從android的(de)Surface Flinger服務啓動分析知道(dào)，開機動畫是(shì)在(zài)SurfaceFlinger實例通過調用startBootAnim()啓動的(de)。
下面我們就(jiù)一起學習BootAnim是(shì)如何啓動和(hé / huò)結束的(de)，我精讀代碼前都喜歡先描出(chū)框架圖，以(yǐ)此圖爲(wéi / wèi)基礎再去研讀會達到(dào)事半功倍的(de)效果。好吧，直接上(shàng)圖。
[img]http://img.blog.csdn.net/20141231162020380?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvaG92YW4=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center
内核起來(lái)後會啓動第一個(gè)進程，即init進程。
init進程會根據init.rc配置啓動surfaceflinger進程。

service surfaceflinger /system/bin/surfaceflinger
    class main
    user system
    group graphics drmrpc
    onrestart restart zygote

surfaceflinger進程便啓動了(le／liǎo)，跟着就(jiù)會跑進程的(de)main()函數。
frameworks/native/services/surfaceflinger/main_surfaceflinger.cpp

int main(int argc, char** argv) {
....

    // instantiate surfaceflinger
    sp<SurfaceFlinger> flinger = new SurfaceFlinger();//創建surfaceflinger服務實例

....
    flinger->init();

    // publish surface flinger
    sp<IServiceManager> sm(defaultServiceManager());
    sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false);//注冊到(dào)service manager裏

    // run in this thread
    flinger->run();//開跑

    return 0;
}

首先new一個(gè)SurfaceFlinger實例，然後init，然後run
frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::init() {
    ALOGI(  "SurfaceFlinger's main thread ready to run. "
            "Initializing graphics H/W...");

 .....
    // start boot animation
    startBootAnim();//開始播放動畫
}

初始化graphics之(zhī)後，就(jiù)調用startBootAnim()播放開機動畫。

void SurfaceFlinger::startBootAnim() {
    // start boot animation
    mBootFinished = false;
    property_set("service.bootanim.exit", "0");//這(zhè)個(gè)會有bootanimation進程周期檢測,=1退出(chū)動畫
    property_set("ctl.start", "bootanim");//通過ctl.start命令啓動bootanim
}

把service.bootanim.exit屬性設爲(wéi / wèi)0，這(zhè)個(gè)屬性bootanimation進程裏會周期檢查，=1時(shí)就(jiù)退出(chū)動畫，這(zhè)裏=0表示要(yào / yāo)播放動畫。
後面通過ctl.start的(de)命令啓動bootanim進程，動畫就(jiù)開始播放了(le／liǎo)。
下面來(lái)到(dào)bootanimation的(de)實現
frameworks/base/cmds/bootanimation/bootanimation_main.cpp

int main(int argc, char** argv)
{


        sp<ProcessState> proc(ProcessState::self());
        ProcessState::self()->startThreadPool();

        // create the boot animation object
        sp<BootAnimation> boot = new BootAnimation();//創建BootAnimation實例

        IPCThreadState::self()->joinThreadPool();//binder線程池，與surfaceflinger通信用的(de)。

    }
    return 0;
}

new一個(gè)BootAnimation實例,然後建個(gè)binder線程池，因爲(wéi / wèi)BootAnimation在(zài)顯示動畫時(shí)要(yào / yāo)與SurfaceFlinger服務進程通信，所以(yǐ)要(yào / yāo)啓個(gè)binder線程池。
frameworks/base/cmds/bootanimation/BootAnimation.cpp

BootAnimation::BootAnimation() : Thread(false)
{
    mSession = new SurfaceComposerClient();//創建一個(gè)對象
}

創建實例時(shí)，構造函數就(jiù)會被調用，new一個(gè)SurfaceComposerClient實例，他(tā)是(shì)用來(lái)與surfaceflinger通信的(de)

void BootAnimation::onFirstRef() {
    status_t err = mSession->linkToComposerDeath(this);//注冊surfaceflinger死亡消息的(de)通知書
    ALOGE_IF(err, "linkToComposerDeath failed (%s) ", strerror(-err));
    if (err == NO_ERROR) {
        run("BootAnimation", PRIORITY_DISPLAY);//開跑
    }
}

linkTocomposerDeath的(de)作用是(shì)當surfaceflinger死掉是(shì)，BootAnimation就(jiù)會得到(dào)通知。
如下，收到(dào)通知後就(jiù)退出(chū)動畫了(le／liǎo)，因爲(wéi / wèi)surfaceflinger都挂掉了(le／liǎo)，播放不(bù)了(le／liǎo)了(le／liǎo)。

void BootAnimation::binderDied(const wp<IBinder>& who)
{
    // woah, surfaceflinger died!
    ALOGD("SurfaceFlinger died, exiting...");

