<iservicemanager> sm(defaultServiceManager());4. return sm->addService(5. String16(SERVICE::getServiceName()),6. new SERVICE(), allowIsolated);7. }</iservicemanager>

即 new 一个 SensorService 后向 ServiceManager 进行注册，
由于 SensorService 是 RefBase 的子类，

. void RefBase::incStrong(const void* id) const2. {3. weakref_impl* const refs = mRefs;4. refs->incWeak(id);5.6. refs->addStrongRef(id);7. const int32_t c = refs->mStrong.fetch_add(1, std::memory_order_relaxed);8. ALOG_ASSERT(c > 0, "incStrong() called on %p after last strong ref", refs);9. #if PRINT_REFS10. ALOGD("incStrong of %p from %p: cnt=%d\n", this, id, c);11. #endif12. if (c != INITIAL_STRONG_VALUE) {13. return;14. }15.16. int32_t old = refs->mStrong.fetch_sub(INITIAL_STRONG_VALUE,17. std::memory_order_relaxed);18. // A decStrong() must still happen after us.19. ALOG_ASSERT(old > INITIAL_STRONG_VALUE, "0x%x too small", old);20. refs->mBase->onFirstRef();21. }
会在类 RefBase 里边调用 SensorService 的 onFirstRef()方法，开始进行 SensorService 的初始化工作，（这个调用应该
是 Binder 的一个通用机制，通过重载该 onFirstRef()方法进行一个各自的初始化工作），
从 onFirstRef()开始启动，
SensorDevice& dev(SensorDevice::getInstance());
//这边取得 SensorDevice 实例，to do1:Sensordevice 类是什麽、用来做什么的后面分析，
1. ssize_t count = dev.getSensorList(&list);2. for (ssize_t i=0 ; i<count 10.="" 11.="" 12.="" 13.="" 14.="" 15.="" 16.="" 17.="" 18.="" 19.="" 20.="" 21.="" 22.="" 23.="" 24.="" 25.="" 26.="" 27.="" 28.="" 29.="" 3.="" 30.="" 31.="" 32.="" 33.="" 34.="" 5.="" 6.="" 7.="" 8.="" 9.="" bool="" case="" else="" hasaccel="true;" hasgyro="true;" hasmag="true;" if="" new="" orientationindex="i;" pre="" sensor_type_accelerometer:="" sensor_type_game_rotation_vector:="" sensor_type_geomagnetic_rotation_vector:="" sensor_type_gravity:="" sensor_type_gyroscope:="" sensor_type_gyroscope_uncalibrated:="" sensor_type_linear_acceleration:="" sensor_type_magnetic_field:="" sensor_type_orientation:="" sensor_type_rotation_vector:="" switch="" usethissensor="true;" virtualsensorsneeds="">遍历 sensorlist ，创建里边每个 sensor 成员对应的一个 HardwareSensor 放到 sensorservice 层的 sensorList，to do2：HardwareSensor 类是什麽、用来干嘛的后面分析，<pre class="brush:java;">1. if (hasGyro && hasAccel && hasMag) {2. // Add Android virtual sensors if they're not already3. // available in the HAL4. bool needRotationVector = (virtualSensorsNeeds & (1<<sensor_type_rotati 10.="" 11.="" 12.="" 13.="" 14.="" 15.="" 16.="" 17.="" 18.="" 19.="" 20.="" 21.="" 23.="" 24.="" 25.="" 26.="" 27.="" 29.="" 30.="" 5.="" 6.="" 7.="" 8.="" are="" bool="" debugging="" for="" hasaccel="" if="" needgamerotationvector="22." needgeomagrotation="" needgeomagrotationvector="28." needgravitysensor="(virtualSensorsNeeds" needlinearacceleration="9." new="" not="" pre="" sensor_type_gravity="" sensors="" user="" virtual="" virtualsensorsneeds="">若有对应物理 sensor 能够支持的虚拟 sensor，注册虚拟 sensor，<pre class="brush:java;">1. mLooper = new Looper(false);//ques1:这个 Looper 目前还不知到拿来干嘛2. mCurrentOperatingMode = NORMAL;3. mNextSensorRegIndex = 0;4. for (int i = 0; i < SENSOR_REGISTRATIONS_BUF_SIZE; ++i) {5. mLastNSensorRegistrations.push();6. }7.8. mInitCheck = NO_ERROR;9. //创建一个 SensorEventAckReceiver 对象10. mAckReceiver = new SensorEventAckReceiver(this);//把自己扔进去给对方的11. mAckReceiver->run("SensorEventAckReceiver", PRIORITY_URGENT_DISPLAY);12. run("SensorService", PRIORITY_URGENT_DISPLAY);//这边进入 threadLoop</pre>new 了几个对象后，调用 SensorEventAckReceiver:run()以及 SensorService:run(),进入它们各自实现其父类 Thread 的 threadLoop 方法里边，先看 SensorEventAckReceiver:threadLoop(),<pre