stl_alloc.h

#ifndef __SGI_STL_INTERNAL_ALLOC_H
#define __SGI_STL_INTERNAL_ALLOC_H

#ifdef __SUNPRO_CC
#  define __PRIVATE public
   // Extra access restrictions prevent us from really making some things
   // private.
#else
#  define __PRIVATE private
#endif

#ifdef __STL_STATIC_TEMPLATE_MEMBER_BUG
#  define __USE_MALLOC
#endif


// This implements some standard node allocators.  These are
// NOT the same as the allocators in the C++ draft standard or in
// in the original STL.  They do not encapsulate different pointer
// types; indeed we assume that there is only one pointer type.
// The allocation primitives are intended to allocate individual objects,
// not larger arenas as with the original STL allocators.

#ifndef __THROW_BAD_ALLOC
#  if defined(__STL_NO_BAD_ALLOC) || !defined(__STL_USE_EXCEPTIONS)
#    include <stdio.h>
#    include <stdlib.h>
#    define __THROW_BAD_ALLOC fprintf(stderr, "out of memory\n"); exit(1)
#  else /* Standard conforming out-of-memory handling */
#    include <new>
#    define __THROW_BAD_ALLOC throw std::bad_alloc()
#  endif
#endif

#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#ifndef __RESTRICT
#  define __RESTRICT
#endif

#ifdef __STL_THREADS
# include <stl_threads.h>
# define __NODE_ALLOCATOR_THREADS true
# ifdef __STL_SGI_THREADS
  // We test whether threads are in use before locking.
  // Perhaps this should be moved into stl_threads.h, but that
  // probably makes it harder to avoid the procedure call when
  // it isn't needed.
    extern "C" {
      extern int __us_rsthread_malloc;
    }
    // The above is copied from malloc.h.  Including <malloc.h>
    // would be cleaner but fails with certain levels of standard
    // conformance.
#   define __NODE_ALLOCATOR_LOCK if (threads && __us_rsthread_malloc) \
                { _S_node_allocator_lock._M_acquire_lock(); }
#   define __NODE_ALLOCATOR_UNLOCK if (threads && __us_rsthread_malloc) \
                { _S_node_allocator_lock._M_release_lock(); }
# else /* !__STL_SGI_THREADS */
#   define __NODE_ALLOCATOR_LOCK \
        { if (threads) _S_node_allocator_lock._M_acquire_lock(); }
#   define __NODE_ALLOCATOR_UNLOCK \
        { if (threads) _S_node_allocator_lock._M_release_lock(); }
# endif
#else
//  Thread-unsafe
#   define __NODE_ALLOCATOR_LOCK
#   define __NODE_ALLOCATOR_UNLOCK
#   define __NODE_ALLOCATOR_THREADS false
#endif

__STL_BEGIN_NAMESPACE

#if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)
#pragma set woff 1174
#endif

// Malloc-based allocator.  Typically slower than default alloc below.
// Typically thread-safe and more storage efficient.
#ifdef __STL_STATIC_TEMPLATE_MEMBER_BUG
# ifdef __DECLARE_GLOBALS_HERE
    void (* __malloc_alloc_oom_handler)() = 0;
    // g++ 2.7.2 does not handle static template data members.
# else
    extern void (* __malloc_alloc_oom_handler)();
# endif
#endif
//第一级配置

template <int __inst>
class __malloc_alloc_template {

private:

//oom：out of memory三个处理函数,因为是以malloc(),free(),realloc()等C函数执行实际内存分配释放，所以不能直接使用C++ new-handler机制(set_new_handler())，因为不是用::operator new来分配。
//如果未设定处理函数，则抛出std::bad_alloc

static void* _S_oom_malloc(size_t);
  static void* _S_oom_realloc(void*, size_t);

#ifndef __STL_STATIC_TEMPLATE_MEMBER_BUG
  static void (* __malloc_alloc_oom_handler)();
#endif

public:

  static void* allocate(size_t __n)
  {
    void* __result = malloc(__n);
    if (0 == __result) __result = _S_oom_malloc(__n);
    return __result;
  }

  static void deallocate(void* __p, size_t /* __n */)
  {
    free(__p);
  }

  static void* reallocate(void* __p, size_t /* old_sz */, size_t __new_sz)
  {
    void* __result = realloc(__p, __new_sz);
    if (0 == __result) __result = _S_oom_realloc(__p, __new_sz);
    return __result;
  }

  static void (* __set_malloc_handler(void (*__f)()))()
  {
    void (* __old)() = __malloc_alloc_oom_handler;
    __malloc_alloc_oom_handler = __f;
    return(__old);
  }

