linux环境下一个简单的malloc实现

/* brk() sbrk() mmap() 更改进程地址空间的映射 系统维护一个数组，反映特定大小的内存的分配情况 当申请的大小类小于128k时用类似于伙伴算法的方法分配，调用brk() else 用mmap分配 */ #include<unistd.h> #include<sys/mman.h> #include"mymalloc.h" #include<stdio.h> #include<string.h> #define LIST_HEAD_INIT(name) { &(name), &(name) } #define LIST_HEAD(name) struct list_head name = LIST_HEAD_INIT(name) #define list_for_each(head,list) \ for(list=(head)->next;list!=(head);list=list->next) #define list_add_head(head,list) \ do{ \ (list)->pre=(head); \ (list)->next=(head)->next; \ (head)->next=(list); \ (list)->next->pre=(list); \ }while(0) #define list_del(list) \ do{ \ list->pre->next=list->next; \ list->next->pre=list->pre; \ }while(0) #define to_entry(ptr, type, member) \ ((type *)((char *)(ptr)-(unsigned long)(&((type *)0)->member))) int inited; /* list_t list_free; list_t list_used; */ list_t list_free=LIST_HEAD_INIT(list_free); list_t list_used=LIST_HEAD_INIT(list_used); int malloc_init() { #ifdef DEBUG printf("initialise,though nothing to do\n"); #endif inited=1; return 0; } void* malloc_mmap(unsigned int bytes) { cnt_t * map_cnt=mmap(NULL,sizeof(cnt_t)+bytes,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANONYMOUS,-1,0); if(map_cnt==(void *) -1) return NULL; memset(map_cnt,0,sizeof(cnt_t)); map_cnt->mmap=1; #ifdef DEBUG printf("mmap the addr:%p \n",map_cnt->addr); #endif return (void *) map_cnt->addr; } void malloc_switch(list_t* list) { list_del(list); list_add_head(&list_used,list); } void free_switch(list_t* list) { list_del(list); list_add_head(&list_free,list); } void * malloc_brk(unsigned int bytes) { cnt_t * block=NULL; list_t *plist; list_for_each(&list_free,plist){ block=to_entry(plist,struct cnt,list); if(block->size<bytes) continue; malloc_switch(plist); //将这个block从空闲链表移到used链表 return (void *)block->addr; } block=sbrk(sizeof(cnt_t)+bytes); if(block==(void*) -1) return NULL; memset(block,0,sizeof(cnt_t)); list_add_head(&list_used,&(block->list)); // block->used=1; block->size=bytes; #ifdef DEBUG printf("get the mem,addr:%p\n",block->addr); #endif return block->addr; } void * mymalloc(unsigned int bytes) { if(!inited && (malloc_init()==-1)) return NULL; if((bytes>>17)>0) return malloc_mmap(bytes); return malloc_brk(bytes); } int addr_valid(void *addr) { return 1; } void myfree(void *ptr) { if(ptr==NULL) return; /*没有检查是否是已分配地址,这里假设是一个ok地址*/ if(!addr_valid(ptr)) return; cnt_t *block=to_entry(ptr,cnt_t,addr); if(block->mmap==1){ #ifdef DEBUG printf("free addr:%p,munmap\n",ptr); #endif munmap(block,sizeof(cnt_t)+block->size); return; } #ifdef DEBUG printf("free addr:%p\n",ptr); #endif free_switch(&block->list); }