Android4.2.2 SurfaceFlinger的相关事件和消息处理机制

本文均属自己阅读源码的点滴总结，转账请注明出处谢谢。

欢迎和大家交流。qq:1037701636 email:[email protected]

Android源码版本Version：4.2.2; 硬件平台 全志A31

 

在这篇博文将会和大家一起分享我所学到的一点SurfaceFlinger中的事件和消息处理机制。

 

在前面的博文中，可以发现在SurfaceFlinger中的OnFirstRef里面有如下函数：

void SurfaceFlinger::onFirstRef()
{
    mEventQueue.init(this);

    run("SurfaceFlinger", PRIORITY_URGENT_DISPLAY);//启动一个新的thread线程，调用thread类的run函数

    // Wait for the main thread to be done with its initialization
    mReadyToRunBarrier.wait();//等待线程完成相关的初始化
}

 

step1: mEventQueue.init(),事件队列MessageQueue初始化

void MessageQueue::init(const sp<SurfaceFlinger>& flinger)
{
    mFlinger = flinger;
    mLooper = new Looper(true);//新建一个消息队列，其内部为建立一个epoll的pipe
    mHandler = new Handler(*this);//新建消息处理句柄
}

这里看到了两个类Looper和Handler，听说这两个类一般是用来构成消息处理机制，下面就看看他的复杂性吧。

 

step2:Looper对象的新建

{
    int wakeFds[2];
    int result = pipe(wakeFds);
    LOG_ALWAYS_FATAL_IF(result != 0, "Could not create wake pipe.  errno=%d", errno);

    mWakeReadPipeFd = wakeFds[0];
    mWakeWritePipeFd = wakeFds[1];//新建管道，2个fd描述符

    result = fcntl(mWakeReadPipeFd, F_SETFL, O_NONBLOCK);
    LOG_ALWAYS_FATAL_IF(result != 0, "Could not make wake read pipe non-blocking.  errno=%d",
            errno);

    result = fcntl(mWakeWritePipeFd, F_SETFL, O_NONBLOCK);
    LOG_ALWAYS_FATAL_IF(result != 0, "Could not make wake write pipe non-blocking.  errno=%d",
            errno);

    // Allocate the epoll instance and register the wake pipe.
    mEpollFd = epoll_create(EPOLL_SIZE_HINT);//epoll关注EPOLL_SIZE_HINT的文件数
    LOG_ALWAYS_FATAL_IF(mEpollFd < 0, "Could not create epoll instance.  errno=%d", errno);

    struct epoll_event eventItem;
    memset(& eventItem, 0, sizeof(epoll_event)); // zero out unused members of data field union
    eventItem.events = EPOLLIN;
    eventItem.data.fd = mWakeReadPipeFd;//监听可读管道mWakeReadPipeFd
    result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mWakeReadPipeFd, & eventItem);//注册上述的信息，用于epoll_wait
    LOG_ALWAYS_FATAL_IF(result != 0, "Could not add wake read pipe to epoll instance.  errno=%d",
            errno);
}

上述代码分别完成了新建一个管道pipe,使用epoll_create和epoll_ctrl来完成对读管道的监听，看是否有数据写入写管道。

 

step3:在SF新启动线程的readyToRun里面有mEventThread = new EventThread(this);//新建一个事件线程用于创建event的消息，处理VSYC同步事件。

EventThread这里姑且理解为事件线程，他继承了thread类，故会启动一个新的线程，先走完当前线程函数。主要用于处理VSYC的同步事件

EventThread::EventThread(const sp<SurfaceFlinger>& flinger)
    : mFlinger(flinger),
      mUseSoftwareVSync(false),
      mDebugVsyncEnabled(false) {

    for (int32_t i=0 ; i<HWC_DISPLAY_TYPES_SUPPORTED ; i++) {
        mVSyncEvent[i].header.type = DisplayEventReceiver::DISPLAY_EVENT_VSYNC;
        mVSyncEvent[i].header.id = 0;
        mVSyncEvent[i].header.timestamp = 0;
        mVSyncEvent[i].vsync.count =  0;//初始化同步事件
    }
}

复杂的地方在这里：

void MessageQueue::setEventThread(const sp<EventThread>& eventThread)
{
    mEventThread = eventThread;
    mEvents = eventThread->createEventConnection();//建立连接
    mEventTube = mEvents->getDataChannel();
    mLooper->addFd(mEventTube->getFd(), 0, ALOOPER_EVENT_INPUT,
            MessageQueue::cb_eventReceiver, this);//   return mReceiveFd;，cb_eventReceiver
}

分解为一下几步：

1.new Connecton,connection是eventthread的内部类。

sp<EventThread::Connection> EventThread::createEventConnection() const {
    return new Connection(const_cast<EventThread*>(this));
}

EventThread::Connection::Connection(
        const sp<EventThread>& eventThread)
    : count(-1), mEventThread(eventThread), mChannel(new BitTube())
{
}

 

2. new BitTube()本质就是新建了一个Socket本地进程间通信，socketpair即可用读也可以写，其中socket[0]作为了用于读取数据，socket[1]作为用于写入数据

BitTube::BitTube()
    : mSendFd(-1), mReceiveFd(-1)
{
    int sockets[2];
    if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sockets) == 0) {//unix本地套接字
        int size = SOCKET_BUFFER_SIZE;
        setsockopt(sockets[0], SOL_SOCKET, SO_SNDBUF, &size, sizeof(size));
        setsockopt(sockets[0], SOL_SOCKET, SO_RCVBUF, &size, sizeof(size));
        setsockopt(sockets[1], SOL_SOCKET, SO_SNDBUF, &size, sizeof(size));
        setsockopt(sockets[1], SOL_SOCKET, SO_RCVBUF, &size, sizeof(size));
        fcntl(sockets[0], F_SETFL, O_NONBLOCK);
        fcntl(sockets[1], F_SETFL, O_NONBLOCK);
        mReceiveFd = sockets[0];
        mSendFd = sockets[1];
    } else {
        mReceiveFd = -errno;
        ALOGE("BitTube: pipe creation failed (%s)", strerror(-mReceiveFd));
    }
}

 3.获取mChannel变量属于BitTube类

    mEventTube = mEvents->getDataChannel();

 

4.将不同的文件描述符添加到mLooper中

int Looper::addFd(int fd, int ident, int events, ALooper_callbackFunc callback, void* data) {
    return addFd(fd, ident, events, callback ? new SimpleLooperCallback(callback) : NULL, data);//建立回调函数
}

fd = mEventTube->getFd()，返回的是之前的mReceived(Socket[0])接收管道。events: ALOOPER_EVENT_INPUT
callback： MessageQueue::cb_eventReceiver回调函数，这里会新的建立一个SimpleLooperCallback对象

继续add调用会将fd加入到epoll轮询里面，同时所有的信息都会添加到一个Request结构体里面，最终将request信息维护到成员mRequests中去。

        Request request;
        request.fd = fd;
        request.ident = ident;
        request.callback = callback;
        request.data = data;

        struct epoll_event eventItem;
        memset(& eventItem, 0, sizeof(epoll_event)); // zero out unused members of data field union
        eventItem.events = epollEvents;
        eventItem.data.fd = fd;

        ssize_t requestIndex = mRequests.indexOfKey(fd);
        if (requestIndex < 0) {//新的句柄
            int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);//设置epoll参数,添加fd注册
            if (epollResult < 0) {
                ALOGE("Error adding epoll events for fd %d, errno=%d", fd, errno);
                return -1;
            }
            mRequests.add(fd, request);

 step4:SF新线程进入threadloop

bool SurfaceFlinger::threadLoop() {
    waitForEvent();//一个新的线程在等待事件消息
    return true;
}

void SurfaceFlinger::waitForEvent() {
    mEventQueue.waitMessage();
}

依次调用流程：mLooper->pollOnce，Looper::pollAll， Looper::pollInner(int timeoutMillis)为止一直处于循环检测状态，消息的监听与处理都是在这里进行的，下面对该函数进行深入分析。

int Looper::pollInner(int timeoutMillis) {
#if DEBUG_POLL_AND_WAKE
    ALOGD("%p ~ pollOnce - waiting: timeoutMillis=%d", this, timeoutMillis);
#endif

