一、前言
本文重要内容
1、bufferqueue 的四大流程；
2、扼要先容四大流程的调用过程；
本文重要解说安卓图形绘制中的buffer queue
页面数据通过canvas/Open GL ES/vulkan绘制后，形成一帧buffer，交给buffer queue，buffer queue再把数据送到屏幕上表现。以是buffer queue是图形绘制中很核心的一环，它自己就是一个缓冲区池与队列相团结的数据布局。
Buffer queue:图像缓冲区，体系中绝大部门图形数据都会缓冲于此。等候surfaceflinger构造进一步的合成和表现
备注：本文摘录的代码只摘录关键代码和路径，需读者自行团结阅读.由于本文的重点在bufferqueue，别的和bufferqueue干系的流程提到的时间会精简列出，作为辅助理解。
二、Buffer queue
2.1、buffer queue的创建
bufferquque构建
//BufferQueue.cpp frameworks\native\libs\guivoid BufferQueue::createBufferQueue(sp<IGraphicBufferProducer>* outProducer, sp<IGraphicBufferConsumer>* outConsumer, bool consumerIsSurfaceFlinger) { sp<BufferQueueCore> core(new BufferQueueCore()); sp<IGraphicBufferProducer> producer(new BufferQueueProducer(core, consumerIsSurfaceFlinger)); sp<IGraphicBufferConsumer> consumer(new BufferQueueConsumer(core)); *outProducer = producer; *outConsumer = consumer;}构建调用流程
下面堆栈表现了底层surface创建bufferqueue的一个过程
04-20 11:45:54.739 674 707 E createBufferQueue: #00 pc 0004ca33 /system/lib/libgui.so (android::BufferQueue::createBufferQueue(android::sp<android::IGraphicBufferProducer>*, android::sp<android::IGraphicBufferConsumer>*, bool)+74)04-20 11:45:54.739 674 707 E createBufferQueue: #01 pc 00068539 /system/lib/libsurfaceflinger.so (android::BufferQueueLayer: nFirstRef()+40)04-20 11:45:54.739 674 707 E createBufferQueue: #02 pc 000d5ad1 /system/lib/libsurfaceflinger.so (android::surfaceflinger: efaultFactory::createBufferQueueLayer(android: ayerCreationArgs const&)+52)04-20 11:45:54.739 674 707 E createBufferQueue: #03 pc 000c11d5 /system/lib/libsurfaceflinger.so (android::SurfaceFlinger::createLayer(android::String8 const&, android::sp<android::Client> const&, unsigned int, unsigned int, int, unsigned int, android:ayerMetadata, android::sp<android::IBinder>*, android::sp<android::IGraphicBufferProducer>*, android::sp<android::IBinder> const&, android::sp<android:ayer> const&, unsigned int*)+1056)04-20 11:45:54.739 674 707 E createBufferQueue: #04 pc 0006e197 /system/lib/libsurfaceflinger.so (android::Client::createSurface(android::String8 const&, unsigned int, unsigned int, int, unsigned int, android::sp<android::IBinder> const&, android:ayerMetadata, android::sp<android::IBinder>*, android::sp<android::IGraphicBufferProducer>*, unsigned int*)+122)04-20 11:45:54.739 674 707 E createBufferQueue: #05 pc 0007b34f /system/lib/libgui.so (int android::SafeBnInterface<android::ISurfaceComposerClient>::MethodCaller<std::__1::tuple<android::String8 const&, unsigned int, unsigned int, int, unsigned int, android::sp<android::IGraphicBufferProducer> const&, android:ayerMetadata, android::sp<android::IBinder>*, android::sp<android::IGraphicBufferProducer>*, unsigned int*> >::callHelper<android::SafeBnInterface<android::ISurfaceComposerClient>, int (android::ISurfaceComposerClient::*)(android::String8 const&, unsigned int, unsigned int, int, unsigned int, android::sp<android::IGraphicBufferProducer> const&, android:ayerMetadata, android::sp<android::IBinder>*, android::sp<android::IGraphicBufferProducer>*, unsigned int*), std::__1::tuple<android::String8, unsigned int, unsigned int, int, unsigned int, android::sp<android::IGraphicBufferProducer>, android:ayerMetadata, android::sp<android::IBinder>, android::sp<android::IGraphicBufferProducer>, unsigned