android source code usual

::self() 一般表示单例 

sp<ProcessState> ProcessState::self()
{
    Mutex::Autolock _l(gProcessMutex); //自动锁，对gProcessMutex加锁，_l超出作用域自动对gProcessMutex解锁
    if (gProcess != NULL) {
        return gProcess;
    }
    gProcess = new ProcessState;
    return gProcess; //进程中的全局变量,以g开头，每个进程中有且仅有一个ProcessState
}

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服务的初始化 ::instantiate()

AudioFlinger::instantiate();

int main(int argc __unused, char** argv)
{
   sp<ProcessState> proc(ProcessState::self());
   sp<IServiceManager> sm = defaultServiceManager();
   ALOGI("ServiceManager: %p", sm.get());
   AudioFlinger::instantiate();
   MediaPlayerService::instantiate();
   CameraService::instantiate();
   AudioPolicyService::instantiate();
   SoundTriggerHwService::instantiate();
   registerExtensions();
   ProcessState::self()->startThreadPool();
   IPCThreadState::self()->joinThreadPool();
}

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