Question

我正在使用自定义分配器来计算多个容器中的内存使用情况。目前我使用静态变量来计算内存使用量。如何在不必重写分配器以使用不同的静态变量的情况下将该帐户分隔到多个容器中？

static size_t allocated = 0;


   template <class T>
   class accounting_allocator {
     public:
       // type definitions
       typedef T        value_type;
       typedef T*       pointer;
       typedef const T* const_pointer;
       typedef T&       reference;
       typedef const T& const_reference;
       typedef std::size_t    size_type;
       typedef std::ptrdiff_t difference_type;
       //static size_t allocated;

       // rebind allocator to type U
       template <class U>
       struct rebind {
           typedef accounting_allocator<U> other;
       };

       // return address of values
       pointer address (reference value) const {
           return &value;
       }
       const_pointer address (const_reference value) const {
           return &value;
       }

       /* constructors and destructor
        * - nothing to do because the allocator has no state
        */
       accounting_allocator() throw() {
       }
       accounting_allocator(const accounting_allocator&) throw() {
       }
       template <class U>
         accounting_allocator (const accounting_allocator<U>&) throw() {
       }
       ~accounting_allocator() throw() {
       }

       // return maximum number of elements that can be allocated
       size_type max_size () const throw() {
        //  std::cout << "max_size()" << std::endl;
           return std::numeric_limits<std::size_t>::max() / sizeof(T);
       }

       // allocate but don't initialize num elements of type T
       pointer allocate (size_type num, const void* = 0) {
           // print message and allocate memory with global new
           //std::cerr << "allocate " << num << " element(s)" << " of size " << sizeof(T) << std::endl;
           pointer ret = (pointer)(::operator new(num*sizeof(T)));
           //std::cerr << " allocated at: " << (void*)ret << std::endl;
           allocated += num * sizeof(T);
            //std::cerr << "allocated: " << allocated/(1024*1024) << " MB" << endl;
           return ret;
       }

       // initialize elements of allocated storage p with value value
       void construct (pointer p, const T& value) {
           // initialize memory with placement new
           new((void*)p)T(value);
      }

       // destroy elements of initialized storage p
       void destroy (pointer p) {
           // destroy objects by calling their destructor
           p->~T();
       }

       // deallocate storage p of deleted elements
       void deallocate (pointer p, size_type num) {
           // print message and deallocate memory with global delete
#if 0
           std::cerr << "deallocate " << num << " element(s)"
                     << " of size " << sizeof(T)
                     << " at: " << (void*)p << std::endl;
#endif
           ::operator delete((void*)p);
           allocated -= num * sizeof(T);
       }
   };
  template<>
    class accounting_allocator<void>
    {
    public:
      typedef size_t      size_type;
      typedef ptrdiff_t   difference_type;
      typedef void*       pointer;
      typedef const void* const_pointer;
      typedef void        value_type;

      template<typename _Tp1>
        struct rebind
        { typedef allocator<_Tp1> other; };
    };


   // return that all specializations of this allocator are interchangeable
   template <class T1, class T2>
   bool operator== (const accounting_allocator<T1>&,
                    const accounting_allocator<T2>&) throw() {
       return true;
   }
   template <class T1, class T2>
   bool operator!= (const accounting_allocator<T1>&,
                    const accounting_allocator<T2>&) throw() {
       return false;
   }

Answer 1

如果您想为每个容器类型设置一个单独的计数器，您可以简单地将容器类型包含为模板参数并取消注释static size_t allocated，这样它就是一个静态成员变量。这样，将为每种类型的容器生成单独的计数器变量。

如果您说要为容器的每个实例设置单独的计数器，则需要使size_t allocated成为非静态成员变量。问题是，你还需要某种钩子，这样你就可以从每个容器外部访问分配计数器。 STL分配器设计使得这很难做到。一些STL容器有一个构造函数，允许您传递分配器的实例，但并非所有容器都支持此。在支持此功能的容器上，您可以在allocator类中包含对某些全局映射的引用，然后将分配器的实例传递给每个容器的构造函数。然后，当您调用accounting_allocator::allocate()时，分配器将记录它在全局映射中分配的字节数。但是，我无法看到如何轻松地将此信息与特定容器实例相关联，因为allocator对象不知道它属于哪个容器。

老实说，如果您只是收集调试信息，那么定义非静态size_t allocated可能更容易，并且accounting_allocator::allocate()只需将统计信息输出到文件或标准输出。或者，请考虑为您开发的平台使用内存分析器工具。

Answer 2

将“static size_t allocated”的声明放入类定义中。每个模板实例化都将在此模板的所有对象之间共享一个单独的计数器。

Answer 3

请参阅我的代码示例：

// uintptr_t represents an object address
// as a numerical value.
// you could use unsigned long insead if 
// sizeof(long) == sizeof(void*) on your system.
struct AllocCounter {
    static size_t *Register(uintptr_t uContainer)
    {
        // insert container address into map, and
        // return an associated allocation counter.
    }
    static bool Unregister(uintptr_t uContainer)
    {
        // remove container address and the 
        // associated allocation counter from the map
    }
    static void DebugCounter(void)
    {
        // statistic of all container objects.
    }
protected:
    static hash_map<uintptr_t, size_t> m_aCounter;
};

此外，您可以通过增强AllocCounter以上来将容器或对象类名称等与分配计数器相关联。

一个容器示例：

class Container 
{
public:
    Container(void) 
    {
        m_pAllocCounter = AllocCounter::Register((uintptr_t)this);
        ....
    }
    ~Container()
    {
        AllocCounter::Unregister((uintptr_t)this);
    }
    pointer ObjectAllocate(void)
    {
        pointer obj;
        *m_pAllocCounter += sizeof *obj;
        obj = new CObject;
        return obj;
    }
    void ObjectDealloc(pointer pObj)
    {
        *m_pAllocCounter -= sizeof *pObj;
        delete pObj;
    }
    ....

private:
    size_t *m_pAllocCounter;
    ....
};

自定义分配器的帐户内存使用情况

3 个答案: