简单说说STL的内存管理
简单说说STL的内存管理
发布时间:2016-12-28 来源:查字典编辑
摘要:1.概述STLAllocator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Al...

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.

<STL 源码剖析>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 <vector>

std::vector<int> Array(100);

本质上,调用的是:

#include <vector>

std::vector<int, std::allocator> Array(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_allocator<T> Simply wraps ::operator new and ::operator delete.

__gnu_cxx::malloc_allocator<T> Simply wraps malloc and free. There is also a hook for an out-of-memory handler

__gnu_cxx::debug_allocator<T> A 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_alloc<bool, int> A high-performance, single pool allocator. The reusable memory is shared among identical instantiations of this type.

__gnu_cxx::__mt_alloc<T> A 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 <vector>

#include <mt_allocator.h>

std::vector<int, __gnu_cxx::__mt_alloc<int>> Array(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 <memory>

template<class T>

class my_allocator : public std::allocator<T>

{

public:

typedef std::allocator<T> base_type;

// 必须要重新定义

template<class Other>

struct rebind

{

typedef my_allocator<Other> other;

};

// 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_allocator<T> const&)

{}

my_allocator<T>& operator=(my_allocator<T> const&)

{

return (*this);

}

template<class Other>

my_allocator(my_allocator<Other> const&)

{}

template<class Other>

my_allocator<T>& operator=(my_allocator<Other> const&)

{

return (*this); }

};

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