int>, 0u, 1u, 2u, 3u, 4u, 5u, 6u, 7u, 8u, 9u>(android04-20 11:45:54.739 674 707 E createBufferQueue: #06 pc 00079e2f /system/lib/libgui.so (int android::SafeBnInterface<android::ISurfaceComposerClient>::callLocal<int (android::ISurfaceComposerClient::*)(android::String8 const&, unsigned int, unsigned int, int, unsigned int, android::sp<android::IBinder> const&, android:ayerMetadata, android::sp<android::IBinder>*, android::sp<android::IGraphicBufferProducer>*, unsigned int*)>(android: arcel const&, android:arcel*, int (android::ISurfaceComposerClient::*)(android::String8 const&, unsigned int, unsigned int, int, unsigned int, android::sp<android::IBinder> const&, android:ayerMetadata, android::sp<android::IBinder>*, android::sp<android::IGraphicBufferProducer>*, unsigned int*))+158)04-20 11:45:54.739 674 707 E createBufferQueue: #07 pc 00079d3f /system/lib/libgui.so (android::BnSurfaceComposerClient:nTransact(unsigned int, android:arcel const&, android:arcel*, unsigned int)+46)BufferQueueCore:bufferqueue的实际实例，由他来衔接生产者和斲丧者
BufferQueueProducer:bufferqueue工厂模式的接口，生产者
BufferQueueConsumer:bufferqueue斲丧接口，斲丧者
BufferQueueCore 负责维护 BufferQueue 的根本数据布局，而 BufferQueueProducer 和 BufferQueueConsumer 则负责提供利用 BufferQueue 的根本接口。
2.2、buffer queue团体流程
2.2.1、流程概要
这张图片清晰的表述的buffer queue的工作方式，两大功能：生产buffer、斲丧buffer。
dequeueBuffer:向buffer queue哀求一个缓冲区，并指定缓冲区的宽度、高度、像素格式和用法标记
queueBuffer:把缓冲区返回到队列
acquireBuffer:获取缓冲区内容
releaseBuffer:把数据返回到队列
这里有两次返回队列，实在都是返回buffer queue的数据布局中。简述两个流程
1、dequeue、queue即是先申请缓冲区，并告诉producer申请乐成，producer就把数据queue给buffer queue数据布局中
2、当consumer要的时间先去acquere获取缓冲区内容，获取后举行合成，合成完了必要开释，就给回buffer queue来开释
3、buffer queue利用数据时不会复制一份数据，只会利用数据自己。
通篇文章，我们就在理解BufferQueueProducer 和 BufferQueueConsumer怎样利用上面这四个流程
requestBuffer
int Surface::dequeueBuffer(android_native_buffer_t** buffer, int* fenceFd) { status_t result = mGraphicBufferProducer->dequeueBuffer(&buf, &fence, reqWidth, reqHeight, reqFormat, reqUsage, &mBufferAge, enableFrameTimestamps ? &frameTimestamps : nullptr); ... if ((result & IGraphicBufferProducer::BUFFER_NEEDS_REALLOCATION) || gbuf == nullptr) { if (mReportRemovedBuffers && (gbuf != nullptr)) { mRemovedBuffers.push_back(gbuf); } result = mGraphicBufferProducer->requestBuffer(buf, &gbuf);requestBuffer单独提一下这个流程，当我们初次dequeueBuffer事后，surface会调用requestBuffer,requestBuffer的重要作用就是把GraphicBuffer传给应用侧，
这个动作只必要做一次，应用侧拿到GraphicBuffer事后就可以把共享内存mmap到应用侧的内存空间，然后才可以绘制图像。
2.2.2、bufferqueue被调用流程
本小结重要目的是，在我们认识bufferqueu的是怎样工作的同时，不脱离surfaceflinger团体框架。简朴提一下它是假如调用来的。以便我们更深入理解。
1、dequeueBuffer&&queueBuffer
当app创建window的时间，会创建surface来表现。实则会创建底层的surface。底层surface创建时会hook住dequeueBuffer和queueBuffer方法。
surface持有mGraphicBufferProducer对象来创建bufferqueue
dequeueBuffer
方法位置：BufferQueueProducer::dequeueBuffer
