android graphic(13)—surface flinger中的“事务”

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surfaceflinger中的事务flags

surfacefligner中所涉及事务的flag包括下面几种，

enum {    //需要处理事务    eTransactionNeeded        = 0x01,    //需要遍历    eTraversalNeeded          = 0x02,    //需要处理display的事务    eDisplayTransactionNeeded = 0x04,    eTransactionMask          = 0x07};

设置和处理flags

mTransactionFlags是surface flinger中的一个成员，注意在layer中也存在一个同名的mTransactionFlags，通过下面的函数设置该flag，

uint32_t SurfaceFlinger::setTransactionFlags(uint32_t flags) {    //或返回的是mTransactionFlags旧的值    uint32_t old = android_atomic_or(flags, &mTransactionFlags);    //如果旧值和flags没有bit是相同的??    if ((old & flags)==0) { // wake the server up        signalTransaction();    }    return old;}

在surfaceflinger中，a, createLayer()，removeLayer()，setClientStateLocked都会去设置事务flag为eTransactionNeeded；b, setClientStateLocked()会去设置eTraversalNeeded；c, createDisplay()，destroyDisplay()，onHotplugReceived()，setDisplayStateLocked()会去设置eDisplayTransactionNeeded。

/*----------------------SurfaceFlinger.cpp-------------------------------*/void SurfaceFlinger::signalTransaction() {    mEventQueue.invalidate();}

进而调用，

#define INVALIDATE_ON_VSYNC 1/*----------------------MessageQueue.cpp-------------------------------*/void MessageQueue::invalidate() {// INVALIDATE_ON_VSYNC宏默认为true#if INVALIDATE_ON_VSYNC    mEvents->requestNextVsync();#else    mHandler->dispatchInvalidate();#endif}

mEvents就是EventThread类中的Connection类，

/*----------------------EventThread.cpp-------------------------------*/void EventThread::Connection::requestNextVsync() {    mEventThread->requestNextVsync(this);}// 关于Connection中的count，当为0时为一次性的事件，即触发一次sync信号// count >= 1 : continuous event. count is the vsync rate// count == 0 : one-shot event that has not fired// count ==-1 : one-shot event that fired this round / disabled        int32_t count;void EventThread::requestNextVsync(        const sp<EventThread::Connection>& connection) {    Mutex::Autolock _l(mLock);    if (connection->count < 0) {        connection->count = 0;        mCondition.broadcast();    }}

从上面代码分析，各种事务都会去触发一次vsync，前面文章分析过，在每次vsync信号到来时，会去调用，

/*----------------------SurfaceFlinger.cpp-------------------------------*/void SurfaceFlinger::onMessageReceived(int32_t what) {    ATRACE_CALL();    switch (what) {    case MessageQueue::TRANSACTION:        handleMessageTransaction();        break;    //这个分支    case MessageQueue::INVALIDATE:        handleMessageTransaction();        handleMessageInvalidate();        signalRefresh();        break;    case MessageQueue::REFRESH:        handleMessageRefresh();        break;    }}

进而调用handleMessageTransaction，进而根据mTransactionFlags中设置的bit值做相应的处理。

/*----------------------SurfaceFlinger.cpp-------------------------------*/void SurfaceFlinger::handleMessageTransaction() {    uint32_t transactionFlags = peekTransactionFlags(eTransactionMask);    if (transactionFlags) {        handleTransaction(transactionFlags);    }}

创建layer时设置flag

下面以surface flinger在创建layer时为例，

/*----------------------SurfaceFlinger.cpp-------------------------------*/status_t SurfaceFlinger::createLayer(        const String8& name,        const sp<Client>& client,        uint32_t w, uint32_t h, PixelFormat format, uint32_t flags,        sp<IBinder>* handle, sp<IGraphicBufferProducer>* gbp){    //ALOGD("createLayer for (%d x %d), name=%s", w, h, name.string());    if (int32_t(w|h) < 0) {        ALOGE("createLayer() failed, w or h is negative (w=%d, h=%d)",                int(w), int(h));        return BAD_VALUE;    }    status_t result = NO_ERROR;    sp<Layer> layer;    switch (flags & ISurfaceComposerClient::eFXSurfaceMask) {        case ISurfaceComposerClient::eFXSurfaceNormal:            result = createNormalLayer(client,                    name, w, h, flags, format,                    handle, gbp, &layer);            break;        case ISurfaceComposerClient::eFXSurfaceDim:            result = createDimLayer(client,                    name, w, h, flags,                    handle, gbp, &layer);            break;        default:            result = BAD_VALUE;            break;    }    if (result == NO_ERROR) {       //①将handle和layer保存到client中       //②将gbp，也就是server端的BufferQueue放到mGraphicBufferProducerList中        addClientLayer(client, *handle, *gbp, layer);       //因为新建了layer，所以设置事务flag为需要处理事务eTransactionNeeded        setTransactionFlags(eTransactionNeeded);    }    return result;}

关于Handle，就是个BBinder，其中保存了surfacefligner和layer，用来传递给client，同时继承了 LayerCleaner ，顾名思义，就是删除layer时做一些工作，

sp<IBinder> Layer::getHandle() {    Mutex::Autolock _l(mLock);    LOG_ALWAYS_FATAL_IF(mHasSurface,            "Layer::getHandle() has already been called");    mHasSurface = true;    /*     * The layer handle is just a BBinder object passed to the client     * (remote process) -- we don't keep any reference on our side such that     * the dtor is called when the remote side let go of its reference.     *     * LayerCleaner ensures that mFlinger->onLayerDestroyed() is called for     * this layer when the handle is destroyed.     */    class Handle : public BBinder, public LayerCleaner {        wp<const Layer> mOwner;    public:        Handle(const sp<SurfaceFlinger>& flinger, const sp<Layer>& layer)            : LayerCleaner(flinger, layer), mOwner(layer) {        }    };    return new Handle(mFlinger, this);}

/*----------------------Layer.cpp-------------------------------*/// LayerCleaner仅仅保存了layer和surfaceflinger，// 在析构时，会调用surfaceflinger的onLayerDestroyed(mLayer)函数，去做// 删除Layer的工作Layer::LayerCleaner::LayerCleaner(const sp<SurfaceFlinger>& flinger,        const sp<Layer>& layer)    : mFlinger(flinger), mLayer(layer) {}Layer::LayerCleaner::~LayerCleaner() {    // destroy client resources    mFlinger->onLayerDestroyed(mLayer);}

/*----------------------SurfaceFlinger.cpp-------------------------------*/void SurfaceFlinger::addClientLayer(const sp<Client>& client,        const sp<IBinder>& handle,        const sp<IGraphicBufferProducer>& gbc,        const sp<Layer>& lbc){    // attach this layer to the client    client->attachLayer(handle, lbc);    // add this layer to the current state list    Mutex::Autolock _l(mStateLock);    // 将新建的layer添加到mCurrentState的layersSortedByZ    mCurrentState.layersSortedByZ.add(lbc);    // 将BufferQueue添加到mGraphicBufferProducerList    // SortedVector< wp<IBinder> > mGraphicBufferProducerList;    mGraphicBufferProducerList.add(gbc->asBinder());}

/*----------------------Client.cpp-------------------------------*/// 应该是每个app对应一个Client// 每个Client里面有这个app对应的所有layers// DefaultKeyedVector< wp<IBinder>, wp<Layer> > mLayers;// handle就是将这个layer和surfaceflinger的信息保存起来，用来析构时候用void Client::attachLayer(const sp<IBinder>& handle, const sp<Layer>& layer){    Mutex::Autolock _l(mLock);    mLayers.add(handle, layer);}