BLASTBufferQueue创建部分
BLASTBufferQueue::BLASTBufferQueue(const std::string& name, bool updateDestinationFrame)
: mSurfaceControl(nullptr),
mSize(1, 1),
mRequestedSize(mSize),
mFormat(PIXEL_FORMAT_RGBA_8888),
mTransactionReadyCallback(nullptr),
mSyncTransaction(nullptr),
mUpdateDestinationFrame(updateDestinationFrame) {
//创建BufferQueue部分，并且会给mProducer，mConsumer进行赋值
createBufferQueue(&mProducer, &mConsumer);
//创建BLASTBufferItemConsumer部分
mBufferItemConsumer = new BLASTBufferItemConsumer(mConsumer,
GraphicBuffer::USAGE_HW_COMPOSER |
GraphicBuffer::USAGE_HW_TEXTURE,
1, false, this);
static int32_t id = 0;
mName = name + "#" + std::to_string(id);
auto consumerName = mName + "(BLAST Consumer)" + std::to_string(id);
mQueuedBufferTrace = "QueuedBuffer - " + mName + "BLAST#" + std::to_string(id);
id++;
mBufferItemConsumer->setName(String8(consumerName.c_str()));
mBufferItemConsumer->setFrameAvailableListener(this);
mBufferItemConsumer->setBufferFreedListener(this);
ComposerService::getComposerService()->getMaxAcquiredBufferCount(&mMaxAcquiredBuffers);
mBufferItemConsumer->setMaxAcquiredBufferCount(mMaxAcquiredBuffers);
mCurrentMaxAcquiredBufferCount = mMaxAcquiredBuffers;
mNumAcquired = 0;
mNumFrameAvailable = 0;
}
BufferQueue部分
下面来看看核心的方法createBufferQueue
void BLASTBufferQueue::createBufferQueue(sp<IGraphicBufferProducer>* outProducer,
sp<IGraphicBufferConsumer>* outConsumer) {
//创建核心的BufferQueueCore
sp<BufferQueueCore> core(new BufferQueueCore());
//基于BufferQueueCore创建BBQBufferQueueProducer
sp<IGraphicBufferProducer> producer(new BBQBufferQueueProducer(core));
//基于BufferQueueCore创建BufferQueueConsumer
sp<BufferQueueConsumer> consumer(new BufferQueueConsumer(core));
consumer->setAllowExtraAcquire(true);
*outProducer = producer;
*outConsumer = consumer;
}
下面重点看看BufferQueueCore
BufferQueueCore::BufferQueueCore()
: mMutex(),//若干个成员变量初始化
mIsAbandoned(false),
mConsumerControlledByApp(false),
mConsumerName(getUniqueName()),
mConsumerListener(),
mConsumerUsageBits(0),
mConsumerIsProtected(false),
mConnectedApi(NO_CONNECTED_API),
mLinkedToDeath(),
mConnectedProducerListener(),
mBufferReleasedCbEnabled(false),
mSlots(),
mQueue(),
mFreeSlots(),
mFreeBuffers(),
mUnusedSlots(),
mActiveBuffers(),
mDequeueCondition(),
mDequeueBufferCannotBlock(false),
mQueueBufferCanDrop(false),
mLegacyBufferDrop(true),
mDefaultBufferFormat(PIXEL_FORMAT_RGBA_8888),
mDefaultWidth(1),
mDefaultHeight(1),
mDefaultBufferDataSpace(HAL_DATASPACE_UNKNOWN),
mMaxBufferCount(BufferQueueDefs::NUM_BUFFER_SLOTS),
mMaxAcquiredBufferCount(1),
mMaxDequeuedBufferCount(1),
mBufferHasBeenQueued(false),
mFrameCounter(0),
mTransformHint(0),
mIsAllocating(false),
mIsAllocatingCondition(),
mAllowAllocation(true),
mBufferAge(0),
mGenerationNumber(0),
mAsyncMode(false),
mSharedBufferMode(false),
mAutoRefresh(false),
mSharedBufferSlot(INVALID_BUFFER_SLOT),
mSharedBufferCache(Rect::INVALID_RECT, 0, NATIVE_WINDOW_SCALING_MODE_FREEZE,
HAL_DATASPACE_UNKNOWN),
mLastQueuedSlot(INVALID_BUFFER_SLOT),
mUniqueId(getUniqueId()),
mAutoPrerotation(false),
mTransformHintInUse(0) {
