Android源码之SurfaceFlinger的启动(一)
page1
在Android系统中,显示系统在底层是通过SurfaceFlinger服务来完成的,因此从今天开始,我们从SurfaceFlinger服务作为入口来分析一下Android显示系统.
SurfaceFlinger服务是在System进程中,而System进程是由Zygote进程启动的,并且是以Java层的SystemServer类的静态成员函数main为入口函数的。
因此，接下来我们就从SystemServer类(定义在SystemServer.java文件中)的静态成员函数main开始，分析SurfaceFlinger服务的启动过程:
1publicstaticvoidmain(String[]args){
2if(System.currentTimeMillis()<EARLIEST_SUPPORTED_TIME){
3//Ifadevice'sclockisbefore1970(before0),alotof
4//APIscrashdealingwithnegativenumbers,notably
5//java.io.File#setLastModified,soinsteadwefakeitand
6//hopethattimefromcelltowersorNTPfixesit
7//shortly.
8Slog.w(TAG,"Systemclockisbefore1970;settingto1970.");
9SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);
10}
11if(SamplingProfilerIntegration.isEnabled()){
12SamplingProfilerIntegration.start();
13timer=newTimer();
14timer.schedule(newTimerTask(){
15@Override
16publicvoidrun(){
17SamplingProfilerIntegration.writeSnapshot("system_server",null);
18}
19},SNAPSHOT_INTERVAL,SNAPSHOT_INTERVAL);
20}
//Mmmmmm...morememory!
21dalvik.system.VMRuntime.getRuntime().clearGrowthLimit();
//Thesystemserverhastorunallofthetime,soitneedstobe
//asefficientaspossiblewithitsmemoryusage.
22VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);
23System.loadLibrary("android_servers");
24init1(args);
25}
第24行(SystemServer.main)会调用init1函数来进行初始化操作,init1函数是个native函数来初始化C++层的服务,会导致com_android_server_SystemServer.cpp的android_server_SystemServer_init1函数的调用,关于com_android_server_SystemServer.cpp的android_server_SystemServer_init1函数的详细分析可以参考page2文件.
page2
1staticvoidandroid_server_SystemServer_init1(JNIEnv*env,jobjectclazz)
2{
3system_init();
4}
第3行(com_android_server_SystemServer->android_server_SystemServer_init1)会调用system_init函数,system_init函数是在system_init.cpp文件中定义的,system_init函数的定义如下:
1extern"C"status_tsystem_init()
2{
3ALOGI("Enteredsystem_init()");
4sp<ProcessState>proc(ProcessState::self());
5sp<IServiceManager>sm=defaultServiceManager();
6ALOGI("ServiceManager:%p\n",sm.get());
7sp<GrimReaper>grim=newGrimReaper();
8sm->asBinder()->linkToDeath(grim,grim.get(),0);
9charpropBuf[PROPERTY_VALUE_MAX];
10property_get("system_init.startsurfaceflinger",propBuf,"1");
11if(strcmp(propBuf,"1")==0){
12//StarttheSurfaceFlinger
13SurfaceFlinger::instantiate();
14}
15property_get("system_init.startsensorservice",propBuf,"1");
16if(strcmp(propBuf,"1")==0){
17//Startthesensorservice
18SensorService::instantiate();
19}
//AndnowstarttheAndroidruntime.Wehavetodothisbit
//ofnastinessbecausetheAndroidruntimeinitializationrequires
//someofthecoresystemservicestoalreadybestarted.
//AllotherserversshouldjuststarttheAndroidruntimeat
//thebeginningoftheirprocesses'smain(),beforecalling
//theinitfunction.
20ALOGI("Systemserver:startingAndroidruntime.\n");
21AndroidRuntime*runtime=AndroidRuntime::getRuntime();
22ALOGI("Systemserver:startingAndroidservices.\n");
23JNIEnv*env=runtime->getJNIEnv();
24if(env==NULL){
25returnUNKNOWN_ERROR;
26}
27jclassclazz=env->FindClass("com/android/server/SystemServer");
28if(clazz==NULL){
29returnUNKNOWN_ERROR;
30}
31jmethodIDmethodId=env->GetStaticMethodID(clazz,"init2","()V");
32if(methodId==NULL){
33returnUNKNOWN_ERROR;
34}
35env->CallStaticVoidMethod(clazz,methodId);
36ALOGI("Systemserver:enteringthreadpool.\n");
37ProcessState::self()->startThreadPool();
38IPCThreadState::self()->joinThreadPool();
39ALOGI("Systemserver:exitingthreadpool.\n");
40returnNO_ERROR;
41}
第9-14行(system_init->system_init)如果发现系统属性中设置了启动SurfaceFlinger服务,第13行(system_init->system_init)会调用SurfaceFlinger的instantiate函数来启动SurfaceFlinger服务,关于SurfaceFlinger的instantiate的详细分析可以参考page3文件.