};

// malloc_alloc out-of-memory handling

#ifndef __STL_STATIC_TEMPLATE_MEMBER_BUG
template <int __inst>
void (* __malloc_alloc_template<__inst>::__malloc_alloc_oom_handler)() = 0;
#endif

template <int __inst>
void*
__malloc_alloc_template<__inst>::_S_oom_malloc(size_t __n)
{
    void (* __my_malloc_handler)();
    void* __result;

    for (;;) {
        __my_malloc_handler = __malloc_alloc_oom_handler;
        if (0 == __my_malloc_handler) { __THROW_BAD_ALLOC; }
        (*__my_malloc_handler)();
        __result = malloc(__n);
        if (__result) return(__result);
    }
}

template <int __inst>
void* __malloc_alloc_template<__inst>::_S_oom_realloc(void* __p, size_t __n)
{
    void (* __my_malloc_handler)();
    void* __result;

    for (;;) {
        __my_malloc_handler = __malloc_alloc_oom_handler;
        if (0 == __my_malloc_handler) { __THROW_BAD_ALLOC; }
        (*__my_malloc_handler)();
        __result = realloc(__p, __n);
        if (__result) return(__result);
    }
}

typedef __malloc_alloc_template<0> malloc_alloc;

//   allocate->_S_oom_malloc->__malloc_alloc_oom_handler
//   reallocate->_S_oom_realloc->__malloc_alloc_oom_handler
//--------------------------------------------------------------------------------------------------

//外面再多一层封装，使Alloc具备标准接口

template<class _Tp, class _Alloc>
class simple_alloc {

public:
    static _Tp* allocate(size_t __n)
      { return 0 == __n ? 0 : (_Tp*) _Alloc::allocate(__n * sizeof (_Tp)); }
    static _Tp* allocate(void)
      { return (_Tp*) _Alloc::allocate(sizeof (_Tp)); }
    static void deallocate(_Tp* __p, size_t __n)
      { if (0 != __n) _Alloc::deallocate(__p, __n * sizeof (_Tp)); }
    static void deallocate(_Tp* __p)
      { _Alloc::deallocate(__p, sizeof (_Tp)); }
};

// Allocator adaptor to check size arguments for debugging.
// Reports errors using assert.  Checking can be disabled with
// NDEBUG, but it's far better to just use the underlying allocator
// instead when no checking is desired.
// There is some evidence that this can confuse Purify.

//带有debug功能的allocator适配器
//新分配地址的头部额外多增加8个字节，用来存放新分配空间的大小，dealloate和reallocate会验证传入的释放空间大小是否等于待释放地址头部8个字节存放的空间大小，

//如果不相等，则abort。

template <class _Alloc>
class debug_alloc {

private:

  enum {_S_extra = 8};   //存储分配空间大小所需的位数

public:

  static void* allocate(size_t __n)
  {
    char* __result = (char*)_Alloc::allocate(__n + (int) _S_extra);
    *(size_t*)__result = __n;
    return __result + (int) _S_extra;
  }

  static void deallocate(void* __p, size_t __n)
  {
    char* __real_p = (char*)__p - (int) _S_extra;
    assert(*(size_t*)__real_p == __n);
    _Alloc::deallocate(__real_p, __n + (int) _S_extra);
  }

  static void* reallocate(void* __p, size_t __old_sz, size_t __new_sz)
  {
    char* __real_p = (char*)__p - (int) _S_extra;
    assert(*(size_t*)__real_p == __old_sz);
    char* __result = (char*)
      _Alloc::reallocate(__real_p, __old_sz + (int) _S_extra,
                                   __new_sz + (int) _S_extra);
    *(size_t*)__result = __new_sz;
    return __result + (int) _S_extra;
  }

};


# ifdef __USE_MALLOC

typedef malloc_alloc alloc;
typedef malloc_alloc single_client_alloc;

