题外话
疫情隔离在家,周末还在努力学习的我 .....
一、前言
上一篇文章中,有基本讲清楚Producer一端的处理逻辑,最后也留下了一个疑问:
Consumer是什么时候来消费数据的?他是自己主动来取的?还是收到了某种通知后再来处理的?
这篇文章,就带着这些疑问来开始分析源码。开头还是把这种流程图贴一下
二、Listener监听器的回调过程解析
生产者写完数据,把buffer还给buffer queue后,又是怎样通知消费者来使用的呢?
下面这些解析步骤,就是回答上面的问题
1. 生产者把数据写入buffer后,调用BufferQueueProducer::queueBuffer 入队列这个buffer;
2. 怎么去通知消费者来取呢? queueBuffer函数中会调用frameAvailableListener->onFrameAvailable(item);
3. frameAvailableListener是什么呢?frameAvailableListener = mCore->mConsumerListener;
4. mCore即为BufferQueueCore, BufferQueueCore中有成员 sp<IConsumerListener> mConsumerListener
5. BufferQueueCore::mConsumerListener 是什么时候设置的呢?
(1) BufferQueueConsumer::connect中设置
status_t BufferQueueConsumer::connect(
const sp<IConsumerListener>& consumerListener, bool controlledByApp) {
....
mCore->mConsumerListener = consumerListener;
mCore->mConsumerControlledByApp = controlledByApp;
}
(2) BufferQueueConsumer::disconnect中清除
status_t BufferQueueConsumer::disconnect() {
...
mCore->mConsumerListener = nullptr;
}
注:BufferQueueProducer和BufferQueueConsumer是BufferQueueCore的友元类,所以可以直接访问其私有成员
6. BufferQueueConsumer::connect、disconnect是在哪里调用的呢?
(1)BufferQueueConsumer::consumerConnect中调用connect设置监听器;
(2)BufferQueueConsumer::consumerDisconnect中调用disconnect清除;
7. 谁调用了consumerConnect呢?
(1)ConsumerBase 的构造函数中调用 mConsumer->consumerConnect(proxy, controlledByApp);
(2)这里的mConsumer是BLASTBufferQueue中创建BLASTBufferItemConsumer时一路设置下来的BufferQueueConsumer对象;
8. 设置是的Listener是从哪里传递过来的呢?
(1)继承关系
(2)BLASTBufferQueue的构造函数中:
9. 所以BufferQueueCore::mConsumerListener设置的就是ConsumerBase的实例
10. 因此,frameAvailableListener->onFrameAvailable(item)回调时,会走到ConsumerBase::onFrameAvailable中
本文作者@二的次方 2022-03-22发布于博客园
=========== 再接着下一个阶段 ==========
11. ConsumerBase::onFrameAvailable中继续调用
void ConsumerBase::onFrameAvailable(const BufferItem& item) {
CB_LOGV("onFrameAvailable");
sp<FrameAvailableListener> listener;
{ // scope for the lock
Mutex::Autolock lock(mFrameAvailableMutex);
listener = mFrameAvailableListener.promote();
}
if (listener != nullptr) {
CB_LOGV("actually calling onFrameAvailable");
listener->onFrameAvailable(item);
}
}
12. ConsumerBase中的成员mFrameAvailableListener是什么东西呢?
(1)ConsumerBase类中成员定义 wp<FrameAvailableListener> mFrameAvailableListener;
(2)继承关系 BLASTBufferQueue继承自ConsumerBase::FrameAvailableListener,并实现onFrameAvailable方法
(3)在BLASTBufferQueue的构造函数中:mBufferItemConsumer->setFrameAvailableListener(this);
(4)最终会调用到ConsumerBase::setFrameAvailableListener
(5)所以ConsumerBase中的成员mFrameAvailableListener指向的是BLASTBufferQueue实例对象
13. 所以,ConsumerBase::onFrameAvailable再继续回调时,流程就回到了BLASTBufferQueue::onFrameAvailable
void BLASTBufferQueue::onFrameAvailable(const BufferItem& item) {
....
processNextBufferLocked(nextTransactionSet /* useNextTransaction */);
}
14. 继续走就进到BLASTBufferQueue::processNextBufferLocked
void BLASTBufferQueue::processNextBufferLocked(bool useNextTransaction) {
....
BufferItem bufferItem;
status_t status =
mBufferItemConsumer->acquireBuffer(&bufferItem, 0 /* expectedPresent */, false);
....
}
15. 消费者调用acquireBuffer去BufferQueue中请求一个可以处理的buffer
16. 处理就回到了BufferQueue的acquireBuffer逻辑
为了验证分析正确,在BufferQueueConsumer中加log,打印stack dump:
11-13 01:23:57.893 3016 3064 E BufferQueueConsumer: stackdump:#00 pc 00056f69 /system/lib/libgui.so (android::BufferQueueConsumer::acquireBuffer(android::BufferItem*, long long, unsigned long long)+72)
11-13 01:23:57.893 3016 3064 E BufferQueueConsumer: stackdump:#01 pc 00076967 /system/lib/libgui.so (android::ConsumerBase::acquireBufferLocked(android::BufferItem*, long long, unsigned long long)+62)
11-13 01:23:57.893 3016 3064 E BufferQueueConsumer: stackdump:#02 pc 000756cd /system/lib/libgui.so (android::BufferItemConsumer::acquireBuffer(android::BufferItem*, long long, bool)+44)
11-13 01:23:57.893 3016 3064 E BufferQueueConsumer: stackdump:#03 pc 0006c8b5 /system/lib/libgui.so (android::BLASTBufferQueue::processNextBufferLocked(bool)+164)
11-13 01:23:57.893 3016 3064 E BufferQueueConsumer: stackdump:#04 pc 0006d8d9 /system/lib/libgui.so (android::BLASTBufferQueue::onFrameAvailable(android::BufferItem const&)+132)
11-13 01:23:57.893 3016 3064 E BufferQueueConsumer: stackdump:#05 pc 000761ab /system/lib/libgui.so (android::ConsumerBase::onFrameAvailable(android::BufferItem const&)+110)
11-13 01:23:57.893 3016 3064 E BufferQueueConsumer: stackdump:#06 pc 000563e9 /system/lib/libgui.so (android::BufferQueue::ProxyConsumerListener::onFrameAvailable(android::BufferItem const&)+52)
11-13 01:23:57.893 3016 3064 E BufferQueueConsumer: stackdump:#07 pc 0005da6f /system/lib/libgui.so (android::BufferQueueProducer::queueBuffer(int, android::IGraphicBufferProducer::QueueBufferInput const&, android::IGraphicBufferProducer::QueueBufferOutput*)+1858)
11-13 01:23:57.893 3016 3064 E BufferQueueConsumer: stackdump:#08 pc 000a0d8b /system/lib/libgui.so (android::Surface::queueBuffer(ANativeWindowBuffer*, int)+442)
如logcat所示,符合我们分析的逻辑过程。
千辛万苦终于走到BufferQueueConsumer::acquireBuffer的地方!
此时流程已经到了开头图片的右半边描述的逻辑,我们下篇文章继续分析
三、小结
这篇文章主要解析了Produncer调用queueBuffer后,如何通过FrameAvailableListener把信息通知到Consumer,也解析了FrameAvailableListener是在哪里设置的。
必读:
Android 12(S) 图像显示系统 - 开篇