04-20 09:48:38.909 6053 6263 E graphic dequeueBuffer: #00 pc 0006dea5 /system/lib/libgui.so (android::BpGraphicBufferProducer::dequeueBuffer(int*, android::sp<android::Fence>*, unsigned int, unsigned int, int, unsigned long long, unsigned long long*, android::FrameEventHistoryDelta*)+136)04-20 09:48:38.909 6053 6263 E graphic dequeueBuffer: #01 pc 000842ed /system/lib/libgui.so (android::Surface::dequeueBuffer(ANativeWindowBuffer**, int*)+316)04-20 09:48:38.909 6053 6263 E graphic dequeueBuffer: #02 pc 0015004b /system/lib/libhwui.so (android::uirenderer::renderthread::ReliableSurface::hook_dequeueBuffer(ANativeWindow*, int (*)(ANativeWindow*, ANativeWindowBuffer**, int*), void*, ANativeWindowBuffer**, int*)+42)04-20 09:48:38.909 6053 6263 E graphic dequeueBuffer: #03 pc 00083181 /system/lib/libgui.so (android::Surface::hook_dequeueBuffer(ANativeWindow*, ANativeWindowBuffer**, int*)+60)//接上面，binder调用到BufferQueueProducer04-20 09:48:38.946 668 697 E dequeueBuffer: #00 pc 00052653 /system/lib/libgui.so (android::BufferQueueProducer::dequeueBuffer(int*, android::sp<android::Fence>*, unsigned int, unsigned int, int, unsigned long long, unsigned long long*, android::FrameEventHistoryDelta*)+250)04-20 09:48:38.946 668 697 E dequeueBuffer: #01 pc 0006d117 /system/lib/libgui.so (android::BnGraphicBufferProducer:nTransact(unsigned int, android:arcel const&, android:arcel*, unsigned int)+374)queueBuffer
方法位置：BufferQueueProducer::queueBuffer
04-20 09:48:38.987 6053 6263 E queueBuffer: #00 pc 0006e4e1 /system/lib/libgui.so (android::BpGraphicBufferProducer::queueBuffer(int, android::IGraphicBufferProducer: ueueBufferInput const&, android::IGraphicBufferProducer:ueueBufferOutput*)+128)04-20 09:48:38.987 6053 6263 E queueBuffer: #01 pc 00084d83 /system/lib/libgui.so (android::Surface::queueBuffer(ANativeWindowBuffer*, int)+722)04-20 09:48:38.987 6053 6263 E queueBuffer: #02 pc 00083259 /system/lib/libgui.so (android::Surface::hook_queueBuffer(ANativeWindow*, ANativeWindowBuffer*, int)+60)//接上面，binder调用到BufferQueueProducer04-20 09:48:39.017 668 697 E queueBuffer: #00 pc 00053877 /system/lib/libgui.so (android::BufferQueueProducer::queueBuffer(int, android::IGraphicBufferProducer:ueueBufferInput const&, android::IGraphicBufferProducer:ueueBufferOutput*)+266)04-20 09:48:39.017 668 697 E queueBuffer: #01 pc 0006d345 /system/lib/libgui.so (android::BnGraphicBufferProducer:nTransact(unsigned int, android:arcel const&, android:arcel*, unsigned int)+932)2、acquireBuffer&&releaseBuffer
1、我们知道体系的革新由Vsync信号控制，一个Vsync信号来时。surfaceflinger代码会走INVALIDATE/REFRESH,终极都是走refresh
2、下面吸收vsync的MessageQueue队列，实际就是surfaceflinger初始化时创建的mEventQueue。
3、EventThread通过Connection关照VSYNC信号到达时可以触发回调关照MessageQueue
4、vsync这个流程对应bufferqueue流程中的acquireBuffer、releaseBuffer，调用流程堆栈下面已列出。
//SurfaceFlinger.cppvoid SurfaceFlinger:nMessageReceived(int32_t what, nsecs_t expectedVSyncTime) { ATRACE_CALL(); switch (what) { case MessageQueue::INVALIDATE: { onMessageInvalidate(expectedVSyncTime); break; } case MessageQueue::REFRESH: { onMessageRefresh(); break; } }}acquireBuffer
方法位置：BufferQueueConsumer::acquireBuffer
04-19 19:33:38.926 666 666 E acquireBuffer: #00 pc 0004d34f /system/lib/libgui.so (android::BufferQueueConsumer::acquireBuffer(android::BufferItem*, long long, unsigned long long)+74)04-19 19:33:38.926 666 666 E acquireBuffer: #01 pc 000645cf /system/lib/libgui.so (android::ConsumerBase::acquireBufferLocked(android::BufferItem*, long long, unsigned long long)+62)04-19 19:33:38.926 666 666 E acquireBuffer: #02 pc 0007a7a1 /system/lib/libsurfaceflinger.so (android::FramebufferSurface::advanceFrame(bool)+112)04-19 