malloc/free实现 源码

采用双向链表，首次适配算法，为将来的优化提供支持：每次释放时从最近一次分配处的下一空闲块开始比较、查找。单任务版本，多任务下需要对分配和释放加锁。

#include "stdafx.h"#include <stdlib.h>#include <stdio.h>#include <time.h>#include <memory.h>typedef struct tagMemMgr_t{struct tagMemMgr_t *pNext;struct tagMemMgr_t *pPrev;intSize;} MemMgr_t;#define MEM_HDR_SIZEsizeof(MemMgr_t)static MemMgr_t*FreeHeader;void InitMemMgr(void * pMemory, int Size){FreeHeader= (MemMgr_t *)pMemory;FreeHeader->pNext = NULL;FreeHeader->pPrev = NULL;FreeHeader->Size  = Size - MEM_HDR_SIZE;}void *_malloc(int Size){MemMgr_t *p;int RemainingSize;Size = (Size + 3)/4 * 4;p = FreeHeader;while(NULL != p) {if (p->Size >= Size) {break;}else {p = p->pNext;}}if (NULL == p) return NULL;RemainingSize = p->Size - Size;if(RemainingSize > MEM_HDR_SIZE) { /* split the free block into 2 free block */MemMgr_t *q;q = (MemMgr_t *)((char *)p + MEM_HDR_SIZE + Size);q->Size = RemainingSize - MEM_HDR_SIZE;q->pNext = p->pNext;q->pPrev = p->pPrev;if(p->pPrev == NULL) {FreeHeader = q;}else {p->pPrev->pNext = q;}if(p->pNext != NULL) {p->pNext->pPrev = q;}p->Size = Size;}else {/* delete p */if(p->pPrev == NULL) {FreeHeader = p->pNext;}else {p->pPrev->pNext = p->pNext;}if(p->pNext != NULL) {p->pNext->pPrev = p->pPrev;}}return (char *)p + MEM_HDR_SIZE;}/* q merges to p */static MemMgr_t * MemMerge(MemMgr_t *p, MemMgr_t *q){if(q == NULL) {return NULL;}if(((char *)p + MEM_HDR_SIZE + p->Size) == (char *)q) {/* delete q */p->pNext = q->pNext;if(q->pNext != NULL) {q->pNext->pPrev = p;}p->Size += MEM_HDR_SIZE + q->Size;return p;}else {return NULL;}}void _free(void * pMem){MemMgr_t *pToFree, *p, *q;pToFree = (MemMgr_t *)((char *)pMem - MEM_HDR_SIZE);if(FreeHeader == NULL) {FreeHeader = pToFree;FreeHeader->pNext = NULL;FreeHeader->pPrev = NULL;return;}q = FreeHeader;p = q->pPrev;while(q != NULL && pToFree > q) {p = q;q = q->pNext;}if(p == NULL) { /* pToFree should be the first free block */pToFree->pNext = FreeHeader;pToFree->pPrev = NULL;FreeHeader->pPrev = pToFree;FreeHeader = pToFree;MemMerge(FreeHeader, FreeHeader->pNext);}else {if(q == NULL) { /* pToFree as the last free block */pToFree->pNext = NULL;pToFree->pPrev = p;p->pNext = pToFree;MemMerge(p, pToFree);}else { /* pToFree insert into the free list */pToFree->pNext = q;pToFree->pPrev = p;p->pNext = pToFree;q->pPrev = pToFree;if(NULL != MemMerge(p, pToFree)) {MemMerge(p, q);}else {MemMerge(pToFree, q);}}}}static int OutputFreeList(void){int Count = 0;MemMgr_t *p = FreeHeader;while(p != NULL) {printf("%08X(% 5d)->", p, p->Size);p = p->pNext;Count++;if(Count % 30 == 0) {printf("\n");}}printf("\nFreeListLength:%d\n", Count);return Count;}#defineMAX_ALLOC_SIZE1024#defineTEST_MEM_ARRAY_SIZE1000#defineFREE_MEM_SIZE(MAX_ALLOC_SIZE * TEST_MEM_ARRAY_SIZE)typedef void * void_p_t;int main(int argc, char* argv[]){void *p;void_p_t pMem[TEST_MEM_ARRAY_SIZE];int i;int RunTimes = 1000000;if(argc > 1) {sscanf(argv[1], "%i", &RunTimes);}p = malloc(FREE_MEM_SIZE);if(NULL == p) return -1;printf("FreeMemoryStartAddress:%08X\n", p);InitMemMgr(p, FREE_MEM_SIZE);for(i = 0; i < TEST_MEM_ARRAY_SIZE; i++) {pMem[i] = NULL;}i = 0;srand((unsigned)time(NULL));while(RunTimes--) {int MemLoc;int MemSize;MemLoc = rand() % TEST_MEM_ARRAY_SIZE;if(pMem[MemLoc] != NULL) {_free(pMem[MemLoc]);}MemSize = rand() % MAX_ALLOC_SIZE;pMem[MemLoc] = _malloc(MemSize);if(NULL == pMem[MemLoc]) {printf("Out of memory\n");break;}memset(pMem[MemLoc], 0x00, MemSize);printf("%08X(% 5d)% 8d\n", pMem[MemLoc], MemSize, i++);}OutputFreeList();for(i = 0; i < TEST_MEM_ARRAY_SIZE; i++) {if(pMem[i] != NULL) {_free(pMem[i]);}}OutputFreeList();free(p);return 0;}