int numStartingBuffers = getMaxBufferCountLocked();
for (int s = 0; s < numStartingBuffers; s++) {
mFreeSlots.insert(s);//初始化时候针对mFreeSlots填入了MaxBufferCount个
}
for (int s = numStartingBuffers; s < BufferQueueDefs::NUM_BUFFER_SLOTS;
s++) {
mUnusedSlots.push_front(s);//除了mFreeSlots部分，其他都是填入mUnusedSlots
}
}
上面的构造中有以下几个成员变量非常关键需要重点介绍
// mSlots is an array of buffer slots that must be mirrored on the producer
// side. This allows buffer ownership to be transferred between the producer
// and consumer without sending a GraphicBuffer over Binder. The entire
// array is initialized to NULL at construction time, and buffers are
// allocated for a slot when requestBuffer is called with that slot's index.
BufferQueueDefs::SlotsType mSlots;
// mQueue is a FIFO of queued buffers used in synchronous mode.
Fifo mQueue;
// mFreeSlots contains all of the slots which are FREE and do not currently
// have a buffer attached.
std::set<int> mFreeSlots;
// mFreeBuffers contains all of the slots which are FREE and currently have
// a buffer attached.
std::list<int> mFreeBuffers;
// mUnusedSlots contains all slots that are currently unused. They should be
// free and not have a buffer attached.
std::list<int> mUnusedSlots;
// mActiveBuffers contains all slots which have a non-FREE buffer attached.
std::set<int> mActiveBuffers;
mQueue —> 存放BufferItem的FIFO队列
mSlots —> BufferSlot结构体数组，数组长度固定为64
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
注意mFreeSlots，mFreeBuffers，mActiveBuffers，mUnusedSlots都其实是一个int集合，内容就是mSlots数组的一个个index
详细剖析一下mSlots这个变量：
namespace BufferQueueDefs {
typedef BufferSlot SlotsType[NUM_BUFFER_SLOTS];
} // namespace BufferQueueDefs
struct BufferSlot {
BufferSlot()
: mGraphicBuffer(nullptr),
mEglDisplay(EGL_NO_DISPLAY),
mBufferState(),
mRequestBufferCalled(false),
mFrameNumber(0),
mEglFence(EGL_NO_SYNC_KHR),
mFence(Fence::NO_FENCE),
mAcquireCalled(false),
mNeedsReallocation(false) {
}
}
可以看到mSlots其实BufferSlot的一个数组，BufferSlot重要包含了mGraphicBuffer和mBufferState两个核心变量，下面来看看核心变量mBufferState，类型是BufferState
// 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 |
//
// FREE indicates that the buffer is available to be dequeued by the
// producer. The slot is "owned" by BufferQueue. It transitions to DEQUEUED
// when dequeueBuffer is called.
//
// DEQUEUED indicates that the buffer has been dequeued by the producer, but
// has not yet been queued or canceled. The producer may modify the
// buffer's contents as soon as the associated release fence is signaled.
// The slot is "owned" by the producer. It can transition to QUEUED (via
// queueBuffer or attachBuffer) or back to FREE (via cancelBuffer or
// detachBuffer).
//
// QUEUED indicates that the buffer has been filled by the producer and
// queued for use by the consumer. The buffer contents may continue to be
// modified for a finite time, so the contents must not be accessed until
// the associated fence is signaled. The slot is "owned" by BufferQueue. It
// can transition to ACQUIRED (via acquireBuffer) or to FREE (if another
// buffer is queued in asynchronous mode).
