freertos的内存管理_freertos动态内存分配-爱代码爱编程
文章目录
7 FreeRTOS内存管理
7.1 内存管理
在之前的学习中，我们经常看到静态分配方式和动态分配方式。我们画一下内存图来理解他们的不同。其中，bss区域也叫做ZI-data（bss）区。
7.1.1 C语言的内存分布图
首先我们复习一下C语言的内存图。
7.1.2 动态分配内存时的FreeRTOS的内存图
7.1.3 静态分配内存时的FreeRTOS的内存图
7.2 heap.c文件
首先思考一个问题，为什么FreeRTOS多数情况不直接使用malloc和free来分配内存：
因为：不安全，主要的原因如下：
- 这些函数在小型的嵌入式系统中总是不可用的，因为小型嵌入式设备的RAM内存总是不足的。而malloc和free需要占掉相当大的一部分内存。
- 执行时间并不确定，每一次调用这些函数的执行时间可能都不一样，在实时操作系统中，分配内存的时间必须是可预测的，pvPortMalloc()和pvPortfree()分配内存时的时间是确定的。
- 这两个函数会使得链接器配置十分复杂。
- malloc分配内存时，是可以覆盖别的已经使用的地方的内存的，如果允许malloc时堆空间不够时覆盖其他变量的占据的内存，那么对于没有mmu的单片机来说，是致命的，任务和任务之间分配好的堆就会出现很大的问题。
在之前移植FreeRTOS的时候，有heap1，2，3，4，5五个文件，这五个文件都是用来分配内存的，但是有不一样的特性：
- heap1.c：没有free的函数，只能分配内存但是不释放，是直接在原有的基础上进行对齐累加的，适合小型，不需要释放任何存储空间的代码。
- heap2.c：有free相关函数，会自动释放之前申请过大的内存块，但是不会进行碎片内存的合并。
- heap3.c：是malloc（）和free（）的抽象层，直接调用C语言库中的这两个函数。同时多加了线程安全措施。
- heap4.c：与heap2.c相同，只不过比起heap.2他拥有了碎片内存合并的功能，所以成为我们最常用的内存文件。
- heap5.c：与heap4.c相同，但是heap5可以跨越不连续区域进行存储，当我们有多篇内存的时候可以使用这种方式。
内存一些重要的宏定义
//系统堆总大小，即ucHeap的大小
#define configTOTAL_HEAP_SIZE ((uint32_t)33 * 1024)
//系统堆对齐字节(8字节)
#define portBYTE_ALIGNMENT 8
//系统堆可分配大小
#define configADJUSTED_HEAP_SIZE (configTOTAL_HEAP_SIZE-portBYTE_ALIGNMENT)
//未初始化的静态数组,即系统堆区
static uint8_t ucHeap[ configTOTAL_HEAP_SIZE ];//就是我们上图中的ucHeap
7.2.1 heap1.c
void * pvPortMalloc( size_t xWantedSize )
{
void * pvReturn = NULL;//申请的内存的首地址，用来返回
static uint8_t * pucAlignedHeap = NULL;//指向堆内存的起始地址。
//对齐操作
#if ( portBYTE_ALIGNMENT != 1 )
{
if( xWantedSize & portBYTE_ALIGNMENT_MASK )
{
/* Byte alignment required. Check for overflow. */
if(( xWantedSize + ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) ) ) > xWantedSize)
{
xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
}
else
{
xWantedSize = 0;
}
}
}
#endif /* if ( portBYTE_ALIGNMENT != 1 ) */
vTaskSuspendAll();//挂起任务调度器（注意实现原理是是停止了任务调度器而不是挂起了所有其他的任务），进入临界区，也就是说一个任务内存分配的时候，不可以有其他任务来打断他。（进入临界区的另一个原因是没有MMU操作的都是真实的物理地址，所以内存资源的分配一定要注意防范冲突！！！），同时它支持嵌套操作，他有一个计数器来计数被挂起了几次，相应的挂起几次就需要我们resume几次，同时要注意的是，它相当于使调度器程序停止了而已，此任务并没有停止，所以这个过程中不存在上下文的切换。
{
if( pucAlignedHeap == NULL )
{
//ucheap的对齐操作（向上对齐）
pucAlignedHeap = ( uint8_t * ) ( ( ( portPOINTER_SIZE_TYPE ) & ucHeap[ portBYTE_ALIGNMENT - 1 ] ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) );
}
//检查是否有足够的空间进行分配
if( ( xWantedSize > 0 ) &&
( ( xNextFreeByte + xWantedSize ) < configADJUSTED_HEAP_SIZE ) &&
( ( xNextFreeByte + xWantedSize ) > xNextFreeByte ) )
{
/* Return the next free byte then increment the index past this
* block. */
pvReturn = pucAlignedHeap + xNextFreeByte;
xNextFreeByte += xWantedSize;
}
traceMALLOC( pvReturn, xWantedSize );//统计被使用的空间
}
( void ) xTaskResumeAll();//恢复调度器，离开临界区。
#if ( configUSE_MALLOC_FAILED_HOOK == 1 )//malloc失败的钩子函数
{
if( pvReturn == NULL )
{
vApplicationMallocFailedHook();//malloc失败的钩子函数，这里包含了malloc失败后该如何处理。
}
}
#endif
return pvReturn;//返回分配的内存的首地址
}
/*-----------------------------------------------------------*/
void vPortFree( void * pv )
{
//在heap1中没有free操作
( void ) pv;
//在heap1中无法释放内存，所以一旦传入除了NULL以外的地址，configASSERT断言宏由于pv == NULL不成立，所以就会停止系统运行并且向标准输出输出错误原因。
configASSERT( pv == NULL );
}
7.2.2 heap2.c
void * pvPortMalloc( size_t xWantedSize )
{
BlockLink_t * pxBlock;
BlockLink_t * pxPreviousBlock;
BlockLink_t * pxNewBlockLink;
PRIVILEGED_DATA static BaseType_t xHeapHasBeenInitialised = pdFALSE;
void * pvReturn = NULL;
size_t xAdditionalRequiredSize;
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 )
{
prvHeapInit();
xHeapHasBeenInitialised = pdTRUE;
}
if( xWantedSize > 0 )
{
/* The wanted size must be increased so it can contain a BlockLink_t
* structure in addition to the requested amount of bytes. Some
* additional increment may also be needed for alignment. */
xAdditionalRequiredSize = heapSTRUCT_SIZE + portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK );
if( heapADD_WILL_OVERFLOW( xWantedSize, xAdditionalRequiredSize ) == 0 )
{
xWantedSize += xAdditionalRequiredSize;
}
else
{
xWantedSize = 0;
}
}
/* Check the block size we are trying to allocate is not so large that the
* top bit is set. The top bit of the block size member of the BlockLink_t
* structure is used to determine who owns the block - the application or
* the kernel, so it must be free. */
if( heapBLOCK_SIZE_IS_VALID( xWantedSize ) != 0 )
{
if( ( xWantedSize > 0 ) && ( xWantedSize <= xFreeBytesRemaining ) )
{
/* 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 ) )
{
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 );
/* 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 )
{
/* 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 ) );
}
xFreeBytesRemaining -= pxBlock->xBlockSize;
/* The block is being returned - it is allocated and owned
* by the application and has no "next" block. */
heapALLOCATE_BLOCK( pxBlock );
pxBlock->pxNextFreeBlock = NULL;
}
}
}
traceMALLOC( pvReturn, xWantedSize );
}
( void ) xTaskResumeAll();
#if ( configUSE_MALLOC_FAILED_HOOK == 1 )
{
if( pvReturn == NULL )
{
vApplicationMallocFailedHook();
}
}
#endif
return pvReturn;
}
/*-----------------------------------------------------------*/
void vPortFree( void * pv )
{
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;
/* This unexpected casting is to keep some compilers from issuing
* byte alignment warnings. */
pxLink = ( void * ) puc;
configASSERT( heapBLOCK_IS_ALLOCATED( pxLink ) != 0 );
configASSERT( pxLink->pxNextFreeBlock == NULL );
if( heapBLOCK_IS_ALLOCATED( pxLink ) != 0 )
{
if( pxLink->pxNextFreeBlock == NULL )
{
/* The block is being returned to the heap - it is no longer
* allocated. */
heapFREE_BLOCK( pxLink );
#if ( configHEAP_CLEAR_MEMORY_ON_FREE == 1 )
{
( void ) memset( puc + heapSTRUCT_SIZE, 0, pxLink->xBlockSize - heapSTRUCT_SIZE );
}
#endif
vTaskSuspendAll();
{
/* Add this block to the list of free blocks. */
prvInsertBlockIntoFreeList( ( ( BlockLink_t * ) pxLink ) );
xFreeBytesRemaining += pxLink->xBlockSize;
traceFREE( pv, pxLink->xBlockSize );
}
( void ) xTaskResumeAll();
}
}
}
}
/*-----------------------------------------------------------*/
7.2.3 heap3.c
void * pvPortMalloc( size_t xWantedSize )
{
void * pvReturn;
vTaskSuspendAll();//进入临界区
{
pvReturn = malloc( xWantedSize );
traceMALLOC( pvReturn, xWantedSize );//统计被使用的空间，traceMALLOC是一个宏，使用它将自动记录每次分配的操作
}
( void ) xTaskResumeAll();//离开临界区
#if ( configUSE_MALLOC_FAILED_HOOK == 1 )//若分配出现错误，并且使能了 configUSE_MALLOC_FAILED_HOOK == 1钩子宏。
{ //那么就进行相应的错误处理
if( pvReturn == NULL )
{
vApplicationMallocFailedHook();
}
}
#endif
return pvReturn;
}
/*-----------------------------------------------------------*/
void vPortFree( void * pv )
{
if( pv != NULL )
{
vTaskSuspendAll();//挂起，进入临界区
{
free( pv );//用free（）函数free对应的内存
traceFREE( pv, 0 );//记录free操作
}
( void ) xTaskResumeAll();//离开临界区
}
}
7.2.4 heap4.c
void * pvPortMalloc( size_t xWantedSize )
{
BlockLink_t * pxBlock;
BlockLink_t * pxPreviousBlock;
BlockLink_t * pxNewBlockLink;
void * pvReturn = NULL;
size_t xAdditionalRequiredSize;
vTaskSuspendAll();
{
/* If this is the first call to malloc then the heap will require
* initialisation to setup the list of free blocks. */
if( pxEnd == NULL )
{
prvHeapInit();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
if( xWantedSize > 0 )
{
/* The wanted size must be increased so it can contain a BlockLink_t
* structure in addition to the requested amount of bytes. Some
* additional increment may also be needed for alignment. */