# else

//  Sun C++ compiler需要在类外定义这些枚举  

#if defined(__SUNPRO_CC) || defined(__GNUC__)
// breaks if we make these template class members:
  enum {_ALIGN = 8};       //小型区块的上调边界
  enum {_MAX_BYTES = 128}; //小型区块的上限
  enum {_NFREELISTS = 16}; // _MAX_BYTES/_ALIGN   free-lists 个数
#endif

//第二级配置器
// 默认的node allocator  
// 如果有合适的编译器, 速度上与原始的STL class-specific allocators大致等价 
// 但是具有产生更少内存碎片的优点  
// Default_alloc_template参数是用于实验性质的, 在未来可能会消失 
// 客户只能在当下使用alloc  
//  
// 重要的实现属性:  
// 1. 如果客户请求一个size > __MAX_BYTE的对象, 则直接使用malloc()分配 
// 2. 对于其它情况下, 我们将请求对象的大小按照内存对齐向上舍入ROUND_UP(requested_size)   
//    Thus the client has enough size information that we can return the object to the proper free list  
//    without permanently losing part of the object.  
//  
  
//  第一个模板参数指定是否有多于一个线程使用本allocator  // 在一个default_alloc实例中分配对象, 在另一个deallocate实例中释放对象, 是安全的 
// 这有效的转换其所有权到另一个对象 
// 这可能导致对我们引用的区域产生不良影响 
// 第二个模板参数仅仅用于创建多个default_alloc实例 
// 不同容器使用不同allocator实例创建的node拥有不同类型, 这限制了此方法的通用性 
 
 //allocate()大于128调用第一级适配器，否则在free-list中找，没找到调用refill()从内存池中填充到free-list
 //refill()调用chunk_alloc从内存池中取空间给free-list使用，然后调整free-list链表
 //内存池中有20个或有但不满20个，则调整内存池的起始位置，返回内存地址，
 //内存池中一个也不能满足了，则如果内存池中还要剩余的一些零头，则编入free-list，然后尝试从heap分配40+n块空间到内存池。分配成功后递归调用返回空间地址
//heap上也没有空间分配了，则先检查free-list中有没比所需块大一点的空间，有则分配给他，堆上也没有则调用第一级配置器，改善或排除异常。

template <bool threads, int inst>
class __default_alloc_template {

private:
  // Really we should use static const int x = N
  // instead of enum { x = N }, but few compilers accept the former.
#if ! (defined(__SUNPRO_CC) || defined(__GNUC__))
    enum {_ALIGN = 8};
    enum {_MAX_BYTES = 128};
    enum {_NFREELISTS = 16}; // _MAX_BYTES/_ALIGN
# endif
  static size_t
  _S_round_up(size_t __bytes)          //向上调整至的倍数
    { return (((__bytes) + (size_t) _ALIGN-1) & ~((size_t) _ALIGN - 1)); }

__PRIVATE:
  union _Obj {
        union _Obj* _M_free_list_link;
        char _M_client_data[1];    /* The client sees this.        */  //柔性数组
  };

/*
int main()
{
    _Obj* test = (_Obj*)"12345678";
    cout << sizeof(_Obj) <<endl;       //4
    cout<<test->_M_client_data<<endl;  //"12345678"
    return 0;
}
*/
private:
# if defined(__SUNPRO_CC) || defined(__GNUC__) || defined(__HP_aCC)
    static _Obj* __STL_VOLATILE _S_free_list[];           ////volatile关键字，优化器在用到这个变量时必须每次都小心地重新读取这个变量的值，而不是使用保存在寄存器里的备份。
        // Specifying a size results in duplicate def for 4.1
# else
    static _Obj* __STL_VOLATILE _S_free_list[_NFREELISTS]; 
# endif
  static  size_t _S_freelist_index(size_t __bytes) { //根据区块大小，使用第n号free-list
        return (((__bytes) + (size_t)_ALIGN-1)/(size_t)_ALIGN - 1);//向上取，再减1
  }

 // // 返回一个大小为n的对象，并可能加入大小为n的其他区块到free-list
  static void* _S_refill(size_t __n);

 //配置一大块空间，可容纳nobjs个大小为size的区块
 //如果配置nobjs个区块有所不便,nobjs可能会减小

  static char* _S_chunk_alloc(size_t __size, int& __nobjs);

  // Chunk allocation state.
  static char* _S_start_free;  // 内存池起始点
  static char* _S_end_free;    // 内存池结束点
  static size_t _S_heap_size;  // 已经在堆上分配的空间大小 

