Vsync信号的产生，都有那些类需要接收vsync信号

小咪咪 2022-05-24 04:13 257阅读 0赞

SurfaceFlinger模块下的HWComposer，其中一个功能就是产生硬件的vsync。

SurfaceFlinger\_hwc1.cpp

初始化HWComposer对象，同时传入参数SurfaceFlinger本身，作为回调事件的接收方。

void SurfaceFlinger::init() {
        mHwc.reset(new HWComposer(this,
                *static_cast<HWComposer::EventHandler *>(this)));
    }

HWComposer\_hwc1.cpp

HWComposer::HWComposer(
            const sp<SurfaceFlinger>& flinger,
            EventHandler& handler)
        : mFlinger(flinger),
          mFbDev(0), mHwc(0), mNumDisplays(1),
          mCBContext(new cb_context),...{
    	
    	loadHwcModule();
    HWC模块加载成功，先给一些函数指针赋值，然后注册硬件回调registerProcs。
    	if (mHwc) {
    		if (mHwc->registerProcs) {
    			mCBContext->hwc = this;
    			mCBContext->procs.invalidate = &hook_invalidate;
    			mCBContext->procs.vsync = &hook_vsync;
    			mHwc->registerProcs(mHwc, &mCBContext->procs);
    		}
    	}
    }

HWComposer\_hwc1.cpp

void HWComposer::loadHwcModule(){
    	hw_module_t const* module;
    	if (hw_get_module(HWC_HARDWARE_MODULE_ID, &module) != 0) {}
    	int err = hwc_open_1(module, &mHwc);
    }

注册的硬件回调类型(其中的procs,类型是hwc\_procs\_t)：

struct HWComposer::cb_context {
        struct callbacks : public hwc_procs_t {
            // these are here to facilitate the transition when adding
            // new callbacks (an implementation can check for NULL before
            // calling a new callback).
            void (*zero[4])(void);
        };
        callbacks procs;
        HWComposer* hwc;
    };

打开的HWComposer硬件模块类型是structhwc\_composer\_device\_1\* mHwc;

hardware/libhardware/include/hardware/Hwcomposer.h

typedef struct hwc_composer_device_1 {
        /*
         * (*registerProcs)() registers callbacks that the h/w composer HAL can
         * later use. It will be called immediately after the composer device is
         * opened with non-NULL procs. It is FORBIDDEN to call any of the callbacks
         * from within registerProcs(). registerProcs() must save the hwc_procs_t
         * pointer which is needed when calling a registered callback.
         */
        void (*registerProcs)(struct hwc_composer_device_1* dev,
                hwc_procs_t const* procs);
    }hwc_composer_device_1_t;

hwc\_composer\_device\_1\_t的具体实现类hwc\_session.h

hardware/qcom/display/sdm/libs/hwc/hwc_session.h
    class HWCSession : hwc_composer_device_1_t, public qClient::BnQClient {}

把注册的回调实例surfaceflinger中的&mCBContext->procs赋值给hwc\_session->hwc\_procs\_

void HWCSession::RegisterProcs(hwc_composer_device_1 *device, hwc_procs_t const *procs) {
      SCOPE_LOCK(locker_);
    
      if (!device || !procs) {
        return;
      }
    
      HWCSession *hwc_session = static_cast<HWCSession *>(device);
      hwc_session->hwc_procs_ = procs;
    }

hardware/qcom/display/sdm/libs/hwc/hwc\_session.h

hwc\_session->hwc\_procs\_跟&mCBContext->procs的类型一致，都是hwc\_procs\_t，所以可以直接赋值。

hwc\_procs\_t const\*hwc\_procs\_ = &hwc\_procs\_default\_;

hwc\_procs\_thwc\_procs\_default\_;

