android的Surface Flinger服务启动分析

这篇文章android启动流程讲到android的启动流程，其实中间还蕴藏了SurfaceFlinger服务的内容，但没有包括进去，目的是为尽可能简单的讲述android启动流程，从整体上把握。

好吧，现在咱们就一起学习下SurfaceFlinger中如何启动的。

在android4.3与android4.4版本上有所不同，下面是两个版本简单的流程图

android的Surface Flinger服务启动分析_第1张图片

在Andoird4.4系统出现以前，Surface Flinger服务是由system server启动的。

frameworks/base/services/java/com/android/server/SystemServer.java

public class SystemServer {<span style="white-space:pre"></span>...    public static void main(String[] args) {        ...        System.loadLibrary("android_servers");//加载库        init1(args);//调用库函数init1()    }<span style="white-space:pre"></span>public static final void init2() {    Slog.i(TAG, "Entered the Android system server!");    Thread thr = new ServerThread();    thr.setName("android.server.ServerThread");    thr.start();  }}

SystemServer进程首先从main静态函数开始执行。

我们看到，首先加载了android_servers的库，然后调用库里的init1()函数完成后面的工作。

小插曲：看到init2()函数没？这个函数后面会被system_init()函数调用。

继而new了一个ServerThread线程，这是非常重要，android启动流程讲到Java系统服务，就是这里被启动的。

init1()函数在下面文件实现

frameworks/base/services/jni/com_android_server_SystemServer.cpp

extern "C" int system_init();static void android_server_SystemServer_init1(JNIEnv* env, jobject clazz){    system_init();//调用这个}/* * JNI registration. */static JNINativeMethod gMethods[] = {    /* name, signature, funcPtr */    { "init1", "([Ljava/lang/String;)V", (void*) android_server_SystemServer_init1 },//映射到这};int register_android_server_SystemServer(JNIEnv* env){    return jniRegisterNativeMethods(env, "com/android/server/SystemServer",            gMethods, NELEM(gMethods));}

init1()函数实际上映射到android_server_SystemServer_init1()。然后调用另外一个函数system_init()完成后面的工作。

system_init1()函数由下面文件实现。

frameworks/base/cmds/system_server/library/system_init.cpp

extern "C" status_t system_init(){    ALOGI("Entered system_init()");<span style="white-space:pre"></span>...    char propBuf[PROPERTY_VALUE_MAX];    property_get("system_init.startsurfaceflinger", propBuf, "1");    if (strcmp(propBuf, "1") == 0) {        // Start the SurfaceFlinger        SurfaceFlinger::instantiate();//启动SurfaceFlinger    }    property_get("system_init.startsensorservice", propBuf, "1");    if (strcmp(propBuf, "1") == 0) {        // Start the sensor service        SensorService::instantiate();//启动SensorService    }    ...    jclass clazz = env->FindClass("com/android/server/SystemServer");    if (clazz == NULL) {        return UNKNOWN_ERROR;    }    jmethodID methodId = env->GetStaticMethodID(clazz, "init2", "()V");//仔细看，这里还调用了java类的init2()函数在上面的systemserver.java里。    if (methodId == NULL) {        return UNKNOWN_ERROR;    } ...}

system_init()函数调用SurfaceFlinger的instantiate()函数来启动SurfaceFlinger。instantiate是实际上来自SurfaceFlinger父类BinderService

下面是函数的实现文件

frameworks/native/include/binder/BinderService.h

class BinderService{public:.....    static void instantiate() { publish(); } ...};

BinderService的静态成员函数又调用了另一个静态函数publish()来完成工作。

下面是实现

template<typename SERVICE>class BinderService{public:  static status_t publish(bool allowIsolated = false) {    sp<IServiceManager> sm(defaultServiceManager());    return sm->addService(//注册到ServiceManager中去。        String16(SERVICE::getServiceName()),        new SERVICE(), allowIsolated);//new一个SurfaceFlinger实例  }...};

BinderService是一个类模板，当BinderService类被SurfaceFlinger类继承时，模板参数SERVICE就是SurfaceFlinger。所以这里的publish()函数实际上是new了一个SurfaceFlinger实例，并把它注册到Service Manager中去。

从sp<IServiceManager> sm(defaultServiceManager());知道sm是一个强指针。

所以addService的第二个参数SurfaceFlinger的引用是属于强指针引用，这时会调用SurfaceFlinger实例的成员函数onFristRef。关于强指针请参考Android系统的智能指针（轻量级指针、强指针和弱指针）的实现原理分析

onFristRef函数实现

frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::onFirstRef(){    mEventQueue.init(this);    run("SurfaceFlinger", PRIORITY_URGENT_DISPLAY);//调用父类Thread的成员函数run()完成后面工作    // Wait for the main thread to be done with its initialization    mReadyToRunBarrier.wait();}

onFirstRef()调用了SurfaceFlinger父类Thread类的run成员函数，把线程跑起来

如下：

frameworks/native/libs/utils/Threads.cpp

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

__threadLoop线程实现

int Thread::_threadLoop(void* user){    ....    do {        bool result;        if (first) {            first = false;            self->mStatus = self->readyToRun();//readyToRun函数，在SurfaceFlinger实例里实现            ...                result = self->threadLoop();            }        } else {            result = self->threadLoop();//threadLoop函数，在SurfaceFlinger实例里实现        }        ....        }                ...    } while(strong != 0);        return 0;}