# ifdef __STL_THREADS
    static _STL_mutex_lock _S_node_allocator_lock;
# endif

    // It would be nice to use _STL_auto_lock here.  But we
    // don't need the NULL check.  And we do need a test whether
    // threads have actually been started.
    class _Lock;
    friend class _Lock;
    class _Lock {
        public:
            _Lock() { __NODE_ALLOCATOR_LOCK; }
            ~_Lock() { __NODE_ALLOCATOR_UNLOCK; }
    };

public:

  /* __n must be > 0      */
  static void* allocate(size_t __n)
  {
    void* __ret = 0;
    // 如果待分配对象大于__MAX_BYTES, 使用一级配置器分配  
    if (__n > (size_t) _MAX_BYTES) {
      __ret = malloc_alloc::allocate(__n);
    }
    else {
      _Obj* __STL_VOLATILE* __my_free_list
          = _S_free_list + _S_freelist_index(__n);
      // Acquire the lock here with a constructor call.
      // This ensures that it is released in exit or during stack
      // unwinding.
#     ifndef _NOTHREADS
      /*REFERENCED*/
      _Lock __lock_instance;
#     endif
      _Obj* __RESTRICT __result = *__my_free_list;
      //没有可用区块，就填充空间

      if (__result == 0)
        __ret = _S_refill(_S_round_up(__n));
      else {
        *__my_free_list = __result -> _M_free_list_link;
        __ret = __result;
      }
    }

    return __ret;
  };

  /* __p may not be 0 */
  static void deallocate(void* __p, size_t __n)
  {
    if (__n > (size_t) _MAX_BYTES)
      malloc_alloc::deallocate(__p, __n);
    else {
      _Obj* __STL_VOLATILE*  __my_free_list
          = _S_free_list + _S_freelist_index(__n);
      _Obj* __q = (_Obj*)__p;

      // acquire lock
#       ifndef _NOTHREADS
      /*REFERENCED*/
      _Lock __lock_instance;
#       endif /* _NOTHREADS */
      __q -> _M_free_list_link = *__my_free_list;
      *__my_free_list = __q;
      // lock is released here
    }
  }

  static void* reallocate(void* __p, size_t __old_sz, size_t __new_sz);

} ;

typedef __default_alloc_template<__NODE_ALLOCATOR_THREADS, 0> alloc;
typedef __default_alloc_template<false, 0> single_client_alloc;

//任意两个allocator都是可互换的；如果a1和a2的类型都是allocator，我们可以自由地通过a1来allocate()内存然后通过 a2来deallocate()它。
//我们因此定义一个比较操作以表明所有allocator对象是等价的

template <bool __threads, int __inst>
inline bool operator==(const __default_alloc_template<__threads, __inst>&,
                       const __default_alloc_template<__threads, __inst>&)
{
  return true;
}

# ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER
template <bool __threads, int __inst>
inline bool operator!=(const __default_alloc_template<__threads, __inst>&,
                       const __default_alloc_template<__threads, __inst>&)
{
  return false;
}
# endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */


// 每次分配一大块内存, 防止多次分配小内存块带来的内存碎片  // 进行分配操作时, 根据具体环境决定是否加锁 
// 我们假定要分配的内存满足内存对齐要求 
template <bool __threads, int __inst>
char*
__default_alloc_template<__threads, __inst>::_S_chunk_alloc(size_t __size, 
                                                            int& __nobjs)
{
    char* __result;
    size_t __total_bytes = __size * __nobjs;
    size_t __bytes_left = _S_end_free - _S_start_free;  // 计算内存池剩余容量 
    
    //  如果内存池中剩余内存>=需要分配的内内存, 返回start_free指向的内存块,  
    // 并且重新设置内存池起始点 
    if (__bytes_left >= __total_bytes) {
        __result = _S_start_free;
        _S_start_free += __total_bytes;
        return(__result);
    } 
    // 如果内存吃中剩余的容量不够分配, 但是能至少分配一个节点时,   
    // 返回所能分配的最多的节点, 返回start_free指向的内存块 
    // 并且重新设置内存池起始点 
    else if (__bytes_left >= __size) {
        __nobjs = (int)(__bytes_left/__size);
        __total_bytes = __size * __nobjs;
        __result = _S_start_free;
        _S_start_free += __total_bytes;
        return(__result);
    } 
    //  内存池剩余内存连一个节点也不够分配  
    else {
        size_t __bytes_to_get = 
      2 * __total_bytes + _S_round_up(_S_heap_size >> 4);
        // Try to make use of the left-over piece.
        // 将剩余的内存分配给指定的free_list[FREELIST_INDEX(bytes_left)]  if (__bytes_left > 0) {
            _Obj* __STL_VOLATILE* __my_free_list =
                        _S_free_list + _S_freelist_index(__bytes_left);