hwc\_session构造时，会创建显示设备，同时把回调实例&hwc\_procs\_,传递给显示硬件。

hwc\_session.cpp

int HWCSession::Init() {
    	status = HWCDisplayPrimary::Create(core_intf_, &buffer_allocator_, &hwc_procs_, qservice_,
                                             &hwc_display_[HWC_DISPLAY_PRIMARY]);
    }

hwc\_display\_primary.cpp

int HWCDisplayPrimary::Create(CoreInterface *core_intf, BufferAllocator *buffer_allocator,
                                  hwc_procs_t const **hwc_procs, qService::QService *qservice,
                                  HWCDisplay **hwc_display) {
      HWCDisplay *hwc_display_primary = new HWCDisplayPrimary(core_intf, buffer_allocator,
                                                              hwc_procs, qservice);
    }

HWCDisplayPrimary::HWCDisplayPrimary(CoreInterface *core_intf,
                                         BufferAllocator *buffer_allocator,
                                         hwc_procs_t const **hwc_procs,
                                         qService::QService *qservice)
      : HWCDisplay(core_intf, hwc_procs, kPrimary, HWC_DISPLAY_PRIMARY, true, qservice,
                   DISPLAY_CLASS_PRIMARY), buffer_allocator_(buffer_allocator) {
    }

hwc\_display.cpp

hwc\_display是最初vsync信号产生的地方。回调实例保存在hwc\_procs\_变量中。

HWCDisplay::HWCDisplay(CoreInterface *core_intf, hwc_procs_t const **hwc_procs, DisplayType type,
                           int id, bool needs_blit, qService::QService *qservice,
                           DisplayClass display_class)
      : core_intf_(core_intf), hwc_procs_(hwc_procs), type_(type), id_(id), needs_blit_(needs_blit),
        qservice_(qservice), display_class_(display_class) {
    }

当有硬件vsync信号产生时，一路回调到HWComposer\_hwc1.cpp中的vsync函数(实际执行的hook\_vsync，因为：mCBContext->procs.vsync= &hook\_vsync;)

DisplayError HWCDisplay::VSync(const DisplayEventVSync &vsync) {
      const hwc_procs_t *hwc_procs = *hwc_procs_;
    
      if (!hwc_procs) {
        return kErrorParameters;
      }
    
      hwc_procs->vsync(hwc_procs, id_, vsync.timestamp);
    
      return kErrorNone;
    }

再次回到HWComposer\_hwc1.cpp

void HWComposer::hook_vsync(const struct hwc_procs* procs, int disp,
            int64_t timestamp) {
        cb_context* ctx = reinterpret_cast<cb_context*>(
                const_cast<hwc_procs_t*>(procs));
        ctx->hwc->vsync(disp, timestamp);
    }

hook\_vsync直接调用了vsync函数。通过mEventHandler也即是SurfaceFlinger实例把vsync传递到了Surfaceflinger中的onVSyncReceived。

void HWComposer::vsync(int disp, int64_t timestamp) {
        if (uint32_t(disp) < HWC_NUM_PHYSICAL_DISPLAY_TYPES) {
            {
                Mutex::Autolock _l(mLock);
    
                // There have been reports of HWCs that signal several vsync events
                // with the same timestamp when turning the display off and on. This
                // is a bug in the HWC implementation, but filter the extra events
                // out here so they don't cause havoc downstream.
                if (timestamp == mLastHwVSync[disp]) {
                    ALOGW("Ignoring duplicate VSYNC event from HWC (t=%" PRId64 ")",
                            timestamp);
                    return;
                }
    
                mLastHwVSync[disp] = timestamp;
            }
    
            char tag[16];
            snprintf(tag, sizeof(tag), "HW_VSYNC_%1u", disp);
            ATRACE_INT(tag, ++mVSyncCounts[disp] & 1);
    
            mEventHandler.onVSyncReceived(this, disp, timestamp);
        }
    }

vsync信号的接收

SurfaceFlinger\_hwc1.cpp

void SurfaceFlinger::onVSyncReceived(HWComposer* /*composer*/, int type,
                                         nsecs_t timestamp) {
    	needsHwVsync = mPrimaryDispSync.addResyncSample(timestamp);
    	enableHardwareVsync();
    }