19:33:38.926 666 666 E acquireBuffer: #03 pc 000edf1f /system/lib/libsurfaceflinger.so (android::compositionengine::impl::RenderSurface::queueBuffer(android::base::unique_fd_impl<android::base:efaultCloser>, bool)+358)04-19 19:33:38.926 666 666 E acquireBuffer: #04 pc 000e46e7 /system/lib/libsurfaceflinger.so (android::compositionengine::impl::Output::finishFrame(android::compositionengine::CompositionRefreshArgs const&)+454)04-19 19:33:38.926 666 666 E acquireBuffer: #05 pc 000de3e5 /system/lib/libsurfaceflinger.so (android::compositionengine::impl:isplay::finishFrame(android::compositionengine::CompositionRefreshArgs const&)+72)04-19 19:33:38.926 666 666 E acquireBuffer: #06 pc 000e3011 /system/lib/libsurfaceflinger.so (android::compositionengine::impl::Output::present(android::compositionengine::CompositionRefreshArgs const&)+92)04-19 19:33:38.926 666 666 E acquireBuffer: #07 pc 000dcfa1 /system/lib/libsurfaceflinger.so (android::compositionengine::impl::CompositionEngine::present(android::compositionengine::CompositionRefreshArgs&)+144)04-19 19:33:38.926 666 666 E acquireBuffer: #08 pc 000baf81 /system/lib/libsurfaceflinger.so (android::SurfaceFlinger:nMessageRefresh()+1280)04-19 19:33:38.926 666 666 E acquireBuffer: #09 pc 000b8b1d /system/lib/libsurfaceflinger.so (android::SurfaceFlinger:nMessageReceived(int, long long)+52)releaseBuffer
方法位置：BufferQueueConsumer::releaseBuffer
04-19 19:33:38.996 666 666 E releaseBuffer: #00 pc 0004e429 /system/lib/libgui.so (android::BufferQueueConsumer::releaseBuffer(int, unsigned long long, android::sp<android::Fence> const&, void*, void*)+72)04-19 19:33:38.996 666 666 E releaseBuffer: #01 pc 0004f3af /system/lib/libgui.so (android::BufferQueueConsumer::releaseBuffer(int, unsigned long long, void*, void*, android::sp<android::Fence> const&)+36)04-19 19:33:38.996 666 666 E releaseBuffer: #02 pc 0006498d /system/lib/libgui.so (android::ConsumerBase::releaseBufferLocked(int, android::sp<android::GraphicBuffer>, void*, void*)+140)04-19 19:33:38.996 666 666 E releaseBuffer: #03 pc 00066cab /system/lib/libsurfaceflinger.so (android::BufferLayerConsumer::releasePendingBuffer()+78)04-19 19:33:38.996 666 666 E releaseBuffer: #04 pc 00067b1d /system/lib/libsurfaceflinger.so (android::BufferQueueLayer::releasePendingBuffer(long long)+28)04-19 19:33:38.996 666 666 E releaseBuffer: #05 pc 000bb0bb /system/lib/libsurfaceflinger.so (android::SurfaceFlinger:nMessageRefresh()+1594)04-19 19:33:38.996 666 666 E releaseBuffer: #06 pc 000b8b1d /system/lib/libsurfaceflinger.so (android::SurfaceFlinger:nMessageReceived(int, long long)+52)2.2.3、认识BufferQueueCore
BufferQueueCore是bufferqueue实现的详细类。BufferQueueCore管理了几个数据布局。利用这几个数据布局，来实现bufferqueue的dequebuffer等方法。
以dequeueBuffer过程来讲，它就是向bufferqueue申请一个GraphicBuffer,用GraphicBuffer来绘制图像。
BufferQueueCore中六个对象比较告急：mQueue、mSlot、FreeSlots、FreeBuffers、ActiveBuffers、UnusedBuffers 下面我会逐一先容
namespace android {class IConsumerListener;class IProducerListener;class BufferQueueCore : public virtual RefBase {private: BufferQueueDefs::SlotsType mSlots; Fifo mQueue; std::set<int> mFreeSlots; std::list<int> mFreeBuffers; std::list<int> mUnusedSlots; std::set<int> mActiveBuffers;1、mQueue&&mSlot
