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malloc（内存分配）在嵌入式下的一种实现

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	衰 2020-10-25 11:55

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发表于 2013-7-26 10:17 |只看该作者 |正序浏览

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想知道malloc是如何实现的吗？这里是一个简单版本，所有的功能都在这个文件实现了。如果你对malloc的原理有兴趣，可以通过这个代码窥视一二。实际上这个实现是著名的嵌入式操作系统vxworks5.5以前的内存分配版本。这里我已经把它实现的更简单易懂了。当然我还有移植到vc++下的版本，更方便调试。有需要请留言

*\file
*\brief
*\details
*
*\author Janson
*\version
*\date 04Jan12
*
*\warning
*
*\history \arg 30Jan12, Janson, Create the file
* modify from VxWorks source
*  Legal Declaration: it is for studying VxWorks only.
*/
#include "includes.h"

/* The memParLib.h file is hear:
https://code.google.com/p/vxwork ... rivate/memPartLib.h
*/

/* optional check for bad blocks */

#define MEM_BLOCK_CHECK 0x10

/* response to errors when allocating memory */

#define MEM_ALLOC_ERROR_LOG_FLAG 0x20
#define MEM_ALLOC_ERROR_SUSPEND_FLAG 0x40

/* response to errors when freeing memory */

#define MEM_BLOCK_ERROR_LOG_FLAG 0x80
#define MEM_BLOCK_ERROR_SUSPEND_FLAG 0x100

#define NEXT_HDR(pHdr)  ((BLOCK_HDR *) ((char *) (pHdr) + (2 * (pHdr)->nWords)))
#define PREV_HDR(pHdr) ((pHdr)->prevHdr)

#define HDR_TO_BLOCK(pHdr) ((char *) ((int) pHdr + sizeof (BLOCK_HDR)))
#define BLOCK_TO_HDR(pBlock) ((BLOCK_HDR *) ((int) pBlock - \
sizeof(BLOCK_HDR)))

#define HDR_TO_NODE(pHdr) (& ((FREE_BLOCK *) pHdr)->node)
#define NODE_TO_HDR(pNode) ((BLOCK_HDR *) ((int) pNode - \
OFFSET (FREE_BLOCK, node)))

static BOOL memPartLibInstalled = FALSE;

static OBJ_CLASS memPartClass;
CLASS_ID memPartClassId = &memPartClass;

static PARTITION memSysPartition;
PART_ID memSysPartId = &memSysPartition;
U32 memDefaultAlign = _ALLOC_ALIGN_SIZE;

static SEMAPHORE semMemSysPartition;

static void memPartSemInit(PART_ID partId);

FUNCTION  memPartSemInitRtn = (FUNCTION) memPartSemInit;

unsigned memPartDefaultOption = MEM_BLOCK_ERROR_SUSPEND_FLAG | MEM_BLOCK_CHECK;

static BOOL memPartBlockIsValid(PART_ID partId, FAST BLOCK_HDR* pHdr, BOOL isFree);
static BLOCK_HDR* memAlignedBlockSplit(PART_ID partId
, FAST BLOCK_HDR* pHdr
, FAST unsigned nWords
, unsigned minWords
, unsigned align);

static STATUS memPartAddToPool(PART_ID partId, char* pPool, unsigned poolSize);

STATUS memPartLibInit(char* pPool, unsigned poolSize)
{
if((!memPartLibInstalled) &&
(OK == classInit(memPartClassId, sizeof(PARTITION), OFFSET(PARTITION, objCore)
, (FUNCTION)memPartCreate, (FUNCTION)memPartInit, (FUNCTION)memPartDestroy)))
{
memPartInit(&memSysPartition, pPool, poolSize);
memPartLibInstalled = TRUE;
}

return ((memPartLibInstalled)? OK : ERROR);
}

PART_ID memPartCreate(char* pPool, unsigned poolSize)
{
PART_ID pPart = (PART_ID)objAlloc(memPartClassId);

if(NULL != pPart)
{
memPartInit(pPart, pPool, poolSize);
}

return pPart;
}

void memPartInit(PART_ID partId, char* pPool, unsigned poolSize)
{
memset((void*)partId, 0, sizeof(*partId));

partId->options = memPartDefaultOption;
partId->minBlockWords = sizeof (FREE_BLOCK) >> 1; /* word not byte */

