簡單說說何為之STL的內(nèi)存管理Allocator
1. 概述
STL Allocator是STL的內(nèi)存管理器，也是最低調(diào)的部分之一，你可能使用了3年stl，但卻不知其為何物。
STL標(biāo)準(zhǔn)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(chǔ)介質(zhì)（例如硬盤）做為stl 容器的存儲(chǔ)空間。由于內(nèi)存是allocator管理的主要部分，因此，本文以STL內(nèi)存管理為出發(fā)點(diǎn)介紹allocator。
Allocator就在我們身邊，通常使用STL的方式：
#include
std::vectorArray(100);
本質(zhì)上，調(diào)用的是：
#include
std::vectorArray(100);
std::allocator就是一個(gè)簡單的Allocator
2. 使用
針對(duì)不同的應(yīng)用場合，STL中實(shí)現(xiàn)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(huán)境下，可以使用：
復(fù)制代碼 代碼如下:
#include
#include
std::vector
3.一個(gè)簡單的Allocator實(shí)現(xiàn)
我們可以實(shí)現(xiàn)自己的allocator
復(fù)制代碼 代碼如下:
#include
template
class my_allocator : public std::allocator
{
public:
typedef std::allocatorbase_type;
// 必須要重新定義
template
struct rebind
{
typedef my_allocatorother;
};
// 內(nèi)存的分配與釋放可以實(shí)現(xiàn)為自定義的算法
pointer allocate(size_type count)
{
return (base_type::allocate(count));
}
void deallocate(pointer ptr, size_type count)
{
base_type::deallocate(ptr, count);
}
// 構(gòu)造函數(shù)
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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