SurfaceFlinger principl

基于Android 6.0源码， 分析SurfaceFlinger原理

frameworks/native/services/surfaceflinger/  - main_surfaceflinger.cpp  - SurfaceFlinger.cpp  - DispSync.cpp  - MessageQueue.cpp  - DisplayHardware/HWComposer.cpp  frameworks/native/libs/gui/DisplayEventReceiver.cppframeworks/native/libs/gui/BitTube.cpp

一. 概述

Android系统的图形处理相关的模块，就不得不提surfaceflinger，这是由init进程所启动的 守护进程，在init.rc中该服务如下：

service surfaceflinger /system/bin/surfaceflinger    class core    user system    group graphics drmrpc    onrestart restart zygote    writepid /dev/cpuset/system-background/tasks

surfaceflinger服务属于核心类(core class)，另外，当surfaceflinger重启时会触发zygote的重启。 surfaceflinger服务启动的起点便是如下的main()函数。

二. 启动过程

2.1 main

[-> main_surfaceflinger.cpp]

int main(int, char**) {    ProcessState::self()->setThreadPoolMaxThreadCount(4);    sp<ProcessState> ps(ProcessState::self());    ps->startThreadPool();    //实例化surfaceflinger【见小节2.2】    sp<SurfaceFlinger> flinger =  new SurfaceFlinger();    setpriority(PRIO_PROCESS, 0, PRIORITY_URGENT_DISPLAY);    set_sched_policy(0, SP_FOREGROUND);    //初始化【见小节2.3】    flinger->init();    //发布surface flinger，注册到Service Manager    sp<IServiceManager> sm(defaultServiceManager());    sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false);    // 运行在当前线程【见小节2.11】    flinger->run();    return 0;}

该方法的主要功能：

• 设定surfaceflinger进程的binder线程池个数上限为4，并启动binder线程池；
• 创建SurfaceFlinger对象；【见小节2.1】
• 设置surfaceflinger进程为高优先级以及前台调度策略；
• 初始化SurfaceFlinger；【见小节2.3】
• 将”SurfaceFlinger”服务注册到Service Manager;
• 在当前主线程执行SurfaceFlinger的run方法。【见小节2.11】

2.2 创建SurfaceFlinger

[-> SurfaceFlinger.cpp]

SurfaceFlinger::SurfaceFlinger()    :   BnSurfaceComposer(),        mTransactionFlags(0),        mTransactionPending(false),        mAnimTransactionPending(false),        mLayersRemoved(false),        mRepaintEverything(0),        mRenderEngine(NULL),        mBootTime(systemTime()),        mVisibleRegionsDirty(false),        mHwWorkListDirty(false),        mAnimCompositionPending(false),        mDebugRegion(0),        mDebugDDMS(0),        mDebugDisableHWC(0),        mDebugDisableTransformHint(0),        mDebugInSwapBuffers(0),        mLastSwapBufferTime(0),        mDebugInTransaction(0),        mLastTransactionTime(0),        mBootFinished(false),        mForceFullDamage(false),        mPrimaryHWVsyncEnabled(false),        mHWVsyncAvailable(false),        mDaltonize(false),        mHasColorMatrix(false),        mHasPoweredOff(false),        mFrameBuckets(),        mTotalTime(0),        mLastSwapTime(0){    ALOGI("SurfaceFlinger is starting");    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);       }

SurfaceFlinger继承于BnSurfaceComposer,IBinder::DeathRecipient,HWComposer::EventHandler

flinger的数据类型为sp 强指针类型，当首次被强指针引用时则执行OnFirstRef()

2.2.1 SF.onFirstRef

void SurfaceFlinger::onFirstRef(){    mEventQueue.init(this);}

2.2.2 MQ.init

[-> MessageQueue.cpp]

void MessageQueue::init(const sp<SurfaceFlinger>& flinger){    mFlinger = flinger;    mLooper = new Looper(true);    mHandler = new Handler(*this); //【见小节2.2.3】}

