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

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);
}