《简单说说何为之STL的内存管理Allocator》-美文赏析-写作素材-范文大全-范文网

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简单说说何为之STL的内存管理Allocator

范文

简单说说何为之STL的内存管理Allocator

1. 概述

STL Allocator是STL的内存管理器，也是最低调的部分之一，你可能使用了3年stl，但却不知其为何物。

STL标准如下介绍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.

将其描述为空间配置器，理由是allocator可以将其它存储介质（例如硬盘）做为stl 容器的存储空间。由于内存是allocator管理的主要部分，因此，本文以STL内存管理为出发点介绍allocator。

Allocator就在我们身边，通常使用STL的方式：

#include

std::vectorArray(100);

本质上，调用的是：

#include

std::vectorArray(100);

std::allocator就是一个简单的Allocator

2. 使用

针对不同的应用场合，STL中实现了不同的'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，在多线程环境下，可以使用：

复制代码代码如下:

#include

std::vectorArray(100);

3.一个简单的Allocator实现

我们可以实现自己的allocator

复制代码代码如下:

#include

template

class my_allocator : public std::allocator

{

public:

typedef std::allocatorbase_type;

// 必须要重新定义

template

struct rebind

{

typedef my_allocatorother;

};

// 内存的分配与释放可以实现为自定义的算法

pointer allocate(size_type count)

{

return (base_type::allocate(count));

}

void deallocate(pointer ptr, size_type count)

{

base_type::deallocate(ptr, count);

}

// 构造函数

my_allocator()

{}

my_allocator(my_allocatorconst&)

{}

my_allocator& operator=(my_allocatorconst&)

{

return (*this);

}

template

my_allocator(my_allocatorconst&)

{}

template

my_allocator& operator=(my_allocatorconst&)

{

return (*this); }

};

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