heap_2.c详解--------FreeRTOS内存管理
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;
}
/*-----------------------------------------------------------*/