    // calling requestExit() is not enough here because the Surface code
    // might be blocked on a condition variable that will never be updated.
    kill( getpid(), SIGKILL );//收到(dào)surfaceflinger死亡的(de)消息，好吧自己也(yě)跟着去了(le／liǎo)。
    requestExit();
}

另一個(gè)函數run()在(zài)BootAnimation的(de)父類Thead裏，用來(lái)創建一個(gè)線程并跑起來(lái)。
父類
system/core/libutils/Threads.cpp

status_t Thread::run(const char* name, int32_t priority, size_t stack)
{
    ...
    
    if (mCanCallJava) {
        res = createThreadEtc(_threadLoop,//創建線程
                this, name, priority, stack, &mThread);
    } else {
        res = androidCreateRawThreadEtc(_threadLoop,
                this, name, priority, stack, &mThread);
    }
    ....
}

創建_threadLoop線程

int Thread::_threadLoop(void* user)
{
....
    do {
        bool result;
        if (first) {
            first = false;
            self->mStatus = self->readyToRun();//這(zhè)個(gè)函數被bootanimation重寫了(le／liǎo)
            result = (self->mStatus == NO_ERROR);

            if (result && !self->exitPending()) {
                ...
                result = self->threadLoop();//這(zhè)個(gè)函數被bootanimation重寫了(le／liǎo)
            }
        } else {
            result = self->threadLoop();
        }

        ...
    
    return 0;
}

 readyToRun函數實現

status_t BootAnimation::readyToRun() {
    mAssets.addDefaultAssets();

    sp<IBinder> dtoken(SurfaceComposerClient::getBuiltInDisplay(
            ISurfaceComposer::eDisplayIdMain));
    DisplayInfo dinfo;
    status_t status = SurfaceComposerClient::getDisplayInfo(dtoken, &dinfo);
    if (status)
        return -1;
    char value[PROPERTY_VALUE_MAX];
    property_get("persist.panel.orientation", value, "0");
    int orient = atoi(value) / 90;

    if(orient == eOrientation90 || orient == eOrientation270) {
        int temp = dinfo.h;
        dinfo.h = dinfo.w;
        dinfo.w = temp;
    }

    Rect destRect(dinfo.w, dinfo.h);
    mSession->setDisplayProjection(dtoken, orient, destRect, destRect);

    // create the native surface
    sp<SurfaceControl> control = session()->createSurface(String8("BootAnimation"),
            dinfo.w, dinfo.h, PIXEL_FORMAT_RGB_565);

    SurfaceComposerClient::openGlobalTransaction();
    control->setLayer(0x40000000);
    SurfaceComposerClient::closeGlobalTransaction();

    sp<Surface> s = control->getSurface();

    // initialize opengl and egl
    const EGLint attribs[] = {
            EGL_RED_SIZE,   8,
            EGL_GREEN_SIZE, 8,
            EGL_BLUE_SIZE,  8,
            EGL_DEPTH_SIZE, 0,
            EGL_NONE
    };
    EGLint w, h, dummy;
    EGLint numConfigs;
    EGLConfig config;
    EGLSurface surface;
    EGLContext context;

    EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);

    eglInitialize(display, 0, 0);
    eglChooseConfig(display, attribs, &config, 1, &numConfigs);
    surface = eglCreateWindowSurface(display, config, s.get(), NULL);
    context = eglCreateContext(display, config, NULL, NULL);
    eglQuerySurface(display, surface, EGL_WIDTH, &w);
    eglQuerySurface(display, surface, EGL_HEIGHT, &h);

    if (eglMakeCurrent(display, surface, surface, context) == EGL_FALSE)
        return NO_INIT;

    mDisplay = display;
    mContext = context;
    mSurface = surface;
    mWidth = w;
    mHeight = h;
    mFlingerSurfaceControl = control;
    mFlingerSurface = s;

    mAndroidAnimation = true;