xAdditionalRequiredSize = xHeapStructSize + portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK );
if( heapADD_WILL_OVERFLOW( xWantedSize, xAdditionalRequiredSize ) == 0 )
{
xWantedSize += xAdditionalRequiredSize;
}
else
{
xWantedSize = 0;
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* Check the block size we are trying to allocate is not so large that the
* top bit is set. The top bit of the block size member of the BlockLink_t
* structure is used to determine who owns the block - the application or
* the kernel, so it must be free. */
if( heapBLOCK_SIZE_IS_VALID( xWantedSize ) != 0 )
{
if( ( xWantedSize > 0 ) && ( xWantedSize <= xFreeBytesRemaining ) )
{
/* Traverse the list from the start (lowest address) block until
* one of adequate size is found. */
pxPreviousBlock = &xStart;
pxBlock = xStart.pxNextFreeBlock;
while( ( pxBlock->xBlockSize < xWantedSize ) && ( pxBlock->pxNextFreeBlock != NULL ) )
{
pxPreviousBlock = pxBlock;
pxBlock = pxBlock->pxNextFreeBlock;
}
/* If the end marker was reached then a block of adequate size
* was not found. */
if( pxBlock != pxEnd )
{
/* Return the memory space pointed to - jumping over the
* BlockLink_t structure at its start. */
pvReturn = ( void * ) ( ( ( uint8_t * ) pxPreviousBlock->pxNextFreeBlock ) + xHeapStructSize );
/* 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 )
{
/* 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 );
configASSERT( ( ( ( size_t ) pxNewBlockLink ) & portBYTE_ALIGNMENT_MASK ) == 0 );
/* 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 );
}
else
{
mtCOVERAGE_TEST_MARKER();
}
xFreeBytesRemaining -= pxBlock->xBlockSize;
if( xFreeBytesRemaining < xMinimumEverFreeBytesRemaining )
{
xMinimumEverFreeBytesRemaining = xFreeBytesRemaining;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* The block is being returned - it is allocated and owned
* by the application and has no "next" block. */
heapALLOCATE_BLOCK( pxBlock );
pxBlock->pxNextFreeBlock = NULL;
xNumberOfSuccessfulAllocations++;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
traceMALLOC( pvReturn, xWantedSize );
}
( void ) xTaskResumeAll();
#if ( configUSE_MALLOC_FAILED_HOOK == 1 )
{
if( pvReturn == NULL )
{
vApplicationMallocFailedHook();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
#endif /* if ( configUSE_MALLOC_FAILED_HOOK == 1 ) */
configASSERT( ( ( ( size_t ) pvReturn ) & ( size_t ) portBYTE_ALIGNMENT_MASK ) == 0 );
return pvReturn;
}
/*-----------------------------------------------------------*/
void vPortFree( void * pv )
{
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 -= xHeapStructSize;
/* This casting is to keep the compiler from issuing warnings. */
pxLink = ( void * ) puc;
configASSERT( heapBLOCK_IS_ALLOCATED( pxLink ) != 0 );
configASSERT( pxLink->pxNextFreeBlock == NULL );
if( heapBLOCK_IS_ALLOCATED( pxLink ) != 0 )
{
if( pxLink->pxNextFreeBlock == NULL )
{
/* The block is being returned to the heap - it is no longer
* allocated. */
heapFREE_BLOCK( pxLink );
#if ( configHEAP_CLEAR_MEMORY_ON_FREE == 1 )
{
( void ) memset( puc + xHeapStructSize, 0, pxLink->xBlockSize - xHeapStructSize );
}
#endif
vTaskSuspendAll();
{
/* Add this block to the list of free blocks. */
xFreeBytesRemaining += pxLink->xBlockSize;
traceFREE( pv, pxLink->xBlockSize );
prvInsertBlockIntoFreeList( ( ( BlockLink_t * ) pxLink ) );
xNumberOfSuccessfulFrees++;
}
( void ) xTaskResumeAll();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
}
/*-----------------------------------------------------------*/
7.2.5 heap5.c
void * pvPortMalloc( size_t xWantedSize )
{
BlockLink_t * pxBlock;
BlockLink_t * pxPreviousBlock;
BlockLink_t * pxNewBlockLink;
void * pvReturn = NULL;
