【Android】Android(安卓)SurfaceFlinger之SurfaceFlinger启动过程

SurfaceFlinger的启动脚本surfaceflinger.rc内容如下：

service surfaceflinger /system/bin/surfaceflinger    class core    user system    group graphics drmrpc readproc    onrestart restart zygote    writepid /dev/stune/foreground/tasks

其main函数在frameworks/native/services/surfaceflinger/main_surfaceflinger.cpp，如下：

int main(int, char**) {    signal(SIGPIPE, SIG_IGN);    // When SF is launched in its own process, limit the number of    // binder threads to 4.    ProcessState::self()->setThreadPoolMaxThreadCount(4);    // start the thread pool    sp<ProcessState> ps(ProcessState::self());    ps->startThreadPool();    // instantiate surfaceflinger    sp<SurfaceFlinger> flinger = new SurfaceFlinger();    setpriority(PRIO_PROCESS, 0, PRIORITY_URGENT_DISPLAY);    set_sched_policy(0, SP_FOREGROUND);#ifdef ENABLE_CPUSETS    // Put most SurfaceFlinger threads in the system-background cpuset    // Keeps us from unnecessarily using big cores    // Do this after the binder thread pool init    set_cpuset_policy(0, SP_SYSTEM);#endif    // initialize before clients can connect    flinger->init();    // publish surface flinger    sp<IServiceManager> sm(defaultServiceManager());    sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false);    // publish GpuService    sp<GpuService> gpuservice = new GpuService();    sm->addService(String16(GpuService::SERVICE_NAME), gpuservice, false);    struct sched_param param = {0};    param.sched_priority = 2;    if (sched_setscheduler(0, SCHED_FIFO, &param) != 0) {        ALOGE("Couldn't set SCHED_FIFO");    }    // run surface flinger in this thread    flinger->run();    return 0;}

1、SurfaceFlinger首先忽略了SIGPIPE信号，为什么要这么做呢？因为在SurfaceFlinger的Client-Server模型中，或者说IPC机制中，很可能会触发SIGPIPE信号，而这个信号的默认动作是终止进程，并不是我们想要的行为，所以主动对SIGPIPE信号进行处理。

2、接着，开启线程池，不过限制了线程的最大数量为4个，如果线程过多，可能会影响程序性能。

3、随后，创建SurfaceFlinger对象，在其构造函数中，主要是一些成员变量的初始化工作，同时还有一个高逼格的DDMS配置，即Dalvik Debug Monitor Service，是一个调试神器。如果配置了DDMS，就会dlopen libsurfaceflinger_ddmconnection.so，并dlsym其中的DdmConnection_start，最后建立SurfaceFlinger与DDMS的连接。

class SurfaceFlinger : public BnSurfaceComposer,                       private IBinder::DeathRecipient,                       private HWComposer::EventHandlerSurfaceFlinger::SurfaceFlinger()    :   BnSurfaceComposer(),        mTransactionFlags(0),        mTransactionPending(false),        mAnimTransactionPending(false),        mLayersRemoved(false),        mRepaintEverything(0),        mRenderEngine(NULL),        mBootTime(systemTime()),        mBuiltinDisplays(),        mVisibleRegionsDirty(false),        mGeometryInvalid(false),        mAnimCompositionPending(false),        mDebugRegion(0),        mDebugDDMS(0),        mDebugDisableHWC(0),        mDebugDisableTransformHint(0),        mDebugInSwapBuffers(0),        mLastSwapBufferTime(0),        mDebugInTransaction(0),        mLastTransactionTime(0),        mBootFinished(false),        mForceFullDamage(false),        mPrimaryDispSync("PrimaryDispSync"),        mPrimaryHWVsyncEnabled(false),        mHWVsyncAvailable(false),        mHasColorMatrix(false),        mHasPoweredOff(false),        mFrameBuckets(),        mTotalTime(0),        mLastSwapTime(0){    ALOGI("SurfaceFlinger is starting");    // debugging stuff...    char value[PROPERTY_VALUE_MAX];    property_get("ro.bq.gpu_to_cpu_unsupported", value, "0");    mGpuToCpuSupported = !atoi(value);    property_get("debug.sf.showupdates", value, "0");    mDebugRegion = atoi(value);    property_get("debug.sf.ddms", value, "0");    mDebugDDMS = atoi(value);    if (mDebugDDMS) {        if (!startDdmConnection()) {            // start failed, and DDMS debugging not enabled            mDebugDDMS = 0;        }    }    ALOGI_IF(mDebugRegion, "showupdates enabled");    ALOGI_IF(mDebugDDMS, "DDMS debugging enabled");    property_get("debug.sf.disable_backpressure", value, "0");    mPropagateBackpressure = !atoi(value);    ALOGI_IF(!mPropagateBackpressure, "Disabling backpressure propagation");    property_get("debug.sf.disable_hwc_vds", value, "0");    mUseHwcVirtualDisplays = !atoi(value);    ALOGI_IF(!mUseHwcVirtualDisplays, "Disabling HWC virtual displays");}

因为这里的SurfaceFlinger对象是一个StrongPointer，所以首先会走到RefBase的onFirstRef，这里就做了一件事情，MessageQueue初始化，保存SurfaceFlinger，并创建了消息队列所需的Looper和Handler。

void SurfaceFlinger::onFirstRef(){    mEventQueue.init(this);}void MessageQueue::init(const sp& flinger){    mFlinger = flinger;    mLooper = new Looper(true);    mHandler = new Handler(*this);}

4、SurfaceFlinger实例化后，设置进程优先级和事务处理策略。

5、然后，进入如下的SurfaceFlinger::init，主要是EGL配置、event线程启动、硬件composer初始化等，而且著名的VSync也在这里出现了。

void SurfaceFlinger::init() {    ALOGI(  "SurfaceFlinger's main thread ready to run. "            "Initializing graphics H/W...");    { // Autolock scope        Mutex::Autolock _l(mStateLock);        // initialize EGL for the default display        mEGLDisplay = eglGetDisplay(EGL_DEFAULT_DISPLAY);        eglInitialize(mEGLDisplay, NULL, NULL);        // start the EventThread        sp vsyncSrc = new DispSyncSource(&mPrimaryDispSync,                vsyncPhaseOffsetNs, true, "app");        mEventThread = new EventThread(vsyncSrc, *this);        sp sfVsyncSrc = new DispSyncSource(&mPrimaryDispSync,                sfVsyncPhaseOffsetNs, true, "sf");        mSFEventThread = new EventThread(sfVsyncSrc, *this);        mEventQueue.setEventThread(mSFEventThread);        // set SFEventThread to SCHED_FIFO to minimize jitter        struct sched_param param = {0};        param.sched_priority = 2;        if (sched_setscheduler(mSFEventThread->getTid(), SCHED_FIFO, ¶m) != 0) {            ALOGE("Couldn't set SCHED_FIFO for SFEventThread");        }        // Get a RenderEngine for the given display / config (can't fail)        mRenderEngine = RenderEngine::create(mEGLDisplay,                HAL_PIXEL_FORMAT_RGBA_8888);    }    // Drop the state lock while we initialize the hardware composer. We drop    // the lock because on creation, it will call back into SurfaceFlinger to    // initialize the primary display.    mHwc = new HWComposer(this);    mHwc->setEventHandler(static_cast(this));    Mutex::Autolock _l(mStateLock);    // retrieve the EGL context that was selected/created    mEGLContext = mRenderEngine->getEGLContext();    LOG_ALWAYS_FATAL_IF(mEGLContext == EGL_NO_CONTEXT,            "couldn't create EGLContext");    // make the GLContext current so that we can create textures when creating    // Layers (which may happens before we render something)    getDefaultDisplayDevice()->makeCurrent(mEGLDisplay, mEGLContext);    mEventControlThread = new EventControlThread(this);    mEventControlThread->run("EventControl", PRIORITY_URGENT_DISPLAY);    // initialize our drawing state    mDrawingState = mCurrentState;    // set initial conditions (e.g. unblank default device)    initializeDisplays();    mRenderEngine->primeCache();    // start boot animation    startBootAnim();    ALOGV("Done initializing");}

6、在Android系统中有一个ServiceManager，专门用来管理所有的服务，而SurfaceFlinger不是由ServiceManager启动的，因此需要向ServiceManager注册SurfaceFlinger，同时还注册了GpuService。

7、最后通过SurfaceFlinger::run，进入消息循环，SurfaceFlinger启动成功，开始工作。

void SurfaceFlinger::run() {    do {        waitForEvent();    } while (true);}

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