(* memPartSemInitRtn) (partId);

dllInit(&partId->freeList);

objCoreInit(&partId->objCore, memPartClassId);

memPartAddToPool(partId, pPool, poolSize);
}

STATUS memPartDestroy(PART_ID partId)
{
return (ERROR);
}

void memAddToPool(FAST char *pPool, FAST unsigned poolSize)
{
(void)memPartAddToPool(&memSysPartition, pPool, poolSize);
}

static STATUS memPartAddToPool(PART_ID partId, char* pPool, unsigned poolSize)
{
BLOCK_HDR* pHdrStart;
BLOCK_HDR* pHdrMid;
BLOCK_HDR* pHdrEnd;
char* tmp;
int reducePool;

if(!(IS_CLASS(partId, memPartClassId))) /* only memPartClass can call this function */
{
return (ERROR);
}

tmp = (char*) MEM_ROUND_UP(pPool);
reducePool = tmp - pPool;

/* adjust the lenght */
if(poolSize >= reducePool)
{
poolSize -= reducePool;
}
else
{
poolSize = 0;
}
pPool = tmp;

poolSize = MEM_ROUND_DOWN(poolSize);

/* at least one valid free block and three header blocks */
if((sizeof(BLOCK_HDR)*3 + (partId->minBlockWords*2)) > poolSize)
{
return (ERROR);
}

/* initialize three blocks */
pHdrStart = (BLOCK_HDR*)pPool;
pHdrStart->prevHdr = NULL;
pHdrStart->free = FALSE; /* never in use */
pHdrStart->nWords = sizeof(BLOCK_HDR) >> 1;

pHdrMid = NEXT_HDR(pHdrStart);
pHdrMid->prevHdr = pHdrStart;
pHdrMid->free = TRUE; /* the main block */
pHdrMid->nWords = (poolSize - 2*sizeof(BLOCK_HDR)) >> 1;

pHdrEnd = NEXT_HDR(pHdrMid);
pHdrEnd->prevHdr = pHdrMid;
pHdrEnd->free = FALSE;
pHdrEnd->nWords = sizeof (BLOCK_HDR) >> 1;

/* TODO take sem hear */
semTake(partId->semPartId, WAIT_FOREVER);

dllInsert(&partId->freeList, (DL_NODE*)NULL, HDR_TO_NODE(pHdrMid));
partId->totalWords += (poolSize >> 1);

/* TODO give sem hear */
semGive(partId->semPartId);

return (OK);
}

void* memPartAllignedAlloc(FAST PART_ID partId, unsigned nBytes, unsigned align)
{
FAST unsigned nWords;
FAST unsigned nWordsExtra;
FAST DL_NODE* pNode;
FAST BLOCK_HDR* pHdr;
BLOCK_HDR* pNewHdr;
BLOCK_HDR* origpHdr;

if(!(IS_CLASS(partId, memPartClassId))) /* only memPartClass can call this function */
{
return (NULL);
}

nWords = (MEM_ROUND_UP(nBytes)+sizeof(BLOCK_HDR)) >>1;

if((nWords<<1) < nBytes)
{
/* TODO suspend the task */
return (NULL);
}

if(nWords < partId->minBlockWords)
{
nWords = partId->minBlockWords;
}

/* TODO task the semaphore hear */
semTake(partId->semPartId, WAIT_FOREVER);
pNode = DLL_FIRST(&partId->freeList);
nWordsExtra = nWords + align/2; /* why? */

for(;;)
{
while(NULL != pNode)
{
if((NODE_TO_HDR(pNode)->nWords > nWordsExtra) ||
((NODE_TO_HDR(pNode)->nWords == nWords) &&
(ALIGNED(HDR_TO_BLOCK(NODE_TO_HDR(pNode)), align))))
{
break;
}

pNode = DLL_NEXT(pNode);
}

if(NULL == pNode)
{
/*TODO give the semaphore */
semGive(partId->semPartId);
return NULL;
}

pHdr = NODE_TO_HDR(pNode);
origpHdr = pHdr;

pNewHdr = memAlignedBlockSplit(partId, pHdr, nWords, partId->minBlockWords, align);
if(NULL != pNewHdr)
{
pHdr = pNewHdr;
break;
}

pNode = DLL_NEXT(pNode);
}

pHdr->free = FALSE;
partId->allBlocksAlloc++;
partId->allWordsAlloc += pHdr->nWords;
partId->curBlocksAlloc++;
partId->curWordsAlloc += pHdr->nWords;

/*TODO give the  semaphore hear */
semGive(partId->semPartId);
return (HDR_TO_BLOCK(pHdr));

}

void* memPartAlloc(FAST PART_ID partId, unsigned bytes)
{
return memPartAllignedAlloc(partId, bytes, memDefaultAlign);
}