这个Handler是MessageQueue的内部类Handler。

2.2.3 MQ.Handler

[-> MessageQueue.cpp]

class MessageQueue {    class Handler : public MessageHandler {        enum {            eventMaskInvalidate     = 0x1,            eventMaskRefresh        = 0x2,            eventMaskTransaction    = 0x4        };        MessageQueue& mQueue;        int32_t mEventMask;    public:        Handler(MessageQueue& queue) : mQueue(queue), mEventMask(0) { }        virtual void handleMessage(const Message& message);        void dispatchRefresh();        void dispatchInvalidate();        void dispatchTransaction();    };    ...}

2.3 SF.init

[-> SurfaceFlinger.cpp]

void SurfaceFlinger::init() {    Mutex::Autolock _l(mStateLock);    //初始化EGL，作为默认的显示    mEGLDisplay = eglGetDisplay(EGL_DEFAULT_DISPLAY);    eglInitialize(mEGLDisplay, NULL, NULL);    // 初始化硬件composer对象【见小节2.4】    mHwc = new HWComposer(this, *static_cast<HWComposer::EventHandler *>(this));    //获取RenderEngine引擎    mRenderEngine = RenderEngine::create(mEGLDisplay, mHwc->getVisualID());    //检索创建的EGL上下文    mEGLContext = mRenderEngine->getEGLContext();    //初始化非虚拟显示屏【见小节2.5】    for (size_t i=0 ; i<DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES ; i++) {        DisplayDevice::DisplayType type((DisplayDevice::DisplayType)i);        //建立已连接的显示设备        if (mHwc->isConnected(i) || type==DisplayDevice::DISPLAY_PRIMARY) {            bool isSecure = true;            createBuiltinDisplayLocked(type);            wp<IBinder> token = mBuiltinDisplays[i];            sp<IGraphicBufferProducer> producer;            sp<IGraphicBufferConsumer> consumer;            //创建BufferQueue的生产者和消费者            BufferQueue::createBufferQueue(&producer, &consumer,                    new GraphicBufferAlloc());            sp<FramebufferSurface> fbs = new FramebufferSurface(*mHwc, i, consumer);            int32_t hwcId = allocateHwcDisplayId(type);            //创建显示设备            sp<DisplayDevice> hw = new DisplayDevice(this,                    type, hwcId, mHwc->getFormat(hwcId), isSecure, token,                    fbs, producer,                    mRenderEngine->getEGLConfig());            if (i > DisplayDevice::DISPLAY_PRIMARY) {                hw->setPowerMode(HWC_POWER_MODE_NORMAL);            }            mDisplays.add(token, hw);        }    }    getDefaultDisplayDevice()->makeCurrent(mEGLDisplay, mEGLContext);    //创建DispSyncSource对象【2.6】    sp<VSyncSource> vsyncSrc = new DispSyncSource(&mPrimaryDispSync,            vsyncPhaseOffsetNs, true, "app");    //创建线程EventThread 【见小节2.7】    mEventThread = new EventThread(vsyncSrc);         sp<VSyncSource> sfVsyncSrc = new DispSyncSource(&mPrimaryDispSync,            sfVsyncPhaseOffsetNs, true, "sf");    mSFEventThread = new EventThread(sfVsyncSrc);        //设置EventThread 【见小节2.8】    mEventQueue.setEventThread(mSFEventThread);    //【见小节2.9】    mEventControlThread = new EventControlThread(this);    mEventControlThread->run("EventControl", PRIORITY_URGENT_DISPLAY);    //当不存在HWComposer时，则设置软件vsync    if (mHwc->initCheck() != NO_ERROR) {        mPrimaryDispSync.setPeriod(16666667);    }    //初始化绘图状态    mDrawingState = mCurrentState;    //初始化显示设备    initializeDisplays();    //启动开机动画【2.10】    startBootAnim();}

主要功能：

• 初始化EGL相关；
• 创建HWComposer对象；
• 初始化非虚拟显示屏；
• 启动app和sf两个EventThread线程；
• 启动开机动画；

2.4 创建HWComposer

[-> HWComposer.cpp]

