libstdc++-v3/include/bits/stl_alloc.h

// Allocators -*- C++ -*-

// Copyright (C) 2001 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

/*
 * Copyright (c) 1996-1997
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */

/** @file stl_alloc.h
 *  This is an internal header file, included by other library headers.
 *  You should not attempt to use it directly.
 */

#ifndef __GLIBCPP_INTERNAL_ALLOC_H
#define __GLIBCPP_INTERNAL_ALLOC_H

/**
 *  @defgroup Allocators Memory Allocators
 *  @maint
 *  stl_alloc.h implements some node allocators.  These are NOT the same as
 *  allocators in the C++ standard, nor in the original H-P STL.  They do not
 *  encapsulate different pointer types; we assume that there is only one
 *  pointer type.  The C++ standard allocators are intended to allocate
 *  individual objects, not pools or arenas.
 *
 *  In this file allocators are of two different styles:  "standard" and
 *  "SGI" (quotes included).  "Standard" allocators conform to 20.4.  "SGI"
 *  allocators differ in AT LEAST the following ways (add to this list as you
 *  discover them):
 *
 *   - "Standard" allocate() takes two parameters (n_count,hint=0) but "SGI"
 *     allocate() takes one paramter (n_size).
 *   - Likewise, "standard" deallocate()'s argument is a count, but in "SGI"
 *     is a byte size.
 *   - max_size(), construct(), and destroy() are missing in "SGI" allocators.
 *   - reallocate(p,oldsz,newsz) is added in "SGI", and behaves as
 *     if p=realloc(p,newsz).
 *
 *  "SGI" allocators may be wrapped in __allocator to convert the interface
 *  into a "standard" one.
 *  @endmaint
 *
 *  The canonical description of these classes is in docs/html/ext/howto.html
 *  or online at http://gcc.gnu.org/onlinedocs/libstdc++/ext/howto.html#3
*/


#include <bits/functexcept.h>   // for __throw_bad_alloc
#include <bits/std_cstddef.h>
#include <bits/std_cstdlib.h>
#include <bits/std_cstring.h>
#include <bits/std_cassert.h>
#include <bits/stl_threads.h>

namespace std
{
  /**
   *  @maint
   *  A new-based allocator, as required by the standard.  Allocation and
   *  deallocation forward to global new and delete.  "SGI" style, minus
   *  reallocate().
   *  @endmaint
   *  (See @link Allocators allocators info @endlink for more.)
  */
  class __new_alloc 
  {
  public:
    static void* 
    allocate(size_t __n)
    { return ::operator new(__n); }
    
    static void 
    deallocate(void* __p, size_t)
    { ::operator delete(__p); }
  };
  

  /**
   *  @maint
   *  A malloc-based allocator.  Typically slower than the
   *  __default_alloc_template (below).  Typically thread-safe and more
   *  storage efficient.  The template argument is unused and is only present
   *  to permit multiple instantiations (but see __default_alloc_template
   *  for caveats).  "SGI" style, plus __set_malloc_handler for OOM conditions.
   *  @endmaint
   *  (See @link Allocators allocators info @endlink for more.)
  */
  template <int __inst>
    class __malloc_alloc_template 
    {
    private:
      static void* _S_oom_malloc(size_t);
      static void* _S_oom_realloc(void*, size_t);
      static void (* __malloc_alloc_oom_handler)();
      
    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
  template <int __inst>
    void (* __malloc_alloc_template<__inst>::__malloc_alloc_oom_handler)() = 0;

  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) 
	    std::__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) 
	    std::__throw_bad_alloc();
	  (*__my_malloc_handler)();
	  __result = realloc(__p, __n);
	  if (__result) 
	    return(__result);
	}
    }


// Determines the underlying allocator choice for the node allocator.
#ifdef __USE_MALLOC
  typedef __malloc_alloc_template<0>  __mem_interface;
#else
  typedef __new_alloc                 __mem_interface;
#endif


  /**
   *  @maint
   *  This is used primarily (only?) in _Alloc_traits and other places to
   *  help provide the _Alloc_type typedef.
   *
   *  This is neither "standard"-conforming nor "SGI".  The _Alloc parameter
   *  must be "SGI" style.
   *  @endmaint
   *  (See @link Allocators allocators info @endlink for more.)
  */
  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()
    { 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)); }
  };


  /**
   *  @maint
   *  An adaptor for an underlying allocator (_Alloc) to check the size
   *  arguments for debugging.  Errors are reported using assert; these
   *  checks can be disabled via NDEBUG, but the space penalty is still
   *  paid, therefore it is far better to just use the underlying allocator
   *  by itelf when no checking is desired.
   *
   *  "There is some evidence that this can confuse Purify." - SGI comment
   *
   *  This adaptor is "SGI" style.  The _Alloc parameter must also be "SGI".
   *  @endmaint
   *  (See @link Allocators allocators info @endlink for more.)
  */
  template <class _Alloc>
  class __debug_alloc
  {
  private:
    enum {_S_extra = 8};  // Size of space used to store size.  Note that this
                          // must be large enough to preserve alignment.
  
