FreeRTOS程式碼閱讀筆記:heap_2.c
阿新 • • 發佈:2018-10-31
FreeRTOS中對於記憶體的管理當前一共有5種實現方式(作者當前的版本是10.1.1),均在【 \Source\portable\MemMang 】下面,這裡筆記下。
重要的引數:
使用方法: 標頭檔案:FreeRTOSConfig.h 配置引數: configTOTAL_HEAP_SIZE 定義系統所用的堆疊大小。 configUSE_MALLOC_FAILED_HOOK 預設0: 1則開啟鉤子函式,記憶體分配失敗則呼叫 函式呼叫: vPortInitialiseBlocks();//初始化 ptr=pvPortMalloc(1024); if(ptr !=NULL) { freemem=xPortGetFreeHeapSize(); printf("剩餘記憶體 %d \r\n",i,freemem); } else { printf("獲取記憶體失敗\r\n");break; }
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heap_2.c分析:
/************************************** 重要的引數備註: (1)FreeRTOS 記憶體堆為:ucHeap[] 大小為 configTOTAL_HEAP_SIZE (2)pucAlignedHeap 作為堆疊位元組對齊後的起始地址(怎麼實現的思考一下) (3)configADJUSTED_HEAP_SIZE 堆疊可操作空間,減去對齊單位,防止越界 (4)xNextFreeByte 記錄已經使用的記憶體數量 (5)//空閒記憶體管理結構體,通過它來管理釋放回來的記憶體 typedef struct A_BLOCK_LINK { struct A_BLOCK_LINK *pxNextFreeBlock; /*<< 指向連結串列中下一個空閒的記憶體塊. */ size_t xBlockSize; /*<< 當前空閒記憶體塊的大小 */ } BlockLink_t; (6)heapSTRUCT_SIZE /* 考慮到位元組對齊後BlockLink_t的大小 */ (7)heapMINIMUM_BLOCK_SIZE 記憶體塊分配後剩餘記憶體大於此數值,就會建立新的空閒記憶體塊 (8)static BlockLink_t xStart, xEnd; 記錄空閒連結串列的首尾。 xFreeBytesRemaining 當前剩餘的空閒記憶體總大小 舉個例子: 記憶體申請:xWantedSize需要獲取的記憶體,在空閒連結串列內找到大小合適的。從空閒連結串列中刪除該記憶體塊。需要注意的是 找到大小合適的記憶體塊後如果其大小減去xWantedSize後,剩餘空間大於heapMINIMUM_BLOCK_SIZE 會將其分配新的記憶體塊,插入空閒連結串列中使用。 記憶體釋放: 被佔用的記憶體由於有BlockLink_t結構體可以知道其塊的大小,所以釋放後,將其重新插入到空閒連結串列中即可。 空閒塊一但被建立後就一直存在。由於不存在記憶體回收機制,反覆分配、回收大小不一的塊,會導致產生記憶體碎片。 **************************************/
/* 一種非常簡單的記憶體實現方式,和heap_1.c的實現差不多,內部也是一個大號的陣列,不過實現了記憶體的回收,但是沒有實現空閒記憶體的整合,因此 會產生記憶體碎片。 */ #include <stdlib.h> /* Defining MPU_WRAPPERS_INCLUDED_FROM_API_FILE prevents task.h from redefining all the API functions to use the MPU wrappers. That should only be done when task.h is included from an application file. */ #define MPU_WRAPPERS_INCLUDED_FROM_API_FILE #include "FreeRTOS.h" #include "task.h" #undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE #if( configSUPPORT_DYNAMIC_ALLOCATION == 0 )//必須是預設支援動態分配的,否則編譯會報錯的 #error This file must not be used if configSUPPORT_DYNAMIC_ALLOCATION is 0 #endif //堆疊可操作空間,減去對齊單位,防止越界 #define configADJUSTED_HEAP_SIZE ( configTOTAL_HEAP_SIZE - portBYTE_ALIGNMENT ) static void prvHeapInit( void ); //初始化堆疊結構體 // 0編譯器決定分配 1 使能自定義堆疊,可制定外部RAM #if( configAPPLICATION_ALLOCATED_HEAP == 1 ) extern uint8_t ucHeap[ configTOTAL_HEAP_SIZE ]; #else static uint8_t ucHeap[ configTOTAL_HEAP_SIZE ]; #endif //空閒記憶體管理結構體,通過它來管理釋放回來的記憶體 typedef struct A_BLOCK_LINK { struct A_BLOCK_LINK *pxNextFreeBlock; /*<< 指向連結串列中下一個空閒的記憶體塊. */ size_t xBlockSize; /*<< 當前空閒記憶體塊的大小 */ } BlockLink_t; /* 考慮到位元組對齊後BlockLink_t的大小 */ static const uint16_t heapSTRUCT_SIZE = ( ( sizeof ( BlockLink_t ) + ( portBYTE_ALIGNMENT - 1 ) ) & ~portBYTE_ALIGNMENT_MASK ); #define heapMINIMUM_BLOCK_SIZE ( ( size_t ) ( heapSTRUCT_SIZE * 2 ) ) /* BlockLink_t是以單向連結串列方式儲存的,這裡儲存下連結串列的頭和尾 */ static BlockLink_t xStart, xEnd; /* 當前剩餘的空閒記憶體總大小 */ 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. */ /* 工具巨集,將一個BlockLink_t的指標插入到單向連結串列中,單向連結串列以空閒記憶體大小為序排列,記憶體小的在頭部 */ #define prvInsertBlockIntoFreeList( pxBlockToInsert ) \ { \ 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; \ } /*-----------------------------------------------------------*/