HWComposer::HWComposer(        const sp<SurfaceFlinger>& flinger,        EventHandler& handler)    : mFlinger(flinger),      mFbDev(0), mHwc(0), mNumDisplays(1),      mCBContext(new cb_context),      mEventHandler(handler),      mDebugForceFakeVSync(false){    ...    bool needVSyncThread = true;    int fberr = loadFbHalModule(); //加载framebuffer的HAL层模块    loadHwcModule(); //加载HWComposer模块    //标记已分配的display ID    for (size_t i=0 ; i<NUM_BUILTIN_DISPLAYS ; i++) {        mAllocatedDisplayIDs.markBit(i);    }    if (mHwc) {        if (mHwc->registerProcs) {            mCBContext->hwc = this;            mCBContext->procs.invalidate = &hook_invalidate;            //VSYNC信号的回调方法            mCBContext->procs.vsync = &hook_vsync;            if (hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_1))                mCBContext->procs.hotplug = &hook_hotplug;            else                mCBContext->procs.hotplug = NULL;            memset(mCBContext->procs.zero, 0, sizeof(mCBContext->procs.zero));            //注册回调函数            mHwc->registerProcs(mHwc, &mCBContext->procs);        }        //进入此处，说明已成功打开硬件composer设备，则不再需要vsync线程        needVSyncThread = false;        eventControl(HWC_DISPLAY_PRIMARY, HWC_EVENT_VSYNC, 0);        ...    }    ...    if (needVSyncThread) {        //不支持硬件的VSYNC，则会创建线程来模拟定时VSYNC信号        mVSyncThread = new VSyncThread(*this);    }}

HWComposer代表着硬件显示设备，注册了VSYNC信号的回调。VSYNC信号本身是由显示驱动产生的， 在不支持硬件的VSYNC，则会创建“VSyncThread”线程来模拟定时VSYNC信号。

2.5 显示设备

[-> SurfaceFlinger.cpp]

void SurfaceFlinger::init() {    ...    for (size_t i=0 ; i<DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES ; i++) {        DisplayDevice::DisplayType type((DisplayDevice::DisplayType)i);        //建立已连接的显示设备        if (mHwc->isConnected(i) || type==DisplayDevice::DISPLAY_PRIMARY) {            bool isSecure = true;            createBuiltinDisplayLocked(type);            wp<IBinder> token = mBuiltinDisplays[i];            sp<IGraphicBufferProducer> producer;            sp<IGraphicBufferConsumer> consumer;            //创建BufferQueue的生产者和消费者            BufferQueue::createBufferQueue(&producer, &consumer,                    new GraphicBufferAlloc());            sp<FramebufferSurface> fbs = new FramebufferSurface(*mHwc, i, consumer);            int32_t hwcId = allocateHwcDisplayId(type);            //创建显示设备            sp<DisplayDevice> hw = new DisplayDevice(this,                    type, hwcId, mHwc->getFormat(hwcId), isSecure, token,                    fbs, producer,                    mRenderEngine->getEGLConfig());            if (i > DisplayDevice::DISPLAY_PRIMARY) {                hw->setPowerMode(HWC_POWER_MODE_NORMAL);            }            mDisplays.add(token, hw);        }    }    ...}

创建IGraphicBufferProducer和IGraphicBufferConsumer，以及FramebufferSurface，DisplayDevice对象。另外， 显示设备有3类：主设备，扩展设备，虚拟设备。其中前两个都是内置显示设备，故NUM_BUILTIN_DISPLAY_TYPES=2，

2.6 DispSyncSource

[-> SurfaceFlinger.cpp]

class DispSyncSource : public VSyncSource, private DispSync::Callback {  DispSyncSource(DispSync* dispSync, nsecs_t phaseOffset, bool traceVsync,      const char* label) :          mValue(0),          mTraceVsync(traceVsync),          mVsyncOnLabel(String8::format("VsyncOn-%s", label)),          mVsyncEventLabel(String8::format("VSYNC-%s", label)),          mDispSync(dispSync),          mCallbackMutex(),          mCallback(),          mVsyncMutex(),          mPhaseOffset(phaseOffset),          mEnabled(false) {}  ...   }