我们先认识这两个最核心的数据布局。
class BufferItem {public: enum { INVALID_BUFFER_SLOT = -1 }; BufferItem() : mGraphicBuffer(nullptr), mFence(Fence::NO_FENCE) {} ~BufferItem() {} sp<GraphicBuffer> mGraphicBuffer; sp<Fence> mFence; Rect mCrop;typedef Vector<BufferItem> Fifo;Fifo mQueue;namespace BufferQueueDefs { typedef BufferSlot SlotsType[NUM_BUFFER_SLOTS];}BufferQueueDefs::SlotsType mSlots;我们平常说的bufferqueue队列实在就是说的BufferItem这个mQueue数据容器。BufferItem拥有GraphicBuffer对象
而mSlot是一个BufferSlot巨细为NUM_BUFFER_SLOTS(即是64)的数组，BufferSlot重要用来绑定GraphicBuffer,BufferSlot和GraphicBuffer逐一对应。
BufferSlot中有一个BufferState对象，它专门用来表现GraphicBuffer的状态
struct BufferSlot { BufferState mBufferState; // BufferState tracks the states in which a buffer slot can be.struct BufferState { // All slots are initially FREE (not dequeued, queued, acquired, or shared). BufferState() : mDequeueCount(0), mQueueCount(0), mAcquireCount(0), mShared(false) { } uint32_t mDequeueCount; uint32_t mQueueCount; uint32_t mAcquireCount; bool mShared; // A buffer can be in one of five states, represented as below: // // | mShared | mDequeueCount | mQueueCount | mAcquireCount | // --------|---------|---------------|-------------|---------------| // FREE | false | 0 | 0 | 0 | // DEQUEUED| false | 1 | 0 | 0 | // QUEUED | false | 0 | 1 | 0 | // ACQUIRED| false | 0 | 0 | 1 | // SHARED | true | any | any | any |2、FreeSlots、FreeBuffers、ActiveBuffers、UnusedBuffers
知道了mQueue&&mSlot作用后，我们再来认识他们四个轻易了,起首建立如许一个等式
mSlots = mFreeSlots + mFreeBuffers + mActiveBuffers + mUnusedSlots
mSlots是全部BufferSlot，而别的四个BufferSlot，则表现差别的状态的BufferSlot。
mFreeSlots：BufferSlot状态为FREE，且没有GraphicBuffer与之相绑定的slot聚集
mFreeBuffers：BufferSlot状态为FREE，且有GraphicBuffer与之相绑定的slot聚集
mActiveBuffers：BufferSlot状态不为FREE（即DEQUEUED、QUEUED、ACQUIRED、SHARED）的slot聚集。既然状态不是FREE，那么该BufferSlot肯定有一个GraphicBuffer与之相绑定
mUnusedSlots：未加入使用的slot聚集，由 mMaxBufferCount 决定
2.2.4、BufferQueueProducer生产者
生产者这边，在bufferqueue流程中，重要负责dequeueBuffer、queueBuffer等流程
class BufferQueueProducer : public BnGraphicBufferProducer {public: friend class BufferQueue; // Needed to access binderDied explicit BufferQueueProducer(const sp<BufferQueueCore>& core, bool consumerIsSurfaceFlinger = false); ~BufferQueueProducer() override; virtual status_t requestBuffer(int slot, sp<GraphicBuffer>* buf); virtual status_t dequeueBuffer(int* outSlot, sp<Fence>* outFence, uint32_t width, uint32_t height, PixelFormat format, uint64_t usage, uint64_t* outBufferAge, FrameEventHistoryDelta* outTimestamps) override; virtual status_t queueBuffer(int slot, const QueueBufferInput& input, QueueBufferOutput* output); ...//等方法1、dequeueBuffer
status_t BufferQueueProducer::dequeueBuffer(int* outSlot, sp<android::Fence>* outFence, uint32_t width, uint32_t height, PixelFormat format, uint64_t usage, uint64_t* outBufferAge, FrameEventHistoryDelta* outTimestamps) { // 获取下一个buffer slot,假如有freeSlot直接拿来用 while (found == BufferItem::INVALID_BUFFER_SLOT) { status_t status = waitForFreeSlotThenRelock(FreeSlotCaller:equeue, lock, &found); if (status != NO_ERROR) { return status; } ... // IGraphicBufferProducer::BUFFER_NEEDS_REALLOCATION 和IGraphicBufferProducer::RELEASE_ALL_BUFFERS标记会走 requestBuffer流程来获取graphicBuffer对应的slot if ((buffer == nullptr) || buffer->needsReallocation(width, height, format, BQ_LAYER_COUNT, usage)) { mSlots[found].mAcquireCalled = false; mSlots[found].mGraphicBuffer = nullptr; mSlots[found].mRequestBufferCalled = false; mSlots[found].mEglDisplay = EGL_NO_DISPLAY; mSlots[found].mEglFence = EGL_NO_SYNC_KHR; mSlots[found].mFence = Fence::NO_FENCE; mCore->mBufferAge = 0; mCore->mIsAllocating = true; returnFlags |= BUFFER_NEEDS_REALLOCATION; }上面摘抄了dequebuffer流程重要的两件事变