第37-38行(system_init->system_init)是启动Binder的线程池,从此开始,SystemServer进程就可以接受Binder的进程间通信了.
page3
我们从SurfaceFlinger的instantiate函数作为入口来分析SurfaceFinger服务的启动.
我们先来看一下SurfaceFlinger类的继承体系:
classSurfaceFlinger:publicBinderService<SurfaceFlinger>,
publicBnSurfaceComposer,
privateIBinder::DeathRecipient,
privateThread,
privateHWComposer::EventHandler
我靠!SurfaceFlinger继承了5个父类.
不管了,先分析instantiate函数,instantiate函数是从BinderService继承而来的,我们先来看一下BinderService类的声明:
template<typenameSERVICE>classBinderService
BinderService接受一个模板参数.
BinderService的instantiate函数定义如下:
staticvoidinstantiate(){
publish();
}
instantiate函数只是调用了publish函数,publish函数的定义如下:
1staticstatus_tpublish(boolallowIsolated=false){
2sp<IServiceManager>sm(defaultServiceManager());
3returnsm->addService(String16(SERVICE::getServiceName()),newSERVICE(),allowIsolated);
4}
第2行(BinderService->publish)获得ServiceManager.
第3行(BinderService->publish)会new一个SERVICE实例,并调用ServiceManager的addService函数来交给ServiceManager管理,这是Binder机制的基础.
因此这里会new一个SurfaceFlinger对象,关于SurfaceFlinger的构造函数的分析可以参考page4文件.
因为ServiceManager的addService函数的参数是个SP类型的,因此这里会导致SurfaceFlinger的onFirstRef函数的调用,onFirstRef函数的定义如下:
1voidSurfaceFlinger::onFirstRef()
2{
3mEventQueue.init(this);
4
5run("SurfaceFlinger",PRIORITY_URGENT_DISPLAY);
6
7//Waitforthemainthreadtobedonewithitsinitialization
8mReadyToRunBarrier.wait();
9}
第3行(SurfaceFlinger->onFirstRef)成员变量mEventQueue是一个MessageQueue类型的,因此这里会调用MessageQueue的init函数.关于MessageQueue的init函数的实现可以参考page5文件.
第5行(SurfaceFlinger->onFirstRef)会调用run函数,run函数是从Thread类继承下来的.关于Thread的run函数的详细分析可以参考page6文件.
page4
我们分析一下SurfaceFlinger的构造函数的实现:
1SurfaceFlinger::SurfaceFlinger()
2:BnSurfaceComposer(),Thread(false),
3mTransactionFlags(0),
4mTransactionPending(false),
5mAnimTransactionPending(false),
6mLayersRemoved(false),
7mRepaintEverything(0),
8mBootTime(systemTime()),
9mVisibleRegionsDirty(false),
10mHwWorkListDirty(false),
11mDebugRegion(0),
12mDebugDDMS(0),
13mDebugDisableHWC(0),
14mDebugDisableTransformHint(0),
15mDebugInSwapBuffers(0),
16mLastSwapBufferTime(0),
17mDebugInTransaction(0),
18mLastTransactionTime(0),
19mBootFinished(false)
20{
21ALOGI("SurfaceFlingerisstarting");
22
23//debuggingstuff...
24charvalue[PROPERTY_VALUE_MAX];
25
26property_get("debug.sf.showupdates",value,"0");
27mDebugRegion=atoi(value);
28
29property_get("debug.sf.ddms",value,"0");
30mDebugDDMS=atoi(value);
31if(mDebugDDMS){
32if(!startDdmConnection()){
33//startfailed,andDDMSdebuggingnotenabled
34mDebugDDMS=0;
35}
36}
37ALOGI_IF(mDebugRegion,"showupdatesenabled");
38ALOGI_IF(mDebugDDMS,"DDMSdebuggingenabled");
39}
可以看到,SurfaceFlinger的构造函数除了初始化成员变量之外,没有什么额外的逻辑.
page5
我们分析一下MessageQueue的init函数的实现,如下所示:
1voidMessageQueue::init(constsp<SurfaceFlinger>&flinger)
2{
3mFlinger=flinger;
4mLooper=newLooper(true);
5mHandler=newHandler(*this);
6}
第3行(MessageQueue->init)会将SurfaceFlinger对象保存到MessageQueue里.
第4行(MessageQueue->init)会new一个Looper对象,用于分发消息.
第5行(MessageQueue->init)会用本MessageQueue去初始化一个Handler对象,注意,Handler是在MessageQueue类里定义的一个内部类,定义如下:
classHandler:publicMessageHandler{
enum{
eventMaskInvalidate=0x1,
eventMaskRefresh=0x2
};
MessageQueue&mQueue;
int32_tmEventMask;
public:
Handler(MessageQueue&queue):mQueue(queue),mEventMask(0){}
virtualvoidhandleMessage(constMessage&message);
voiddispatchRefresh();
voiddispatchInvalidate();
};