class="brush:java;">1. bool SensorService::SensorEventAckReceiver::threadLoop() {2. ALOGD("new thread SensorEventAckReceiver");3. sp<looper> looper = mService->getLooper();//获取 SennsorService 的 mLooper4. do {5. bool wakeLockAcquired = mService->isWakeLockAcquired();6. int timeout = -1;7. if (wakeLockAcquired) timeout = 5000;8. int ret = looper->pollOnce(timeout);9. if (ret == ALOOPER_POLL_TIMEOUT) {10. mService->resetAllWakeLockRefCounts();11. }12. } while(!Thread::exitPending());13. return false;14. }</looper></pre>这边目前没有看见什么信息，主要是对 SensorService:onFirsrRef()里边创建的 mLooper 的 通过调用其 pollOnece()方法进行不断的等待、唤醒。 看 SensorService:threadLoop()<h3>1.2 SensorService:threadLoop()</h3>SensorDevice& device(SensorDevice::getInstance());首先获取一个 SensorDevice 实例，<pre class="brush:java;">1. ssize_t count = device.poll(mSensorEventBuffer, numEventMax);2. if (count < 0) {3. ALOGE("sensor poll failed (%s)", strerror(-count));4. break;5. }6. // Reset sensors_event_t.flags to zero for all events in the buffer.7. for (int i = 0; i < count; i++) {8. mSensorEventBuffer[i].flags = 0;9. }</pre>SensorDevice::poll() 大致是通过 hidl 调用 google-hal 的 poll 后，将 hal 层数据装到 sensors_event_t 类型的 mSensorEventBuffer 里边，返回可读取 event 的数目。其中 sensors_event_t 类型是在 hal 层定义的。 SensorService 主要是通过 SensorDevice 与 google-hal 的交互 接着看， <pre class="brush:java;">1. // Make a copy of the connection vector as some connections may be removed during the course2. // of this loop (especially when one-shot sensor events are present in the sensor_event3. // buffer). Promote all connections to StrongPointers before the lock is acquired. If the4. // destructor of the sp gets called when the lock is acquired, it may result in a deadlock5. // as ~SensorEventConnection() needs to acquire mLock again for cleanup. So copy all the6. // strongPointers to a vector before the lock is acquired.7. SortedVector< sp<sensoreventconnection> > activeConnections;8. populateActiveConnections(&activeConnections);</sensoreventconnection></pre> 注释已经说了，就是将 mActiveConnections 做一份拷贝，拷贝到 activeConnections 里边， 继续看，<pre class="brush:java;">1. // handle virtual sensors2. if (count && vcount) {3. sensors_event_t const * const event = mSensorEventBuffer;4. if (!mActiveVirtualSensors.empty()) {5. size_t k = 0;6. SensorFusion& fusion(SensorFusion::getInstance());//获取一个 SensorFusion7. if (fusion.isEnabled()) {8. for (size_t i=0 ; i<size_t(count) 10.="" 11.="" 12.="" 13.="" 14.="" 9.="" :="" count="" for="" handle="" i="0" if="" int="" k="" minbuffersize="" size_t="">= minBufferSize) {15. ALOGE("buffer too small to hold all events: "16. "count=%zd, k=%zu, size=%zu",17. count, k, minBufferSize);18. break;19. }20. sensors_event_t out;21. // 根据 handle 获取到在22. //SensorService::onFirstRef 里边注册的 SensorInterface23. sp<sensorinterface> si = mSensors.getInterface(handle);24. if (si == nullptr) {25. ALOGE("handle %d is not an valid virtual sensor", handle);26. continue;27. }28. //看看这边做了什么，估计是取数据后存数据29. //调用对应 SensorInterface 实例的 process 方法30. if (si->process(&out, event[i])) {31. mSensorEventBuffer[count + k] = out;32. k++;33. }34. }35. }36. if (k) {37. // record the last synthesized values38. recordLastValueLocked(&mSensorEventBuffer[count], k);39. count += k;40. // sort the buffer by time-stamps41. sortEventBuffer(mSensorEventBuffer, count);42. }43. }44. }</sensorinterface></size_t(count)></pre>那么，接下来，先回过头去将 onFirstRef 里边的 registerSensor( new HardwareSensor(list[i]) );<pre class="brush:java;">1. const Sensor& SensorService::registerSensor(SensorInterface* s, bool isDebug, bool isVirtual) {2. int handle = s->getSensor().getHandle();3. int type = s->getSensor().getType();4. if (mSensors.add(handle, s, isDebug, isVirtual)){5. mRecentEvent.emplace(handle, new RecentEventLogger(type));6. return s->getSensor();7. } else {8. return mSensors.getNonSensor();9. }10. }</pre>，将每个sensor_t类型的sensor初始化一个对应的HardwareSensor对象后和对应的handle一起放到mSensors里边， 这个 mSensor 对象为 SensorList 类型。 