            ((_Obj*)_S_start_free) -> _M_free_list_link = *__my_free_list;
            *__my_free_list = (_Obj*)_S_start_free;
        }
        //配置heap空间，补充内存池
        _S_start_free = (char*)malloc(__bytes_to_get);
        if (0 == _S_start_free) {  //malloc()失败
            size_t __i;
            _Obj* __STL_VOLATILE* __my_free_list;
        _Obj* __p;
            
           //尝试检查我们手上拥有的东西，这不会造成伤害。我们不打算尝试配置较小的区块。
           //因为那在多进程机器上容易造成灾难
           
           //以下搜寻未使用的比size大的free-list区块
            for (__i = __size;
                 __i <= (size_t) _MAX_BYTES;
                 __i += (size_t) _ALIGN) {
                __my_free_list = _S_free_list + _S_freelist_index(__i);
                __p = *__my_free_list;
                if (0 != __p) { //有未用区块则调整free-list以释出未用区块
                    *__my_free_list = __p -> _M_free_list_link;
                    _S_start_free = (char*)__p;
                    _S_end_free = _S_start_free + __i;
                    //递归调用自己，以修正nobjs
                    return(_S_chunk_alloc(__size, __nobjs));

                    //注意，残余零头终将被编入适当的free-list中备用
                }
            }
             _S_end_free = 0;    // In case of exception.
            _S_start_free = (char*)malloc_alloc::allocate(__bytes_to_get); 
            //调用第一级配置器，看看out-of-memory机制能否尽力，或抛出异常。
        }
        _S_heap_size += __bytes_to_get;
        _S_end_free = _S_start_free + __bytes_to_get;
        return(_S_chunk_alloc(__size, __nobjs));
    }
}

//  返回一个大小为n的对象, 并且加入到free_list[FREELIST_INDEX(n)]  // 进行分配操作时, 根据具体环境决定是否加锁  // 我们假定要分配的内存满足内存对齐要求
template <bool __threads, int __inst>
void*
__default_alloc_template<__threads, __inst>::_S_refill(size_t __n)
{
    int __nobjs = 20;
    char* __chunk = _S_chunk_alloc(__n, __nobjs);
    _Obj* __STL_VOLATILE* __my_free_list;
    _Obj* __result;
    _Obj* __current_obj;
    _Obj* __next_obj;
    int __i;

    if (1 == __nobjs) return(__chunk);
    __my_free_list = _S_free_list + _S_freelist_index(__n);

    /* Build free list in chunk */
      __result = (_Obj*)__chunk;
      *__my_free_list = __next_obj = (_Obj*)(__chunk + __n);
      for (__i = 1; ; __i++) {
        __current_obj = __next_obj;
        __next_obj = (_Obj*)((char*)__next_obj + __n);
        if (__nobjs - 1 == __i) {
            __current_obj -> _M_free_list_link = 0;
            break;
        } else {
            __current_obj -> _M_free_list_link = __next_obj;
        }
      }
    return(__result);
}

template <bool threads, int inst>
void*
__default_alloc_template<threads, inst>::reallocate(void* __p,
                                                    size_t __old_sz,
                                                    size_t __new_sz)
{
    void* __result;
    size_t __copy_sz;

    if (__old_sz > (size_t) _MAX_BYTES && __new_sz > (size_t) _MAX_BYTES) {
        return(realloc(__p, __new_sz));
    }
    if (_S_round_up(__old_sz) == _S_round_up(__new_sz)) return(__p);
    __result = allocate(__new_sz);
    __copy_sz = __new_sz > __old_sz? __old_sz : __new_sz;
    memcpy(__result, __p, __copy_sz);
    deallocate(__p, __old_sz);
    return(__result);
}