2.7 EventThread线程

[-> EventThread.cpp]

EventThread::EventThread(const sp<VSyncSource>& src)    : mVSyncSource(src),      mUseSoftwareVSync(false),      mVsyncEnabled(false),      mDebugVsyncEnabled(false),      mVsyncHintSent(false) {    for (int32_t i=0 ; i<DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES ; i++) {        mVSyncEvent[i].header.type = DisplayEventReceiver::DISPLAY_EVENT_VSYNC;        mVSyncEvent[i].header.id = 0;        mVSyncEvent[i].header.timestamp = 0;        mVSyncEvent[i].vsync.count =  0;    }    struct sigevent se;    se.sigev_notify = SIGEV_THREAD;    se.sigev_value.sival_ptr = this;    se.sigev_notify_function = vsyncOffCallback;    se.sigev_notify_attributes = NULL;    timer_create(CLOCK_MONOTONIC, &se, &mTimerId);}

EventThread继承于Thread和VSyncSource::Callback两个类。

2.7.1 ET.onFirstRef

[-> EventThread.cpp]

void EventThread::onFirstRef() {    //运行EventThread线程【见小节2.7.2】    run("EventThread", PRIORITY_URGENT_DISPLAY + PRIORITY_MORE_FAVORABLE);}

2.7.2 ET.threadLoop

[-> EventThread.cpp]

bool EventThread::threadLoop() {    DisplayEventReceiver::Event event;    Vector< sp<EventThread::Connection> > signalConnections;    // 等待事件【见小节2.7.3】    signalConnections = waitForEvent(&event);     //分发事件给所有的监听者    const size_t count = signalConnections.size();    for (size_t i=0 ; i<count ; i++) {        const sp<Connection>& conn(signalConnections[i]);        //传递事件【见小节3.10】        status_t err = conn->postEvent(event);        if (err == -EAGAIN || err == -EWOULDBLOCK) {            //可能此时connection已满，则直接抛弃事件            ALOGW("EventThread: dropping event (%08x) for connection %p",                    event.header.type, conn.get());        } else if (err < 0) {            //发生致命错误，则清理该连接            removeDisplayEventConnection(signalConnections[i]);        }    }    return true;}

2.7.3 waitForEvent

[-> EventThread.cpp]