    // If the device has encryption turned on or is in process 
    // of being encrypted we show the encrypted boot animation.
    char decrypt[PROPERTY_VALUE_MAX];
    property_get("vold.decrypt", decrypt, "");

    bool encryptedAnimation = atoi(decrypt) != 0 || !strcmp("trigger_restart_min_framework", decrypt);

    if ((encryptedAnimation &&
            (access(SYSTEM_ENCRYPTED_BOOTANIMATION_FILE, R_OK) == 0) &&
            (mZip.open(SYSTEM_ENCRYPTED_BOOTANIMATION_FILE) == NO_ERROR)) ||

            ((access(USER_BOOTANIMATION_FILE, R_OK) == 0) &&
            (mZip.open(USER_BOOTANIMATION_FILE) == NO_ERROR)) ||

            ((access(SYSTEM_BOOTANIMATION_FILE, R_OK) == 0) &&
            (mZip.open(SYSTEM_BOOTANIMATION_FILE) == NO_ERROR))) {
        mAndroidAnimation = false;
    }

    return NO_ERROR;
}

threadloop實現

bool BootAnimation::threadLoop()
{
    bool r;
    if (mAndroidAnimation) {
        r = android();//顯示android默認動畫
    } else {
        r = movie();//顯示自定義的(de)動畫
    }

    // No need to force exit anymore
    property_set(EXIT_PROP_NAME, "0");

    eglMakeCurrent(mDisplay, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
    eglDestroyContext(mDisplay, mContext);
    eglDestroySurface(mDisplay, mSurface);
    mFlingerSurface.clear();
    mFlingerSurfaceControl.clear();
    eglTerminate(mDisplay);
    IPCThreadState::self()->stopProcess();
    return r;
}

movie()的(de)實現

bool BootAnimation::movie()
{
    //讀取bootanimation.zip文件并解釋

      // clear screen
   //下面是(shì)循環顯示 
       for (int i=0 ; i<pcount ; i++) {
        const Animation::Part& part(animation.parts[i]);
        const size_t fcount = part.frames.size();
        glBindTexture(GL_TEXTURE_2D, 0);

        for (int r=0 ; !part.count || r<part.count ; r++) {
            // Exit any non playuntil complete parts immediately
            if(exitPending() && !part.playUntilComplete)
                break;

            for (int j=0 ; j<fcount && (!exitPending() || part.playUntilComplete) ; j++) {
                const Animation::Frame& frame(part.frames[j]);
                nsecs_t lastFrame = systemTime();

                if (r > 0) {
                    glBindTexture(GL_TEXTURE_2D, frame.tid);
                } else {
                    if (part.count != 1) {
                        glGenTextures(1, &frame.tid);
                        glBindTexture(GL_TEXTURE_2D, frame.tid);
                        glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
                        glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
                    }
                    initTexture(
                            frame.map->getDataPtr(),
                            frame.map->getDataLength());
                }

                if (!clearReg.isEmpty()) {
                    Region::const_iterator head(clearReg.begin());
                    Region::const_iterator tail(clearReg.end());
                    glEnable(GL_SCISSOR_TEST);
                    while (head != tail) {
                        const Rect& r(*head++);
                        glScissor(r.left, mHeight - r.bottom,
                                r.width(), r.height());
                        glClear(GL_COLOR_BUFFER_BIT);
                    }
                    glDisable(GL_SCISSOR_TEST);
                }
                glDrawTexiOES(xc, yc, 0, animation.width, animation.height);
                eglSwapBuffers(mDisplay, mSurface);

                nsecs_t now = systemTime();
                nsecs_t delay = frameDuration - (now - lastFrame);
                //ALOGD("%lld, %lld", ns2ms(now - lastFrame), ns2ms(delay));
                lastFrame = now;

                if (delay > 0) {
                    struct timespec spec;
                    spec.tv_sec  = (now + delay) / 1000000000;
                    spec.tv_nsec = (now + delay) % 1000000000;
                    int err;
                    do {
                        err = clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &spec, NULL);
                    } while (err<0 && errno == EINTR);
                }

                checkExit();//檢測是(shì)否退出(chū)動畫
            }

            usleep(part.pause * ns2us(frameDuration));

            // For infinite parts, we've now played them at least once, so perhaps exit
            if(exitPending() && !part.count)
                break;
        }

