SurfaceFlinger处理vsync信号

Posted 2022-10-17 Achillisjack

surfaceflinger创建Connection对象的过程前面已经论述过,在此就不赘述了。

Surfaceflinger中接收vsync信号的入口为MessageQueue的cb_eventReceiver方法,调用流程图如下,

cb_eventReceiver方法如下,直接调用eventReceiver方法,

MessageQueue* queue = reinterpret_cast<MessageQueue *>(data);
    return queue->eventReceiver(fd, events);

eventReceiver方法主要逻辑如下,

1,调用DisplayEventReceiver的getEvents方法循环读取mEventTube对象中的数据,

while ((n = DisplayEventReceiver::getEvents(&mEventTube, buffer, 8)) > 0) 

2,如果是vsync信号,就调用Handler的dispatchInvalidate处理,

if (buffer[i].header.type == DisplayEventReceiver::DISPLAY_EVENT_VSYNC) 
    mHandler->dispatchInvalidate();
    break;

此处的Handler是MessageQueue.cpp中的一个类,其dispatchInvalidate方法如下,

if ((android_atomic_or(eventMaskInvalidate, &mEventMask) & eventMaskInvalidate) == 0) 
   mQueue.mLooper->sendMessage(this, Message(MessageQueue::INVALIDATE));

调用主线程的Looper调用sendMessage方法发送INVALIDATE消息,切换到主线程中执行。Handler Looper机制再次不论述了,只需要知道会执行handleMessage方法, Handler的handleMessage方法对INVALIDATE消息处理如下,

case INVALIDATE:
   android_atomic_and(~eventMaskInvalidate, &mEventMask);
   mQueue.mFlinger->onMessageReceived(message.what);
   break;

此处的mFlinger是SurfaceFlinger对象, SurfaceFlinger的onMessageReceived方法对INVALIDATE消息处理如下,

switch (what) 
  case MessageQueue::INVALIDATE: 
      bool refreshNeeded = handleMessageTransaction();
      refreshNeeded |= handleMessageInvalidate();
      refreshNeeded |= mRepaintEverything;
      if (refreshNeeded) 
          •••
          signalRefresh();
       
  break;

signalRefresh方法后面会详细论述。