【例子】“首次匹配法”动态内存分配的实现

 #include <stdio.h> #include <stdlib.h> typedef unsigned int UINT; #define MEM_SIZE (1<<20) UINT memPool[MEM_SIZE]; //双向链表 struct VListHead { VListHead() { initListHead(); } void addListNext( VListHead *head ) { addFreeList( head, head->next ); } //将当前节点从链表中删除 void delList() { removeFromList( prev, next); next = NULL; prev = NULL; } void initListHead() { next = this; prev = this; } void addFreeList( VListHead *prv, VListHead *nxt ) { nxt->prev = this; this->next = nxt; this->prev = prv; prv->next = this; } //移除prv和nxt之间的节点 static void removeFromList( VListHead *prv, VListHead *nxt ) { nxt->prev = prv; prv->next = nxt; } VListHead *next; VListHead *prev; }; VListHead listHead; #define SetBlockHeadSize(pInfo, dwords) ( (*(pInfo) &= 0x3 ) |= ( (dwords)<<2) ) //设置块大小 #define GetBlockHeadSize(pInfo) ( *(pInfo) >> 2 ) //返回DWORD数 #define BLOCK_USE_MASK (0x1) //最低位标记块是否使用 #define IsBlockUsed(pInfo) ( *(pInfo) & BLOCK_USE_MASK ) #define UseBlock(pInfo) ( *(pInfo) |= BLOCK_USE_MASK ) #define UnUseBlock(pInfo) ( *(pInfo) &= ~BLOCK_USE_MASK ) void setBlockFoot( UINT *pBlockHead ) //设置内存块尾部信息字，合并时使用 { pBlockHead[(*pBlockHead>>2)-1] = pBlockHead[0]; } //用于遍历隐式链表 UINT * nextBlock( UINT *pBlockHead ) //到下一个内存块 { return &pBlockHead[*pBlockHead>>2]; } UINT * prevBlock( UINT *pBlockHead ) //到上一个内存块 { return &pBlockHead[-(*(pBlockHead-1)>>2)]; } //空闲表节点的加入和删除 void addFreeList( UINT *pBlockHead ) { ((VListHead*)(pBlockHead+1))->addListNext( &listHead ); } void delFreeList( UINT *pBlockHead ) { ((VListHead*)(pBlockHead+1))->delList(); } //得到当前分配的内存大小(包括内部碎片) UINT getAllocDwords() { UINT *ptr = nextBlock(memPool); UINT dwords = 0; //遍历隐式表 int blkSz; while( blkSz = GetBlockHeadSize(ptr) ) { if ( IsBlockUsed(ptr) ) { dwords += blkSz; } ptr = nextBlock( ptr ); } return dwords; } //初始化空闲表和隐式链表 void initMemPool() { //先建立隐式表头 UINT *ptr = memPool; UseBlock( ptr ); SetBlockHeadSize( ptr, 2 ); //占用2个DWORD setBlockFoot(ptr); //设置表体 ptr = nextBlock(ptr); UnUseBlock( ptr ); SetBlockHeadSize( ptr, MEM_SIZE - 3 ); setBlockFoot(ptr); //加入空闲表 addFreeList( ptr ); //设置表尾 ptr = nextBlock(ptr); UseBlock( ptr ); SetBlockHeadSize( ptr, 0 ); } void *Malloc( UINT sz ) { void *pRet = NULL; VListHead *pTmpList = listHead.next; sz = (sz+3)/4+2; //转换为DWORD数，再加上2个DWORD的附加信息 if (sz < 4 ) //最小块是4个DWORD { sz = 4; } while ( pTmpList != &listHead ) //遍历空闲表(首次匹配) { UINT *pBlockHead = (UINT*)pTmpList - 1; UINT objSz = GetBlockHeadSize(pBlockHead); if ( objSz >= sz ) //找到满足要求的空闲块 { pRet = pTmpList; UseBlock( pBlockHead ); //设置使用标记 pTmpList->delList(); //从空闲表中去除 //判断是否要分割 if ( objSz >= sz + 4 ) //最小分割块的大小是4个DWORD（用于建立隐式表和空闲表） { SetBlockHeadSize( pBlockHead, sz ); setBlockFoot( pBlockHead ); pBlockHead = nextBlock( pBlockHead ); //将新的空闲块加入空闲表 UnUseBlock(pBlockHead); SetBlockHeadSize( pBlockHead, objSz - sz ); setBlockFoot( pBlockHead ); addFreeList( pBlockHead ); //加入空闲表 } else { SetBlockHeadSize( pBlockHead, objSz ); setBlockFoot( pBlockHead ); } break; } pTmpList = pTmpList->next; } return pRet; } void Free( void * pObj ) { if ( pObj ) { UINT *pBlockHead = (UINT *)pObj - 1; UINT *pPrevBlock = prevBlock( pBlockHead ); UINT *pNextBlock = nextBlock( pBlockHead ); UnUseBlock(pBlockHead); //更新标记 //判断是否需要合并 if ( !IsBlockUsed(pNextBlock) ) { delFreeList(pNextBlock); int newSz = GetBlockHeadSize(pBlockHead) + GetBlockHeadSize(pNextBlock); SetBlockHeadSize( pBlockHead, newSz ); } if ( IsBlockUsed(pPrevBlock) ) { //将当前空闲块链入空闲表 addFreeList( pBlockHead ); setBlockFoot( pBlockHead ); } else { int newSz = GetBlockHeadSize(pBlockHead) + GetBlockHeadSize(pPrevBlock); SetBlockHeadSize( pPrevBlock, newSz );//直接合并到前一个内存块 setBlockFoot( pPrevBlock ); } } } /////////////////////////////////////测试部分//////////////////////////////// #define TEST_MAX (10000) char *test[TEST_MAX]; int main(int argc, char* argv[]) { initMemPool(); srand( (int)srand ); for ( int i = 0; i < TEST_MAX; ++i) { if ( !(test[i] = (char*)Malloc( rand()%MEM_SIZE ) ) ) { //计算内存使用率 printf( "using ratio:%f/n", getAllocDwords()/(float)MEM_SIZE ); int freeIdx = rand()%i; while( !test[freeIdx] ) { freeIdx = (freeIdx+1)%i; } Free( test[freeIdx] ); test[freeIdx] = NULL; } } return 0; }

//分配粒度是DWORD，最小块的大小是4个DWORD，2个DWORD用于建立空闲表，2个DWORD用于建立隐式表。