    // Adjust the timeout based on when the next message is due.
    if (timeoutMillis != 0 && mNextMessageUptime != LLONG_MAX) {
        nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
        int messageTimeoutMillis = toMillisecondTimeoutDelay(now, mNextMessageUptime);
        if (messageTimeoutMillis >= 0
                && (timeoutMillis < 0 || messageTimeoutMillis < timeoutMillis)) {
            timeoutMillis = messageTimeoutMillis;
        }
#if DEBUG_POLL_AND_WAKE
        ALOGD("%p ~ pollOnce - next message in %lldns, adjusted timeout: timeoutMillis=%d",
                this, mNextMessageUptime - now, timeoutMillis);
#endif
    }

    // Poll.
    int result = ALOOPER_POLL_WAKE;
    mResponses.clear();
    mResponseIndex = 0;

    struct epoll_event eventItems[EPOLL_MAX_EVENTS];
    int eventCount = epoll_wait(mEpollFd, eventItems, EPOLL_MAX_EVENTS, timeoutMillis);//epoll等待

    // Acquire lock.
    mLock.lock();

    // Check for poll error.
    if (eventCount < 0) {
        if (errno == EINTR) {
            goto Done;
        }
        ALOGW("Poll failed with an unexpected error, errno=%d", errno);
        result = ALOOPER_POLL_ERROR;
        goto Done;
    }

    // Check for poll timeout.
    if (eventCount == 0) {
#if DEBUG_POLL_AND_WAKE
        ALOGD("%p ~ pollOnce - timeout", this);
#endif
        result = ALOOPER_POLL_TIMEOUT;
        goto Done;
    }

    // Handle all events.
#if DEBUG_POLL_AND_WAKE
    ALOGD("%p ~ pollOnce - handling events from %d fds", this, eventCount);
#endif

    for (int i = 0; i < eventCount; i++) {
        int fd = eventItems[i].data.fd;
        uint32_t epollEvents = eventItems[i].events;
        if (fd == mWakeReadPipeFd) {//只是简单的wake，一般是消息发出
            if (epollEvents & EPOLLIN) {
                awoken();
            } else {
                ALOGW("Ignoring unexpected epoll events 0x%x on wake read pipe.", epollEvents);
            }
        } else {
            ssize_t requestIndex = mRequests.indexOfKey(fd);//事件
            if (requestIndex >= 0) {
                int events = 0;
                if (epollEvents & EPOLLIN) events |= ALOOPER_EVENT_INPUT;
                if (epollEvents & EPOLLOUT) events |= ALOOPER_EVENT_OUTPUT;
                if (epollEvents & EPOLLERR) events |= ALOOPER_EVENT_ERROR;
                if (epollEvents & EPOLLHUP) events |= ALOOPER_EVENT_HANGUP;
                pushResponse(events, mRequests.valueAt(requestIndex));//相关请求写入mResponses里面进行请求的处理
            } else {
                ALOGW("Ignoring unexpected epoll events 0x%x on fd %d that is "
                        "no longer registered.", epollEvents, fd);
            }
        }
    }
Done: ;

    // Invoke pending message callbacks.消息的handle处理
    mNextMessageUptime = LLONG_MAX;
    while (mMessageEnvelopes.size() != 0) {//消息包络组里面有信息
        nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
        const MessageEnvelope& messageEnvelope = mMessageEnvelopes.itemAt(0);//提取一个消息包
        if (messageEnvelope.uptime <= now) {
            // Remove the envelope from the list.
            // We keep a strong reference to the handler until the call to handleMessage
            // finishes.  Then we drop it so that the handler can be deleted *before*
            // we reacquire our lock.
            { // obtain handler
                sp<MessageHandler> handler = messageEnvelope.handler;
                Message message = messageEnvelope.message;
                mMessageEnvelopes.removeAt(0);
                mSendingMessage = true;
                mLock.unlock();