#ifdef __STL_THREADS
    template <bool __threads, int __inst>
    _STL_mutex_lock
    __default_alloc_template<__threads, __inst>::_S_node_allocator_lock
        __STL_MUTEX_INITIALIZER;
#endif


template <bool __threads, int __inst>
char* __default_alloc_template<__threads, __inst>::_S_start_free = 0;

template <bool __threads, int __inst>
char* __default_alloc_template<__threads, __inst>::_S_end_free = 0;

template <bool __threads, int __inst>
size_t __default_alloc_template<__threads, __inst>::_S_heap_size = 0;

template <bool __threads, int __inst>
typename __default_alloc_template<__threads, __inst>::_Obj* __STL_VOLATILE
__default_alloc_template<__threads, __inst> ::_S_free_list[
# if defined(__SUNPRO_CC) || defined(__GNUC__) || defined(__HP_aCC)
    _NFREELISTS
# else
    __default_alloc_template<__threads, __inst>::_NFREELISTS
# endif
] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, };
// The 16 zeros are necessary to make version 4.1 of the SunPro
// compiler happy.  Otherwise it appears to allocate too little
// space for the array.

#endif /* ! __USE_MALLOC */

// This implements allocators as specified in the C++ standard.  
//
// Note that standard-conforming allocators use many language features
// that are not yet widely implemented.  In particular, they rely on
// member templates, partial specialization, partial ordering of function
// templates, the typename keyword, and the use of the template keyword
// to refer to a template member of a dependent type.

#ifdef __STL_USE_STD_ALLOCATORS

template <class _Tp>
class allocator {
  typedef alloc _Alloc;          // The underlying allocator.
public:
  typedef size_t     size_type;
  typedef ptrdiff_t  difference_type;
  typedef _Tp*       pointer;
  typedef const _Tp* const_pointer;
  typedef _Tp&       reference;
  typedef const _Tp& const_reference;
  typedef _Tp        value_type;

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

  allocator() __STL_NOTHROW {}
  allocator(const allocator&) __STL_NOTHROW {}
  template <class _Tp1> allocator(const allocator<_Tp1>&) __STL_NOTHROW {}
  ~allocator() __STL_NOTHROW {}

  pointer address(reference __x) const { return &__x; }
  const_pointer address(const_reference __x) const { return &__x; }

  // __n is permitted to be 0.  The C++ standard says nothing about what
  // the return value is when __n == 0.
  _Tp* allocate(size_type __n, const void* = 0) {
    return __n != 0 ? static_cast<_Tp*>(_Alloc::allocate(__n * sizeof(_Tp))) 
                    : 0;
  }

  // __p is not permitted to be a null pointer.
  void deallocate(pointer __p, size_type __n)
    { _Alloc::deallocate(__p, __n * sizeof(_Tp)); }

  size_type max_size() const __STL_NOTHROW 
    { return size_t(-1) / sizeof(_Tp); }

  void construct(pointer __p, const _Tp& __val) { new(__p) _Tp(__val); }
  void destroy(pointer __p) { __p->~_Tp(); }
};

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


template <class _T1, class _T2>
inline bool operator==(const allocator<_T1>&, const allocator<_T2>&) 
{
  return true;
}

template <class _T1, class _T2>
inline bool operator!=(const allocator<_T1>&, const allocator<_T2>&)
{
  return false;
}

// Allocator adaptor to turn an SGI-style allocator (e.g. alloc, malloc_alloc)
// into a standard-conforming allocator.   Note that this adaptor does
// *not* assume that all objects of the underlying alloc class are
// identical, nor does it assume that all of the underlying alloc's
// member functions are static member functions.  Note, also, that 
// __allocator<_Tp, alloc> is essentially the same thing as allocator<_Tp>.

template <class _Tp, class _Alloc>
struct __allocator {
  _Alloc __underlying_alloc;

  typedef size_t    size_type;
  typedef ptrdiff_t difference_type;
  typedef _Tp*       pointer;
  typedef const _Tp* const_pointer;
  typedef _Tp&       reference;
  typedef const _Tp& const_reference;
  typedef _Tp        value_type;

  template <class _Tp1> struct rebind {
    typedef __allocator<_Tp1, _Alloc> other;
  };

  __allocator() __STL_NOTHROW {}
  __allocator(const __allocator& __a) __STL_NOTHROW
    : __underlying_alloc(__a.__underlying_alloc) {}
  template <class _Tp1> 
  __allocator(const __allocator<_Tp1, _Alloc>& __a) __STL_NOTHROW
    : __underlying_alloc(__a.__underlying_alloc) {}
  ~__allocator() __STL_NOTHROW {}

  pointer address(reference __x) const { return &__x; }
  const_pointer address(const_reference __x) const { return &__x; }

