MessageQueue创建

MessageQueue在native层初始化

jlong android_os_MessageQueue_nativeInit(JNIEnv* env,jclass clazz){

    NativeMessageQueue* nativeMessageQueue = new NativeMessageQueue();

    return reinterpret_cast(nativeMessageQueue);

}

当前线程Looper::getForThread()里面拿到局部缓存的looper,

NativeMessageQueue::NativeMessageQueue(){

    mLooper = Looper::getForThread();

     if(mLooper == NULL){

         mLooper = new Looper(flase);

         Looper::setForThread(mLooper);

     }

}

Looper::getForThread()局部缓存：调用了liunx的接口pthread_getspecific接口

  sp Looper::getForThread(){

     int result = pthread__once(&gTLSOnce,initTLSKey);

     return(Looper*)pthread_getspecific(gTLSKey);

 }

native层的looper,消息循环的核心部分

Looper::Looper(bool allowNonCallbacks){

    mWakeEventFd = eventfd(0,EFD_NONBLOCK);

    rebuildEpollLocked();

}  eventfd计数器性能比普通管道好

void Looper::rebuildEpollLocked(){

  mEpollFd = epoll_create(EPOLL_SIZE_HINT);

  struct epoll_event eventltem;

  memset(&eventItem,0,sizeof(epoll_event));

  eventltem.events = EPOLLIN;

  eventltem.data.fd = mWakeEventFd;

  epoll_ctl(mEpollFd,EPOLL_CTL_ADD,mWakeEventFd,&eventltem);

  ......

}

void Looper::wake(){

    uint64_t inc = 1;

    ssize_t nWrite = write(mWakeEventFd,&inc,sizeof(uint64_t));

}

int Looper::pollOnce(int timeoutMillis,int*outFd,...){

for(::){

     polllnner(timeoutMillis);

   }

}

polllnner函数的核心是epoll_wait

int Loopet::polllnner(int timeoutMillis){

     struct epoll_event eventltems[EPOLL_MAX_EVENTS];

     int eventCount = epoll_wait(mEpollFd,eventltems,...);

     for(int i=0;i

           int fd = eventltems[i].data.fd;

           uint32_t epollEvents = eventltems[i].events;

           if(fd==mWakeEventFd &&(epollEvents&EPOLLIN)){

             awoken();

           }

            ......}......}

awoken读事件，消化事件

        void Looper ::awoken(){

                uint64_t counter;

                 read(mWakeEventFd,&counter,sizeof(uint64_t)));

}

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