这样的话，前边 sp<sensorinterface> si = mSensors.getInterface(handle);</sensorinterface>通过 handle 获取 SensorInterface，就是将前面装进去的 HardwareSensor 对象取出来，进而调用其 si->process(&out, event[i])函数，那么看看 HardwareSensor 的 process()方法咯 <pre class="brush:java;">1. bool HardwareSensor::process(sensors_event_t* outEvent,2. const sensors_event_t& event) {3. *outEvent = event;4. return true;5. }</pre>，那么 event[i]呢，看看这东西是在哪儿被赋值的，为<pre class="brush:java;">1. ssize_t count = device.poll(mSensorEventBuffer, numEventMax);2. sensors_event_t const * const event = mSensorEventBuffer;</pre>mSensorEventBuffer 就是在前边通过 device.poll 获取 hal 层的数据的嘛，是作为指针指向底层的一个数组的，再传给 event，event再转给这边的out，饶了一大圈，原来只不过si->process(&out, event[i])是将hal层的各个sensors_event_t 的 sensor 内容装到 out 里边。 继续看 SensorService:threadLoop()方法，<pre class="brush:java;">1. if (si->process(&out, event[i])) {2. mSensorEventBuffer[count + k] = out;3. k++;4. }</pre>又把 out 装到 mSensorEventBuffer 的空余的下一个单元,<pre class="brush:java;">1. // Send our events to clients. Check the state of wake lock for each client and release the2. // lock if none of the clients need it.3. bool needsWakeLock = false;4. size_t numConnections = activeConnections.size();5. for (size_t i=0 ; i < numConnections; ++i) {6. if (activeConnections[i] != 0) {7. activeConnections[i]->sendEvents(mSensorEventBuffer, count,8. mSensorEventScratch,mMapFlushEventsToConnections);9. needsWakeLock |= activeConnections[i]->needsWakeLock();10. // If the connection has one-shot sensors, it may be cleaned up after first trigger.11. // Early check for one-shot sensors.12. if (activeConnections[i]->hasOneShotSensors()) {13. cleanupAutoDisabledSensorLocked(activeConnections[i],14. mSensorEventBuffer,count);15. }16. }17. }</pre>通过 activeConnections[i]->sendEvents() 将数据发送出去，然后继续循环， ssize_t size = SensorEventQueue::write(mChannel, reinterpret_cast(scratch), count); 这边发送的话最后是通过一个通过 unix socket 发出去的， 这边接收的就不分析了，估计是 SensorManager 读取到数据后给应用，取数据的方式设计思想应该和这边与 hal 层 交互一样，留到后面分析 SensorManager 再分析。 小总结一下，SensorService 通过 SensorService::onFirstRef() 执行一些初始化后，就在 SensorService::threadLoop()里 边不断通过 poll 从 hal 层取数据然后通过 unix socket 发送出去.<h2>2 主要类分析</h2><h3>2.1 SensorList 类</h3>里边的 mHandleMap 成员为 map 类型，主要是用来装 SensorInterface 和 handle 的，<img style="width: 630px; height: 127.729px;" alt="\" src="/uploadfile/Collfiles/20180510/20180510092639772.png">对于 SensorService::registerSensor()方法，注册一个 sensor，也就是将 从 google-hal 层获取到的 sensor_t 初始化一个 HardwareSensor 对象后，将其与其对应的 handle 添加进一个 map 里边.<pre class="brush:java;">1. const Sensor& SensorService::registerSensor(SensorInterface* s, bool isDebug, bool isVirtual) {2. int handle = s->getSensor().getHandle();3. int type = s->getSensor().getType();4. if (mSensors.add(handle, s, isDebug, isVirtual)){5. mRecentEvent.emplace(handle, new RecentEventLogger(type));6. return s->getSensor();7. } else {8. return mSensors.getNonSensor();9. }10. }11.12. mSensors 为 SensorList 类型，看其 add()方法，13. bool SensorList::add(14. int handle, SensorInterface* si, bool isForDebug, bool