  // __n is permitted to be 0.
  _Tp* allocate(size_type __n, const void* = 0) {
    return __n != 0 
        ? static_cast<_Tp*>(__underlying_alloc.allocate(__n * sizeof(_Tp))) 
        : 0;
  }

  // __p is not permitted to be a null pointer.
  void deallocate(pointer __p, size_type __n)
    { __underlying_alloc.deallocate(__p, __n * sizeof(_Tp)); }

  size_type max_size() const __STL_NOTHROW 
    { return size_t(-1) / sizeof(_Tp); }

  void construct(pointer __p, const _Tp& __val) { new(__p) _Tp(__val); }
  void destroy(pointer __p) { __p->~_Tp(); }
};

template <class _Alloc>
class __allocator<void, _Alloc> {
  typedef size_t      size_type;
  typedef ptrdiff_t   difference_type;
  typedef void*       pointer;
  typedef const void* const_pointer;
  typedef void        value_type;

  template <class _Tp1> struct rebind {
    typedef __allocator<_Tp1, _Alloc> other;
  };
};

template <class _Tp, class _Alloc>
inline bool operator==(const __allocator<_Tp, _Alloc>& __a1,
                       const __allocator<_Tp, _Alloc>& __a2)
{
  return __a1.__underlying_alloc == __a2.__underlying_alloc;
}

#ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER
template <class _Tp, class _Alloc>
inline bool operator!=(const __allocator<_Tp, _Alloc>& __a1,
                       const __allocator<_Tp, _Alloc>& __a2)
{
  return __a1.__underlying_alloc != __a2.__underlying_alloc;
}
#endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */

// Comparison operators for all of the predifined SGI-style allocators.
// This ensures that __allocator<malloc_alloc> (for example) will
// work correctly.

template <int inst>
inline bool operator==(const __malloc_alloc_template<inst>&,
                       const __malloc_alloc_template<inst>&)
{
  return true;
}

#ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER
template <int __inst>
inline bool operator!=(const __malloc_alloc_template<__inst>&,
                       const __malloc_alloc_template<__inst>&)
{
  return false;
}
#endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */


template <class _Alloc>
inline bool operator==(const debug_alloc<_Alloc>&,
                       const debug_alloc<_Alloc>&) {
  return true;
}

#ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER
template <class _Alloc>
inline bool operator!=(const debug_alloc<_Alloc>&,
                       const debug_alloc<_Alloc>&) {
  return false;
}
#endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */

// Another allocator adaptor: _Alloc_traits.  This serves two
// purposes.  First, make it possible to write containers that can use
// either SGI-style allocators or standard-conforming allocator.
// Second, provide a mechanism so that containers can query whether or
// not the allocator has distinct instances.  If not, the container
// can avoid wasting a word of memory to store an empty object.

// This adaptor uses partial specialization.  The general case of
// _Alloc_traits<_Tp, _Alloc> assumes that _Alloc is a
// standard-conforming allocator, possibly with non-equal instances
// and non-static members.  (It still behaves correctly even if _Alloc
// has static member and if all instances are equal.  Refinements
// affect performance, not correctness.)

// There are always two members: allocator_type, which is a standard-
// conforming allocator type for allocating objects of type _Tp, and
// _S_instanceless, a static const member of type bool.  If
// _S_instanceless is true, this means that there is no difference
// between any two instances of type allocator_type.  Furthermore, if
// _S_instanceless is true, then _Alloc_traits has one additional
// member: _Alloc_type.  This type encapsulates allocation and
// deallocation of objects of type _Tp through a static interface; it
// has two member functions, whose signatures are
//    static _Tp* allocate(size_t)
//    static void deallocate(_Tp*, size_t)

// The fully general version.
/*
另一个allocator适配器_Alloc_traits, 它有两个意图
  1.使容易既看使用sgi风格的allocator，也可以使用标准规格的allocator
  2.提供了一种机制:容器可以查询allocator是否拥有明确的实体，如果没有，容易可以避免浪费内存去存储空对象