//記憶體的分配
void *pvPortMalloc( size_t xWantedSize )
{
BlockLink_t *pxBlock, *pxPreviousBlock, *pxNewBlockLink;
static BaseType_t xHeapHasBeenInitialised = pdFALSE; //初始化標誌
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 )//第一次執行會呼叫該函式初始化一下
{
prvHeapInit();
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;
/* 空餘記憶體的頭部要放一個BlockLink_t來管理,因此這裡需要人為的擴充下申請的記憶體大小 */
if( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) != 0 )
{
/* 保證位元組對齊 */
xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
}
}
if( ( xWantedSize > 0 ) && ( xWantedSize < configADJUSTED_HEAP_SIZE ) )
{
//從空餘記憶體連結串列的頭部開始找,(連結串列是從大到小排序)如果該空餘記憶體的大小>xWantedSize,
//就從這塊記憶體中摳出一部分記憶體返回,剩餘的記憶體生成新的BlockLink_t插入連結串列中
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 )
{
/* 找到了,就把該塊記憶體返回給使用者,注意記憶體的頭部有BlockLink_t,需要偏移掉 */
pvReturn = ( void * ) ( ( ( uint8_t * ) pxPreviousBlock->pxNextFreeBlock ) + heapSTRUCT_SIZE );
//把這塊記憶體從連結串列中刪除
pxPreviousBlock->pxNextFreeBlock = pxBlock->pxNextFreeBlock;
//這個地方需要注意一下,如果剩下的記憶體大小符合heapMINIMUM_BLOCK_SIZE要求,就把它放到空餘記憶體連結串列中
//被分配的記憶體塊雖然不在空閒列表裡面了,但是其最最關鍵的是其 BlockLink_t ,通過指標可以找到這個結構體
// ....->xBlockSize 可以找到這個塊的大小,釋放後放回空餘記憶體連結串列即可
//如果分配記憶體小於最小塊尺寸,剩餘的空間會建立新的空閒塊。釋放之後沒有記憶體合併,謹慎記憶體碎片產生。
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 );//產生新的空閒塊
/* 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; //剩餘空間大小
}
}
traceMALLOC( pvReturn, xWantedSize );
}
( void ) xTaskResumeAll();
#if( configUSE_MALLOC_FAILED_HOOK == 1 ) //鉤子函式
{
if( pvReturn == NULL )
{
extern void vApplicationMallocFailedHook( void );
vApplicationMallocFailedHook();
}
}
#endif
return pvReturn;
}
//記憶體的釋放
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;
vTaskSuspendAll();
{
/* Add this block to the list of free blocks. */
prvInsertBlockIntoFreeList( ( ( BlockLink_t * ) pxLink ) );//空閒記憶體插入連結串列
xFreeBytesRemaining += pxLink->xBlockSize; //剩餘記憶體大小
traceFREE( pv, pxLink->xBlockSize );
}
( void ) xTaskResumeAll();
}
}
/*-----------------------------------------------------------*/
size_t xPortGetFreeHeapSize( void )
{
return xFreeBytesRemaining;
}
/*-----------------------------------------------------------*/
void vPortInitialiseBlocks( void )
{
/* This just exists to keep the linker quiet. */
}
//連結串列的初始化
static void prvHeapInit( void )
{
BlockLink_t *pxFirstFreeBlock;
uint8_t *pucAlignedHeap;
//保證pucAlignedHeap也是在按照指定記憶體要求對齊的,通過這裡可以知道,初始化pucAlignedHeap時並不是一定等於&ucHeap[0]的,
//而是會根據位元組對齊的要求,在&ucHeap[0]和&ucHeap[portBYTE_ALIGNMENT]之間,這就會導致ucHeap的前幾個位元組可能會被浪費到,
//這也是為什麼會有一個configADJUSTED_HEAP_SIZE。
pucAlignedHeap = ( uint8_t * ) ( ( ( portPOINTER_SIZE_TYPE ) &ucHeap[ portBYTE_ALIGNMENT ] ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) );
/*初始化連結串列的頭部 */
xStart.pxNextFreeBlock = ( void * ) pucAlignedHeap;
xStart.xBlockSize = ( size_t ) 0;
/*初始化連結串列的尾部 */
xEnd.xBlockSize = configADJUSTED_HEAP_SIZE;
xEnd.pxNextFreeBlock = NULL;
/* 將pxFirstFreeBlock 放入空閒連結串列中 */
pxFirstFreeBlock = ( void * ) pucAlignedHeap;
pxFirstFreeBlock->xBlockSize = configADJUSTED_HEAP_SIZE;
//注意這裡的空餘記憶體大小標記為configADJUSTED_HEAP_SIZE,並沒有減去BlockLink_t的大小,因此在後面的記憶體申請中又人為的加了一個heapSTRUCT_SIZE。
pxFirstFreeBlock->pxNextFreeBlock = &xEnd;
}