一、Camx内存池架构简介
1.1内存池使用的好处
首先，在项目中如果频繁的使用malloc申请内存空间，堆上分配和释放内存，会导致性能的损失。由于堆空间申请的存储地址是不连续的，也会使系统中出现的大量的内存碎片，降低内存的利用率，而内存池的使用就很好的解决了这些性能和内存上的问题。
其次，内存池使用映射到连续物理地址的Ion Buffer(本质是linux的file文件)，通过文件描述符可以实现各个进程间数据的共享，比堆空间的使用范围大多了，能更好的link上下路各个模块间的链路。
1.2Camx内存池架构总览
高通Camx架构中的imageBuffer在pipeline的流转中扮演着重要的作用，而管理imagerBuffer的ImageBufferManager与MemPool Manager共同承担起高通Camx架构中的内存池的调度角色，下图简单绘制了一下相互的调用关系。
二、Camx ImageBufferManager
代码路径：vendor\qcom\proprietary\camx\src\core\camximagebuffermanager.cpp
vendor\qcom\proprietary\camx\src\core\camximagebuffer.cpp
2.1 ImageBufferManager相关函数解析
2.1.1 ImageBufferManager::Create函数实现如下
CamxResult ImageBufferManager::Create(const CHAR* pBufferManagerName,BufferManagerCreateData* pCreateData,ImageBufferManager** ppImageBufferManager){CamxResult result = CamxResultSuccess;ImageBufferManager* pImageBufferManager = NULL;if (CamxResultSuccess == result){*ppImageBufferManager = NULL;pImageBufferManager = CAMX_NEW ImageBufferManager();}if (CamxResultSuccess == result){// 从内存池中为ImageBufferManager分配内存result = pImageBufferManager->Initialize(pBufferManagerName, pCreateData);if (CamxResultSuccess == result){CAMX_LOG_INFO(CamxLogGroupMemMgr, "[%s] : allocRequired=%d, immediateAllocBufferCount=%d, maxBufferCount=%d", pBufferManagerName, pCreateData->allocateBufferMemory, pCreateData->immediateAllocBufferCount, pCreateData->maxBufferCount);// 初始化ImageBufferManager中的buffers，这里是重点result = pImageBufferManager->InitializeBuffers(pCreateData);}}if (CamxResultSuccess == result){*ppImageBufferManager = pImageBufferManager;}return result;2.1.2 ImageBufferManager::InitializeBuffer实现如下
CamxResult ImageBufferManager::InitializeBuffers(
BufferManagerCreateData* pCreateData) {m_createData = *pCreateData;m_currentFormat = pCreateData->bufferProperties.imageFormat;m_maxBufferCount = pCreateData->maxBufferCount;m_immediateAllocBufferCount = pCreateData->immediateAllocBufferCount;// Allocate the minimum number of buffers needed immediately seriallyfor (UINT i = 0; i < m_immediateAllocBufferCount; i++){// ①new bufferImageBuffer* pBuffer = CAMX_NEW ImageBuffer();if (NULL != pBuffer){// ②buffer初始化，buffer相关信息放在全局变量m_createData中result = pBuffer->Initialize(m_pBufferManagerName, &m_createData, &m_currentFormat, this,m_hMemPoolBufMgrHandle);// ③Allocate the bufferresult = pBuffer->Allocate();LDLLNode* pNode = static_cast<LDLLNode*>(CAMX_CALLOC(sizeof(LDLLNode)));if (NULL != pNode){pNode->pData = pBuffer;// ④Add the buffer to the free buffer listm_freeBufferList.InsertToTail(pNode);}}2.1.3 ImageBufferManager::GetImageBuffer函数实现如下
①从free-list中找buffer；如果没有
②再去busy-list中找引用计数为0的buffer；还是没有
③看看能不能自己创建buffer；如果不能创建
④超时等待n次去获取busy-list中引用计数为0的buffer
经过上述操作，如果能获取到buffer，先添加buffer的引用计数，然后封装成node，放到busy-list链表尾