//
// ACQUIRED indicates that the buffer has been acquired by the consumer. As
// with QUEUED, the contents must not be accessed by the consumer until the
// acquire fence is signaled. The slot is "owned" by the consumer. It
// transitions to FREE when releaseBuffer (or detachBuffer) is called. A
// detached buffer can also enter the ACQUIRED state via attachBuffer.
//
// SHARED indicates that this buffer is being used in shared buffer
// mode. It can be in any combination of the other states at the same time,
// except for FREE (since that excludes being in any other state). It can
// also be dequeued, queued, or acquired multiple times.
可以看到这里的BufferState就是我们常说的一下几个状态
// FREE
// DEQUEUED
// QUEUED
// ACQUIRED
// SHARED
但是大家可以看到，每一个状态并不是用类似enum这种变量的,而是用对对应整形计数变量表示，比如：
inline void dequeue() {
mDequeueCount++;
}
inline bool isDequeued() const {
return mDequeueCount > 0;
}
isDequeued（）方法就是代表状态，dequeue就是操作变量，简单就是改变状态，都是使用各自计数来的
所有的状态方法如下：
//是否为Free状态就是判断一下其他三个状态计数是否为0
inline bool isFree() const {
return !isAcquired() && !isDequeued() && !isQueued();
}
inline bool isDequeued() const {
return mDequeueCount > 0;
}
inline bool isQueued() const {
return mQueueCount > 0;
}
inline bool isAcquired() const {
return mAcquireCount > 0;
}
inline bool isShared() const {
return mShared;
}
inline void reset() {
*this = BufferState();
}
const char* string() const;
inline void dequeue() {
//dequeue操作就是简单的把mDequeueCount进行加操作
mDequeueCount++;
}
inline void detachProducer() {
if (mDequeueCount > 0) {
mDequeueCount--;
}
}
inline void attachProducer() {
mDequeueCount++;
}
inline void queue() {
//会对mDequeueCount先进行减
if (mDequeueCount > 0) {
mDequeueCount--;
}
//再对mQueueCount进行加操作
mQueueCount++;
}
inline void cancel() {
if (mDequeueCount > 0) {
mDequeueCount--;
}
}
inline void freeQueued() {
if (mQueueCount > 0) {
mQueueCount--;
}
}
inline void acquire() {
//首先对mQueueCount会进行减操作
if (mQueueCount > 0) {
mQueueCount--;
}
//然后再是对mAcquireCount进行加操作
mAcquireCount++;
}
inline void acquireNotInQueue() {
mAcquireCount++;
}
inline void release() {//release只对mAcquireCount进行了减操作
if (mAcquireCount > 0) {
mAcquireCount--;
}
}
inline void detachConsumer() {
if (mAcquireCount > 0) {
mAcquireCount--;
}
}
inline void attachConsumer() {
mAcquireCount++;
}
};
总结图：
补充一下几个状态转移图：
–>1、一开始如果什么都没发生那肯定BufferSlot对应BufferState是FREE状态
---->2、生产者app一般先进行dequue操作，这个时候状态就变成了 DEQUEUE状态
------->3、生产者app dequeue获取了graphicbuffer后，绘制完成进行queue操作，变成了QUEUED状态
------------>4、queuebuffer后通知消费者，消费者接受通知后，会进行acquire操作，这个时候状态变成了ACQUIRED
--------------->5、消费者对buffer消费完成后就可以对bufferslot进行relaese操作，这个时候就变成FREE状态
dequeueBuffer() --生产者方法
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) {
//省略
int found = BufferItem::INVALID_BUFFER_SLOT;//作为入参found
while (found == BufferItem::INVALID_BUFFER_SLOT) {
//核心方法从mSlots数组找到一个可以用的BufferSlot,把相关的index赋值到found这个变量
status_t status = waitForFreeSlotThenRelock(FreeSlotCaller::Dequeue, lock, &found);
//省略
}
ATRACE_FORMAT("dequeueBuffer found = %d",found);
const sp<GraphicBuffer>& buffer(mSlots[found].mGraphicBuffer);
*outSlot = found;
ATRACE_BUFFER_INDEX(found);