#if DEBUG_POLL_AND_WAKE || DEBUG_CALLBACKS
                ALOGD("%p ~ pollOnce - sending message: handler=%p, what=%d",
                        this, handler.get(), message.what);
#endif
                handler->handleMessage(message);//MessageHandler消息的handle处理
            } // release handler

            mLock.lock();
            mSendingMessage = false;
            result = ALOOPER_POLL_CALLBACK;
        } else {
            // The last message left at the head of the queue determines the next wakeup time.
            mNextMessageUptime = messageEnvelope.uptime;
            break;
        }
    }

    // Release lock.
    mLock.unlock();

    // Invoke all response callbacks.，处理请求的回调函数
    for (size_t i = 0; i < mResponses.size(); i++) {
        Response& response = mResponses.editItemAt(i);
        if (response.request.ident == ALOOPER_POLL_CALLBACK) {
            int fd = response.request.fd;
            int events = response.events;
            void* data = response.request.data;
#if DEBUG_POLL_AND_WAKE || DEBUG_CALLBACKS
            ALOGD("%p ~ pollOnce - invoking fd event callback %p: fd=%d, events=0x%x, data=%p",
                    this, response.request.callback.get(), fd, events, data);
#endif
            int callbackResult = response.request.callback->handleEvent(fd, events, data);//调用addfd的回调函数ALooper_callbackFunc
            if (callbackResult == 0) {
                removeFd(fd);
            }
            // Clear the callback reference in the response structure promptly because we
            // will not clear the response vector itself until the next poll.
            response.request.callback.clear();
            result = ALOOPER_POLL_CALLBACK;
        }
    }
    return result;
}

int Looper::pollAll(int timeoutMillis, int* outFd, int* outEvents, void** outData) {
    if (timeoutMillis <= 0) {
        int result;
        do {
            result = pollOnce(timeoutMillis, outFd, outEvents, outData);
        } while (result == ALOOPER_POLL_CALLBACK);
        return result;
    } else {
        nsecs_t endTime = systemTime(SYSTEM_TIME_MONOTONIC)
                + milliseconds_to_nanoseconds(timeoutMillis);

        for (;;) {
            int result = pollOnce(timeoutMillis, outFd, outEvents, outData);
            if (result != ALOOPER_POLL_CALLBACK) {
                return result;
            }

            nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
            timeoutMillis = toMillisecondTimeoutDelay(now, endTime);
            if (timeoutMillis == 0) {
                return ALOOPER_POLL_TIMEOUT;
            }
        }
    }
}

1.epoll_wait进入轮询等待有数据可以读取。

2.epoll_wait等打有eventcount产生，开始对其节进行解析，假设现在epoll检测到了数据，则继续执行

3.前面可以知道epoll检测的文件描述符包括Pipe产生的mWakeReadPipeFd，双工通信socketpair的mReceived两个。

4、那么在哪来会触发后者呢，我们要回归到eventthread的threadloop函数，这里是在检测底层硬件的VSYC信号，先来看看他的实现

bool EventThread::threadLoop() {
    DisplayEventReceiver::Event event;
    Vector< sp<EventThread::Connection> > signalConnections;
    signalConnections = waitForEvent(&event);//轮询等待event的发生，一般是硬件的请求

    // dispatch events to listeners...
    const size_t count = signalConnections.size();
    for (size_t i=0 ; i<count ; i++) {
        const sp<Connection>& conn(signalConnections[i]);
        // now see if we still need to report this event
        status_t err = conn->postEvent(event);//发送事件，一般的硬件触发了事件的发生
        if (err == -EAGAIN || err == -EWOULDBLOCK) {
            // The destination doesn't accept events anymore, it's probably
            // full. For now, we just drop the events on the floor.
            // FIXME: Note that some events cannot be dropped and would have
            // to be re-sent later.
            // Right-now we don't have the ability to do this.
            ALOGW("EventThread: dropping event (%08x) for connection %p",
                    event.header.type, conn.get());
        } else if (err < 0) {
            // handle any other error on the pipe as fatal. the only
            // reasonable thing to do is to clean-up this connection.
            // The most common error we'll get here is -EPIPE.
            removeDisplayEventConnection(signalConnections[i]);
        }
    }
    return true;
}

