android开机动画启动流程

从android的Surface Flinger服务启动分析知道，开机动画是在SurfaceFlinger实例通过调用startBootAnim()启动的。

下面我们就一起学习BootAnim是如何启动和结束的，我精读代码前都喜欢先描出框架图，以此图为基础再去研读会达到事半功倍的效果。好吧，直接上图。

内核起来后会启动第一个进程，即init进程。

init进程会根据init.rc配置启动surfaceflinger进程。

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

surfaceflinger进程便启动了，跟着就会跑进程的main()函数。

frameworks/native/services/surfaceflinger/main_surfaceflinger.cpp

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

    // instantiate surfaceflinger
    sp<SurfaceFlinger> flinger = new SurfaceFlinger();//创建surfaceflinger服务实例

....
    flinger->init();

    // publish surface flinger
    sp<IServiceManager> sm(defaultServiceManager());
    sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false);//注册到service manager里

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

    return 0;
}

首先new一个SurfaceFlinger实例，然后init，然后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();//开始播放动画
}

初始化graphics之后，就调用startBootAnim()播放开机动画。

void SurfaceFlinger::startBootAnim() {
    // start boot animation
    mBootFinished = false;
    property_set("service.bootanim.exit", "0");//这个会有bootanimation进程周期检测,=1退出动画
    property_set("ctl.start", "bootanim");//通过ctl.start命令启动bootanim
}

把service.bootanim.exit属性设为0，这个属性bootanimation进程里会周期检查，=1时就退出动画，这里=0表示要播放动画。

后面通过ctl.start的命令启动bootanim进程，动画就开始播放了。

下面来到bootanimation的实现

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();//创建BootAnimation实例

        IPCThreadState::self()->joinThreadPool();//binder线程池，与surfaceflinger通信用的。

    }
    return 0;
}

new一个BootAnimation实例,然后建个binder线程池，因为BootAnimation在显示动画时要与SurfaceFlinger服务进程通信，所以要启个binder线程池。

frameworks/base/cmds/bootanimation/BootAnimation.cpp

BootAnimation::BootAnimation() : Thread(false)
{
    mSession = new SurfaceComposerClient();//创建一个对象
}

创建实例时，构造函数就会被调用，new一个SurfaceComposerClient实例，他是用来与surfaceflinger通信的

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

linkTocomposerDeath的作用是当surfaceflinger死掉是，BootAnimation就会得到通知。

如下，收到通知后就退出动画了，因为surfaceflinger都挂掉了，播放不了了。

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surfaceflinger死亡的消息，好吧自己也跟着去了。
    requestExit();
}

另一个函数run()在BootAnimation的父类Thead里，用来创建一个线程并跑起来。

父类

system/core/libutils/Threads.cpp

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

创建_threadLoop线程

int Thread::_threadLoop(void* user)
{
....
    do {
        bool result;
        if (first) {
            first = false;
            self->mStatus = self->readyToRun();//这个函数被bootanimation重写了
            result = (self->mStatus == NO_ERROR);

            if (result && !self->exitPending()) {
                ...
                result = self->threadLoop();//这个函数被bootanimation重写了
            }
        } else {
            result = self->threadLoop();
        }

        ...
    
    return 0;
}

 readyToRun函数实现

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实现

bool BootAnimation::threadLoop()
{
    bool r;
    if (mAndroidAnimation) {
        r = android();//显示android默认动画
    } else {
        r = movie();//显示自定义的动画
    }

    // 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()的实现

bool BootAnimation::movie()
{
    //读取bootanimation.zip文件并解释

      // clear screen
   //下面是循环显示 
       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();//检测是否退出动画
            }

            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;
}

那么到movie为止，动画是在播放了，而且还在循环检测是否退出，即checkExit()

checkExit()的实现

void BootAnimation::checkExit() {
    // Allow surface flinger to gracefully request shutdown
    char value[PROPERTY_VALUE_MAX];
    property_get(EXIT_PROP_NAME, value, "0");//属性为1，说明要退出了
    int exitnow = atoi(value);
    if (exitnow) {
        requestExit();
    }
}

property_get(EXIT_PROP_NAME, value, "0");检测这个属性，=1就退出动画

#define EXIT_PROP_NAME "service.bootanim.exit"

这个属性就是上面讲到的，等到launcher跑起来后就会置1

那动画是什么时候退出的？

当launcher应用程序主线程跑起来后，如果主线程处于空闲，就会向ActivityManagerService发送一个activityIdle的消息。

应用程序主线程是ActivityThread.java来描述的，activityIdle是这个类来实现的

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
                        }
                    ....
    }

上面的ActivityManagerNavtive.getDefault()得到am

来到frameworks/base/core/java/android/app/ActivityManagerNative.java

    static public IActivityManager getDefault() {
        return gDefault.get();//getDefault的实现
    }

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实际上是IActivityManager,往下看

class ActivityManagerProxy implements IActivityManager
{

ActivityManagerProxy实现了IActivityManager

那么am.activityIdle()就是ActivityManagerProxy里的函数，如下

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

  ....
    }

发送了ACTIVITY_IDLE_TRANSACTION的进程间通信，这个消息被ActivityManagerNative接收处理了。

case ACTIVITY_IDLE_TRANSACTION: {//收到消息
            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);//这个函数在ActivityManagerService被重写
            }
            reply.writeNoException();
            return true;
        }

收到消息后就调用了activityIdle函数，这个函数被ActivityManagerService重写了，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);
    }

调用activityIdleInternalLocked函数，在下面实现

frameworks/base/services/java/com/android/server/am/ActivityStackSupervisor.java

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

        if (enableScreen) {
            mService.enableScreenAfterBoot();//调ActivityManagerService类的enableScreenAfterBoot()函数
         }
....
        if (activityRemoved) {
            resumeTopActivitiesLocked();
        }

        return r;
    }

来到frameworks/base/services/java/com/android/server/am/ActivityManagerService.java

void enableScreenAfterBoot() {
        EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_ENABLE_SCREEN,
                SystemClock.uptimeMillis());
        mWindowManager.enableScreenAfterBoot();//调WindowManagerService类里的enableScreenAfterBoot()函数

        synchronized (this) {
            updateEventDispatchingLocked();
        }
    }

来到frameworks/base/services/java/com/android/server/wm/WindowManagerService.java

    public void enableScreenAfterBoot() {
     ....

        performEnableScreen();
    }

performEnableScreen()实现

    public void performEnableScreen() {
        

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

发送了FIRST_CALL_TRANSACTION的请求

因为从下面知道FIRST_CALL_TRANSACTION = BOOT_FINISHED

所以BnSurfaceComposer收到消息

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();//调用 bootFinished()
            return NO_ERROR;
        }
        
        ....
    }
    // should be unreachable
    return NO_ERROR;
}

bootFinished()函数BpSurfaceComposer里实现，但发现没有，他又发了一个BOOT_FINISHED，死循环了，其实没有。bootFinished()被SurfaceFlinger类重写了

class BpSurfaceComposer : public BpInterface<ISurfaceComposer>
{

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

 重写

frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

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

把service.bootanim.exit写成1，然后bootanimation进程的checkExit()检测到就退出进程，停止播放。