heap_4.c 内存堆管理
heap_4也是用链表来管理，但是链表头用的是结构体，链表尾用的是指针，链表尾占用ucHeap内存
数据结构如下
typedef struct A_BLOCK_LINK
{
struct A_BLOCK_LINK *pxNextFreeBlock;
size_t xBlockSize;
} BlockLink_t;
头尾链表如下，注意pxEnd是指针
static BlockLink_t xStart, *pxEnd = NULL;
分配
void *pvPortMalloc( size_t xWantedSize )
{
BlockLink_t *pxBlock, *pxPreviousBlock, *pxNewBlockLink;
void *pvReturn = NULL;
//挂起调度器，防止函数重入
vTaskSuspendAll();
{
//pxEnd是NULL则是第一次调用，需要初始化堆
if( pxEnd == NULL )
{
prvHeapInit();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
//xBlockAllocatedBit = 0x8000_0000;
//待分配的内存不能大于0x7FFF_FFFF，否则失败
if( ( xWantedSize & xBlockAllocatedBit ) == 0 )
{
if( xWantedSize > 0 )
{
//加上管理结构体占用大小
xWantedSize += xHeapStructSize;
//xWantedSize大小进行字节对齐调整
if( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) != 0x00 )
{
xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
configASSERT( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) == 0 );
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
//xWantedSize大于0且小于等于此时还剩字节数才能往下申请
if( ( xWantedSize > 0 ) && ( xWantedSize <= xFreeBytesRemaining ) )
{
//pxPreviousBlock指向头链表
pxPreviousBlock = &xStart;
//pxBlock指向头链表的下一个即第一个空闲块
pxBlock = xStart.pxNextFreeBlock;
//开始遍历找到第一个比xWantedSize大的空闲块
while( ( pxBlock->xBlockSize < xWantedSize ) && ( pxBlock->pxNextFreeBlock != NULL ) )
{
//pxPreviousBlock保存空闲块的上一个
pxPreviousBlock = pxBlock;
pxBlock = pxBlock->pxNextFreeBlock;
}
//遍历完成pxBlock != pxEnd说明找到符合的空闲块
if( pxBlock != pxEnd )
{
//返回给用户的内存地址要跳过管理结构体占用的内存大小
pvReturn = ( void * ) ( ( ( uint8_t * ) pxPreviousBlock->pxNextFreeBlock ) + xHeapStructSize );
//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 );
configASSERT( ( ( ( size_t ) pxNewBlockLink ) & portBYTE_ALIGNMENT_MASK ) == 0 );
//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结构体地址升序插入到空闲链表
prvInsertBlockIntoFreeList( pxNewBlockLink );
}
else
{
mtCOVERAGE_TEST_MARKER();
}
//还剩空闲字节数要减去分配出去的
xFreeBytesRemaining -= pxBlock->xBlockSize;
//更新历史最小剩余字节数
if( xFreeBytesRemaining < xMinimumEverFreeBytesRemaining )
{
xMinimumEverFreeBytesRemaining = xFreeBytesRemaining;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
//xBlockSize最高位置1表示被这块内存被分配出去
pxBlock->xBlockSize |= xBlockAllocatedBit;
//所以管理结构体的next要指向NULL
pxBlock->pxNextFreeBlock = NULL;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
traceMALLOC( pvReturn, xWantedSize );
}//解挂调度器
( void ) xTaskResumeAll();
//如果定义了分配失败钩子函数，分配失败则执行钩子函数
#if( configUSE_MALLOC_FAILED_HOOK == 1 )
{
if( pvReturn == NULL )
{
extern void vApplicationMallocFailedHook( void );
vApplicationMallocFailedHook();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
#endif
//返回给用户
configASSERT( ( ( ( size_t ) pvReturn ) & ( size_t ) portBYTE_ALIGNMENT_MASK ) == 0 );
return pvReturn;
}
内存堆初始化
static void prvHeapInit( void )
{
BlockLink_t *pxFirstFreeBlock;
uint8_t *pucAlignedHeap;
size_t uxAddress;
size_t xTotalHeapSize = configTOTAL_HEAP_SIZE;
uxAddress = ( size_t ) ucHeap;
//这里进行字节对齐
if( ( uxAddress & portBYTE_ALIGNMENT_MASK ) != 0 )
{
uxAddress += ( portBYTE_ALIGNMENT - 1 );
uxAddress &= ~( ( size_t ) portBYTE_ALIGNMENT_MASK );
//此时xTotalHeapSize表示管理的总内存字节数
xTotalHeapSize -= uxAddress - ( size_t ) ucHeap;
}
//pucAlignedHeap指向对齐后首址
pucAlignedHeap = ( uint8_t * ) uxAddress;
//初始化头链表
xStart.pxNextFreeBlock = ( void * ) pucAlignedHeap;
xStart.xBlockSize = ( size_t ) 0;
//uxAddress此时指向管理内存最后
uxAddress = ( ( size_t ) pucAlignedHeap ) + xTotalHeapSize;
//退回一个BlockLink_t(字节对齐后)大小字节数
uxAddress -= xHeapStructSize;
