char *default_alloc::chunk_alloc(size_t size, int &nobjs)
{
char *result = 0;
size_t total_bytes = size*nobjs;
size_t bytes_left = end_free - start_free; //内存池剩余空间
if (bytes_left >= total_bytes)
{//内存池足够提供所需内存
result = start_free;
start_free += total_bytes;
return result;
}
else if (bytes_left >= size)
{//内存池足够供应一个以上的区块
nobjs = bytes_left / size;
total_bytes = nobjs * size;
result = start_free;
start_free += total_bytes;
return result;
}
else
{//内存池一块区块也供应不了
size_t bytes_to_get = 2 * total_bytes + ROUND_UP(heap_size >> 4);;
if (bytes_left>0)
{//将内存池的零头分配给合适的freelist
obj **my_free_list = free_list + FREELIST_INDEX(bytes_left);
((obj *)start_free)->next = *my_free_list;
*my_free_list = (obj *)start_free;
}
start_free = (char *)malloc(bytes_to_get);
if (!start_free)
{//系统堆内存不足，寻找还未使用的freelist
obj *p = 0;
obj **my_free_list = 0;
for (int i = size; i < MAX_BYTES; ++i)
{
my_free_list = free_list + FREELIST_INDEX(i);
p = *my_free_list;
if (0 != p)
{//还有未使用的freelist
start_free = (char *)p;
*my_free_list = p->next;
end_free = start_free + i;
//递归调用，修正nobjs
return chunk_alloc(size, nobjs);
}
}
//没内存可用，寄希望于第一级的new-handler或抛出异常
end_free = 0;
start_free = (char *)malloc_alloc::allocate(bytes_to_get);
}
heap_size += bytes_to_get;
end_free = start_free + bytes_to_get;
return chunk_alloc(size, nobjs);//递归调用，修正nobjs
}
}