size_t xAdditionalRequiredSize;
/* The heap must be initialised before the first call to
* prvPortMalloc(). */
configASSERT( pxEnd );
vTaskSuspendAll();
{
if( xWantedSize > 0 )
{
/* The wanted size must be increased so it can contain a BlockLink_t
* structure in addition to the requested amount of bytes. Some
* additional increment may also be needed for alignment. */
xAdditionalRequiredSize = xHeapStructSize + portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK );
if( heapADD_WILL_OVERFLOW( xWantedSize, xAdditionalRequiredSize ) == 0 )
{
xWantedSize += xAdditionalRequiredSize;
}
else
{
xWantedSize = 0;
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* Check the block size we are trying to allocate is not so large that the
* top bit is set. The top bit of the block size member of the BlockLink_t
* structure is used to determine who owns the block - the application or
* the kernel, so it must be free. */
if( heapBLOCK_SIZE_IS_VALID( xWantedSize ) != 0 )
{
if( ( xWantedSize > 0 ) && ( xWantedSize <= xFreeBytesRemaining ) )
{
/* Traverse the list from the start (lowest address) block until
* one of adequate size is found. */
pxPreviousBlock = &xStart;
pxBlock = xStart.pxNextFreeBlock;
while( ( pxBlock->xBlockSize < xWantedSize ) && ( pxBlock->pxNextFreeBlock != NULL ) )
{
pxPreviousBlock = pxBlock;
pxBlock = pxBlock->pxNextFreeBlock;
}
/* If the end marker was reached then a block of adequate size
* was not found. */
if( pxBlock != pxEnd )
{
/* Return the memory space pointed to - jumping over the
* BlockLink_t structure at its start. */
pvReturn = ( void * ) ( ( ( uint8_t * ) pxPreviousBlock->pxNextFreeBlock ) + xHeapStructSize );
/* 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 )
{
/* 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 ) );
}
else
{
mtCOVERAGE_TEST_MARKER();
}
xFreeBytesRemaining -= pxBlock->xBlockSize;
if( xFreeBytesRemaining < xMinimumEverFreeBytesRemaining )
{
xMinimumEverFreeBytesRemaining = xFreeBytesRemaining;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* The block is being returned - it is allocated and owned
* by the application and has no "next" block. */
heapALLOCATE_BLOCK( pxBlock );
pxBlock->pxNextFreeBlock = NULL;
xNumberOfSuccessfulAllocations++;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
traceMALLOC( pvReturn, xWantedSize );
}
( void ) xTaskResumeAll();
#if ( configUSE_MALLOC_FAILED_HOOK == 1 )
{
if( pvReturn == NULL )
{
vApplicationMallocFailedHook();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
#endif /* if ( configUSE_MALLOC_FAILED_HOOK == 1 ) */
return pvReturn;
}
/*-----------------------------------------------------------*/
void vPortFree( void * pv )
{
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 -= xHeapStructSize;
/* This casting is to keep the compiler from issuing warnings. */
pxLink = ( void * ) puc;
configASSERT( heapBLOCK_IS_ALLOCATED( pxLink ) != 0 );
configASSERT( pxLink->pxNextFreeBlock == NULL );
if( heapBLOCK_IS_ALLOCATED( pxLink ) != 0 )
{
if( pxLink->pxNextFreeBlock == NULL )
{
/* The block is being returned to the heap - it is no longer
* allocated. */
heapFREE_BLOCK( pxLink );
#if ( configHEAP_CLEAR_MEMORY_ON_FREE == 1 )
{
( void ) memset( puc + xHeapStructSize, 0, pxLink->xBlockSize - xHeapStructSize );
}
#endif
vTaskSuspendAll();
{
/* Add this block to the list of free blocks. */
xFreeBytesRemaining += pxLink->xBlockSize;
traceFREE( pv, pxLink->xBlockSize );
prvInsertBlockIntoFreeList( ( ( BlockLink_t * ) pxLink ) );
xNumberOfSuccessfulFrees++;
}
( void ) xTaskResumeAll();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
}
/*-----------------------------------------------------------*/