Vector< sp<EventThread::Connection> > EventThread::waitForEvent(        DisplayEventReceiver::Event* event){    Mutex::Autolock _l(mLock);    Vector< sp<EventThread::Connection> > signalConnections;    do {        bool eventPending = false;        bool waitForVSync = false;        size_t vsyncCount = 0;        nsecs_t timestamp = 0;        for (int32_t i=0 ; i<DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES ; i++) {            timestamp = mVSyncEvent[i].header.timestamp;            if (timestamp) {                *event = mVSyncEvent[i];                mVSyncEvent[i].header.timestamp = 0;                vsyncCount = mVSyncEvent[i].vsync.count;                break;            }        }        if (!timestamp) {            //没有vsync事件，则查看其它事件            eventPending = !mPendingEvents.isEmpty();            if (eventPending) {                //存在其它事件可用于分发                *event = mPendingEvents[0];                mPendingEvents.removeAt(0);            }        }        //查找正在等待事件的连接        size_t count = mDisplayEventConnections.size();        for (size_t i=0 ; i<count ; i++) {            sp<Connection> connection(mDisplayEventConnections[i].promote());            if (connection != NULL) {                bool added = false;                if (connection->count >= 0) {                    //需要vsync事件，由于至少存在一个连接正在等待vsync                    waitForVSync = true;                    if (timestamp) {                        if (connection->count == 0) {                            connection->count = -1;                            signalConnections.add(connection);                            added = true;                        } else if (connection->count == 1 ||                                (vsyncCount % connection->count) == 0) {                            signalConnections.add(connection);                            added = true;                        }                    }                }                if (eventPending && !timestamp && !added) {                    //没有vsync事件需要处理(timestamp==0),但存在pending消息                    signalConnections.add(connection);                }            } else {                //该连接已死亡，则直接清理                mDisplayEventConnections.removeAt(i);                --i; --count;            }        }        if (timestamp && !waitForVSync) {            //接收到VSYNC，但没有client需要它，则直接关闭VSYNC            disableVSyncLocked();        } else if (!timestamp && waitForVSync) {            //至少存在一个client，则需要使能VSYNC            enableVSyncLocked();        }        if (!timestamp && !eventPending) {            if (waitForVSync) {                bool softwareSync = mUseSoftwareVSync;                nsecs_t timeout = softwareSync ? ms2ns(16) : ms2ns(1000);                if (mCondition.waitRelative(mLock, timeout) == TIMED_OUT) {                    mVSyncEvent[0].header.type = DisplayEventReceiver::DISPLAY_EVENT_VSYNC;                    mVSyncEvent[0].header.id = DisplayDevice::DISPLAY_PRIMARY;                    mVSyncEvent[0].header.timestamp = systemTime(SYSTEM_TIME_MONOTONIC);                    mVSyncEvent[0].vsync.count++;                }            } else {                //不存在对vsync感兴趣的连接，即将要进入休眠                mCondition.wait(mLock);            }        }    } while (signalConnections.isEmpty());    //到此处，则保证存在timestamp以及连接    return signalConnections;}

EventThread线程，进入mCondition的wait()方法，等待唤醒。

2.8 setEventThread

[-> MessageQueue.cpp]

void MessageQueue::setEventThread(const sp<EventThread>& eventThread){    mEventThread = eventThread;    //创建连接    mEvents = eventThread->createEventConnection();    //获取BitTube对象    mEventTube = mEvents->getDataChannel();    //监听BitTube，一旦有数据，则调用cb_eventReceiver    mLooper->addFd(mEventTube->getFd(), 0, Looper::EVENT_INPUT,            MessageQueue::cb_eventReceiver, this);}

2.9 EventControlThread线程

[-> EventControlThread.cpp]

EventControlThread::EventControlThread(const sp<SurfaceFlinger>& flinger):        mFlinger(flinger),        mVsyncEnabled(false) {}bool EventControlThread::threadLoop() {    Mutex::Autolock lock(mMutex);    bool vsyncEnabled = mVsyncEnabled;    mFlinger->eventControl(HWC_DISPLAY_PRIMARY, SurfaceFlinger::EVENT_VSYNC,            mVsyncEnabled);    while (true) {        status_t err = mCond.wait(mMutex);        ...                if (vsyncEnabled != mVsyncEnabled) {            mFlinger->eventControl(HWC_DISPLAY_PRIMARY,                    SurfaceFlinger::EVENT_VSYNC, mVsyncEnabled);            vsyncEnabled = mVsyncEnabled;        }    }    return false;}

EventControlThread也是继承于Thread。

2.10 startBootAnim

[-> SurfaceFlinger.cpp]

void SurfaceFlinger::startBootAnim() {    property_set("service.bootanim.exit", "0");    property_set("ctl.start", "bootanim");}

通过控制ctl.start属性，设置成bootanim值，则触发init进程来创建开机动画进程bootanim， 到此，则开始显示开机过程的动画。 从小节[2.4 ~2.9]都是介绍SurfaceFlinger的init()过程， 紧接着便执行其run()方法。

2.11 SF.run

[-> SurfaceFlinger.cpp]

void SurfaceFlinger::run() {    do {        //不断循环地等待事件【见小节2.12】        waitForEvent();     } while (true);}