        // free the textures for this part
        if (part.count != 1) {
            for (int j=0 ; j<fcount ; j++) {
                const Animation::Frame& frame(part.frames[j]);
                glDeleteTextures(1, &frame.tid);
            }
        }
    }

    return false;
}

那麽到(dào)movie爲(wéi / wèi)止，動畫是(shì)在(zài)播放了(le／liǎo)，而(ér)且還在(zài)循環檢測是(shì)否退出(chū)，即checkExit()
checkExit()的(de)實現

void BootAnimation::checkExit() {
    // Allow surface flinger to gracefully request shutdown
    char value[PROPERTY_VALUE_MAX];
    property_get(EXIT_PROP_NAME, value, "0");//屬性爲(wéi / wèi)1，說(shuō)明要(yào / yāo)退出(chū)了(le／liǎo)
    int exitnow = atoi(value);
    if (exitnow) {
        requestExit();
    }
}

property_get(EXIT_PROP_NAME, value, "0");檢測這(zhè)個(gè)屬性，=1就(jiù)退出(chū)動畫

#define EXIT_PROP_NAME "service.bootanim.exit"

這(zhè)個(gè)屬性就(jiù)是(shì)上(shàng)面講到(dào)的(de)，等到(dào)launcher跑起來(lái)後就(jiù)會置1
那動畫是(shì)什麽時(shí)候退出(chū)的(de)？
當launcher應用程序主線程跑起來(lái)後，如果主線程處于(yú)空閑，就(jiù)會向ActivityManagerService發送一個(gè)activityIdle的(de)消息。
應用程序主線程是(shì)ActivityThread.java來(lái)描述的(de)，activityIdle是(shì)這(zhè)個(gè)類來(lái)實現的(de)

private class Idler implements MessageQueue.IdleHandler {
...
                IActivityManager am = ActivityManagerNative.getDefault();
    ...
                        try {
                            am.activityIdle(a.token, a.createdConfig, stopProfiling);
                            a.createdConfig = null;
                        } catch (RemoteException ex) {
                            // Ignore
                        }
                    ....
    }

上(shàng)面的(de)ActivityManagerNavtive.getDefault()得到(dào)am
來(lái)到(dào)frameworks/base/core/java/android/app/ActivityManagerNative.java

    static public IActivityManager getDefault() {
        return gDefault.get();//getDefault的(de)實現
    }

private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {
        protected IActivityManager create() {
            IBinder b = ServiceManager.getService("activity");
            if (false) {
                Log.v("ActivityManager", "default service binder = " + b);
            }
            IActivityManager am = asInterface(b);
            if (false) {
                Log.v("ActivityManager", "default service = " + am);
            }
            return am;
        }
    };

gDefault實際上(shàng)是(shì)IActivityManager,往下看

class ActivityManagerProxy implements IActivityManager
{

ActivityManagerProxy實現了(le／liǎo)IActivityManager
那麽am.activityIdle()就(jiù)是(shì)ActivityManagerProxy裏的(de)函數，如下

public void activityIdle(IBinder token, Configuration config, boolean stopProfiling)
            throws RemoteException
    {
        ...
        mRemote.transact(ACTIVITY_IDLE_TRANSACTION, data, reply, IBinder.FLAG_ONEWAY);//發送ACTIVITY_IDLE_TRANSACTION

  ....
    }

發送了(le／liǎo)ACTIVITY_IDLE_TRANSACTION的(de)進程間通信，這(zhè)個(gè)消息被ActivityManagerNative接收處理了(le／liǎo)。

case ACTIVITY_IDLE_TRANSACTION: {//收到(dào)消息
            data.enforceInterface(IActivityManager.descriptor);
            IBinder token = data.readStrongBinder();
            Configuration config = null;
            if (data.readInt() != 0) {
                config = Configuration.CREATOR.createFromParcel(data);
            }
            boolean stopProfiling = data.readInt() != 0;
            if (token != null) {
                activityIdle(token, config, stopProfiling);//這(zhè)個(gè)函數在(zài)ActivityManagerService被重寫
            }
            reply.writeNoException();
            return true;
        }

收到(dào)消息後就(jiù)調用了(le／liǎo)activityIdle函數，這(zhè)個(gè)函數被ActivityManagerService重寫了(le／liǎo)，如下
frameworks/base/services/java/com/android/server/am/ActivityManagerService.java