ImageBuffer* ImageBufferManager::GetImageBuffer(){// first：先从free_list的头部取出buffer节点LDLLNode* pNode = m_freeBufferList.RemoveFromHead(); ImageBuffer* pBuffer = NULL;// Check the free List for an available bufferif (NULL != pNode){// 取出buffer节点中的bufferpBuffer = static_cast<ImageBuffer*>(pNode->pData); CAMX_FREE(pNode); // 释放该节点所占用的内存pNode = NULL;}// second：如果free_list中没有可用buffer，就去busy_list中去取if (NULL == pBuffer) { // 从头遍历busy_list中的节点pNode = m_busyBufferList.Head();while (NULL != pNode){ImageBuffer* pBusyBuffer = static_cast<ImageBuffer*>(pNode->pData); LDLLNode* pNext = LightweightDoublyLinkedList::NextNode(pNode); if (0 == pBusyBuffer->GetReferenceCount()) { // 如果该busy-buffer的引用计数为0，说明该buffer可以被使用m_busyBufferList.RemoveNode(pNode);// 就从busy_list中取出node，这里会先移出，然后后面会再次添加到busy-list的尾部if (NULL == pBuffer) {// We will keep this bufferpBuffer = pBusyBuffer; // 将上述busy-buffer赋值给pBufferCAMX_FREE(pNode); // 释放该节点所占用的内存pNode = NULL;}else{// 如果从busy-list取节点时刚好发现pBuffer不为空了，而pNode都从busy-list中取出来了，这次不用就下次再用吧，将其放到free-list中m_freeBufferList.InsertToTail(pNode);}}pNode = pNext; }}// third：如果free-list和busy-list中没有找到引用计数为0的buffer，看看能不能创建bufferif (NULL == pBuffer) { UINT numOfFreeBuffers = m_freeBufferList.NumNodes();UINT numOfBusyBuffers = m_busyBufferList.NumNodes();// If no free buffers were found either in the free list or the busy list, we check to see if an additional buffer// can be allocated immediatelyif ((numOfFreeBuffers + numOfBusyBuffers) < m_maxBufferCount){ // 只要没有达到创建buffer的max值，就能额外创建bufferCamxResult result = CamxResultSuccess;// 下面就是buffer创建三部曲pBuffer = CAMX_NEW ImageBuffer();if (NULL != pBuffer){result = pBuffer->Initialize(m_pBufferManagerName, &m_createData, &m_currentFormat, this, m_hMemPoolBufMgrHandle); } else {CAMX_LOG_ERROR(CamxLogGroupMemMgr, "[%s] Ran out of memory to allocate", GetBufferManagerName());result = CamxResultENoMemory;}if (CamxResultSuccess == result){if ((TRUE == m_createData.allocateBufferMemory) &&(FALSE == m_createData.bEnableLateBinding)){// Allocate the bufferresult = pBuffer->Allocate();}}}}// four:如果上面三种情况都不满足，那么就只能等待busy-list中的buffer释放了if (NULL == pBuffer){ pNode = NULL;while (NULL == pNode){ // 设置超时等待，接收busy-list中的buffer释放信号 result = m_pWaitFreeBuffer->TimedWait(m_pLock->GetNativeHandle(), BufferTimeoutMilliseconds);pNode = m_freeBufferList.RemoveFromHead();if (timeoutCount >= MaxTimeoutCount){ // 这里会进行几次超时等待，如果超过最大等待次数就退出循环，等不下去了，累了！！CAMX_LOG_ERROR(CamxLogGroupMemMgr, "[%s] Waited %ux%u times and failed to get buffer, returning a null buffer", GetBufferManagerName(), timeoutCount, BufferTimeoutMilliseconds);break;}else if (CamxResultETimeout == result){ // 继续超时等待，死等，还挺执着！！// timeout happened, print an error log and continue waitingtimeoutCount++;CAMX_LOG_WARN(CamxLogGroupMemMgr, "[%s] Waiting %ux%d ms timedout, there might be a leak or performance issue", GetBufferManagerName(), timeoutCount, BufferTimeoutMilliseconds);}else if (CamxResultSuccess != result){ // 函数执行期间遇到错误，退出循环timeoutCount++;CAMX_LOG_ERROR(CamxLogGroupMemMgr, "[%s] Waiting %dx%d ms failed for unknown reason, result=%s",GetBufferManagerName(), timeoutCount,BufferTimeoutMilliseconds,Utils::CamxResultToString(result));break;}}// 如果free-list中取到节点了，万事大吉，取其buffer。念念不忘，必有回响！if (NULL != pNode){pBuffer = static_cast<ImageBuffer*>(pNode->pData);CAMX_FREE(pNode);pNode = NULL;CAMX_LOG_INFO(CamxLogGroupMemMgr, "[%s] Returning a buffer [%p] from the free list after wait ended",GetBufferManagerName(), pBuffer);}}// 几经波折，如果能取到buffer，会进一步处理if (NULL != pBuffer){m_pLock->Unlock();pBuffer->AddImageReference(); // 添加buffer的引用计数m_pLock->Lock();pBuffer->SetBusyState(TRUE); // 我很忙pBuffer->ClearReferenceHolderData();pNode = static_cast<LDLLNode*>(CAMX_CALLOC(sizeof(LDLLNode)));if (NULL != pNode){pNode->pData = pBuffer;m_busyBufferList.InsertToTail(pNode); // 将节点插入到busy-list的尾部m_peakBufferHolders = Utils::MaxUINT(m_peakBufferHolders, m_busyBufferList.NumNodes());}} return pBuffer;
}2.1.4 ImageBufferManager::AddReference函数实现如下
①查看该buffer是否在free-list中，如果在则将其从free-list中移到busy-list中，并添加该buffer的引用计数；如果不在
②查看该buffer是否在busy-list中，如果在则增加该buffer的引用计数。
UINT ImageBufferManager::AddReference(
ImageBuffer* pImageBuffer) {BOOL doneFlag = FALSE;UINT count = 0; LDLLNode* pNode;// 看看该buffer是不是在free-list中，如果是，则将其从中移除并添加到busy-list中pNode = m_freeBufferList.Head();while (NULL != pNode){if (pImageBuffer == static_cast<ImageBuffer*>(pNode->pData)){// Add reference to the image buffercount = pImageBuffer->AddImageReference();// Move if from free list to busy listm_freeBufferList.RemoveNode(pNode);pImageBuffer->SetBusyState(TRUE);m_busyBufferList.InsertToTail(pNode);CAMX_LOG_VERBOSE(CamxLogGroupMemMgr, "[%s] Image buffer %p in free list, reference count after adding = %d",GetBufferManagerName(), pImageBuffer, pImageBuffer->GetReferenceCount());doneFlag = TRUE;break;}pNode = LightweightDoublyLinkedList::NextNode(pNode);}// 添加引用的buffer不在freelist中if (FALSE == doneFlag){pNode = m_busyBufferList.Head();// Didn't find the image buffer in free list, then search busy listwhile (NULL != pNode){// Found the image buffer in busy listif (pImageBuffer == static_cast<ImageBuffer*>(pNode->pData)){// Add reference to the image buffercount = pImageBuffer->AddImageReference();CAMX_LOG_VERBOSE(CamxLogGroupMemMgr, "[%s] Image buffer %p in busy list, reference count after adding = %d",GetBufferManagerName(), pImageBuffer, pImageBuffer->GetReferenceCount());doneFlag = TRUE;break;}pNode = LightweightDoublyLinkedList::NextNode(pNode);}}if (FALSE == doneFlag){CAMX_LOG_ERROR(CamxLogGroupMemMgr, "[%s] Add reference to image buffer %p failed.",GetBufferManagerName(), pImageBuffer);}m_pLock->Unlock();return count;
}CAMX_INLINE UINT AddImageReference()
{UINT count = CamxAtomicIncU(&m_aReferenceCount); // 引用计数+1return count; // 返回添加引用计数后的数值
}
2.1.5 ImageBufferManager::ReleaseReference函数实现如下
①查看该buffer是否在busy-list中；如果在
②查看将该buffer引用计数-1后的引用计数值；如果为0
③将其从busy-list移动到free-list链表中，并发送信号通知那些等待buffer的线程去取buffer（GetImageBuffer中如果取不到buffer，会设置超时等待）
UINT ImageBufferManager::ReleaseReference(
ImageBuffer* pImageBuffer){BOOL doneFlag = FALSE;UINT count = 0;LDLLNode* pNode = m_busyBufferList.Head();while (NULL != pNode){// Found the image buffer in busy list，if (pImageBuffer == static_cast<ImageBuffer*>(pNode->pData)){if (0 < pImageBuffer->GetReferenceCount()) {// count为该buffer引用计数-1后的结果count = pImageBuffer->ReleaseImageReference();if (0 == count){// Move the buffer to the free listm_busyBufferList.RemoveNode(pNode);if ((TRUE == m_createData.bEnableLateBinding) &&(TRUE == m_createData.allocateBufferMemory) &&(TRUE == pImageBuffer->HasBackingBuffer())){// If late binding is enabled, release the buffer and just add the holder ImageBuffer object into// free list. When this ImageBuffer is acquired, explicit BindBuffer on this ImageBuffer object will be// called to allocate or bind the buffer back to this ImageBufferpImageBuffer->Release(FALSE);}pImageBuffer->SetBusyState(FALSE);// 为即将插入到free-list中的buffer设置状态时传参false，为busy-list时传参truem_freeBufferList.InsertToTail(pNode); // 发送信号通知等待此buffer的线程，有buffer用了，不用等了m_pWaitFreeBuffer->Signal(); }}doneFlag = TRUE;break;}pNode = LightweightDoublyLinkedList::NextNode(pNode);}if (FALSE == doneFlag){CAMX_LOG_ERROR(CamxLogGroupMemMgr, "[%s] Didn't find the image buffer %p in busy list.",GetBufferManagerName(), pImageBuffer);}return count;
}三、Camx MemPoolManager
在对ImageBufferManager接口进行详细说明后，对MemPoolMgr中如何获取ImagerBufferManager所需的ImageBuffer进行了下图的关系说明。
四、Camx ImageBuffer
imageBuffer在pipeline中扮演着非常重要的决策，负责图像数据在node之间的流转。在pipeline中node之间的连接是靠port来链接的，而port的连接正是通过共享内存（一组imageBuffer）来实现的
高通Camx架构通过一个 Import 操作，把MemPoolBuffer的bufferInfo，传递给 imagebuffer的bufferInfo。 ImageBuffer 在 pipeline node port口 之间是通过传递这个bufferInfo，把一个node 的outputport 传递给 inputport的。
以下是简单的ImageBuffer在pipeline里面的流转示意图：
五、Ending
本博文主要对一些文章中高通内存池架构/ImageBuffer进行拆分进行框架上的梳理，很多具体的各个模块细节可参考以下博文：
1.ImageBufferManager具体在整个流程中的调用以及ImgeBuffer在pipeline之间的流转：ImageBufferManager介绍-CSDN博客
DMABuffer剖析_dma buffer-CSDN博客
2.MemPoolMgr与ImageBufferManager之间更详细的link以及更深层次的涉及理解：DMABuffer剖析_dma buffer-CSDN博客
3.关于ION buffer本质与mmap映射使用更详细的说明：
Android ION 相关信息查看方法_kernel查看ion-CSDN博客
ION基本概念介绍和原理分析_ion buffer-CSDN博客
