寻技术

Android开发graphics bufferqueue整体流程

寻技术 Android 2024年05月31日 124

一、引言

1、bufferqueue 的四大流程；

2、简要介绍四大流程的调用过程；

本文主要讲解安卓图形绘制中的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显示。所以buffer queue是图形绘制中很核心的一环，它本身就是一个缓冲区池与队列相结合的数据结构。

Buffer queue:

图像缓冲区，系统中绝大部分图形数据都会缓冲于此。等待surfaceflinger组织进一步的合成和显示

备注：本文摘录的代码只摘录关键代码和路径，需读者自行结合阅读.由于本文的重点在bufferqueue，其它和bufferqueue相关的流程提到的时候会精简列出，作为辅助理解。

二、Buffer queue

2.1、buffer queue的创建

bufferquque构建

//BufferQueue.cpp    frameworks\native\libs\gui
void 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

下面堆栈表示了底层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::onFirstRef()+40)
04-20 11:45:54.739   674   707 E createBufferQueue: #02 pc 000d5ad1  /system/lib/libsurfaceflinger.so (android::surfaceflinger::DefaultFactory::createBufferQueueLayer(android::LayerCreationArgs 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::LayerMetadata, android::sp<android::IBinder>*, android::sp<android::IGraphicBufferProducer>*, android::sp<android::IBinder> const&, android::sp<android::Layer> 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::LayerMetadata, 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::LayerMetadata, 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::LayerMetadata, 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::LayerMetadata, android::sp<android::IBinder>, android::sp<android::IGraphicBufferProducer>, unsigned int>, 0u, 1u, 2u, 3u, 4u, 5u, 6u, 7u, 8u, 9u>(android
04-20 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::LayerMetadata, android::sp<android::IBinder>*, android::sp<android::IGraphicBufferProducer>*, unsigned int*)>(android::Parcel const&, android::Parcel*, int (android::ISurfaceComposerClient::*)(android::String8 const&, unsigned int, unsigned int, int, unsigned int, android::sp<android::IBinder> const&, android::LayerMetadata, 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::onTransact(unsigned int, android::Parcel const&, android::Parcel*, unsigned int)+46)

BufferQueueCore:bufferqueue的实际实例，由他来衔接生产者和消费者

BufferQueueProducer:bufferqueue工厂模式的接口，生产者

BufferQueueConsumer:bufferqueue消费接口，消费者

BufferQueueCore 负责维护 BufferQueue 的基本数据结构，而 BufferQueueProducer 和 BufferQueueConsumer 则负责提供操作 BufferQueue 的基本接口。

2.2、buffer queue整体流程

2.2.1、流程概要

image.png

这张图片清晰的表述的buffer queue的工作方式，两大功能：生产buffer、消费buffer。

dequeueBuffer:向buffer queue请求一个缓冲区，并指定缓冲区的宽度、高度、像素格式和用法标志

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，其实都是返回buffer queue的数据结构中。简述两个流程

  • 1、dequeue、queue等于先申请缓冲区，并告诉producer申请成功，producer就把数据queue给buffer queue数据结构中
  • 2、当consumer要的时候先去acquere获取缓冲区内容，获取后进行合成，合成完了需要释放，就给回buffer queue来释放
  • 3、buffer queue操作数据时不会复制一份数据，只会操作数据本身。

通篇文章，我们就在理解BufferQueueProducer 和 BufferQueueConsumer如何操作上面这四个流程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，当我们首次dequeueBuffer过后，surface会调用requestBuffer,requestBuffer的主要作用就是把GraphicBuffer传给应用侧，
这个动作只需要做一次，应用侧拿到GraphicBuffer过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

本小结主要目的是，在我们认识bufferqueu的是如何工作的同时，不脱离surfaceflinger整体框架。简单提一下它是如果调用来的。以便我们更深入理解。

1、dequeueBuffer&&queueBuffe

r当app创建window的时候，会创建surface来显示。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BufferQueueProducer
04-20 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::onTransact(unsigned int, android::Parcel const&, android::Parcel*, 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::QueueBufferInput const&, android::IGraphicBufferProducer::QueueBufferOutput*)+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BufferQueueProducer
04-20 09:48:39.017   668   697 E queueBuffer: #00 pc 00053877  /system/lib/libgui.so (android::BufferQueueProducer::queueBuffer(int, android::IGraphicBufferProducer::QueueBufferInput const&, android::IGraphicBufferProducer::QueueBufferOutput*)+266)
04-20 09:48:39.017   668   697 E queueBuffer: #01 pc 0006d345  /system/lib/libgui.so (android::BnGraphicBufferProducer::onTransact(unsigned int, android::Parcel const&, android::Parcel*, unsigned int)+932)