2.12 SF.waitForEvent

[-> SurfaceFlinger.cpp]

void SurfaceFlinger::waitForEvent() {    mEventQueue.waitMessage(); //【2.13】}

mEventQueue的数据类型为MessageQueue。

2.13 MQ.waitMessage

[-> MessageQueue.cpp]

void MessageQueue::waitMessage() {    do {        IPCThreadState::self()->flushCommands();        int32_t ret = mLooper->pollOnce(-1);        ...    } while (true);}

可见SurfaceFlinger主线程进入waitMessage来等待消息的到来。

三. Vsync信号

HWComposer对象创建过程，会注册一些回调方法，当硬件产生VSYNC信号时，则会回调hook_vsync()方法。

3.1 HWC.hook_vsync

[-> HWComposer.cpp]

void HWComposer::hook_vsync(const struct hwc_procs* procs, int disp,        int64_t timestamp) {    cb_context* ctx = reinterpret_cast<cb_context*>(            const_cast<hwc_procs_t*>(procs));    ctx->hwc->vsync(disp, timestamp); //【见小节3.2】}

3.2 HWC.vsync

[-> HWComposer.cpp]

void HWComposer::vsync(int disp, int64_t timestamp) {    if (uint32_t(disp) < HWC_NUM_PHYSICAL_DISPLAY_TYPES) {        {            Mutex::Autolock _l(mLock);            if (timestamp == mLastHwVSync[disp]) {                return; //忽略重复的VSYNC信号            }            mLastHwVSync[disp] = timestamp;        }        //【见小节3.3】        mEventHandler.onVSyncReceived(disp, timestamp);    }}

当收到VSYNC信号则会回调EventHandler的onVSyncReceived()方法，此处mEventHandler是指SurfaceFlinger对象。

3.3 SF.onVSyncReceived

[-> SurfaceFlinger.cpp]

void SurfaceFlinger::onVSyncReceived(int type, nsecs_t timestamp) {    bool needsHwVsync = false;    {        Mutex::Autolock _l(mHWVsyncLock);        if (type == 0 && mPrimaryHWVsyncEnabled) {            // 此处mPrimaryDispSync为DispSync类【见小节3.4】            needsHwVsync = mPrimaryDispSync.addResyncSample(timestamp);        }    }    if (needsHwVsync) {        enableHardwareVsync();    } else {        disableHardwareVsync(false);    }}

3.4 DS.addResyncSample

此处调用addResyncSample对象的addResyncSample方法，那么先来看看DispSync对象的初始化过程

3.4.1 创建DispSync

[-> DispSync.cpp]

DispSync::DispSync() :        mRefreshSkipCount(0),        mThread(new DispSyncThread()) {    //【见小节3.4.2】    mThread->run("DispSync", PRIORITY_URGENT_DISPLAY + PRIORITY_MORE_FAVORABLE);    reset();    beginResync();    ...}

3.4.2 DispSyncThread线程

[-> DispSync.cpp]

virtual bool threadLoop() {     status_t err;     nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);     nsecs_t nextEventTime = 0;     while (true) {         Vector<CallbackInvocation> callbackInvocations;         nsecs_t targetTime = 0;         { // Scope for lock             Mutex::Autolock lock(mMutex);             if (mStop) {                 return false;             }             if (mPeriod == 0) {                 err = mCond.wait(mMutex);                 continue;             }             nextEventTime = computeNextEventTimeLocked(now);             targetTime = nextEventTime;             bool isWakeup = false;             if (now < targetTime) {                 err = mCond.waitRelative(mMutex, targetTime - now);                 if (err == TIMED_OUT) {                     isWakeup = true;                 } else if (err != NO_ERROR) {                     return false;                 }             }             now = systemTime(SYSTEM_TIME_MONOTONIC);             if (isWakeup) {                 mWakeupLatency = ((mWakeupLatency * 63) +                         (now - targetTime)) / 64;                 if (mWakeupLatency > 500000) {                     mWakeupLatency = 500000;                 }             }             //收集vsync信号的所有回调方法             callbackInvocations = gatherCallbackInvocationsLocked(now);         }         if (callbackInvocations.size() > 0) {             //回调所有对象的onDispSyncEvent方法             fireCallbackInvocations(callbackInvocations);         }     }     return false; }

