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103 lines
3.2 KiB
103 lines
3.2 KiB
---
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Vsync 信号机制
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---
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1. Vsync 信号的生成机制
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2. Vsync 在 SurfaceFlinger 中的分发流程
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3. Vsync 信号的分发原理
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```c++
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void SurfaceFlinger::init(){
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sp<VsyncSource> vsyncSrc = new DispSyncSource(&mPrimaryDispSync, vsyncPhaseOffsetNs, true, "app");
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mEventThread = new EventThread(vsyncSrc);
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sp<VsyncSource> sfVsyncSrc = new DisSyncSource(&mPrimaryDispSync, sfVsyncPhaseOffsetNs, true, "sf");
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mSFEventThread = new EventThread(sfVsyncSrc);
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mHwc = new HWComposer(this, *static_cast<HWCompiser::EventHandler *>(this));
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}
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// 主要用于生成 Vsync 信号
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HWComposer::HWComposer(const sp<SurfaceFlinger>& flinger, ...){
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bool needVsyncThread = true;
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loadHwcModule();
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if(mHwc){
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mCBContext->procs.vsync = &hook_vsync;
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needVsyncThread = false;
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}
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if(needVsyncThread){
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mVsyncThread = new VsyncThread(*this);
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}
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}
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// hook_vsync
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void HWComposer::vsync(int disp, int64_t timestamp){
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mEventHandler.onVSyncReceived(disp, timestamp);
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}
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// 软件分发
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bool HWComposer::VSyncThread::threadLoop(){
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clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &spec, NULL);
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mHwc.mEventHandler.onVSyncReceived(0, next_vsync);
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return true;
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}
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void SurfaceFlinger::onVSyncReceived(int type, nsece_t timestamp){
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mPrimaryDispSync.addResyncSample(timestamp);
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}
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bool DispSync::addResyncSample(nsecs_t timestamp){
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mResyncSamples[idx] = timestamp;
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updateModelLocked();
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}
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void DispSync::updateModelLocked(){
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mThread->updateModel(mPeriod, mPhase);
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}
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DispSync::DispSync():mThread(new DispSyncThread()){
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mThread->run("DispSync", ...);
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}
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// 工作线程的处理流程
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virtual bool threadLoop(){
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while(true){
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if(mPeriod == 0){
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mCond.wait(mMutex);
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continue;
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}
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now = systemTime(SYSTEM_TIME_MONOTONIC);
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callbackInvocations = gatherCallbackInvocationsLocked(now);
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fireCallbackInvocations(callbackInvocations);
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}
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return false;
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}
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```
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```c++
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void EventThread::onVSyncEvent(nsecs_t timestamp){
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mVSyncEvent[0].header.timestamp = timestamp;
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mCondition.broadcast();
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}
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Vector<sp<EventThread::Connection>> EventThread::waitForEvent(...){
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do{
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// 检查 mVSyncEvent 数组，看有没有 VSync 触发
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// 如果有就遍历所有注册的 connection
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// 如果 count>=0 就加到 signalConnections 里，加的时候重置为 -1
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if(!timestamp){
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if(waitForVSync){
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mCondition.waitRelative(mLock, timeout);
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}
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}
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}while(signalConnections.isEmpty());
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return signalConnections;
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}
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```
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```c++
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status_t EventThread::Connection::postEvent(...){
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DisplayEventReceiver::sendEvents(mChannel, &event, 1);
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}
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ssize_t DisplayEventReceiver::sendEvents(const sp<BitTube>&dataChannel, Event const* events, size_t count){
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return BitTube::sendObjects(dataChannel, events, count);
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}
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ssize_t BitTube::sendObjects(const sp<BitTube>&tube, void const* events, size_t count, size_t objSize){
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const char* vaddr = reinterpret_cast<const char*>(events);
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sszie_t size = tube->write(vaddr, count*objSize);
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}
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```
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