2、acquireBuffer&&releaseBuffer

  • 1、我们知道系统的刷新由Vsync信号控制，一个Vsync信号来时。surfaceflinger代码会走INVALIDATE/REFRESH,最终都是走refresh
  • 2、下面接收vsync的MessageQueue队列，实际就是surfaceflinger初始化时创建的mEventQueue。
  • 3、EventThread通过Connection通知VSYNC信号到达时可以触发回调通知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.cpp
void SurfaceFlinger::onMessageReceived(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::DefaultCloser>, 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::Display::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::onMessageRefresh()+1280)
04-19 19:33:38.926   666   666 E acquireBuffer: #09 pc 000b8b1d  /system/lib/libsurfaceflinger.so (android::SurfaceFlinger::onMessageReceived(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::onMessageRefresh()+1594)
04-19 19:33:38.996   666   666 E releaseBuffer: #06 pc 000b8b1d  /system/lib/libsurfaceflinger.so (android::SurfaceFlinger::onMessageReceived(int, long long)+52)

2.2.3、认识BufferQueueCore

BufferQueueCore是bufferqueue实现的具体类。BufferQueueCore管理了几个数据结构。操作这几个数据结构，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中六个对象比较重要：mQueue、mSlot、FreeSlots、FreeBuffers、ActiveBuffers、UnusedBuffers 下面我会一一介绍

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结构。

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;

我们平时说的bufferqueue队列其实就是说的BufferItem这个mQueue数据容器。BufferItem拥有GraphicBuffer对象

而mSlot是一个BufferSlot大小为NUM_BUFFER_SLOTS(等于64)的数组，BufferSlot主要用来绑定GraphicBuffer,BufferSlot和GraphicBuffer一一对应。

BufferSlot中有一个BufferState对象，它专门用来表示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容易了,首先成立这样一个等式
mSlots = mFreeSlots + mFreeBuffers + mActiveBuffers + mUnusedSlots
mSlots是所有BufferSlot，而其它四个BufferSlot，则表示不同的状态的BufferSlot。

mFreeSlots：BufferSlot状态为FREE，且没有GraphicBuffer与之相绑定的slot集合

mFreeBuffers：BufferSlot状态为FREE，且有GraphicBuffer与之相绑定的slot集合

mActiveBuffers：BufferSlot状态不为FREE（即DEQUEUED、QUEUED、ACQUIRED、SHARED）的slot集合。既然状态不是FREE，那么该BufferSlot必然有一个GraphicBuffer与之相绑定

mUnusedSlots：未参与使用的slot集合，由 mMaxBufferCount 决定

2.2.4、BufferQueueProducer生产者

生产者这边，在bufferqueue流程中，主要负责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,如果有freeSlot直接拿来用
    while (found == BufferItem::INVALID_BUFFER_SLOT) {
            status_t status = waitForFreeSlotThenRelock(FreeSlotCaller::Dequeue, 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流程主要的两件事情

  • 1、获取下一个buffer slot,如果有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将已填充的缓冲区返回给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比较简单，主要两步

1、构建bufferItem，赋值等

2、把bufferItem返回到mQueue队列中

2.2.4、BufferQueueConsumer消费者

1、acquireBuffer

acquireBuffer方法从缓冲队列中尝试取下一个挂起的BufferItem有这些情况：

队列为空直接返回；如果缓冲已被获取，返回之前获取的缓冲项；如果expectedPresent标记为非0，缓冲会即将显示；如果缓冲时间戳在将来，不会被获取；

status_t BufferQueueConsumer::acquireBuffer(BufferItem* outBuffer,
        nsecs_t expectedPresent, uint64_t maxFrameNumber) {
    // 新旧缓冲区显示逻辑，决定显示的buffer
    if (expectedPresent != 0 && !mCore->mQueue.empty()) {
            while (mCore->mQueue.size() > 1 && !mCore->mQueue[0].mIsAutoTimestamp) {
                const BufferItem& bufferItem(mCore->mQueue[1]);
    ...

此段逻辑比较简单，就是拿缓存，逻辑主要是怎么拿，最后回调

2、releaseBuffer

releaseBuffer将bufferslot返回到bufferqueue队列。可以在bufferqueue任在访问时进行，当buffer不再可用，fence机制会发出信号。

如果releaseBuffer收到STALE_BUFFER_SLOT信号，那么consumer必须直接放弃所有引用。直接释放。

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是整个安卓图形处理的核心，把数据生产者和数据消费者连接起来。
生产者dequeuebuffer申请一个缓冲区，并指定宽高等。填充缓冲区数据后用queueBuffer返回到队列。随后aquirebuffer获取缓冲区，消费者处理完后。则返回到队列release

以上就是Android开发graphics bufferqueue整体流程的详细内容，更多关于Android graphics bufferqueue的资料请关注寻技术其它相关文章！

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