首先是要waitForEvent进入事件循环检测，在收到事件信号后，就是对连接信号的解析，这里是获取eventthread内部类Connection来进行事件的传递。依次调用如下：

DisplayEventReceiver::sendEvents(mChannel, &event, 1)——>BitTube::sendObjects(dataChannel, events, count);回到了前面的socket管道通信中来了，继续看
DisplayEventReceiver::sendEvents(mChannel, &event, 1)DisplayEventReceiver::sendEvents

ssize_t BitTube::sendObjects(const sp<BitTube>& tube,
        void const* events, size_t count, size_t objSize)
{
    ssize_t numObjects = 0;
    for (size_t i=0 ; i<count ; i++) {
        const char* vaddr = reinterpret_cast<const char*>(events) + objSize * i;
        ssize_t size = tube->write(vaddr, objSize);
        if (size < 0) {
            // error occurred
            return size;
        } else if (size == 0) {
            // no more space
            break;
        }
        numObjects++;
    }
    return numObjects;
}

这里是将Vsync这个evnet变量进行打包，多个event的话还需要循环进行，然后调用write函数：

ssize_t BitTube::write(void const* vaddr, size_t size)
{
    ssize_t err, len;
    do {
        len = ::send(mSendFd, vaddr, size, MSG_DONTWAIT | MSG_NOSIGNAL);
        err = len < 0 ? errno : 0;
    } while (err == EINTR);
    return err == 0 ? len : -err;

}

很清楚的是调用了socket专属的send函数，而这里的fd正是mSendFd,而epoll_wait那里等待就是mRecieved的读管道口。这样就可以通过进程间通信，触发我们的SF的2号线程epoll_wait进行处理。

下面我们继续回到Looper::pollInner这个复杂的函数内部，在epoll_wait执行之后，主要是先对message进行业务的处理，然后才是对应的event的事件回调。

 if (requestIndex >= 0) {
                int events = 0;
                if (epollEvents & EPOLLIN) events |= ALOOPER_EVENT_INPUT;
                if (epollEvents & EPOLLOUT) events |= ALOOPER_EVENT_OUTPUT;
                if (epollEvents & EPOLLERR) events |= ALOOPER_EVENT_ERROR;
                if (epollEvents & EPOLLHUP) events |= ALOOPER_EVENT_HANGUP;
                pushResponse(events, mRequests.valueAt(requestIndex))

上述代码完成的是将epoll的事件类型转为ALOOPER自身的类型，这里是事件输入。pushResponse主要是将mRequests中的事件请求从Looper维护的内存里面提取出来，requestIndex = mRequests.indexOfKey(fd)可以看到，这个请求的索引值是通过当前的fd来提取的，而之前保存的时候正是通过fd来关联的。

void Looper::pushResponse(int events, const Request& request) {
    Response response;
    response.events = events;
    response.request = request;
    mResponses.push(response);
}

mResponses里面存储着events，request等信息，主要在下面对回调解析时使用。

    // Invoke all response callbacks.，处理请求的回调函数
    for (size_t i = 0; i < mResponses.size(); i++) {
        Response& response = mResponses.editItemAt(i);
        if (response.request.ident == ALOOPER_POLL_CALLBACK) {
            int fd = response.request.fd;
            int events = response.events;
            void* data = response.request.data;
#if DEBUG_POLL_AND_WAKE || DEBUG_CALLBACKS
            ALOGD("%p ~ pollOnce - invoking fd event callback %p: fd=%d, events=0x%x, data=%p",
                    this, response.request.callback.get(), fd, events, data);
#endif
            int callbackResult = response.request.callback->handleEvent(fd, events, data);//调用addfd的回调函数ALooper_callbackFunc
            if (callbackResult == 0) {
                removeFd(fd);
            }
            // Clear the callback reference in the response structure promptly because we
            // will not clear the response vector itself until the next poll.
            response.request.callback.clear();
            result = ALOOPER_POLL_CALLBACK;
        }
    }