DispSync.cpp

bool DispSync::addResyncSample(nsecs_t timestamp) {
    唤醒DispSync中的DispSyncThread线程
    	mThread->updateModel(mPeriod, mPhase, mReferenceTime);
    }

class DispSyncThread: public Thread {
    	virtual bool threadLoop() {
    收集需要回调的监听者，执行回调。
    		callbackInvocations = gatherCallbackInvocationsLocked(now);
                if (callbackInvocations.size() > 0) {
                    fireCallbackInvocations(callbackInvocations);
                }
    	}
    }

回调其 onDispSyncEvent函数。
        void fireCallbackInvocations(const Vector<CallbackInvocation>& callbacks) {
            if (kTraceDetailedInfo) ATRACE_CALL();
            for (size_t i = 0; i < callbacks.size(); i++) {
                callbacks[i].mCallback->onDispSyncEvent(callbacks[i].mEventTime);
            }
        }

都有哪些对vsync感兴趣的监听者呢？

回到SurfaceFlinger\_hwc1.cpp

这里会注册一个对vsync的监听到DispSync中。

void SurfaceFlinger::init() {
    	mSFEventThread = new EventThread(sfVsyncSrc, *this, true);
    	mEventQueue.setEventThread(mSFEventThread);
    ｝

EventThread.cpp
    bool EventThread::threadLoop() {
    	signalConnections = waitForEvent(&event);
    }

Vector< sp<EventThread::Connection> > EventThread::waitForEvent(
            DisplayEventReceiver::Event* event){
    	enableVSyncLocked();
    }

void EventThread::enableVSyncLocked() {
    	mVSyncSource->setVSyncEnabled(true);
    }

SurfaceFlinger\_hwc1.cpp

class DispSyncSource : public VSyncSource, private DispSync::Callback {
    往DisySync中添加一个对vsync感兴趣的监听者，就是DispSyncSource实例。所以vsync信号回调时会传递到 DispSyncSource的onDispSyncEvent方法中。
    	virtual void setVSyncEnabled(bool enable) {
    		status_t err = mDispSync->addEventListener(mName, mPhaseOffset,
    			static_cast<DispSync::Callback*>(this));
    	}	
    ｝

DispSyncSource的onDispSyncEvent方法

virtual void onDispSyncEvent(nsecs_t when) {
            sp<VSyncSource::Callback> callback;
            {
                Mutex::Autolock lock(mCallbackMutex);
                callback = mCallback;
    
                if (mTraceVsync) {
                    mValue = (mValue + 1) % 2;
                    ATRACE_INT(mVsyncEventLabel.string(), mValue);
                }
            }
    
            if (callback != NULL) {
                callback->onVSyncEvent(when);
            }
        }

那么onDispSyncEvent这里的回调callback= mCallback;又是谁呢？

回到EventThread.cpp，通过mVSyncSource->setCallback设置的回调就是onDispSyncEvent的中mCallback。

void EventThread::enableVSyncLocked() {
        if (!mUseSoftwareVSync) {
            // never enable h/w VSYNC when screen is off
            if (!mVsyncEnabled) {
                mVsyncEnabled = true;
                mVSyncSource->setCallback(static_cast<VSyncSource::Callback*>(this));
                mVSyncSource->setVSyncEnabled(true);
            }
        }
        mDebugVsyncEnabled = true;
        sendVsyncHintOnLocked();
    }

所以vsync信号又被传递到了EventThread.cpp中的onVSyncEvent。

EventThread.cpp
    void EventThread::onVSyncEvent(nsecs_t timestamp) {
        Mutex::Autolock _l(mLock);
        mVSyncEvent[0].header.type = DisplayEventReceiver::DISPLAY_EVENT_VSYNC;
        mVSyncEvent[0].header.id = 0;
        mVSyncEvent[0].header.timestamp = timestamp;
        mVSyncEvent[0].vsync.count++;
        mCondition.broadcast();
    }

