onComposerHalRefresh方法是SurfaceFlinger中的一个函数。该方法的作用是在Composer HAL刷新时被调用，用于更新显示内容。onComposerHalRefresh方法会在SurfaceFlinger接收到Composer HAL刷新事件时被调用。Composer HAL是硬件抽象层的一部分，负责与硬件显示设备进行通信。当Composer HAL完成一次刷新操作后，会通知SurfaceFlinger进行相应的处理。
在onComposerHalRefresh方法中，SurfaceFlinger会执行一系列操作，包括更新屏幕上的图像内容、处理显示层的合成和混合等。通过这些操作，SurfaceFlinger能够将应用程序的图像内容正确地显示在屏幕上。
SurfaceFlinger的onComposerHalRefresh方法代码如下：
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| //frameworks/native/services/surfaceflinger/Surfaceflinger.cpp
void SurfaceFlinger::onComposerHalRefresh(hal::HWDisplayId) {
Mutex::Autolock lock(mStateLock);
scheduleComposite(FrameHint::kNone);
}
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SurfaceFlinger scheduleComposite
调用SurfaceFlinger的scheduleComposite方法：
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| //frameworks/native/services/surfaceflinger/Surfaceflinger.cpp
void SurfaceFlinger::scheduleComposite(FrameHint hint) {
mMustComposite = true;
scheduleCommit(hint);
}
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调用scheduleCommit方法：
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| //frameworks/native/services/surfaceflinger/Surfaceflinger.cpp
std::unique_ptr<scheduler::Scheduler> mScheduler;
void SurfaceFlinger::scheduleCommit(FrameHint hint) {
if (hint == FrameHint::kActive) {
mScheduler->resetIdleTimer();
}
mPowerAdvisor->notifyDisplayUpdateImminent();
mScheduler->scheduleFrame();
}
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MessageQueue scheduleFrame
调用Scheduler的scheduleFrame方法，Scheduler继承MessageQueue，调用MessageQueue的scheduleFrame方法：
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| //frameworks/native/services/surfaceflinger/Scheduler/MessageQueue.cpp
void MessageQueue::scheduleFrame() {
ATRACE_CALL();
{
std::lock_guard lock(mInjector.mutex);
if (CC_UNLIKELY(mInjector.connection)) {
ALOGD("%s while injecting VSYNC", __FUNCTION__);
//请求下一个 VSync 信号
mInjector.connection->requestNextVsync();
return;
}
}
std::lock_guard lock(mVsync.mutex);
mVsync.scheduledFrameTime =
mVsync.registration->schedule({.workDuration = mVsync.workDuration.get().count(),
.readyDuration = 0,
.earliestVsync = mVsync.lastCallbackTime.count()});
}
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调用了VSyncCallbackRegistration的schedule方法：
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| //frameworks/native/services/surfaceflinger/Scheduler/VSyncCallbackRegistration.cpp
std::reference_wrapper<VSyncDispatch> mDispatch;
ScheduleResult VSyncCallbackRegistration::schedule(VSyncDispatch::ScheduleTiming scheduleTiming) {
if (!mValidToken) {
return std::nullopt;
}
return mDispatch.get().schedule(mToken, scheduleTiming);
}
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VSyncDispatchTimerQueue schedule
调用mDispatch(VSyncDispatch)的schedule方法，实际调用的是VSyncDispatchTimerQueue的schedule方法：
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| //frameworks/native/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.cpp
ScheduleResult VSyncDispatchTimerQueueEntry::schedule(VSyncDispatch::ScheduleTiming timing,
VSyncTracker& tracker, nsecs_t now) {
auto nextVsyncTime = tracker.nextAnticipatedVSyncTimeFrom(
std::max(timing.earliestVsync, now + timing.workDuration + timing.readyDuration));
auto nextWakeupTime = nextVsyncTime - timing.workDuration - timing.readyDuration;
bool const wouldSkipAVsyncTarget =
mArmedInfo && (nextVsyncTime > (mArmedInfo->mActualVsyncTime + mMinVsyncDistance));
bool const wouldSkipAWakeup =
mArmedInfo && ((nextWakeupTime > (mArmedInfo->mActualWakeupTime + mMinVsyncDistance)));
if (wouldSkipAVsyncTarget && wouldSkipAWakeup) {
return getExpectedCallbackTime(nextVsyncTime, timing);
}
bool const alreadyDispatchedForVsync = mLastDispatchTime &&
((*mLastDispatchTime + mMinVsyncDistance) >= nextVsyncTime &&
(*mLastDispatchTime - mMinVsyncDistance) <= nextVsyncTime);
if (alreadyDispatchedForVsync) {
nextVsyncTime =
tracker.nextAnticipatedVSyncTimeFrom(*mLastDispatchTime + mMinVsyncDistance);
nextWakeupTime = nextVsyncTime - timing.workDuration - timing.readyDuration;
}
// 如果计时器线程即将运行，通过回调计时器重新计算应用此工作更新，以避免取消即将触发的回调。
auto const nextReadyTime = nextVsyncTime - timing.readyDuration;
mScheduleTiming = timing;
mArmedInfo = {nextWakeupTime, nextVsyncTime, nextReadyTime};
return getExpectedCallbackTime(nextVsyncTime, timing);
}
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