Android6.0显示系统(三)管理图像缓冲区.doc

Android6.0 显示系统（三） 管理图像缓冲区一、BufferQueueCore BufferQueueProducer BufferQueueConsumer上篇博客在Layer的onFirstRef函数中，调用了下面函数，创建了3个对象BufferQueueCore BufferQueueProducer BufferQueueConsumer。其中BufferCore是核心，把BufferQueueProducer和BufferQueueConsumer对象连接在一起。cpp view plain copy 在CODE上查看代码片派生到我的代码片void BufferQueue:createBufferQueue(sp* outProducer, sp* outConsumer, const sp& allocator) sp core(new BufferQueueCore(allocator); sp producer(new BufferQueueProducer(core); sp consumer(new BufferQueueConsumer(core); *outProducer = producer; *outConsumer = consumer; 1.1 生产者和core的联系IGraphicBufferProducer 的大致接口如下，BufferQueueProducer类是接口IGraphicBufferProducer 的实现，使用BufferQueueProducer之前先要调用connect函数，使用结束后调用disconnect断开连接。cpp view plain copy 在CODE上查看代码片派生到我的代码片class IGraphicBufferProducer : public IInterface public: virtual status_t requestBuffer(int slot, sp* buf) = 0; virtual status_t setBufferCount(int bufferCount) = 0; virtual status_t dequeueBuffer(int* slot, sp* fence, bool async, uint32_t w, uint32_t h, PixelFormat format, uint32_t usage) = 0; virtual status_t detachBuffer(int slot) = 0; virtual status_t detachNextBuffer(sp* outBuffer, sp* outFence) = 0; virtual status_t attachBuffer(int* outSlot, const sp& buffer) = 0; virtual status_t queueBuffer(int slot, const QueueBufferInput& input, QueueBufferOutput* output) = 0; virtual void cancelBuffer(int slot, const sp& fence) = 0; virtual int query(int what, int* value) = 0; virtual status_t connect(const sp& listener, int api, bool producerControlledByApp, QueueBufferOutput* output) = 0; virtual status_t disconnect(int api) = 0; virtual status_t setSidebandStream(const sp& stream) = 0; virtual void allocateBuffers(bool async, uint32_t width, uint32_t height, PixelFormat format, uint32_t usage) = 0; virtual status_t allowAllocation(bool allow) = 0; virtual status_t setGenerationNumber(uint32_t generationNumber) = 0; virtual String8 getConsumerName() const = 0; ; 在BufferQueueCore类中定义了一个64项的数据mSlots。cpp view plain copy 在CODE上查看代码片派生到我的代码片BufferQueueDefs:SlotsType mSlots; cpp view plain copy 在CODE上查看代码片派生到我的代码片typedef BufferSlot SlotsTypeNUM_BUFFER_SLOTS; 每个缓冲区的类型是BufferSlot类型。它有两个重要的成员变量，mGraphicBuffer是指向图像缓冲区GraphicBuffer的指针，mBufferState表示图像缓冲区的状态。cpp view plain copy 在CODE上查看代码片派生到我的代码片sp mGraphicBuffer; . BufferState mBufferState; BufferState的状态有下面几个cpp view plain copy 在CODE上查看代码片派生到我的代码片enum BufferState FREE = 0,/空闲 DEQUEUED = 1,/生产状态，被生产者拥有 QUEUED = 2,/保存数据状态，被BufferQueue拥有 ACQUIRED = 3/消费状态，被消费者拥有 ; BufferQueueProducer的dequeueBuffer函数用来向BufferQueueCore申请一个空闲的slot，这个slot可能已经有缓冲区，也可能没有，如果没有缓冲区，dequeueBuffer函数会分配一块新的缓冲区。得到空闲的slot后，还需要调用requestBuffer函数来取得一块缓冲区。得到缓冲区，如果不需要了，可以使用cancelBuffer函数来释放这个slot。调用dequeueBuffer函数之后，缓冲区的拥有者是生产者，缓冲区处于DEQUEUED状态。一旦缓冲区复制数据完成，通过queueBuffer函数把缓冲区的控制权交还给BufferQueueCore，这时候缓冲区将处于QUEUED状态。1.2 消费者和core的联系下面是IGraphicBufferComsumer接口的几个主要函数：cpp view plain copy 在CODE上查看代码片派生到我的代码片virtual status_t acquireBuffer(BufferItem* outBuffer, nsecs_t expectedPresent, uint64_t maxFrameNumber = 0) override; . virtual status_t releaseBuffer(int slot, uint64_t frameNumber, const sp& releaseFence, EGLDisplay display, EGLSyncKHR fence); virtual status_t connect(const sp& consumerListener, bool controlledByApp); virtual status_t disconnect(); BufferQueueConsumer类是接口IGraphicBufferComsumer的实现，在使用它之前，先要调用connect函数建立联系，这里传递的参数是IConsumerListener对象，是一个回调接口，如果BufferQueue中有数据准备好了就会调用它的onFrameAvailable函数来通知消费者取走数据。取走数据的时候，需要调用acquireBuffer函数，将缓冲区状态变成ACQUIRED，使用完之后调用releaseBuffer函数可以吧缓冲区数据归还给BufferQueueCore，这样缓冲区就变成FREE。1.3 三者联系对象BufferQueueProducer和BufferQueueConsumer好像没有直接联系，其实都是通过共同的BufferQueueCore对象连接在一起的，很多操作时直接使用BufferQueueCore对象的成员变量而不是函数来完成的。二、GraphicBuffer对象的创建对Surface而言，图像缓冲区是一个重要的数据结构，它是用户进程和图像显示器之间的纽带，下面我们来看看Surface的图像缓冲区是如何创建的。2.1 内存缓冲区的创建前面介绍了过dequeueBuffer函数，图像缓冲区GraphicBuffer就是在这个函数中创建的，当从BufferQueueCore中获取到空间的slot时，如果这个slot没有缓冲区就要新建一个。下面是dequeueBuffer函数的部分代码，在从BufferQueueCore中获取到slot的时候，如果需要重新分配图像缓冲区就会调用mCore-mAllocator-createGraphicBuffer函数来重新创建一个图像缓冲区。cpp view plain copy 在CODE上查看代码片派生到我的代码片 . *outSlot = found;/found复制到outslot ATRACE_BUFFER_INDEX(found); attachedByConsumer = mSlotsfound.mAttachedByConsumer; mSlotsfound.mBufferState = BufferSlot:DEQUEUED;/slot的状态修改变成生产状态 const sp& buffer(mSlotsfound.mGraphicBuffer); if (buffer = NULL) |/为空，或者需要重新分配 buffer-needsReallocation(width, height, format, usage) mSlotsfound.mAcquireCalled = false; mSlotsfound.mGraphicBuffer = NULL; mSlotsfound.mRequestBufferCalled = false; mSlotsfound.mEglDisplay = EGL_NO_DISPLAY; mSlotsfound.mEglFence = EGL_NO_SYNC_KHR; mSlotsfound.mFence = Fence:NO_FENCE; mCore-mBufferAge = 0; returnFlags |= BUFFER_NEEDS_REALLOCATION;/需要重启分配缓冲区 else / We add 1 because that will be the frame number when this buffer / is queued mCore-mBufferAge = mCore-mFrameCounter + 1 - mSlotsfound.mFrameNumber; BQ_LOGV(dequeueBuffer: setting buffer age to % PRIu64, mCore-mBufferAge); if (CC_UNLIKELY(mSlotsfound.mFence = NULL) BQ_LOGE(dequeueBuffer: about to return a NULL fence - slot=%d w=%d h=%d format=%u, found, buffer-width, buffer-height, buffer-format); eglDisplay = mSlotsfound.mEglDisplay; eglFence = mSlotsfound.mEglFence; *outFence = mSlotsfound.mFence; mSlotsfound.mEglFence = EGL_NO_SYNC_KHR; mSlotsfound.mFence = Fence:NO_FENCE; mCore-validateConsistencyLocked(); / Autolock scope if (returnFlags & BUFFER_NEEDS_REALLOCATION) /如果需要重启分配图像缓冲区 status_t error; BQ_LOGV(dequeueBuffer: allocating a new buffer for slot %d, *outSlot); sp graphicBuffer(mCore-mAllocator-createGraphicBuffer(/创建图像缓冲区 width, height, format, usage, &error); if (graphicBuffer = NULL) BQ_LOGE(dequeueBuffer: createGraphicBuffer failed); return error; / Autolock scope Mutex:Autolock lock(mCore-mMutex); if (mCore-mIsAbandoned) BQ_LOGE(dequeueBuffer: BufferQueue has been abandoned); return NO_INIT; graphicBuffer-setGenerationNumber(mCore-mGenerationNumber); mSlots*outSlot.mGraphicBuffer = graphicBuffer; / Autolock scope . mAllocator的类型是IGraphicBufferAlloc，也是一个Binder对象，它是在BufferQueueCore的构造函数中得到的，这个时候allocator为空的，具体要从Layer的构造函数中调用BufferQueue:createBufferQueue函数是，那个时候allocator参数就为空。然后通过getComposerService来调用createGraphicBufferAlloc函数来创建这个mAllocator对象。之前的博客分析过getComposerService返回的是和SurfaceFlinger进程的Binder对象，因此最后是到SurfaceFlinger的createGraphicBufferAlloc函数中去了（但是这里有点搞不明白明明是在一个进程中为什么要用Binder呢？）。cpp view plain copy 在CODE上查看代码片派生到我的代码片. if (allocator = NULL) sp composer(ComposerService:getComposerService(); mAllocator = mposer-createGraphicBufferAlloc(); if (mAllocator = NULL) BQ_LOGE(createGraphicBufferAlloc failed); . 下面我们来看SurfaceFlinger的createGraphicBufferAlloc函数。cpp view plain copy 在CODE上查看代码片派生到我的代码片sp SurfaceFlinger:createGraphicBufferAlloc() sp gba(new GraphicBufferAlloc(); return gba; 因此最后BufferQueueProducer中的dequeueBuffer函数中调用mCore-mAllocator的createGraphicBuffer函数就是调用了GraphicBufferAlloc的createGraphicBufferAlloc函数。cpp view plain copy 在CODE上查看代码片派生到我的代码片sp GraphicBufferAlloc:createGraphicBuffer(uint32_t width, uint32_t height, PixelFormat format, uint32_t usage, status_t* error) sp graphicBuffer( new GraphicBuffer(width, height, format, usage); status_t err = graphicBuffer-initCheck(); *error = err; ./错误处理 return graphicBuffer; 我们来看下GraphicBuffer对象的构造函数中调用了initSize函数。cpp view plain copy 在CODE上查看代码片派生到我的代码片GraphicBuffer:GraphicBuffer(uint32_t inWidth, uint32_t inHeight, PixelFormat inFormat, uint32_t inUsage) : BASE(), mOwner(ownData), mBufferMapper(GraphicBufferMapper:get(), mInitCheck(NO_ERROR), mId(getUniqueId() . mInitCheck = initSize(inWidth, inHeight, inFormat, inUsage); 在initSize函数中调用GraphicBufferAllocator的alloc来分配内存。cpp view plain copy 在CODE上查看代码片派生到我的代码片status_t GraphicBuffer:initSize(uint32_t inWidth, uint32_t inHeight, PixelFormat inFormat, int32_t inUsage) GraphicBufferAllocator& allocator = GraphicBufferAllocator:get(); uint32_t outStride = 0; status_t err = allocator.alloc(inWidth, inHeight, inFormat, inUsage, &handle, &outStride); if (err = NO_ERROR) width = static_cast(inWidth); height = static_cast(inHeight); format = inFormat; usage = static_cast(inUsage); stride = static_cast(outStride); return err; alloc又调用了成员变量mAllocDev的alloc函数。cpp view plain copy 在CODE上查看代码片派生到我的代码片status_t GraphicBufferAllocator:alloc(uint32_t width, uint32_t height, PixelFormat format, uint32_t usage, buffer_handle_t* handle, uint32_t* stride) . err = mAllocDev-alloc(mAllocDev, static_cast(width), static_cast(height), format, static_cast(usage), handle, &outStride); 在GraphicBufferAllocator的构造函数中装载了Gralloc模块，因此mAllocDev指向了Gralloc模块。这个会在后面的博客中分析cpp view plain copy 在CODE上查看代码片派生到我的代码片GraphicBufferAllocator:GraphicBufferAllocator() : mAllocDev(0) hw_module_t const* module; int err = hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module); ALOGE_IF(err, FATAL: cant find the %s module, GRALLOC_HARDWARE_MODULE_ID); if (err = 0) gralloc_open(module, &mAllocDev); 这里调用alloc分配了一块共享的内存缓冲区，alloc函数将返回共享区的fd和缓冲区的指针。既然GraphicBuffer中的缓冲区是共享内存，我们知道使用共享内存需要传递共享内存的句柄fd。下面我们看看是如何传到客户进程的。2.2 内存缓冲区的fd传递到客户进程GraphicBuffer类从模板类Flattenable派生，这个派生类可以通过Parcel传递，通常派生类需要重载flatten和unflatten方法，用于对象的序列化和反序列化。cpp view plain copy 在CODE上查看代码片派生到我的代码片class GraphicBuffer : public ANativeObjectBase, public Flattenable 我们先来看下flatten函数，fds参数用来传递文件句柄，函数把handle中的句柄复制到fds中，因此这些句柄就能通过binder传递到目标进程中去。cpp view plain copy 在CODE上查看代码片派生到我的代码片status_t GraphicBuffer:flatten(void*& buffer, size_t& size, int*& fds, size_t& count) const size_t sizeNeeded = GraphicBuffer:getFlattenedSize(); if (size sizeNeeded) return NO_MEMORY; size_t fdCountNeeded = GraphicBuffer:getFdCount(); if (count fdCountNeeded) return NO_MEMORY; int32_t* buf = static_cast(buffer); buf0 = GBFR; buf1 = width; buf2 = height; buf3 = stride; buf4 = format; buf5 = usage; buf6 = static_cast(mId 32); buf7 = static_cast(mId & 0xFFFFFFFFull); buf8 = static_cast(mGenerationNumber); buf9 = 0; buf10 = 0; if (handle) buf9 = handle-numFds; buf10 = handle-numInts; memcpy(fds, handle-data,/把handle中的中复制到fds中 static_cast(handle-numFds) * sizeof(int); memcpy(&buf11, handle-data + handle-numFds, static_cast(handle-numInts) * sizeof(int); buffer = static_cast(static_cast(buffer) + sizeNeeded); size -= sizeNeeded; if (hanc