从上面看出，__threadLoop线程分别调用了readyToRun函数，然后就循环执行threadLoop()函数。

这两个函数都在SurfaceFlinger实例里重写了。

如下：

frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

status_t SurfaceFlinger::readyToRun(){    ALOGI(  "SurfaceFlinger's main thread ready to run. "            "Initializing graphics H/W...");    .....    for (size_t i=0 ; i<DisplayDevice::NUM_DISPLAY_TYPES ; i++) {        DisplayDevice::DisplayType type((DisplayDevice::DisplayType)i);        // set-up the displays that are already connected        if (mHwc->isConnected(i) || type==DisplayDevice::DISPLAY_PRIMARY) {            // All non-virtual displays are currently considered secure.            bool isSecure = true;            createBuiltinDisplayLocked(type);            wp<IBinder> token = mBuiltinDisplays[i];            sp<DisplayDevice> hw = new DisplayDevice(this,                    type, allocateHwcDisplayId(type), isSecure, token,                    new FramebufferSurface(*mHwc, i),                    mEGLConfig);            if (i > DisplayDevice::DISPLAY_PRIMARY) {                // FIXME: currently we don't get blank/unblank requests                // for displays other than the main display, so we always                // assume a connected display is unblanked.                ALOGD("marking display %d as acquired/unblanked", i);                hw->acquireScreen();            }            mDisplays.add(token, hw);        }    }...    //  initialize OpenGL ES    DisplayDevice::makeCurrent(mEGLDisplay, hw, mEGLContext);    initializeGL(mEGLDisplay);    // start the EventThread    mEventThread = new EventThread(this);    mEventQueue.setEventThread(mEventThread);....

如上ReadyToRun开始初步化display devices,然后创建消息线程，然后就调用startBootAnim();

好吧，可以看见开机动画了。

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上面是android4.3的流程，下面分析一下android4.4流程，有点不太一样哦

android4.3是systemserver进程调用init1()函数来完成surfaceFlinger启动的。

android4.4则不同，由init直接创建。

init.rc

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

init进程直接根据init.rc配置启动了surfaceflinger进程。

frameworks/native/services/surfaceflinger/main_surfaceflinger.cpp

int main(int argc, char** argv) {....    // instantiate surfaceflinger    sp<SurfaceFlinger> flinger = new SurfaceFlinger();//新实例...    // initialize before clients can connect    flinger->init();//调用surfaceflinger的初始化函数    // publish surface flinger    sp<IServiceManager> sm(defaultServiceManager());    sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false);//向service manager注册服务    // run in this thread    flinger->run();//开跑    return 0;}

来到surfaceflinger进程的main函数，new一个SurfaceFlinger实例，跟着调用SurfaceFlinger类的init()函数完成后面工作，然后向service manager注册服务

然后thread开跑。

frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::init() {    ALOGI(  "SurfaceFlinger's main thread ready to run. "            "Initializing graphics H/W...");    .....    // initialize our non-virtual displays    for (size_t i=0 ; i<DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES ; i++) {        DisplayDevice::DisplayType type((DisplayDevice::DisplayType)i);        // set-up the displays that are already connected        if (mHwc->isConnected(i) || type==DisplayDevice::DISPLAY_PRIMARY) {            // All non-virtual displays are currently considered secure.            bool isSecure = true;            createBuiltinDisplayLocked(type);            wp<IBinder> token = mBuiltinDisplays[i];            sp<BufferQueue> bq = new BufferQueue(new GraphicBufferAlloc());            sp<FramebufferSurface> fbs = new FramebufferSurface(*mHwc, i, bq);            sp<DisplayDevice> hw = new DisplayDevice(this,                    type, allocateHwcDisplayId(type), isSecure, token,                    fbs, bq,                    mEGLConfig);            if (i > DisplayDevice::DISPLAY_PRIMARY) {                // FIXME: currently we don't get blank/unblank requests                // for displays other than the main display, so we always                // assume a connected display is unblanked.                ALOGD("marking display %d as acquired/unblanked", i);                hw->acquireScreen();            }            mDisplays.add(token, hw);        }    }...    // start the EventThread    ...    mSFEventThread = new EventThread(sfVsyncSrc);    mEventQueue.setEventThread(mSFEventThread);    mEventControlThread = new EventControlThread(this);    mEventControlThread->run("EventControl", PRIORITY_URGENT_DISPLAY);...    // set initial conditions (e.g. unblank default device)    initializeDisplays();    // start boot animation    startBootAnim();}

这个init()函数与4.3系统的ReadyToRun()函数的功能是一样的，内容上有些不同，但大体也分成三个部分，第一硬件初始化，第二建立消息线程，第三启动开机动画。

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

最后调用run()函数开跑，看见没有，一直在等待消息呢。

后续我还会分析android L的代码，看看有什么不同。

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