在前面addFd处，将SF的EventThread新建的BitTube添加到了mLooper里面，当时的fd设置的request的ident就是ALOOPER_POLL_CALLBACK。接着取出响应response的信息，开始进行准备回调handleEvent().那么这个callback是什么呢？还是要回到addfd里面，可以看到request.callback = callback;这样可以定位到mLooper->addFd(mEventTube->getFd(), 0, ALOOPER_EVENT_INPUT,MessageQueue::cb_eventReceiver, this); 故这里的callback MessageQueue的成员函数cb_eventReceiver，但是他是作为new SimpleLooperCallback(callback)初始化到了一个SimpleLoopeCallback对象中，而该类继承了LooperCallback这个基类，也就是说callback->handleEvent()也就是调用派生类SimpleLooperCallback的handleEvent(),如下：

int SimpleLooperCallback::handleEvent(int fd, int events, void* data) {
    return mCallback(fd, events, data);
}

的确，mCallBack才是ALooper_callbackFunc这个函数指针，当初是赋值为了cb_eventReceiver，故回调该函数。

int MessageQueue::cb_eventReceiver(int fd, int events, void* data) {
    MessageQueue* queue = reinterpret_cast<MessageQueue *>(data);
    return queue->eventReceiver(fd, events);
}

而上面的data一就是MessageQueue::setEventThread时传入的this即SurfaceFlinger的mMessageQueue成员，现在开始执行事件的接收，其实就是开始做消息的发送了，也就是进入消息处理机制。

int MessageQueue::eventReceiver(int fd, int events) {
    ssize_t n;
    DisplayEventReceiver::Event buffer[8];
    while ((n = DisplayEventReceiver::getEvents(mEventTube, buffer, 8)) > 0) {//得到事件的数据
        for (int i=0 ; i<n ; i++) {
            if (buffer[i].header.type == DisplayEventReceiver::DISPLAY_EVENT_VSYNC) {
#if INVALIDATE_ON_VSYNC
                mHandler->dispatchInvalidate();
#else
                mHandler->dispatchRefresh();//刷新
#endif
                break;
            }
        }
    }
    return 1;
}

getevents最终是调用recv来获得基于Unix域单连接的socket端发send过来的数据,判断数据的类型是不是显示帧同步事件，可以很容易的看到在EventThread的waitevent中的event事件结构体初始化：

    for (int32_t i=0 ; i<HWC_DISPLAY_TYPES_SUPPORTED ; i++) {
        mVSyncEvent[i].header.type = DisplayEventReceiver::DISPLAY_EVENT_VSYNC;
        mVSyncEvent[i].header.id = 0;
        mVSyncEvent[i].header.timestamp = 0;
        mVSyncEvent[i].vsync.count =  0;//初始化同步事件
    }

故直接进入mHandler->dispatchRefresh()函数，

void MessageQueue::Handler::dispatchRefresh() {
    if ((android_atomic_or(eventMaskRefresh, &mEventMask) & eventMaskRefresh) == 0) {
        mQueue.mLooper->sendMessage(this, Message(MessageQueue::REFRESH));
    }
}

 

void Looper::sendMessage(const sp<MessageHandler>& handler, const Message& message) {
    nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
    sendMessageAtTime(now, handler, message); //及时发送消息
}

 

void Looper::sendMessageAtTime(nsecs_t uptime, const sp<MessageHandler>& handler,
        const Message& message) {
#if DEBUG_CALLBACKS
    ALOGD("%p ~ sendMessageAtTime - uptime=%lld, handler=%p, what=%d",
            this, uptime, handler.get(), message.what);
#endif

    size_t i = 0;
    { // acquire lock
        AutoMutex _l(mLock);

        size_t messageCount = mMessageEnvelopes.size();
        while (i < messageCount && uptime >= mMessageEnvelopes.itemAt(i).uptime) {
            i += 1;
        }

        MessageEnvelope messageEnvelope(uptime, handler, message);
        mMessageEnvelopes.insertAt(messageEnvelope, i, 1);//加入消息包到loop中去

        // Optimization: If the Looper is currently sending a message, then we can skip
        // the call to wake() because the next thing the Looper will do after processing
        // messages is to decide when the next wakeup time should be.  In fact, it does
        // not even matter whether this code is running on the Looper thread.
        if (mSendingMessage) {
            return;
        }
    } // release lock