1、获取下一个buffer slot,假如有freeSlot直接拿来用
2、IGraphicBufferProducer::BUFFER_NEEDS_REALLOCATION 和IGraphicBufferProducer::RELEASE_ALL_BUFFERS标记会走 requestBuffer流程来获取graphicBuffer对应的slot
2、queueBuffer
queueBuffer将已添补的缓冲区返回给BufferQueue，即把bufferslot封装成BufferItem返回到BufferItem队列mQueue。
status_t BufferQueueProducer::queueBuffer(int slot, const QueueBufferInput &input, QueueBufferOutput *output) { // 构建bufferitem并赋值 BufferItem item; item.mAcquireCalled = mSlots[slot].mAcquireCalled; item.mGraphicBuffer = mSlots[slot].mGraphicBuffer; ... item.mSlot = slot; item.mFence = acquireFence; item.mFenceTime = acquireFenceTime; //bufferItem 入队 if (mCore->mQueue.empty()) { // When the queue is empty, we can ignore mDequeueBufferCannotBlock // and simply queue this buffer mCore->mQueue.push_back(item); frameAvailableListener = mCore->mConsumerListener; } else { // When the queue is not empty, we need to look at the last buffer // in the queue to see if we need to replace it const BufferItem& last = mCore->mQueue.itemAt( mCore->mQueue.size() - 1); if (last.mIsDroppable) { if (!last.mIsStale) { mSlots[last.mSlot].mBufferState.freeQueued();queueBuffer比较简朴，重要两步
1、构建bufferItem，赋值等
2、把bufferItem返回到mQueue队列中
2.2.4、BufferQueueConsumer斲丧者
1、acquireBuffer
acquireBuffer方法从缓冲队列中实验取下一个挂起的BufferItem有这些环境：
队列为空直接返回；假如缓冲已被获取，返回之前获取的缓冲项；假如expectedPresent标记为非0，缓冲会即将表现；假如缓冲时间戳在未来，不会被获取；
status_t BufferQueueConsumer::acquireBuffer(BufferItem* outBuffer, nsecs_t expectedPresent, uint64_t maxFrameNumber) { // 新旧缓冲区表现逻辑，决定表现的buffer if (expectedPresent != 0 && !mCore->mQueue.empty()) { while (mCore->mQueue.size() > 1 && !mCore->mQueue[0].mIsAutoTimestamp) { const BufferItem& bufferItem(mCore->mQueue[1]); ...此段逻辑比较简朴，就是拿缓存，逻辑重要是怎么拿，末了回调
2、releaseBuffer
releaseBuffer将bufferslot返回到bufferqueue队列。可以在bufferqueue任在访问时举行，当buffer不再可用，fence机制会发出信号。
假如releaseBuffer收到STALE_BUFFER_SLOT信号，那么consumer必须直接放弃全部引用。直接开释。
代码就是release为主
status_t BufferQueueConsumer::releaseBuffer(int slot, uint64_t frameNumber, const sp<Fence>& releaseFence, EGLDisplay eglDisplay, EGLSyncKHR eglFence) { sp<IProducerListener> listener; { // Autolock scope std::lock_guard<std::mutex> lock(mCore->mMutex); if (frameNumber != mSlots[slot].mFrameNumber && !mSlots[slot].mBufferState.isShared()) { return STALE_BUFFER_SLOT; } if (!mSlots[slot].mBufferState.isAcquired()) { BQ_LOGE("releaseBuffer: attempted to release buffer slot %d " "but its state was %s", slot, mSlots[slot].mBufferState.string()); return BAD_VALUE; } mSlots[slot].mEglDisplay = eglDisplay; mSlots[slot].mEglFence = eglFence; mSlots[slot].mFence = releaseFence; mSlots[slot].mBufferState.release();三、bufferqueue总结
bufferqueue是整个安卓图形处置惩罚的核心，把数据生产者和数据斲丧者毗连起来。
生产者dequeuebuffer申请一个缓冲区，并指定宽高等。添补缓冲区数据后用queueBuffer返回到队列。随后aquirebuffer获取缓冲区，斲丧者处置惩罚完后。则返回到队列release |