//再次字节对齐
uxAddress &= ~( ( size_t ) portBYTE_ALIGNMENT_MASK );
//初始化尾链表
pxEnd = ( void * ) uxAddress;
pxEnd->xBlockSize = 0;
pxEnd->pxNextFreeBlock = NULL;
//初始化第一个空闲块
pxFirstFreeBlock = ( void * ) pucAlignedHeap;
//第一个空闲块字节数=uxAddress(此时值=pxEnd) - pxFirstFreeBlock(此时值=pucAlignedHeap)
pxFirstFreeBlock->xBlockSize = uxAddress - ( size_t ) pxFirstFreeBlock;
//第一个空闲块指向尾节点
pxFirstFreeBlock->pxNextFreeBlock = pxEnd;
//更新历史还剩最少空闲字节数
xMinimumEverFreeBytesRemaining = pxFirstFreeBlock->xBlockSize;
//更新实时还剩字节数
xFreeBytesRemaining = pxFirstFreeBlock->xBlockSize;
//这里sizeof( size_t ) = 4,heapBITS_PER_BYTE=8,表示1字节有8bit
//xBlockAllocatedBit = 1<<(4*8-1) = 0x8000_0000;
//FreeRTOS用xBlockSize最高位来标记此内存块是否空闲
//所以heap4最大只能管理0x7FFF_FFFF字节内存
xBlockAllocatedBit = ( ( size_t ) 1 ) << ( ( sizeof( size_t ) * heapBITS_PER_BYTE ) - 1 );
}
初始化后的示意图如下
注意xEnd结构体占用的时堆内存
把新构造的结构体插入空闲链表
static void prvInsertBlockIntoFreeList( BlockLink_t *pxBlockToInsert )
{
BlockLink_t *pxIterator;
uint8_t *puc;
//这里是根据内存块的地址大小来迭代寻找和pxBlockToInsert相邻的前一个空闲的内存块
for( pxIterator = &xStart; pxIterator->pxNextFreeBlock < pxBlockToInsert; pxIterator = pxIterator->pxNextFreeBlock )
{
}
//这里判断pxBlockToInsert是否能与pxBlockToInsert相邻的前一个空闲的内存块合并
puc = ( uint8_t * ) pxIterator;
if( ( puc + pxIterator->xBlockSize ) == ( uint8_t * ) pxBlockToInsert )
{ //这里做向前合并,xBlockSize相加
pxIterator->xBlockSize += pxBlockToInsert->xBlockSize;
//pxBlockToInsert指向pxIterator
pxBlockToInsert = pxIterator;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
//这里再判断是否能与后一个内存块合并
puc = ( uint8_t * ) pxBlockToInsert;
if( ( puc + pxBlockToInsert->xBlockSize ) == ( uint8_t * ) pxIterator->pxNextFreeBlock )
{ //这里做向后合并，如果要合并的后向不是pxEnd
if( pxIterator->pxNextFreeBlock != pxEnd )
{ //这里把后项合入到pxBlockToInsert
pxBlockToInsert->xBlockSize += pxIterator->pxNextFreeBlock->xBlockSize;
//pxBlockToInsert的下一个指向后项指向的空闲块
pxBlockToInsert->pxNextFreeBlock = pxIterator->pxNextFreeBlock->pxNextFreeBlock;
}
else//如果后项是pxEnd就不能合并，指向pxEnd
{
pxBlockToInsert->pxNextFreeBlock = pxEnd;
}
}
else//不相邻就只能插入链表
{
pxBlockToInsert->pxNextFreeBlock = pxIterator->pxNextFreeBlock;
}
//这里如果不等，说明没有做前向合并操作，
//需要更新下链表插入
if( pxIterator != pxBlockToInsert )
{
pxIterator->pxNextFreeBlock = pxBlockToInsert;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
释放
void vPortFree( void *pv )
{
uint8_t *puc = ( uint8_t * ) pv;
BlockLink_t *pxLink;
if( pv != NULL )
{
//偏移回地址
puc -= xHeapStructSize;
pxLink = ( void * ) puc;
//检查这个内存块是否是heap4之前分配的
configASSERT( ( pxLink->xBlockSize & xBlockAllocatedBit ) != 0 );
configASSERT( pxLink->pxNextFreeBlock == NULL );
if( ( pxLink->xBlockSize & xBlockAllocatedBit ) != 0 )
{
if( pxLink->pxNextFreeBlock == NULL )
{
//把分配的xBlockSize最高位标记清除
pxLink->xBlockSize &= ~xBlockAllocatedBit;
//挂起调度器
vTaskSuspendAll();
{
//更新剩余内存数
xFreeBytesRemaining += pxLink->xBlockSize;
traceFREE( pv, pxLink->xBlockSize );
//插入空闲内存链表
prvInsertBlockIntoFreeList( ( ( BlockLink_t * ) pxLink ) );
}//解挂调度器
( void ) xTaskResumeAll();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
}还剩空闲字节数
size_t xPortGetFreeHeapSize( void )
{
return xFreeBytesRemaining;
}
历史剩余最小字节数
size_t xPortGetMinimumEverFreeHeapSize( void )
{
return xMinimumEverFreeBytesRemaining;
}
适用范围、特点
heap4在heap2基础上加入了合并内存碎片算法，把相邻的内存碎片合并成一个更大的块、且xEnd结构体占用的是内存堆空间。
heap2的管理结构体链表是按照xBlockSize大小升序串起来，所以空闲块插入也是按照空闲块大小升序插入，而heap4管理结构体是按照空闲块管理结构体地址大小升序串起来，这样做是为了判断地址是否连续，若连续则能进行碎片合并，且用xBlockSize的最高为标记是否是已经分配的。
以上就是FreeRTOS动态内存分配管理heap_4示例的详细内容，更多关于FreeRTOS动态内存分配的资料请关注编程网其它相关文章！