attachedByConsumer = mSlots[found].mNeedsReallocation;
mSlots[found].mNeedsReallocation = false;
mSlots[found].mBufferState.dequeue();//把状态变成Dequeue
if ((buffer == nullptr) ||
buffer->needsReallocation(width, height, format, BQ_LAYER_COUNT, usage))
{
//如果需要进行buffer申请
returnFlags |= BUFFER_NEEDS_REALLOCATION;
} else {
// We add 1 because that will be the frame number when this buffer
// is queued
mCore->mBufferAge = mCore->mFrameCounter + 1 - mSlots[found].mFrameNumber;
}
//省略部分
if (!(returnFlags & BUFFER_NEEDS_REALLOCATION)) {//不需要allocation
if (mCore->mConsumerListener != nullptr) {//通知回调一下consumeronFrameDequeued
mCore->mConsumerListener->onFrameDequeued(mSlots[*outSlot].mGraphicBuffer->getId());
}
}
} // Autolock scope
if (returnFlags & BUFFER_NEEDS_REALLOCATION) {
//开始申请GraphicBuffer
sp<GraphicBuffer> graphicBuffer = new GraphicBuffer(
width, height, format, BQ_LAYER_COUNT, usage,
{mConsumerName.string(), mConsumerName.size()});
status_t error = graphicBuffer->initCheck();
//申请GraphicBuffer成功
if (error == NO_ERROR && !mCore->mIsAbandoned) {
graphicBuffer->setGenerationNumber(mCore->mGenerationNumber);
//把申请成功的buffer赋值到了mSlots的mGraphicBuffer中
mSlots[*outSlot].mGraphicBuffer = graphicBuffer;
if (mCore->mConsumerListener != nullptr) {
mCore->mConsumerListener->onFrameDequeued(
mSlots[*outSlot].mGraphicBuffer->getId());
}
}
} // Autolock scope
}
//省略
return returnFlags;
}
接下来看看核心方法waitForFreeSlotThenRelock
status_t BufferQueueProducer::waitForFreeSlotThenRelock(FreeSlotCaller caller,
std::unique_lock<std::mutex>& lock, int* found) const {
while (tryAgain) {
int dequeuedCount = 0;
int acquiredCount = 0;
for (int s : mCore->mActiveBuffers) {
if (mSlots[s].mBufferState.isDequeued()) {
++dequeuedCount;
}
if (mSlots[s].mBufferState.isAcquired()) {
++acquiredCount;
}
}
*found = BufferQueueCore::INVALID_BUFFER_SLOT;
//省略部分
if (tooManyBuffers) {
} else {
// If in shared buffer mode and a shared buffer exists, always
// return it.
if (mCore->mSharedBufferMode && mCore->mSharedBufferSlot !=
BufferQueueCore::INVALID_BUFFER_SLOT) {
*found = mCore->mSharedBufferSlot;
} else {
if (caller == FreeSlotCaller::Dequeue) {//如果dequeue方法
// If we're calling this from dequeue, prefer free buffers
int slot = getFreeBufferLocked();//先从FreeBuffer的数组中获取
if (slot != BufferQueueCore::INVALID_BUFFER_SLOT) {
*found = slot;
} else if (mCore->mAllowAllocation) {//如果没有找到则到FreeSlot数组中找
*found = getFreeSlotLocked();
}
} else {
// If we're calling this from attach, prefer free slots
int slot = getFreeSlotLocked();//先从FreeSlot数组中找
if (slot != BufferQueueCore::INVALID_BUFFER_SLOT) {
*found = slot;
} else {//没找到再去FreeBuffer中找
*found = getFreeBufferLocked();
}
}
}
}
//省略
return NO_ERROR;
}
int BufferQueueProducer::getFreeSlotLocked() const {
if (mCore->mFreeSlots.empty()) {
return BufferQueueCore::INVALID_BUFFER_SLOT;
}
int slot = *(mCore->mFreeSlots.begin());
mCore->mFreeSlots.erase(slot);
return slot;
}
上面waitForFreeSlotThenRelock就是其实就是去FreeBuffer或者FreeSlot中寻找一个BufferSlot，返回这个slot的在数组的index,赋值给found
dequeueBuffer主要干的事情如下：
1、通过waitForFreeSlotThenRelock寻找到Free状态的BufferSlot
2、判断这个BufferSlot是否需要重新申请buffer，如果需要则进行构造新的GraphicBuffer
