实现SurfaceFlinger的主动刷新

最新推荐文章于 2025-10-28 17:34:50 发布

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最新推荐文章于 2025-10-28 17:34:50 发布 · 1.8k 阅读

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#AR操作系统

本文深入探讨SurfaceFlinger如何处理Vsync事件，从SurfaceFlinger.cpp的init()开始，详细解析EventThread的工作流程，通过修改EventThread::Connection的count实现每个Vsync事件都调用handleMessageInvalidate()。

实现SurfaceFlinger的主动刷新

Abstract

SurfaceFlinger在收到来自硬件层的Vsync事件之后，不是每次都会调用SurfaceFlinger::handleMessageInvalidate()的。而SurfaceFlinger中处理Vsync事件涉及到的类有：DispSyncThread, DispSync, SurfaceFlinger::DispSyncSource, EventThread, EventThread::Connection, MessageQueue.

本文首先研究这些类之间的关系，以及自Vysnc事件发生后这些类的处理流程。最终，通过修改EventThread::Connection中的成员count实现了每个Vsync事件都会调用SurfaceFlinger::handleMessageInvalidate()的功能。

Process

从SurfaceFlinger.cpp的init()开始

在SurfaceFlinger.cpp的init()方法中，通过如下的代码初始化了DispSyncSource和EventThread，并将mSFEventThread关联到成员变量MessageQueue mEventQueue中:

sp<VSyncSource> vsyncSrc = new DispSyncSource(&mPrimaryDispSync,
      vsyncPhaseOffsetNs, true, "app");
mEventThread = new EventThread(vsyncSrc, *this, false);
sp<VSyncSource> sfVsyncSrc = new DispSyncSource(&mPrimaryDispSync,
      sfVsyncPhaseOffsetNs, true, "sf");
mSFEventThread = new EventThread(sfVsyncSrc, *this, true);
mEventQueue.setEventThread(mSFEventThread);

在EventThread.cpp中可以看到当EventThread的实例创建时，在其onFirstRef()中会开启线程:

void EventThread::onFirstRef() {
    run("EventThread", PRIORITY_URGENT_DISPLAY + PRIORITY_MORE_FAVORABLE);
}

而在MessageQueue::setEventThread()中，会创建EventThread::Connection:

void MessageQueue::setEventThread(const sp<EventThread>& eventThread)
{
   if (mEventThread == eventThread) {
      return;
   }

   if (mEventTube.getFd() >= 0) {
      mLooper->removeFd(mEventTube.getFd());
   }

   mEventThread = eventThread;
   mEvents = eventThread->createEventConnection();
   mEvents->stealReceiveChannel(&mEventTube);
   mLooper->addFd(mEventTube.getFd(), 0, Looper::EVENT_INPUT,
         MessageQueue::cb_eventReceiver, this);
}

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(gui::BitTube::DefaultSize) {}

注意 count的初始值是-1。
在EventThread::Connection的onFirstConnection中，会将Connection的实例传给EventThread，并加到其成员变量mDisplayEventConnections:

void EventThread::Connection::onFirstRef() {
   mEventThread->registerDisplayEventConnection(this);
}

status_t EventThread::registerDisplayEventConnection(
      const sp<EventThread::Connection>& connection) {
   Mutex::Autolock _l(mLock);
   mDisplayEventConnections.add(connection);

   if (!mFirstConnectionInited) {
      // additional external displays can't be enumerated by default,
      // need to report additional hotplug to listeners
      for (int32_t type = DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES;
            type < (int32_t)mHotplugEvent.size(); type++) {
         if (mHotplugEvent[type].hotplug.connected) {
               connection->postEvent(mHotplugEvent[type]);
         }
      }
      mFirstConnectionInited = true;
   }

   mCondition.broadcast();
   return NO_ERROR;
}

第一次执行EventThread::waitForEvent()

当EventThread::threadLoop()运行起来后，首先会执行EventThread::waitForEvent()方法：

Vector< sp<EventThread::Connection> > EventThread::waitForEvent(
      DisplayEventReceiver::Event* event)
{
   Mutex::Autolock _l(mLock);
   Vector< sp<EventThread::Connection> > signalConnections;

   do {
      bool