这里把vsync包装成一个event事件，然后mCondition.broadcast();唤醒一个线程，也就是EventThread::threadLoop()。

EventThread.cpp
    bool EventThread::threadLoop() {
    将会调用 signalConnections中的listener的postEvent方法。
        Vector< sp<EventThread::Connection> > signalConnections;
        signalConnections = waitForEvent(&event);
        // 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);
    	}
    }

EventThread.cpp
    Vector< sp<EventThread::Connection> > EventThread::waitForEvent(
            DisplayEventReceiver::Event* event){
    signalConnections中的listener来自 mDisplayEventConnections。
    	        // find out connections waiting for events
            size_t count = mDisplayEventConnections.size();
            for (size_t i=0 ; i<count ; i++) {
                sp<Connection> connection(mDisplayEventConnections[i].promote());
    		signalConnections.add(connection);
    	}
    }

mDisplayEventConnections中的元素来源：

EventThread.cpp
    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;
    }

void EventThread::Connection::onFirstRef() {
        // NOTE: mEventThread doesn't hold a strong reference on us
        mEventThread->registerDisplayEventConnection(this);
    }

mDisplayEventConnections中的元素，其中一个就是EventThread.cpp中的内部类Connection。

所以包装着vsync信号的事件，被传递到了EventThread::Connection的postEvent。

status_t EventThread::Connection::postEvent(
            const DisplayEventReceiver::Event& event) {
        ssize_t size = DisplayEventReceiver::sendEvents(&mChannel, &event, 1);
        return size < 0 ? status_t(size) : status_t(NO_ERROR);
    }

上面的函数DisplayEventReceiver::sendEvents，将把事件写入到socket中的输入端。其中&mChannel的类型gui::BitTubemChannel;本质是一个socket。

Frameworks/native/libs/gui/DisplayEventReceiver.cpp

EventThread::Connection的postEvent，会往socket中写入事件

ssize_t DisplayEventReceiver::sendEvents(gui::BitTube* dataChannel,
            Event const* events, size_t count)
    {
        return gui::BitTube::sendObjects(dataChannel, events, count);
    }

从socket中读取事件

ssize_t DisplayEventReceiver::getEvents(DisplayEventReceiver::Event* events,
            size_t count) {
        return DisplayEventReceiver::getEvents(mDataChannel.get(), events, count);
    }

那么都有谁是这个socket的接收端，或者读取端呢？

首先看EventThread.cpp中，mChannel变量是在其构造时创建的

mChannel(gui::BitTube::DefaultSize)。

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

其中函数

stealReceiveChannel

用来设置socket 的接收端。

status_t EventThread::Connection::stealReceiveChannel(gui::BitTube* outChannel) {
        outChannel->setReceiveFd(mChannel.moveReceiveFd());
        return NO_ERROR;
    }

都有那些类会希望接收vsync信号呢？

一，SurfaceFigner，通过其中的MessageQueue来接收vsync信号。

MessageQueue.cpp

void MessageQueue::setEventThread(const sp<EventThread>& eventThread)
    {
        if (mEventThread == eventThread) {
            return;
        }
    
        if (mEventTube.getFd() >= 0) {
            mLooper->removeFd(mEventTube.getFd());
        }
    调用 stealReceiveChannel设置socket的接收端为 mEventTube，
        mEventThread = eventThread;
        mEvents = eventThread->createEventConnection();
        mEvents->stealReceiveChannel(&mEventTube);
    在socket有数据写入时，执行回调 cb_eventReceiver，然后调用eventReceiver，通过mHandler->dispatchInvalidate()把事件放入消息队列，
    具体是MessageQueue的looper带有的消息队列。
        mLooper->addFd(mEventTube.getFd(), 0, Looper::EVENT_INPUT,
                MessageQueue::cb_eventReceiver, this);
    }

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

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);
                break;
        }
    }

最终通过mQueue.mFlinger->onMessageReceived(message.what);把vsync信号，作为msg传到Surfacefligner中的onMessageReceived函数。

二，RenderThread.cpp也需要接收vsync，

RenderThread.cpp

void RenderThread::initializeDisplayEventReceiver() {
        LOG_ALWAYS_FATAL_IF(mDisplayEventReceiver, "Initializing a second DisplayEventReceiver?");
        mDisplayEventReceiver = new DisplayEventReceiver();
        status_t status = mDisplayEventReceiver->initCheck();
        LOG_ALWAYS_FATAL_IF(status != NO_ERROR, "Initialization of DisplayEventReceiver "
                "failed with status: %d", status);
    
        // Register the FD
        mLooper->addFd(mDisplayEventReceiver->getFd(), 0,
                Looper::EVENT_INPUT, RenderThread::displayEventReceiverCallback, this);
    }

在有vsync信号时，执行设置的回调enderThread::displayEventReceiverCallback：

int RenderThread::displayEventReceiverCallback(int fd, int events, void* data) {
        if (events & (Looper::EVENT_ERROR | Looper::EVENT_HANGUP)) {
            ALOGE("Display event receiver pipe was closed or an error occurred.  "
                    "events=0x%x", events);
            return 0; // remove the callback
        }
    
        if (!(events & Looper::EVENT_INPUT)) {
            ALOGW("Received spurious callback for unhandled poll event.  "
                    "events=0x%x", events);
            return 1; // keep the callback
        }
    
        reinterpret_cast<RenderThread*>(data)->drainDisplayEventQueue();
    
        return 1; // keep the callback
    }

三，前面都是native层对vsync信号的接收，java层也需要接收vsync信号，比如动画的执行，UI的填充，他们是通过Choreographer.java的来接收的，然后回调动画的执行，UI的填充。

Choreographer.java

其他类通过调用Choreographer的postFrameCallback，postCallback来请求vsync。会调用到scheduleVsyncLocked函数。

Choreographer　内部类FrameDisplayEventReceiver，

private finalclass FrameDisplayEventReceiver extends DisplayEventReceiver\{\}

间接调用到：

private void scheduleVsyncLocked() {
            mDisplayEventReceiver.scheduleVsync();
        }

scheduleVsync调用的父类DisplayEventReceiver的方法。

DisplayEventReceiver.java
        /**
         * Schedules a single vertical sync pulse to be delivered when the next
         * display frame begins.
         */
        public void scheduleVsync() {
            if (mReceiverPtr == 0) {
                Log.w(TAG, "Attempted to schedule a vertical sync pulse but the display event "
                        + "receiver has already been disposed.");
            } else {
                nativeScheduleVsync(mReceiverPtr);
            }
        }

转到native层

nativeScheduleVsync

：

android_view_DisplayEventReceiver.cpp
    static void nativeScheduleVsync(JNIEnv* env, jclass clazz, jlong receiverPtr) {
        sp<NativeDisplayEventReceiver> receiver =
                reinterpret_cast<NativeDisplayEventReceiver*>(receiverPtr);
        status_t status = receiver->scheduleVsync();
        if (status) {
            String8 message;
            message.appendFormat("Failed to schedule next vertical sync pulse.  status=%d", status);
            jniThrowRuntimeException(env, message.string());
        }
    }

jni中的receiver->scheduleVsync()，将调用NativeDisplayEventReceiver的父类DisplayEventDispatcher中的scheduleVsync函数。

DisplayEventDispatcher.cpp

DisplayEventDispatcher类中的成员变量DisplayEventReceivermReceiver就是前面的Frameworks/native/libs/gui/DisplayEventReceiver.cpp。

DisplayEventReceivermReceiver;

