Android Graphic SurfaceFlinger 疑难解答

参考代码：android4.4.2 aosp
名称约定：
SF : SurfaceFlinger
BQ : BufferQueue

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Q：SF如何同步所有Client的合成、设置等需求？
A：mStateLock、SF中的mCurrentStates/mDrawingStates、Layer中的mCurrentStates/mDrawingStates；
mCurrentStates,mCurrentStates是相同的类型，但是在SF中和Layer中分别代表不同的结构：
Layer:

State mCurrentStates;State mDrawingStates;struct State {        Geometry active;        Geometry requested;        uint32_t z;        uint32_t layerStack;                                                        uint8_t alpha;        uint8_t flags;        uint8_t reserved[2];        int32_t sequence; // changes when visible regions can change                Transform transform;        // the transparentRegion hint is a bit special, it's latched only        // when we receive a buffer -- this is because it's "content"               // dependent.        Region activeTransparentRegion;        Region requestedTransparentRegion;    };

SurfaceFlinger:

State mCurrentStates;State mDrawingStates;struct DisplayDeviceState {        DisplayDeviceState();        DisplayDeviceState(DisplayDevice::DisplayType type);        bool isValid() const { return type >= 0; }        bool isMainDisplay() const { return type == DisplayDevice::DISPLAY_PRIMARY; }        bool isVirtualDisplay() const { return type >= DisplayDevice::DISPLAY_VIRTUAL; }        DisplayDevice::DisplayType type;        sp<IGraphicBufferProducer> surface;        uint32_t layerStack;        Rect viewport;        Rect frame;        uint8_t orientation;        String8 displayName;        bool isSecure;    };      struct State {        LayerVector layersSortedByZ;        DefaultKeyedVector< wp<IBinder>, DisplayDeviceState> displays;    };

使用方法：
当Client设置完后，通过各种方法最终调用到request_vsync()；当VSYNC到来后

void SurfaceFlinger::onMessageReceived(int32_t what) {    ATRACE_CALL();    switch (what) {    case MessageQueue::TRANSACTION:        handleMessageTransaction();        break;    case MessageQueue::INVALIDATE:        handleMessageTransaction();        handleMessageInvalidate();        signalRefresh();        break;    case MessageQueue::REFRESH:        handleMessageRefresh();        break;    }    }SurfaceFlinger::handleMessageTransaction    SurfaceFlinger::handleTransaction        Mutex::Autolock _l(mStateLock)

在handleMessageTransaction函数中：
获取mStateLock，
经过一系列的处理，最终SF将mCurrentStates赋值到mDrawingStates，以for循环方式将layersSortedByZ中的layer的mCurrentStates赋值到mDrawingStates；
释放mStateLock；

在获取mStateLock后，所有Client对SF或者对Layer的操作都无法执行，因为它们也需要获取mStateLock；
在释放mStateLock后，所有Client的操作都正常了，Client可以创建新的Surface，也可以设置Surface的参数；
因为在获取释放mStateLock期间，已经将SF、Layer的状态已经保存在mDrawingStates中；而Client每次都是用的是mCurrentStates；

列出几个需要mStateLock的函数：

创建Surface或者说Layer的地方Client::createSurface    SurfaceFlinger::createLayer        SurfaceFlinger::addClientLayer            Mutex::Autolock _l(mStateLock);            mCurrentState.layersSortedByZ.add(lbc);设置Surface的各种参数SurfaceFlinger::setTransactionState    Mutex::Autolock _l(mStateLock);VSYNC信号来时，SF用来处理当前状态的地方SurfaceFlinger::handleMessageTransaction    SurfaceFlinger::handleTransaction        Mutex::Autolock _l(mStateLock)

未完，其他问题待续。。。。。。