@Override
    public final void activityIdle(IBinder token, Configuration config, boolean stopProfiling) {
        final long origId = Binder.clearCallingIdentity();
        synchronized (this) {
            ActivityStack stack = ActivityRecord.getStackLocked(token);
            if (stack != null) {
                ActivityRecord r =
                        mStackSupervisor.activityIdleInternalLocked(token, false, config);
                if (stopProfiling) {
                    if ((mProfileProc == r.app) && (mProfileFd != null)) {
                        try {
                            mProfileFd.close();
                        } catch (IOException e) {
                        }
                        clearProfilerLocked();
                    }
                }
            }
        }
        Binder.restoreCallingIdentity(origId);
    }

調用activityIdleInternalLocked函數，在(zài)下面實現
frameworks/base/services/java/com/android/server/am/ActivityStackSupervisor.java

    final ActivityRecord activityIdleInternalLocked(final IBinder token, boolean fromTimeout,
            Configuration config) {
        ....        

        if (enableScreen) {
            mService.enableScreenAfterBoot();//調ActivityManagerService類的(de)enableScreenAfterBoot()函數
         }
....
        if (activityRemoved) {
            resumeTopActivitiesLocked();
        }

        return r;
    }

來(lái)到(dào)frameworks/base/services/java/com/android/server/am/ActivityManagerService.java

void enableScreenAfterBoot() {
        EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_ENABLE_SCREEN,
                SystemClock.uptimeMillis());
        mWindowManager.enableScreenAfterBoot();//調WindowManagerService類裏的(de)enableScreenAfterBoot()函數

        synchronized (this) {
            updateEventDispatchingLocked();
        }
    }

來(lái)到(dào)frameworks/base/services/java/com/android/server/wm/WindowManagerService.java

    public void enableScreenAfterBoot() {
     ....

        performEnableScreen();
    }

performEnableScreen()實現

    public void performEnableScreen() {
        

.....
                    surfaceFlinger.transact(IBinder.FIRST_CALL_TRANSACTION, // BOOT_FINISHED
                                            data, null, 0);
   ....
    }

發送了(le／liǎo)FIRST_CALL_TRANSACTION的(de)請求


因爲(wéi / wèi)從下面知道(dào)FIRST_CALL_TRANSACTION = BOOT_FINISHED
所以(yǐ)BnSurfaceComposer收到(dào)消息

frameworks/native/include/gui/ISurfaceComposer.h

class BnSurfaceComposer: public BnInterface<ISurfaceComposer> {
public:
    enum {
        // Note: BOOT_FINISHED must remain this value, it is called from
        // Java by ActivityManagerService.
        BOOT_FINISHED = IBinder::FIRST_CALL_TRANSACTION,
        ...
    };

    virtual status_t onTransact(uint32_t code, const Parcel& data,
            Parcel* reply, uint32_t flags = 0);
};

</pre></p><p><span style="color:#333333;">frameworks/native/libs/gui/ISurfaceComposer.cpp</span></p><p><span style="color:#333333;"></span><pre name="code" class="cpp">status_t BnSurfaceComposer::onTransact(
    uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
    switch(code) {
        
        ....
        case BOOT_FINISHED: {
            CHECK_INTERFACE(ISurfaceComposer, data, reply);
            bootFinished();//調用 bootFinished()
            return NO_ERROR;
        }
        
        ....
    }
    // should be unreachable
    return NO_ERROR;
}

bootFinished()函數BpSurfaceComposer裏實現，但發現沒有，他(tā)又發了(le／liǎo)一個(gè)BOOT_FINISHED，死循環了(le／liǎo)，其實沒有。bootFinished()被SurfaceFlinger類重寫了(le／liǎo)

class BpSurfaceComposer : public BpInterface<ISurfaceComposer>
{

    virtual void bootFinished()
    {
        Parcel data, reply;
        data.writeInterfaceToken(ISurfaceComposer::getInterfaceDescriptor());
        remote()->transact(BnSurfaceComposer::BOOT_FINISHED, data, &reply);
    }

 重寫
frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::bootFinished()
{
...
    property_set("service.bootanim.exit", "1");
}

把service.bootanim.exit寫成1，然後bootanimation進程的(de)checkExit()檢測到(dào)就(jiù)退出(chū)進程，停止播放。