这个适配器使用了偏特化。
_Alloc_traits<_Tp, _Alloc>假定_Alloc是一个服从标准的allocator，可能有不相等的实例和非静态成员。
(如果各实例相等或拥有静态成员，也表现正确。 优化影响执行效率，不影响正确性)

有两个成员
1. allocator_type 服从标准的分配_Tp类型对象的allocator类型
2. _S_instanceless一个static const bool成员
   如果为true，则表示任何两个allocator_type实例之间没有差别,同时,_Alloc_traits有额外的成员_Alloc_type
_Alloc_type通过一个静态接口封装了分配和回收_Tp类型对象，它有两个成员函数，原型为
 static _Tp* allocate(size_t)
 static void deallocate(_Tp*, size_t)
*/

//写自定义分配器的时候也是，必须重写rebind，且不能有非静态成员。并假定任何同类型的allocator相等，即_S_instanceless为true
template <class _Tp, class _Allocator>
struct _Alloc_traits
{
  static const bool _S_instanceless = false;
  typedef typename _Allocator::__STL_TEMPLATE rebind<_Tp>::other 
          allocator_type;
};

template <class _Tp, class _Allocator>
const bool _Alloc_traits<_Tp, _Allocator>::_S_instanceless;

// The version for the default allocator.
//给默认allocator的版本
template <class _Tp, class _Tp1>
struct _Alloc_traits<_Tp, allocator<_Tp1> >
{
  static const bool _S_instanceless = true;
  typedef simple_alloc<_Tp, alloc> _Alloc_type;
  typedef allocator<_Tp> allocator_type;
};

// Versions for the predefined SGI-style allocators.

template <class _Tp, int __inst>
struct _Alloc_traits<_Tp, __malloc_alloc_template<__inst> >
{
  static const bool _S_instanceless = true;
  typedef simple_alloc<_Tp, __malloc_alloc_template<__inst> > _Alloc_type;
  typedef __allocator<_Tp, __malloc_alloc_template<__inst> > allocator_type;
};

template <class _Tp, bool __threads, int __inst>
struct _Alloc_traits<_Tp, __default_alloc_template<__threads, __inst> >
{
  static const bool _S_instanceless = true;
  typedef simple_alloc<_Tp, __default_alloc_template<__threads, __inst> > 
          _Alloc_type;
  typedef __allocator<_Tp, __default_alloc_template<__threads, __inst> > 
          allocator_type;
};

template <class _Tp, class _Alloc>
struct _Alloc_traits<_Tp, debug_alloc<_Alloc> >
{
  static const bool _S_instanceless = true;
  typedef simple_alloc<_Tp, debug_alloc<_Alloc> > _Alloc_type;
  typedef __allocator<_Tp, debug_alloc<_Alloc> > allocator_type;
};

// Versions for the __allocator adaptor used with the predefined
// SGI-style allocators.

template <class _Tp, class _Tp1, int __inst>
struct _Alloc_traits<_Tp, 
                     __allocator<_Tp1, __malloc_alloc_template<__inst> > >
{
  static const bool _S_instanceless = true;
  typedef simple_alloc<_Tp, __malloc_alloc_template<__inst> > _Alloc_type;
  typedef __allocator<_Tp, __malloc_alloc_template<__inst> > allocator_type;
};

template <class _Tp, class _Tp1, bool __thr, int __inst>
struct _Alloc_traits<_Tp, 
                      __allocator<_Tp1, 
                                  __default_alloc_template<__thr, __inst> > >
{
  static const bool _S_instanceless = true;
  typedef simple_alloc<_Tp, __default_alloc_template<__thr,__inst> > 
          _Alloc_type;
  typedef __allocator<_Tp, __default_alloc_template<__thr,__inst> > 
          allocator_type;
};

template <class _Tp, class _Tp1, class _Alloc>
struct _Alloc_traits<_Tp, __allocator<_Tp1, debug_alloc<_Alloc> > >
{
  static const bool _S_instanceless = true;
  typedef simple_alloc<_Tp, debug_alloc<_Alloc> > _Alloc_type;
  typedef __allocator<_Tp, debug_alloc<_Alloc> > allocator_type;
};


#endif /* __STL_USE_STD_ALLOCATORS */

#if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)
#pragma reset woff 1174
#endif

__STL_END_NAMESPACE

#undef __PRIVATE

#endif /* __SGI_STL_INTERNAL_ALLOC_H */

// Local Variables:
// mode:C++
// End: