FreeRTOS动态内存分配管理heap_2示例

typedef struct A_BLOCK_LINK
{
   //指向下一个空闲内存块管理结构体
	struct A_BLOCK_LINK *pxNextFreeBlock;	
	//记录申请的字节数，包括链表占用所占字节数
	size_t xBlockSize;						
} BlockLink_t;

//链表结构体对齐后所占字节数
static const uint16_t heapSTRUCT_SIZE	= ( ( sizeof ( BlockLink_t ) + ( portBYTE_ALIGNMENT - 1 ) ) & ~portBYTE_ALIGNMENT_MASK );
//2倍链表结构体对齐后所占字节数，这作为一个阈值，在分配时起作用
#define heapMINIMUM_BLOCK_SIZE	( ( size_t ) ( heapSTRUCT_SIZE * 2 ) )

//定义2个局部静态全局结构体变量用于管理
static BlockLink_t xStart, xEnd;

static size_t xFreeBytesRemaining = configADJUSTED_HEAP_SIZE;

void *pvPortMalloc( size_t xWantedSize )
{
BlockLink_t *pxBlock, *pxPreviousBlock, *pxNewBlockLink;
static BaseType_t xHeapHasBeenInitialised = pdFALSE;
void *pvReturn = NULL;
//挂起调度器，防止函数重入
	vTaskSuspendAll();
	{
		
		//第一次调用会初始化内存堆
		if( xHeapHasBeenInitialised == pdFALSE )
		{
			prvHeapInit();
			xHeapHasBeenInitialised = pdTRUE;
		}

		
		if( xWantedSize > 0 )
		{
		    //用户分配字节数+管理结构体占用字节数
			xWantedSize += heapSTRUCT_SIZE;

			
			//总的字节数再做此字节对齐
			if( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) != 0 )
			{
				
				xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
			}
		}
        //待分配字节数大于0且小于总共堆字节数
		if( ( xWantedSize > 0 ) && ( xWantedSize < configADJUSTED_HEAP_SIZE ) )
		{
			
			//pxPreviousBlock指向头链表
			pxPreviousBlock = &xStart;
			//pxBlock指向第一个开始空闲块
			pxBlock = xStart.pxNextFreeBlock;
			//当pxBlock所管理的空闲块字节数小于待分配的
			//且没有遍历到空闲块管理链表尾部则一直遍历
			while( ( pxBlock->xBlockSize < xWantedSize ) && ( pxBlock->pxNextFreeBlock != NULL ) )
			{
				//pxPreviousBlock这里是保存当前空闲块管理结构体,为了后面找到返回的内存地址
				pxPreviousBlock = pxBlock;
				//指向下一个空闲块管理结构体
				pxBlock = pxBlock->pxNextFreeBlock;
			}
			
			//pxBlock不等于结尾说明找到符合大小的空闲块
			if( pxBlock != &xEnd )
			{
				
				//pvReturn用作返回给用户，这里要偏移一个空闲块管理结构体占用内存大小
				pvReturn = ( void * ) ( ( ( uint8_t * ) pxPreviousBlock->pxNextFreeBlock ) + heapSTRUCT_SIZE );

				
				//因为pxPreviousBlock->pxNextFreeBlock指向的空闲块被分配了，
				//所以要把pxPreviousBlock->pxNextFreeBlock指向的空闲块移除出去，
				//也就是pxPreviousBlock->pxNextFreeBlock指向pxBlock->pxNextFreeBlock
				//也就是跳过分配出去的那个块
				pxPreviousBlock->pxNextFreeBlock = pxBlock->pxNextFreeBlock;

				
				//这里判断，
				//如果将要分配出去的内存块大小xBlockSize比分配出去的还要大heapMINIMUM_BLOCK_SIZE(2倍管理结构体)
				//为了节约就把再分成2块，一块返回给用户，
				//一块构造一个新的空闲管理结构体后插入空闲链表
				if( ( pxBlock->xBlockSize - xWantedSize ) > heapMINIMUM_BLOCK_SIZE )
				{
					
					//注意这里xWantedSize是管理结构体和和真正需要字节数之和
					//所以是在pxBlock基础上偏移xWantedSize作为新的管理结构体
					pxNewBlockLink = ( void * ) ( ( ( uint8_t * ) pxBlock ) + xWantedSize );

					
					//pxNewBlockLink新的管理结构体大小
					//是待分配pxBlock->xBlockSize-xWantedSize
					pxNewBlockLink->xBlockSize = pxBlock->xBlockSize - xWantedSize;
					//更新pxBlock->xBlockSize大小为xWantedSize
					pxBlock->xBlockSize = xWantedSize;

					
					//把新构造的空闲管理结构体按xBlockSize大小升序插入到空闲链表
					prvInsertBlockIntoFreeList( ( pxNewBlockLink ) );
				}
                //还剩空闲字节数要减去分配出去的
				xFreeBytesRemaining -= pxBlock->xBlockSize;
			}
		}

		traceMALLOC( pvReturn, xWantedSize );
	}//解挂调度器
	( void ) xTaskResumeAll();
//如果定义了申请失败钩子函数，这里将执行
	#if( configUSE_MALLOC_FAILED_HOOK == 1 )
	{
		if( pvReturn == NULL )
		{
			extern void vApplicationMallocFailedHook( void );
			vApplicationMallocFailedHook();
		}
	}
	#endif
//返回给用户
	return pvReturn;
}

static size_t xFreeBytesRemaining = configADJUSTED_HEAP_SIZE;

static void prvHeapInit( void )
{
BlockLink_t *pxFirstFreeBlock;
uint8_t *pucAlignedHeap;
	
    //与heap1操作相同，确保portBYTE_ALIGNMENT字节对齐，实际使用的首址是pucAlignedHeap
	pucAlignedHeap = ( uint8_t * ) ( ( ( portPOINTER_SIZE_TYPE ) &ucHeap[ portBYTE_ALIGNMENT ] ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) );
	
	//空闲链表结构体头部初始化,pxNextFreeBlock指向实际使用的首址pucAlignedHeap
	xStart.pxNextFreeBlock = ( void * ) pucAlignedHeap;
	//空闲链表结构体头部没有可用内存，所以xBlockSize是0
	xStart.xBlockSize = ( size_t ) 0;
	
	//空闲链表结构体尾部初始化,xBlockSize=configADJUSTED_HEAP_SIZE仅仅是为了后面的升序排列,不代表可以空闲字节数
	xEnd.xBlockSize = configADJUSTED_HEAP_SIZE;
	//空闲链表结构体尾部初始化,pxNextFreeBlock指向NULL表示结尾
	xEnd.pxNextFreeBlock = NULL;
	
	//第一个空闲块,pxFirstFreeBlock,即上面xStart指向的pucAlignedHeap
	pxFirstFreeBlock = ( void * ) pucAlignedHeap;
	//可以空闲内存为configADJUSTED_HEAP_SIZE
	pxFirstFreeBlock->xBlockSize = configADJUSTED_HEAP_SIZE;
	//指向空闲链表结构体尾部
	pxFirstFreeBlock->pxNextFreeBlock = &xEnd;
}

#define prvInsertBlockIntoFreeList( pxBlockToInsert )								\
{																					\
BlockLink_t *pxIterator;															\
size_t xBlockSize;																	\																					\
    //这里获得新构造的空闲结构体成员xBlockSize大小等下用于升序插入
	xBlockSize = pxBlockToInsert->xBlockSize;										\																					\
		\
												\
	//从头开始找到要插入的位置
	for( pxIterator = &xStart; pxIterator->pxNextFreeBlock->xBlockSize < xBlockSize; pxIterator = pxIterator->pxNextFreeBlock )	\
	{																				\
			\
	}																				\																					\
			\
																		\
	//插入
	pxBlockToInsert->pxNextFreeBlock = pxIterator->pxNextFreeBlock;					\
	pxIterator->pxNextFreeBlock = pxBlockToInsert;									\
}

void vPortFree( void *pv )
{
uint8_t *puc = ( uint8_t * ) pv;
BlockLink_t *pxLink;

	if( pv != NULL )
	{
		
		//偏移回地址
		puc -= heapSTRUCT_SIZE;
		
		pxLink = ( void * ) puc;
       //挂起调度器
		vTaskSuspendAll();
		{
			
		    //插入空闲链表
			prvInsertBlockIntoFreeList( ( ( BlockLink_t * ) pxLink ) );
			//剩余空闲内存增加
			xFreeBytesRemaining += pxLink->xBlockSize;
			traceFREE( pv, pxLink->xBlockSize );
		}//解挂调度器
		( void ) xTaskResumeAll();
	}
}

size_t xPortGetFreeHeapSize( void )
{
	return xFreeBytesRemaining;
}