自己动手写malloc函数

/************************************************************************* > File Name: mymalloc.c > Author: Liyazhou > Mail: Liyazhou@ncic.ac.cn > Created Time: 2015年03月25日 星期三 19时58分26秒 ************************************************************************/ #include "mymalloc.h" void* free_list_begin() { //if the head is null if(!free_list_head) { return NULL; } else { void* tmp = free_list_head; while(tmp != (void*)sbrk(0)) { int* size = (int*)tmp; int* flag = (int*)(tmp+4);//the flag to indicate whether this space is in use if(*flag == SPACE_AVAILABLE) { return tmp; } else { tmp += *size; } } return NULL; } } void* free_list_next(void *node) { if(!free_list_head || !node) { return NULL; } if(node < free_list_head || node > sbrk(0)) { printf("illeagal address\n"); return NULL; } int flag = 0; void *tmp = free_list_head; while(tmp < sbrk(0)) { int* size = (int*)tmp; if(tmp == node) { tmp += *size; break; } tmp += *size; } if(tmp == sbrk(0)) { return NULL; } while(tmp < sbrk(0)) { int* size = (int*)tmp; int* flag = (int*)(tmp+4); if((*flag) == SPACE_AVAILABLE) { return tmp; } tmp += (*size); } return NULL; } void* my_malloc_new(size_t size) { size_t new_size = size; align8(new_size); new_size += 8; if(new_size >= MINIMUM_SBRK_SPACE) { void* res = sbrk(new_size); if((void*)-1 == res) { printf("error occured when allocation space\n"); return NULL; } *((int*)res) = new_size; *((int*)(res + 4)) = SPACE_IN_USE; return res; } else { size_t gap = MINIMUM_SBRK_SPACE - new_size; align8(gap); gap+=8; void* res = sbrk(gap + new_size); if((void*)-1 == res) { printf("error occured when allocating space\n"); return NULL; } *((int*)res) = new_size; *((int*)(res + 4)) = SPACE_IN_USE; res += new_size; *((int*)res) = gap; *((int*)(res + 4)) = SPACE_AVAILABLE; res -= new_size; return res; } } void* my_malloc(size_t size) { //create a new node if(NULL == free_list_begin()) { void* res = my_malloc_new(size); free_list_head = res; return res + 8; } else { void* tmp = free_list_begin(); size_t new_size = size; align8(new_size); new_size += 8; while(tmp != NULL) { int cur_size = *((int*)tmp); if(cur_size >= new_size) { if(cur_size >= new_size + 12) { *((int*)tmp) = new_size; *((int*)(tmp + 4)) = SPACE_IN_USE; void* new_tmp = tmp + new_size; *((int*)(new_tmp)) = cur_size - new_size; *((int*)(new_tmp + 4)) = SPACE_AVAILABLE; } else { *((int*)(tmp + 4)) = SPACE_IN_USE; } return tmp + 8; } tmp = free_list_next(tmp); } void* res = my_malloc_new(size); return res + 8; } } void my_free(void *ptr) { if(ptr < free_list_head || sbrk(0) < ptr) { printf("illegal pointer\n"); return; } printf("free ptr:%p\n", ptr); int* flag = (int*)(ptr - 4); *flag = SPACE_AVAILABLE; return; } void coalesce_free_list() { void *first, *second, *tail; first = free_list_begin(); int tmp_size = *((int*)first); int size = tmp_size; second = first + tmp_size; tail = sbrk(0); while(second < tail && first < tail) { while(second < tail && *((int*)(second + 4)) == SPACE_AVAILABLE ) { tmp_size = *((int*)second); size += tmp_size; second += tmp_size; } *((int*)first) = size; first = second; while(first < tail && *((int*)(first + 4)) == SPACE_IN_USE ) { first += *((int*)first); } if(first == tail) { return; } else { size = *((int*)first); second = first + size; } } return; }