线程”DispSync”停留在mCond的wait()过程，等待被唤醒。

3.4.3 addResyncSample

[-> DispSync.cpp]

bool DispSync::addResyncSample(nsecs_t timestamp) {    Mutex::Autolock lock(mMutex);    size_t idx = (mFirstResyncSample + mNumResyncSamples) % MAX_RESYNC_SAMPLES;    mResyncSamples[idx] = timestamp;    if (mNumResyncSamples < MAX_RESYNC_SAMPLES) {        mNumResyncSamples++;    } else {        mFirstResyncSample = (mFirstResyncSample + 1) % MAX_RESYNC_SAMPLES;    }    updateModelLocked(); //【见小节3.5】    if (mNumResyncSamplesSincePresent++ > MAX_RESYNC_SAMPLES_WITHOUT_PRESENT) {        resetErrorLocked();    }    if (kIgnorePresentFences) {        return mThread->hasAnyEventListeners();    }    return mPeriod == 0 || mError > kErrorThreshold;}

3.5 DS.updateModelLocked

[-> DispSync.cpp]

void DispSync::updateModelLocked() {    ...    //【见小节3.6】    mThread->updateModel(mPeriod, mPhase);}

3.6 DST.updateModel

[-> DispSyncThread.cpp]

class DispSyncThread: public Thread {    void updateModel(nsecs_t period, nsecs_t phase) {        Mutex::Autolock lock(mMutex);        mPeriod = period;        mPhase = phase;        mCond.signal(); //唤醒目标线程    }}

唤醒DispSyncThread线程，接下里进入DispSyncThread线程。

3.7 DispSyncThread线程

[-> DispSync.cpp]

virtual bool threadLoop() {     ...     while (true) {         Vector<CallbackInvocation> callbackInvocations;         nsecs_t targetTime = 0;         { // Scope for lock             Mutex::Autolock lock(mMutex);            ...             if (now < targetTime) {                 err = mCond.waitRelative(mMutex, targetTime - now);                 ...             }             ...             //收集vsync信号的所有回调方法             callbackInvocations = gatherCallbackInvocationsLocked(now);         }         if (callbackInvocations.size() > 0) {             //回调所有对象的onDispSyncEvent方法 【见小节3.7.1】             fireCallbackInvocations(callbackInvocations);         }     }     return false; }

3.7.1 fireCallbackInvocations

void fireCallbackInvocations(const Vector<CallbackInvocation>& callbacks) {    for (size_t i = 0; i < callbacks.size(); i++) {        //【见小节3.8】        callbacks[i].mCallback->onDispSyncEvent(callbacks[i].mEventTime);    }}

在前面小节SurfaceFlinger调用init()的过程，创建了两个DispSyncSource对象。接下里便是回调该对象的 onDispSyncEvent。

3.8 DSS.onDispSyncEvent

[-> SurfaceFlinger.cpp ::DispSyncSource]

virtual void onDispSyncEvent(nsecs_t when) {    sp<VSyncSource::Callback> callback;    {       Mutex::Autolock lock(mCallbackMutex);       callback = mCallback;    }    if (callback != NULL) {      callback->onVSyncEvent(when); //【见小节3.9】    }}

3.9 ET.onVSyncEvent

[-> EventThread.java]

void EventThread::onVSyncEvent(nsecs_t timestamp) {    Mutex::Autolock _l(mLock);    mVSyncEvent[0].header.type = DisplayEventReceiver::DISPLAY_EVENT_VSYNC;    mVSyncEvent[0].header.id = 0;    mVSyncEvent[0].header.timestamp = timestamp;    mVSyncEvent[0].vsync.count++;    mCondition.broadcast(); //唤醒EventThread线程}

mCondition.broadcast能够唤醒处理waitForEvent()过程的EventThread【见小节2.7.2】，并往下执行conn的postEvent().

