119 lines
3.2 KiB
C++
119 lines
3.2 KiB
C++
#include "../Alloc.h"
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namespace TinySTL{
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char *alloc::start_free = 0;
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char *alloc::end_free = 0;
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size_t alloc::heap_size = 0;
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alloc::obj *alloc::free_list[alloc::ENFreeLists::NFREELISTS] = {
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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};
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void *alloc::allocate(size_t bytes){
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if (bytes > EMaxBytes::MAXBYTES){
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return malloc(bytes);
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}
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size_t index = FREELIST_INDEX(bytes);
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obj *list = free_list[index];
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if (list){//此list还有空间给我们
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free_list[index] = list->next;
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return list;
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}
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else{//此list没有足够的空间，需要从内存池里面取空间
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return refill(ROUND_UP(bytes));
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}
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}
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void alloc::deallocate(void *ptr, size_t bytes){
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if (bytes > EMaxBytes::MAXBYTES){
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free(ptr);
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}
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else{
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size_t index = FREELIST_INDEX(bytes);
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obj *node = static_cast<obj *>(ptr);
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node->next = free_list[index];
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free_list[index] = node;
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}
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}
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void *alloc::reallocate(void *ptr, size_t old_sz, size_t new_sz){
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deallocate(ptr, old_sz);
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ptr = allocate(new_sz);
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return ptr;
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}
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//返回一个大小为n的对象，并且有时候会为适当的free list增加节点
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//假设bytes已经上调为8的倍数
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void *alloc::refill(size_t bytes){
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size_t nobjs = ENObjs::NOBJS;
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//从内存池里取
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char *chunk = chunk_alloc(bytes, nobjs);
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obj **my_free_list = 0;
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obj *result = 0;
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obj *current_obj = 0, *next_obj = 0;
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if (nobjs == 1){//取出的空间只够一个对象使用
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return chunk;
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}
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else{
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my_free_list = free_list + FREELIST_INDEX(bytes);
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result = (obj *)(chunk);
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*my_free_list = next_obj = (obj *)(chunk + bytes);
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//将取出的多余的空间加入到相应的free list里面去
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for (int i = 1;; ++i){
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current_obj = next_obj;
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next_obj = (obj *)((char *)next_obj + bytes);
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if (nobjs - 1 == i){
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current_obj->next = 0;
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break;
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}
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else{
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current_obj->next = next_obj;
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}
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}
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return result;
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}
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}
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//假设bytes已经上调为8的倍数
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char *alloc::chunk_alloc(size_t bytes, size_t& nobjs){
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char *result = 0;
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size_t total_bytes = bytes * nobjs;
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size_t bytes_left = end_free - start_free;
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if (bytes_left >= total_bytes){//内存池剩余空间完全满足需要
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result = start_free;
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start_free = start_free + total_bytes;
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return result;
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}
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else if (bytes_left >= bytes){//内存池剩余空间不能完全满足需要，但足够供应一个或以上的区块
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nobjs = bytes_left / bytes;
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total_bytes = nobjs * bytes;
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result = start_free;
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start_free += total_bytes;
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return result;
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}
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else{//内存池剩余空间连一个区块的大小都无法提供
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size_t bytes_to_get = 2 * total_bytes + ROUND_UP(heap_size >> 4);
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if (bytes_left > 0){
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obj **my_free_list = free_list + FREELIST_INDEX(bytes_left);
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((obj *)start_free)->next = *my_free_list;
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*my_free_list = (obj *)start_free;
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}
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start_free = (char *)malloc(bytes_to_get);
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if (!start_free){
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obj **my_free_list = 0, *p = 0;
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for (int i = 0; i <= EMaxBytes::MAXBYTES; i += EAlign::ALIGN){
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my_free_list = free_list + FREELIST_INDEX(i);
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p = *my_free_list;
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if (p != 0){
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*my_free_list = p->next;
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start_free = (char *)p;
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end_free = start_free + i;
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return chunk_alloc(bytes, nobjs);
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}
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}
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end_free = 0;
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}
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heap_size += bytes_to_get;
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end_free = start_free + bytes_to_get;
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return chunk_alloc(bytes, nobjs);
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}
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}
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} |