    // Wake the poll loop only when we enqueue a new message at the head.
    if (i == 0) {
        wake();//在消息队列头检测到有一个新的消息后唤醒
    }
}

。sendMessageAtTime这里理解为及时发送消息，那消息是以什么形式存在的呢？其实可以注意到Message message传入的类型为Refresh。        size_t messageCount = mMessageEnvelopes.size();来获取Looper中所存在的消息包的个数，可以看到如果之前looper还有消息没有处理，那么i+=1，直到当前消息放在最后，实现的代码如下，将消息加入到了mMessageEnvelops中去了。

MessageEnvelope messageEnvelope(uptime, handler, message);
mMessageEnvelopes.insertAt(messageEnvelope, i, 1);//加入消息包到loop中去

那么怎么触发消息的处理呢，如果只有当前的一个消息，直接wake()之前的pollInner内的epoll_wai函数，做消息的处理，接着就看pollInner内的消息处理机制吧：

    // Invoke pending message callbacks.消息的handle处理
    mNextMessageUptime = LLONG_MAX;
    while (mMessageEnvelopes.size() != 0) {//消息包络组里面有信息
        nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
        const MessageEnvelope& messageEnvelope = mMessageEnvelopes.itemAt(0);//提取一个消息包
        if (messageEnvelope.uptime <= now) {
            // Remove the envelope from the list.
            // We keep a strong reference to the handler until the call to handleMessage
            // finishes.  Then we drop it so that the handler can be deleted *before*
            // we reacquire our lock.
            { // obtain handler
                sp<MessageHandler> handler = messageEnvelope.handler;
                Message message = messageEnvelope.message;
                mMessageEnvelopes.removeAt(0);
                mSendingMessage = true;
                mLock.unlock();

#if DEBUG_POLL_AND_WAKE || DEBUG_CALLBACKS
                ALOGD("%p ~ pollOnce - sending message: handler=%p, what=%d",
                        this, handler.get(), message.what);
#endif
                handler->handleMessage(message);//MessageHandler消息的handle处理
            } // release handler

            mLock.lock();
            mSendingMessage = false;
            result = ALOOPER_POLL_CALLBACK;
        } else {
            // The last message left at the head of the queue determines the next wakeup time.
            mNextMessageUptime = messageEnvelope.uptime;
            break;
        }
    }

核心的过程解析messageEnvelope消息包，取出对应的消息以及消息处理的handle,进行处理，那么立即的handle是什么呢？回归到mHandler->dispatchRefresh()——》MessageQueue::Handler::dispatchRefresh()里面可以看到 mQueue.mLooper->sendMessage(this, Message(MessageQueue::REFRESH));，这个handle就是mHandle啦，故来看MessageQueue的内部Handle的成员函数handleMessage，很高兴的是，果然与之前设置的message.what结合在一起了。最终把消息的处理权还是提交给了mFlinger

void MessageQueue::Handler::handleMessage(const Message& message) {
    switch (message.what) {
        case INVALIDATE:
            android_atomic_and(~eventMaskInvalidate, &mEventMask);
            mQueue.mFlinger->onMessageReceived(message.what);
            break;
        case REFRESH:
            android_atomic_and(~eventMaskRefresh, &mEventMask);
            mQueue.mFlinger->onMessageReceived(message.what);//线程接收到了消息后处理
            break;
    }
}

onMessageReceived——>handleMessageRefresh处理屏幕刷新这个消息，主要调用composer来完成。

void SurfaceFlinger::handleMessageRefresh() {//处理layer的刷新，实际是调用SF绘图
    ATRACE_CALL();
    preComposition();
    rebuildLayerStacks();
    setUpHWComposer();
    doDebugFlashRegions();
    doComposition();
    postComposition();
}

 

通过以上内容就走完了Surface的屏幕刷新事件提交以及事件处理，消息触发，以及消息的处理。最终还是回归到SurfaceFlinger来完成最终的消息处理。本文最终将SF的消息和事件处理机制总结成以下的流程图，加速理解。蓝色核心框图是SurfaceFlinger的主要业务和服务的处理线程。