requestBuffer()–生产者方法
主要就是实现了根据传递进来的slot这个index，然后吧对应mSlots的mGraphicBuffer赋值给参数buf指针
status_t BufferQueueProducer::requestBuffer(int slot, sp<GraphicBuffer>* buf) {
mSlots[slot].mRequestBufferCalled = true;
*buf = mSlots[slot].mGraphicBuffer;
return NO_ERROR;
}
queueBuffer()–生产者方法
//注意传递参数里面有一个关键的slot即mSlots中的index
status_t BufferQueueProducer::queueBuffer(int slot,
const QueueBufferInput &input, QueueBufferOutput *output) {
BufferItem item;
{
mSlots[slot].mFence = acquireFence;
mSlots[slot].mBufferState.queue();//这个地方就会调用mBufferState的queue，状态就改变了
//开始把mSlots[slot]挨个赋值给BufferItem
item.mAcquireCalled = mSlots[slot].mAcquireCalled;
item.mGraphicBuffer = mSlots[slot].mGraphicBuffer;
item.mCrop = crop;
item.mTransform = transform &
~static_cast<uint32_t>(NATIVE_WINDOW_TRANSFORM_INVERSE_DISPLAY);
item.mTransformToDisplayInverse =
(transform & NATIVE_WINDOW_TRANSFORM_INVERSE_DISPLAY) != 0;
item.mScalingMode = static_cast<uint32_t>(scalingMode);
item.mTimestamp = requestedPresentTimestamp;
item.mIsAutoTimestamp = isAutoTimestamp;
item.mDataSpace = dataSpace;
item.mHdrMetadata = hdrMetadata;
item.mFrameNumber = currentFrameNumber;
item.mSlot = slot;
item.mFence = acquireFence;
item.mFenceTime = acquireFenceTime;
item.mIsDroppable = mCore->mAsyncMode ||
(mConsumerIsSurfaceFlinger && mCore->mQueueBufferCanDrop) ||
(mCore->mLegacyBufferDrop && mCore->mQueueBufferCanDrop) ||
(mCore->mSharedBufferMode && mCore->mSharedBufferSlot == slot);
item.mSurfaceDamage = surfaceDamage;
item.mQueuedBuffer = true;
item.mAutoRefresh = mCore->mSharedBufferMode && mCore->mAutoRefresh;
item.mApi = mCore->mConnectedApi;
if (mCore->mQueue.empty()) {//如果mQueue为空
mCore->mQueue.push_back(item);//直接push到mQueue的
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);//获取末尾的Item
//判断末尾Item是不是可以被丢弃的
if (last.mIsDroppable) {
//省略
} else {
mCore->mQueue.push_back(item);//直接push
frameAvailableListener = mCore->mConsumerListener;
}
}
if (frameAvailableListener != nullptr) {
frameAvailableListener->onFrameAvailable(item);//这里核心部分，会调用到消费者的onFrameAvailable
} else if (frameReplacedListener != nullptr) {
frameReplacedListener->onFrameReplaced(item);
}
return NO_ERROR;
}
上面queueBuffer主要干了以下几件事：
1、根据入参slot，把mSlots中的BufferState变成Queued状态
2、根据BufferSlot相关变量构建出一个新的BufferItem对象，且塞入mQueue集合
3、最后通过onFrameAvailable通知消费者
onFrameAvailable
void BLASTBufferQueue::onFrameAvailable(const BufferItem& item) {
std::function<void(SurfaceComposerClient::Transaction*)> prevCallback = nullptr;
SurfaceComposerClient::Transaction* prevTransaction = nullptr;
bool waitForTransactionCallback = !mSyncedFrameNumbers.empty();
ATRACE_CALL();
{
BBQ_TRACE();
std::unique_lock _lock{mMutex};
const bool syncTransactionSet = mTransactionReadyCallback != nullptr;
BQA_LOGV("onFrameAvailable-start syncTransactionSet=%s", boolToString(syncTransactionSet));
if (syncTransactionSet) {
bool mayNeedToWaitForBuffer = true;
// If we are going to re-use the same mSyncTransaction, release the buffer that may
// already be set in the Transaction. This is to allow us a free slot early to continue
// processing a new buffer.
if (!mAcquireSingleBuffer) {
auto bufferData = mSyncTransaction->getAndClearBuffer(mSurfaceControl);
if (bufferData) {
BQA_LOGD("Releasing previous buffer when syncing: framenumber=%" PRIu64,
bufferData->frameNumber);
releaseBuffer(bufferData->generateReleaseCallbackId(),
bufferData->acquireFence);
// Because we just released a buffer, we know there's no need to wait for a free
// buffer.
mayNeedToWaitForBuffer = false;
}
}
if (mayNeedToWaitForBuffer) {
flushAndWaitForFreeBuffer(_lock);
}
}
// add to shadow queue
mNumFrameAvailable++;
if (waitForTransactionCallback && mNumFrameAvailable >= 2) {
acquireAndReleaseBuffer();
}
ATRACE_INT(mQueuedBufferTrace.c_str(),
mNumFrameAvailable + mNumAcquired - mPendingRelease.size());
BQA_LOGV("onFrameAvailable framenumber=%" PRIu64 " syncTransactionSet=%s",
item.mFrameNumber, boolToString(syncTransactionSet));
{
ATRACE_FORMAT("onFrameAvailable syncTransactionSet = %d",syncTransactionSet);
}
if (syncTransactionSet) {
acquireNextBufferLocked(mSyncTransaction);
// Only need a commit callback when syncing to ensure the buffer that's synced has been
// sent to SF
incStrong((void*)transactionCommittedCallbackThunk);
mSyncTransaction->addTransactionCommittedCallback(transactionCommittedCallbackThunk,
static_cast<void*>(this));
mSyncedFrameNumbers.emplace(item.mFrameNumber);
if (mAcquireSingleBuffer) {
prevCallback = mTransactionReadyCallback;
prevTransaction = mSyncTransaction;
mTransactionReadyCallback = nullptr;
mSyncTransaction = nullptr;
}
} else if (!waitForTransactionCallback) {
acquireNextBufferLocked(std::nullopt);
}
}
if (prevCallback) {
prevCallback(prevTransaction);
}
}
acquireNextBufferLocked
void BLASTBufferQueue::acquireNextBufferLocked(
const std::optional<SurfaceComposerClient::Transaction*> transaction) {
BufferItem bufferItem;
status_t status =
mBufferItemConsumer->acquireBuffer(&bufferItem, 0 /* expectedPresent */, false);//消费者中获取bufferItem
auto buffer = bufferItem.mGraphicBuffer;
auto releaseBufferCallback =
std::bind(releaseBufferCallbackThunk, wp<BLASTBufferQueue>(this) /* callbackContext */,
std::placeholders::_1, std::placeholders::_2, std::placeholders::_3);
sp<Fence> fence = bufferItem.mFence ? new Fence(bufferItem.mFence->dup()) : Fence::NO_FENCE;
//最为关键吧buffer设置到了事务中
t->setBuffer(mSurfaceControl, buffer, fence, bufferItem.mFrameNumber, releaseBufferCallback);
t->setDataspace(mSurfaceControl, static_cast<ui::Dataspace>(bufferItem.mDataSpace));
t->setHdrMetadata(mSurfaceControl, bufferItem.mHdrMetadata);
t->setSurfaceDamageRegion(mSurfaceControl, bufferItem.mSurfaceDamage);
t->addTransactionCompletedCallback(transactionCallbackThunk, static_cast<void*>(this));
//省略
}
acquireBuffer()–消费者方法
//注意这有个入参outBuffer
status_t BufferQueueConsumer::acquireBuffer(BufferItem* outBuffer,
nsecs_t expectedPresent, uint64_t maxFrameNumber) {
BufferQueueCore::Fifo::iterator front(mCore->mQueue.begin());//注意这个front就是mQueue的第一个
//省略
if (sharedBufferAvailable && mCore->mQueue.empty()) {
} else if (acquireNonDroppableBuffer && front->mIsDroppable) {
return NO_BUFFER_AVAILABLE;
} else {
//把front的slot及指向对象赋值给outBuffer这个入参
slot = front->mSlot;
*outBuffer = *front;
}
if (!outBuffer->mIsStale) {
mSlots[slot].mAcquireCalled = true;
if (mCore->mQueue.empty()) {
mSlots[slot].mBufferState.acquireNotInQueue();
} else {
//下面就是BufferState进行相关的改变，调用acquire方法
mSlots[slot].mBufferState.acquire();
}
mSlots[slot].mFence = Fence::NO_FENCE;
}
//mQueue中移除掉这个front
mCore->mQueue.erase(front);
return NO_ERROR;
}
可以看到acquireBuffer主要干的事情如：
1、mQueue中取出最顶部的BufferItem
2、把顶部的BufferItem的slot获取，且让入参outBuffer指向该BufferItem
3、把mSlots中对应的BufferState变成acquired，且mQueue移除掉front
releaseBuffer()–消费者方法
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);
//省略部分
mSlots[slot].mEglDisplay = eglDisplay;
mSlots[slot].mEglFence = eglFence;
mSlots[slot].mFence = releaseFence;
//最重要调用了mBufferState的release方法
mSlots[slot].mBufferState.release();
//省略部分
//下面就把slot从 mCore->mActiveBuffers移除，放入到 mCore->mFreeBuffers
if (!mSlots[slot].mBufferState.isShared()) {
mCore->mActiveBuffers.erase(slot);
mCore->mFreeBuffers.push_back(slot);
}
//省略部分
return NO_ERROR;
}
整个release方法就干了2件事
1、调用了mBufferState的release方法，让状态就变成了FREE
2、从 mCore->mActiveBuffers移除，放入到 mCore->mFreeBuffers
相关release触发流程，这里以perffetto来结合代码看
每次的sf在合成时候都会触发上一帧画面的releaseBuffer操作
但是刚启动第一帧明显没有看到有releaseBuffer，第二帧才看见
第一帧，只见到了onTransactionCompleted：
第二帧，见到了onTransactionCompleted同时，也见到了releaseBuffer相关，因为这次release是上一帧的buffer：
看看前后两次差异到底在哪里？为啥第一次就没有releaseBuffer相关调用，第二次就有了呢？
看一下onTransactionCompleted方法的差异化执行：
void TransactionCompletedListener::onTransactionCompleted(ListenerStats listenerStats) {
std::unordered_map<CallbackId, CallbackTranslation, CallbackIdHash> callbacksMap;
std::multimap<int32_t, sp<JankDataListener>> jankListenersMap;
ATRACE_CALL();
// handle on complete callbacks
for (auto callbackId : transactionStats.callbackIds) {
if (callbackId.type != CallbackId::Type::ON_COMPLETE) {
continue;
}
auto& [callbackFunction, callbackSurfaceControls] = callbacksMap[callbackId];
if (!callbackFunction) {
ALOGE("cannot call null callback function, skipping");
continue;
}
std::vector<SurfaceControlStats> surfaceControlStats;
for (const auto& surfaceStats : transactionStats.surfaceStats) {
surfaceControlStats
.emplace_back(callbacksMap[callbackId]
.surfaceControls[surfaceStats.surfaceControl],
transactionStats.latchTime, surfaceStats.acquireTimeOrFence,
transactionStats.presentFence,
surfaceStats.previousReleaseFence, surfaceStats.transformHint,
surfaceStats.eventStats,
surfaceStats.currentMaxAcquiredBufferCount);
if (callbacksMap[callbackId].surfaceControls[surfaceStats.surfaceControl]) {
callbacksMap[callbackId]
.surfaceControls[surfaceStats.surfaceControl]
->setTransformHint(surfaceStats.transformHint);
}
//这里就是是否会执行releaseBuffer的关键，靠传递过来的previousReleaseCallbackId是不是有效
if (surfaceStats.previousReleaseCallbackId != ReleaseCallbackId::INVALID_ID) {
ReleaseBufferCallback callback;
{
std::scoped_lock<std::mutex> lock(mMutex);
callback = popReleaseBufferCallbackLocked(
surfaceStats.previousReleaseCallbackId);
}
if (callback) {
callback(surfaceStats.previousReleaseCallbackId,
surfaceStats.previousReleaseFence
? surfaceStats.previousReleaseFence
: Fence::NO_FENCE,
surfaceStats.currentMaxAcquiredBufferCount);
}
}
}
callbackFunction(transactionStats.latchTime, transactionStats.presentFence,
surfaceControlStats);
}
//省略
}
这里的previousReleaseCallbackId设置其实服务端sf进行的设置，下面会进行详细介绍。
sf如何触发的release呢？
触发流程如下：
sf端是在线程中发起的触发跨进程onTransactionCompleted调用
这里sf子线程跨进程调用是由主线程sendCallbacks方法触发的
sendCallbacks方法
void TransactionCallbackInvoker::sendCallbacks(bool onCommitOnly) {
ATRACE_CALL();
// For each listener
//获取全局的mCompletedTransactions变量再进行遍历
auto completedTransactionsItr = mCompletedTransactions.begin();
BackgroundExecutor::Callbacks callbacks;
while (completedTransactionsItr != mCompletedTransactions.end()) {
//省略部分
// If the listener has completed transactions
if (!listenerStats.transactionStats.empty()) {
// If the listener is still alive
if (listener->isBinderAlive()) {
//塞入callbacks集合
callbacks.emplace_back([stats = std::move(listenerStats)]() {
ATRACE_NAME("ITransactionCompletedListener onTransactionCompleted");
interface_cast<ITransactionCompletedListener>(stats.listener)
->onTransactionCompleted(stats);
});
}
}
completedTransactionsItr++;
}
BackgroundExecutor::getInstance().sendCallbacks(std::move(callbacks));
}
重点看看mCompletedTransactions这个集合的哪来的，通过查询主要是findOrCreateTransactionStats方法进行加入相关的元素，追踪后发现实际上这里主要是看addCallbackHandles方法会填入对应，最终发现是在releasePendingBuffer方法中塞入：
void BufferStateLayer::releasePendingBuffer(nsecs_t dequeueReadyTime) {
for (const auto& handle : mDrawingState.callbackHandles) {
handle->transformHint = mTransformHint;
handle->dequeueReadyTime = dequeueReadyTime;
handle->currentMaxAcquiredBufferCount =
mFlinger->getMaxAcquiredBufferCountForCurrentRefreshRate(mOwnerUid);
}
//注意这里是把mPreviousReleaseCallbackId变量赋值给 handle->previousReleaseCallbackId
for (auto& handle : mDrawingState.callbackHandles) {
if (handle->releasePreviousBuffer &&
mDrawingState.releaseBufferEndpoint == handle->listener) {
handle->previousReleaseCallbackId = mPreviousReleaseCallbackId;
break;
}
}
//调用addCallbackHandles
mFlinger->getTransactionCallbackInvoker().addCallbackHandles(
mDrawingState.callbackHandles, jankData);
}
这里的mPreviousReleaseCallbackId是哪里来的呢？那么就需要看updateActiveBuffer
updateActiveBuffer
updateActiveBuffer方法会对mPreviousReleaseCallbackId这个变量进行赋值，大家注意这里的为啥叫做前一帧的CallbackId，因为下面这个updateActiveBuffer就是赋值是先进行的mPreviousReleaseCallbackId赋值，然后才进行的新buffer的赋值，所以这个mPreviousReleaseCallbackId其实上一个的buffer的Id，不是当前这次的
综上既可以解释releaseBuffer是在下一帧上帧后才由sf调用到app层面让其releaseBuffer。
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