3.10 ET.postEvent

[-> EventThread.java]

status_t EventThread::Connection::postEvent(        const DisplayEventReceiver::Event& event) {    ssize_t size = DisplayEventReceiver::sendEvents(mChannel, &event, 1);    return size < 0 ? status_t(size) : status_t(NO_ERROR);}

3.11 DER.sendEvents

[-> DisplayEventReceiver.cpp]

ssize_t DisplayEventReceiver::sendEvents(const sp<BitTube>& dataChannel,        Event const* events, size_t count){    return BitTube::sendObjects(dataChannel, events, count);}

根据小节【2.8】可知监听BitTube，此处调用BitTube来sendObjects。一旦收到数据，则调用MQ.cb_eventReceiver()方法。

3.11.1 MQ.cb_eventReceiver

[-> MessageQueue.cpp]

int MessageQueue::cb_eventReceiver(int fd, int events, void* data) {    MessageQueue* queue = reinterpret_cast<MessageQueue *>(data);    return queue->eventReceiver(fd, events);}

3.11.2 MQ.eventReceiver

[-> MessageQueue.cpp]

int MessageQueue::eventReceiver(int /*fd*/, int /*events*/) {    ssize_t n;    DisplayEventReceiver::Event buffer[8];    while ((n = DisplayEventReceiver::getEvents(mEventTube, buffer, 8)) > 0) {        for (int i=0 ; i<n ; i++) {            if (buffer[i].header.type == DisplayEventReceiver::DISPLAY_EVENT_VSYNC) {#if INVALIDATE_ON_VSYNC                mHandler->dispatchInvalidate();#else                mHandler->dispatchRefresh(); //【见小节3.12】#endif                break;            }        }    }    return 1;}

3.12 MQ.dispatchRefresh

void MessageQueue::Handler::dispatchRefresh() {    if ((android_atomic_or(eventMaskRefresh, &mEventMask) & eventMaskRefresh) == 0) {        //发送消息，则进入handleMessage过程【见小节3.13】        mQueue.mLooper->sendMessage(this, Message(MessageQueue::REFRESH));    }}

3.13 MQ.handleMessage

void MessageQueue::Handler::handleMessage(const Message& message) {    switch (message.what) {        case INVALIDATE:            android_atomic_and(~eventMaskInvalidate, &mEventMask);            mQueue.mFlinger->onMessageReceived(message.what);            break;        case REFRESH:            android_atomic_and(~eventMaskRefresh, &mEventMask);            mQueue.mFlinger->onMessageReceived(message.what);//【见小节3.14】            break;        case TRANSACTION:            android_atomic_and(~eventMaskTransaction, &mEventMask);            mQueue.mFlinger->onMessageReceived(message.what);            break;    }}

对于REFRESH操作，则进入onMessageReceived().

3.14 SF.onMessageReceived

[-> SurfaceFlinger.cpp]

void SurfaceFlinger::onMessageReceived(int32_t what) {    ATRACE_CALL();    switch (what) {        case MessageQueue::TRANSACTION: {            handleMessageTransaction();            break;        }        case MessageQueue::INVALIDATE: {            bool refreshNeeded = handleMessageTransaction();            refreshNeeded |= handleMessageInvalidate();            refreshNeeded |= mRepaintEverything;            if (refreshNeeded) {                signalRefresh();            }            break;        }        case MessageQueue::REFRESH: {            handleMessageRefresh();            break;        }    }}

3.15 SF.handleMessageRefresh

[-> SurfaceFlinger.cpp]

void SurfaceFlinger::handleMessageRefresh() {    ATRACE_CALL();    preComposition();    rebuildLayerStacks();    setUpHWComposer();    doDebugFlashRegions();    doComposition();    postComposition();}

下一篇文章，再来介绍图形输出过程。

四 总结

前面讲述过程中所涉及到的线程情况：

• 主线程“/system/bin/surfaceflinger”: 主线程
• 线程”EventThread”：EventThread
• 线程”EventControl”： EventControlThread
• 线程”DispSync”：DispSyncThread

Vsync处理流程图：点击查看大图

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