isVirtual) {15. std::lock_guard<std::mutex> lk(mLock);16. if (handle == si->getSensor().getHandle() &&17. mUsedHandle.insert(handle).second) {18. // will succeed as the mUsedHandle does not have this handle19. mHandleMap.emplace(handle, Entry(si, isForDebug, isVirtual));20. return true;21. }22. // handle exist already or handle mismatch23. return false;24. }</std::mutex></pre>用 si 初始化一个匿名 Entry 类型后，与 handle 一起添加进 mHandleMap <h3>2.2 sensors_event_t</h3>由 google-hal 定义在/android/hardware/libhardware/include/hardware/sensors.h 里边<img style="width: 238px; height: 68px;" alt="\" src="/uploadfile/Collfiles/20180510/20180510092639773.png"><h3>2.3 SensorEventConnection</h3><img style="width: 630px; height: 260.588px;" alt="\" src="/uploadfile/Collfiles/20180510/20180510092639774.png"><h2>3 遗留问题分析</h2>/************************************************/ to do1:Sensordevice 类是什麽、用来做什么的后面分析， to do2:harwareSensor 类是什麽、用来干嘛的后面分析， 好了，接下来对前面遗留的疑问做个分析， 3.1 to do1:SensorDevice 类是什麽、用来做什么的 ans:SensorDevice 主要是获取到 hal 层的对象 sp mSensors 后，利用 mSensors 通过 hidl 机制调用 hal 层的方法。 该 ISensors 类型定义在 android/hardware/interfaces/sensors/1.0/ISensors.hal SensorDevice 类 SensorDevice 继承了 BinderService<sensorservice>,BnSensorServer,Thread 先看构造函数</sensorservice></android::hardware::sensors::v1_0::isensors><pre class="brush:java;">1. SensorDevice::SensorDevice() : mHidlTransportErrors(20) {2. if (!connectHidlService()) {3. return;4. }5.6. float minPowerMa = 0.001; // 1 microAmp7.8. checkReturn(mSensors->getSensorsList(9. [&](const auto &list) {10. const size_t count = list.size();11.12. mActivationCount.setCapacity(count);13. Info model;14. for (size_t i=0 ; i < count; i++) {15. sensor_t sensor;16. convertToSensor(list[i], &sensor);17. // Sanity check and clamp power if it is 0 (or close)18. if (sensor.power < minPowerMa) {19. ALOGE("Reported power %f not deemed sane, clamping to %f",20. sensor.power, minPowerMa);21. sensor.power = minPowerMa;22. }23. mSensorList.push_back(sensor);24.25. mActivationCount.add(list[i].sensorHandle, model);26.27. checkReturn(mSensors->activate(list[i].sensorHandle, 0 /* enabled */));28. }29. }));30.31. mIsDirectReportSupported =32. (checkReturn(mSensors->unregisterDirectChannel(-1)) != Result::INVALID_OPERATION);33. }</pre>对于变量类型 sensor_t，sensor_t 是在 google-hal 里边定义的， 路径: android/hardware/libhardware/include/hardware/sensors.h<img style="width: 238px; height: 156px;" alt="\" src="/uploadfile/Collfiles/20180510/20180510092640775.png">先调用 connectHidlService ()方法，在这里边通过 hidl 机制获取 mSensors, mSensors = ISensors::getService(); //获取 hal 层对象实例，这样的话接下来就能够通过该 mSensors 来调用 hal 层的服务了。 mSensors 类型为 sp mSensors， 接着通过 mSensors（sp mSensors）调用 hal 层的 getSensorsList，然后通 过 convertToSensor(list[i], &sensor)获取 sensor 后装进 mSensorList 里边; 这边获取到 hal 层的 sensor 为 sensor_t 类型，定义在 android/hardware/libhardware/include/hardware/sensors.h 里边，</android::hardware::sensors::v1_0::isensors></android::hardware::sensors::v1_0::isensors>一句话概括构造函数，就是: 通过 connectHidlService ()与 hal 层建立联系后获取 hal 层的 SensorList<h3>3.2 to do2: harwareSensor 类是什麽、用来干嘛的</h3>要分析 HardwareSensor 类，首先要去分析 dev.getSensorList(&list) 以及变量类型 sensor_t， 那就要先分析 SensorDevice 了 通过 dev.getSensorList(&list)获取到的 hal 层的 sensor_t 的变量，用来初始化 HardwareSensor 对象，其实就是对其父 类 BaseSensor 的 mSensor（Sensor mSensor）成员进行初始化，该 Sensor 类我目前估计就是 framework 层的 Sensor 类通用表示了，定义在 frameworks/native/libs/sensor/include/sensor 里边，也就是将 hal 层获取到的 sensor_t 类型 变量转换层 framework 层的 Sensor 类型变量。</asensorevent></sensor_type_rotati> </pre></count>