heap_2.c源码分析 #undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE #if( configSUPPORT_DYNAMIC_ALLOCATION == 0 ) #error This file must not be used if configSUPPORT_DYNAMIC_ALLOCATION is 0 #endif /* A few bytes might be lost to byte aligning the heap start address. */ #define configADJUSTED_HEAP_SIZE ( configTOTAL_HEAP_SIZE - portBYTE_ALIGNMENT ) /* * Initialises the heap structures before their first use. */ static void prvHeapInit( void ); /* Allocate the memory for the heap. */ #if( configAPPLICATION_ALLOCATED_HEAP == 1 ) /* The application writer has already defined the array used for the RTOS heap - probably so it can be placed in a special segment or address. */ extern uint8_t ucHeap[ configTOTAL_HEAP_SIZE ]; #else static uint8_t ucHeap[ configTOTAL_HEAP_SIZE ]; #endif /* configAPPLICATION_ALLOCATED_HEAP */ /* Define the linked list structure. This is used to link free blocks in order of their size. */ typedef struct A_BLOCK_LINK { struct A_BLOCK_LINK *pxNextFreeBlock; /*<< The next free block in the list. */指向链表中下一个空闲内存块 size_t xBlockSize; /*<< The size of the free block. */当前内存块的大小 } BlockLink_t; static const uint16_t heapSTRUCT_SIZE = ( ( sizeof ( BlockLink_t ) + ( portBYTE_ALIGNMENT - 1 ) ) & ~portBYTE_ALIGNMENT_MASK ); #define heapMINIMUM_BLOCK_SIZE ( ( size_t ) ( heapSTRUCT_SIZE * 2 ) ) /* Create a couple of list links to mark the start and end of the list. */ static BlockLink_t xStart, xEnd; /* Keeps track of the number of free bytes remaining, but says nothing about fragmentation. */ static size_t xFreeBytesRemaining = configADJUSTED_HEAP_SIZE; /* STATIC FUNCTIONS ARE DEFINED AS MACROS TO MINIMIZE THE FUNCTION CALL DEPTH. */ /* * Insert a block into the list of free blocks - which is ordered by size of * the block. Small blocks at the start of the list and large blocks at the end * of the list. */ #define prvInsertBlockIntoFreeList( pxBlockToInsert ) //添加到空闲内存块列表 添加时从小到大添加的 从start到end { \ BlockLink_t *pxIterator; \ size_t xBlockSize; \ \ xBlockSize = pxBlockToInsert->xBlockSize; \ \ /* Iterate through the list until a block is found that has a larger size */ \ /* than the block we are inserting. */ \ for( pxIterator = &xStart; pxIterator->pxNextFreeBlock->xBlockSize < xBlockSize; pxIterator = pxIterator->pxNextFreeBlock ) \ { \ /* There is nothing to do here - just iterate to the correct position. */ \ } \ \ /* Update the list to include the block being inserted in the correct */ \ /* position. */ \ pxBlockToInsert->pxNextFreeBlock = pxIterator->pxNextFreeBlock; \ pxIterator->pxNextFreeBlock = pxBlockToInsert; \ } /*-----------------------------------------------------------*/ void *pvPortMalloc( size_t xWantedSize ) { BlockLink_t *pxBlock, *pxPreviousBlock, *pxNewBlockLink; static BaseType_t xHeapHasBeenInitialised = pdFALSE; void *pvReturn = NULL; vTaskSuspendAll(); { /* If this is the first call to malloc then the heap will require initialisation to setup the list of free blocks. */ if( xHeapHasBeenInitialised == pdFALSE ) //内存堆有没有初始化 { prvHeapInit(); //第一次启动调用rvInsertBlockIntoFreeList（）初始化内存堆 xHeapHasBeenInitialised = pdTRUE; } /* The wanted size is increased so it can contain a BlockLink_t structure in addition to the requested amount of bytes. */ if( xWantedSize > 0 ) { xWantedSize += heapSTRUCT_SIZE; //申请的内存大小加上结构体的大小 /* Ensure that blocks are always aligned to the required number of bytes. */ //做字节对齐处理 if( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) != 0 ) { /* Byte alignment required. */ xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) ); } } if( ( xWantedSize > 0 ) && ( xWantedSize < configADJUSTED_HEAP_SIZE ) ) { /* Blocks are stored in byte order - traverse the list from the start (smallest) block until one of adequate size is found. */ pxPreviousBlock = &xStart; pxBlock = xStart.pxNextFreeBlock; while( ( pxBlock->xBlockSize < xWantedSize ) && ( pxBlock->pxNextFreeBlock != NULL ) ) //找内存块大于我想要的内存跳出循环从xStart开始寻找满足要求的可用内存块pxBlock { pxPreviousBlock = pxBlock; pxBlock = pxBlock->pxNextFreeBlock; } /* If we found the end marker then a block of adequate size was not found. */ if( pxBlock != &xEnd ) { /* Return the memory space - jumping over the BlockLink_t structure at its start. */ pvReturn = ( void * ) ( ( ( uint8_t * ) pxPreviousBlock->pxNextFreeBlock ) + heapSTRUCT_SIZE ); //返回我们所需内存块的首地址 需要从结构体的内存的地址开始 跳过结构体 获取返回给应用层代码的可用内存首地址 注意跳过结构体lockLink_t大小 /* This block is being returned for use so must be taken out of the list of free blocks. */ pxPreviousBlock->pxNextFreeBlock = pxBlock->pxNextFreeBlock; /* If the block is larger than required it can be split into two. */ if( ( pxBlock->xBlockSize - xWantedSize ) > heapMINIMUM_BLOCK_SIZE ) //内存太大 { /* This block is to be split into two. Create a new block following the number of bytes requested. The void cast is used to prevent byte alignment warnings from the compiler. */ pxNewBlockLink = ( void * ) ( ( ( uint8_t * ) pxBlock ) + xWantedSize ); /* Calculate the sizes of two blocks split from the single block. */ pxNewBlockLink->xBlockSize = pxBlock->xBlockSize - xWantedSize; pxBlock->xBlockSize = xWantedSize; /* Insert the new block into the list of free blocks. */ prvInsertBlockIntoFreeList( ( pxNewBlockLink ) ); //添加到空闲内存块列表 } xFreeBytesRemaining -= pxBlock->xBlockSize; //更新剩余内存 } } traceMALLOC( pvReturn, xWantedSize ); } ( void ) xTaskResumeAll(); #if( configUSE_MALLOC_FAILED_HOOK == 1 ) { if( pvReturn == NULL ) { extern void vApplicationMallocFailedHook( void ); vApplicationMallocFailedHook(); } } #endif return pvReturn; } /*-----------------------------------------------------------*/ void vPortFree( void *pv ) //内存释放 { uint8_t *puc = ( uint8_t * ) pv; BlockLink_t *pxLink; if( pv != NULL ) { /* The memory being freed will have an BlockLink_t structure immediately before it. */ puc -= heapSTRUCT_SIZE; //减去结构体大小 /* This unexpected casting is to keep some compilers from issuing byte alignment warnings. */ pxLink = ( void * ) puc; vTaskSuspendAll(); { /* Add this block to the list of free blocks. */ prvInsertBlockIntoFreeList( ( ( BlockLink_t * ) pxLink ) ); //添加到空闲列表 xFreeBytesRemaining += pxLink->xBlockSize; //更新变量xFreeBytesRemaining traceFREE( pv, pxLink->xBlockSize ); } ( void ) xTaskResumeAll(); } } /*-----------------------------------------------------------*/ size_t xPortGetFreeHeapSize( void ) //获取空闲块大小 { return xFreeBytesRemaining; } /*-----------------------------------------------------------*/ void vPortInitialiseBlocks( void ) { /* This just exists to keep the linker quiet. */ } /*-----------------------------------------------------------*/ //内存堆初始化1ucHeap的可用始地址pucAlignedHeap做字节对齐2，初始化xTart和xEend 把ucHeap当做一个超大的内存块，并且初始化这个内存块对应的 BlockLink_t类型的结构体 static void prvHeapInit( void ) { BlockLink_t *pxFirstFreeBlock; uint8_t *pucAlignedHeap; /* Ensure the heap starts on a correctly aligned boundary. */ pucAlignedHeap = ( uint8_t * ) ( ( ( portPOINTER_SIZE_TYPE ) &ucHeap[ portBYTE_ALIGNMENT ] ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) ); /* xStart is used to hold a pointer to the first item in the list of free blocks. The void cast is used to prevent compiler warnings. */ xStart.pxNextFreeBlock = ( void * ) pucAlignedHeap; xStart.xBlockSize = ( size_t ) 0; /* xEnd is used to mark the end of the list of free blocks. */ xEnd.xBlockSize = configADJUSTED_HEAP_SIZE; xEnd.pxNextFreeBlock = NULL; /* To start with there is a single free block that is sized to take up the entire heap space. */ pxFirstFreeBlock = ( void * ) pucAlignedHeap; pxFirstFreeBlock->xBlockSize = configADJUSTED_HEAP_SIZE; pxFirstFreeBlock->pxNextFreeBlock = &xEnd; } /*-----------------------------------------------------------*/