STATUS memPartFree(PART_ID partId, char* pBlock)
{
FAST BLOCK_HDR *pHdr;
FAST unsigned nWords;
FAST BLOCK_HDR *pNextHdr;

if(!IS_CLASS(partId, memPartClassId))
{
return (ERROR);
}

if(NULL == pBlock)
{
return (OK);
}

pHdr =  BLOCK_TO_HDR(pBlock);

semTake(partId->semPartId, WAIT_FOREVER);

if((partId->options & MEM_BLOCK_CHECK)
&& !memPartBlockIsValid(partId, pHdr, FALSE))
{
semGive(partId->semPartId);
return (ERROR);
}

nWords = pHdr->nWords;
if(PREV_HDR(pHdr)->free)
{/* the prev hdr is free and than coalesce with it */
pHdr->free = FALSE;
pHdr = PREV_HDR(pHdr);
pHdr->nWords += nWords;
}
else
{
pHdr->free = TRUE;
dllInsert(&partId->freeList, (DL_NODE*)NULL, HDR_TO_NODE(pHdr));
}

/* check to coalesce with the next */
pNextHdr = NEXT_HDR(pHdr);
if(pNextHdr->free)
{
pHdr->nWords += pNextHdr->nWords;
dllRemove(&partId->freeList, HDR_TO_NODE(pNextHdr));
}

/* cannot use pNextHdr->prevHdr=pHdr hear */
NEXT_HDR(pHdr)->prevHdr = pHdr;

partId->curBlocksAlloc--;
partId->curWordsAlloc -= nWords;

/* TODO give sem hear */
semGive(partId->semPartId);

return (OK);
}

static BOOL memPartBlockIsValid(PART_ID partId, FAST BLOCK_HDR* pHdr, BOOL isFree)
{
BOOL valid;

TASK_LOCK();
semGive(partId->semPartId);

valid = MEM_ALIGNED(pHdr)
&& MEM_ALIGNED(pHdr->nWords*2)
&& (pHdr->nWords < partId->totalWords)
&& (pHdr->free == isFree)
&& (pHdr == PREV_HDR(NEXT_HDR(pHdr)))
&& (pHdr == NEXT_HDR(PREV_HDR(pHdr)));

semTake(partId->semPartId, WAIT_FOREVER);
TASK_UNLOCK();

return valid;
}

static BLOCK_HDR* memAlignedBlockSplit(PART_ID partId
, FAST BLOCK_HDR* pHdr
, FAST unsigned nWords
, unsigned minWords
, unsigned align)
{
FAST BLOCK_HDR *pNewHdr;
FAST BLOCK_HDR *pNextHdr;
FAST char *endOfBlock;
FAST char *pNewBlock;
int blockSize;

endOfBlock = (char*)pHdr + (pHdr->nWords*2);

pNewBlock = (char*)((unsigned)endOfBlock - ((nWords - sizeof(BLOCK_HDR)/2)*2));

pNewBlock = (char*)((unsigned)pNewBlock & (~(align-1)));

pNewHdr = BLOCK_TO_HDR(pNewBlock);

blockSize = ((char*)pNewHdr - (char*)pHdr)/2;

if(blockSize < minWords)
{
if(pNewHdr == pHdr)
{
dllRemove(&partId->freeList, HDR_TO_NODE(pHdr));
}
else
{
return NULL;
}
}
else
{ /* recaculate pHdr */
pNewHdr->prevHdr = pHdr;
pHdr->nWords = blockSize;
}

if(((U32)endOfBlock - (U32)pNewHdr - (nWords*2)) < (minWords*2))
{
pNewHdr->nWords = (endOfBlock - pNewBlock + sizeof(BLOCK_HDR))/2;
pNewHdr->free = TRUE;

NEXT_HDR(pNewHdr)->prevHdr = pNewHdr;
}
else
{/* space left is enough to be a fragment on the free list then */
pNewHdr->nWords = nWords;
pNewHdr->free = TRUE;

pNextHdr = NEXT_HDR(pNewHdr);
/* words 包括BlockHdr */
pNextHdr->nWords = ((U32)endOfBlock - (U32)pNextHdr) / 2;
pNextHdr->prevHdr = pNewHdr;
pNextHdr->free = TRUE;

dllAdd(&partId->freeList, HDR_TO_NODE(pNextHdr));

NEXT_HDR(pNextHdr)->prevHdr = pNewHdr;
}

return (pNewHdr);
}

static void memPartSemInit(PART_ID partId)
{
semBInit(&semMemSysPartition, SEM_Q_FIFO, SEM_FULL);

partId->semPartId = &semMemSysPartition;
}

void* malloc(unsigned bytes)
{
return memPartAlloc(memSysPartId, bytes);
}

void free(void* p)
{
memPartFree(memSysPartId, (char*)p);
}

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