DisplayEventDispatcher.cpp

在DisplayEventDispatcher执行初始化时，通过mReceiver.getFd()获取到socket的描述符号，getFd获取的是接收文件描述符。同时把当前类设置为事件的接收回调函数，DisplayEventDispatcher继承了　publicLooperCallback ，所以相应执行的回调函数就是LooperCallback中的handleEvent。

status_t DisplayEventDispatcher::initialize() {
        status_t result = mReceiver.initCheck();
        if (result) {
            ALOGW("Failed to initialize display event receiver, status=%d", result);
            return result;
        }
    
        int rc = mLooper->addFd(mReceiver.getFd(), 0, Looper::EVENT_INPUT,
                this, NULL);
        if (rc < 0) {
            return UNKNOWN_ERROR;
        }
        return OK;
    }

DisplayEventDispatcher.cpp
    int DisplayEventDispatcher::handleEvent(int, int events, void*) {
    	dispatchVsync(vsyncTimestamp, vsyncDisplayId, vsyncCount);
    }

从native层通过jni回调到java层，

android_view_DisplayEventReceiver.cpp
    void NativeDisplayEventReceiver::dispatchVsync(nsecs_t timestamp, int32_t id, uint32_t count) {
    	env->CallVoidMethod(receiverObj.get(),
                    gDisplayEventReceiverClassInfo.dispatchVsync, timestamp, id, count);
    }

DisplayEventReceiver.java

private void dispatchVsync(long timestampNanos, int builtInDisplayId, int frame) {
            onVsync(timestampNanos, builtInDisplayId, frame);
        }

最后调用了Choreographer.java的FrameDisplayEventReceiver的onVsync函数。

Choreographer.java

private final class FrameDisplayEventReceiver extends DisplayEventReceiver{
    	public void onVsync(long timestampNanos, int builtInDisplayId, int frame) {
    FrameDisplayEventReceiver 实现了Runnable接口，所以可以通过post msg的形式，执行其run()，也就是说 FrameDisplayEventReceiver将
    作为Runnable类型，封装成msg的回调函数，当把这个msg从消息队列取出时，会优先执行这个msg的回调函数（也即是其runnable的方法），
    如果msg没有设置回调函数，才会通过handler的handlemessage方法执行。
                Message msg = Message.obtain(mHandler, this);
                msg.setAsynchronous(true);
                mHandler.sendMessageAtTime(msg, timestampNanos / TimeUtils.NANOS_PER_MS);
    	}
    
         public void run() {
                mHavePendingVsync = false;
                doFrame(mTimestampNanos, mFrame);
            }	
    }

doFrame执行相应的回调：

void doFrame(long frameTimeNanos, int frame) {
                AnimationUtils.lockAnimationClock(frameTimeNanos / TimeUtils.NANOS_PER_MS);
    
                mFrameInfo.markInputHandlingStart();
                doCallbacks(Choreographer.CALLBACK_INPUT, frameTimeNanos);
    
                mFrameInfo.markAnimationsStart();
                doCallbacks(Choreographer.CALLBACK_ANIMATION, frameTimeNanos);
    
                mFrameInfo.markPerformTraversalsStart();
                doCallbacks(Choreographer.CALLBACK_TRAVERSAL, frameTimeNanos);
    
                doCallbacks(Choreographer.CALLBACK_COMMIT, frameTimeNanos);
    }

DisplayEventReceiver有两个函数值得注意一下，这两个函数最终作用到IDisplayEventConnection.cpp中

DisplayEventReceiver.h

设置vsync的传递频率，参数值为１表示每个vsync事件都传递，参数值为２表示每隔一个vsync产地一次，参数值为０表示不传递，除非主动调用requestNextVsync。

status\_tsetVsyncRate(uint32\_t count);

requestNextVsync函数要想起作用，需要上一个函数设置vsyncrate为０．

status\_trequestNextVsync();