簡單說說何為之STL的內存管理Allocator

2021-06-12 說說

　　1. 概述

　　STL Allocator是STL的內存管理器，也是最低調的.部分之一，你可能使用了3年stl，但卻不知其為何物。

　　STL標準如下介紹Allocator

　　the STL includes some low-level mechanisms for allocating and deallocating memory. Allocators are very specialized, and you can safely ignore them for almost all purposes. Allocators encapsulate allocation and deallocation of memory. They provide a low-level interface that permits efficient allocation of many small objects; different allocator types represent different schemes for memory management.

　　將其描述為空間配置器，理由是allocator可以將其它存儲介質（例如硬盤）做為stl 容器的存儲空間。由于內存是allocator管理的主要部分，因此，本文以STL內存管理為出發點介紹allocator。

　　Allocator就在我們身邊，通常使用STL的方式：

　　#include

　　std::vectorArray(100);

　　本質上，調用的是：

　　#include

　　std::vectorArray(100);

　　std::allocator就是一個簡單的Allocator

　　2. 使用

　　針對不同的應用場合，STL中實現了不同的Allocator，如下（gcc-3.4：http://www.cs.huji.ac.il/~etsman/Docs/gcc-3.4-base/libstdc++/html/20_util/allocator.html）:

　　__gnu_cxx::new_allocatorSimply wraps ::operator new and ::operator .

　　__gnu_cxx::malloc_allocatorSimply wraps malloc and free. There is also a hook for an out-of-memory handler

　　__gnu_cxx::debug_allocatorA wrapper around an arbitrary allocator A. It passes on slightly increased size requests to A, and uses the extra memory to store size information.

　　__gnu_cxx::__pool_allocA high-performance, single pool allocator. The reusable memory is shared among identical instantiations of this type.

　　__gnu_cxx::__mt_allocA high-performance fixed-size allocatorthat was initially developed specifically to suit the needs of multi threaded applications

　　__gnu_cxx::bitmap_allocato A high-performance allocator that uses a bit-map to keep track of the used and unused memory locations

　　例如，在多線程環境下，可以使用：

　　復制代碼代碼如下:

　　#include

　　std::vectorArray(100);

　　3.一個簡單的Allocator實現

　　我們可以實現自己的allocator

　　復制代碼代碼如下:

　　#include

　　template

　　class my_allocator : public std::allocator

　　{