  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 __mem_interface __alloc;
typedef __mem_interface __single_client_alloc;

#else


/**
 *  @maint
 *  Default node allocator.  "SGI" style.  Uses __mem_interface for its
 *  underlying requests (and makes as few requests as possible).
 *  **** Currently __mem_interface is always __new_alloc, never __malloc*.
 * 
 *  Important implementation properties:
 *  1. If the clients request an object of size > _MAX_BYTES, the resulting
 *     object will be obtained directly from the underlying __mem_interface.
 *  2. In all other cases, we allocate an object of size exactly
 *     _S_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.
 * 
 *  The first template parameter specifies whether more than one thread may
 *  use this allocator.  It is safe to allocate an object from one instance
 *  of a default_alloc and deallocate it with another one.  This effectively
 *  transfers its ownership to the second one.  This may have undesirable
 *  effects on reference locality.
 *
 *  The second parameter is unused and serves only to allow the creation of
 *  multiple default_alloc instances.  Note that containers built on different
 *  allocator instances have different types, limiting the utility of this
 *  approach.  If you do not wish to share the free lists with the main
 *  default_alloc instance, instantiate this with a non-zero __inst.
 *
 *  @endmaint
 *  (See @link Allocators allocators info @endlink for more.)
*/
template <bool __threads, int __inst>
class __default_alloc_template
{

private:
  enum {_ALIGN = 8};
  enum {_MAX_BYTES = 128};
  enum {_NFREELISTS = _MAX_BYTES / _ALIGN};

  static size_t
  _S_round_up(size_t __bytes) 
    { return (((__bytes) + (size_t) _ALIGN-1) & ~((size_t) _ALIGN - 1)); }

  union _Obj {
    union _Obj* _M_free_list_link;
    char        _M_client_data[1];    // The client sees this.
  };

  static _Obj* volatile _S_free_list[]; 
  static size_t _S_freelist_index(size_t __bytes)
    { return (((__bytes) + (size_t)_ALIGN-1)/(size_t)_ALIGN - 1); }

  // Returns an object of size __n, and optionally adds to size __n free list.
  static void* _S_refill(size_t __n);
  // Allocates a chunk for nobjs of size size.  nobjs may be reduced
  // if it is inconvenient to allocate the requested number.
  static char* _S_chunk_alloc(size_t __size, int& __nobjs);

  // Chunk allocation state.
  static char* _S_start_free;
  static char* _S_end_free;
  static size_t _S_heap_size;

  static _STL_mutex_lock _S_node_allocator_lock;

  // It would be nice to use _STL_auto_lock here.  But we need a test whether
  // threads are in use.
  class _Lock {
    public:
      _Lock() { if (__threads) _S_node_allocator_lock._M_acquire_lock(); }
      ~_Lock() { if (__threads) _S_node_allocator_lock._M_release_lock(); }
  } __attribute__ ((__unused__));
  friend class _Lock;

public:

  // __n must be > 0
  static void* allocate(size_t __n)
  {
    void* __ret = 0;

    if (__n > (size_t) _MAX_BYTES) 
      __ret = __mem_interface::allocate(__n);
    else 
      {
	_Obj* 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.
	_Lock __lock_instance;
	_Obj* __restrict__ __result = *__my_free_list;
	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)
      __mem_interface::deallocate(__p, __n);
    else 
      {
	_Obj* volatile*  __my_free_list
          = _S_free_list + _S_freelist_index(__n);
	_Obj* __q = (_Obj*)__p;
	
	// Acquire the lock here with a constructor call.  This ensures that
	// it is released in exit or during stack unwinding.
	_Lock __lock_instance;
	__q -> _M_free_list_link = *__my_free_list;
	*__my_free_list = __q;
      }
  }
  
  static void* reallocate(void* __p, size_t __old_sz, size_t __new_sz);
};


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

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


// We allocate memory in large chunks in order to avoid fragmenting the
// malloc heap (or whatever __mem_interface is using) too much.  We assume
// that __size is properly aligned.  We hold the allocation lock.
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;

    if (__bytes_left >= __total_bytes) 
      {
        __result = _S_start_free;
        _S_start_free += __total_bytes;
        return(__result);
      } 
    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);
    } 
    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.
        if (__bytes_left > 0) 
	  {
	    _Obj* 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;
	  }
        _S_start_free = (char*) __mem_interface::allocate(__bytes_to_get);
        if (0 == _S_start_free) 
	  {
            size_t __i;
            _Obj* volatile* __my_free_list;
	    _Obj* __p;
            // Try to make do with what we have.  That can't hurt.  We
            // do not try smaller requests, since that tends to result
            // in disaster on multi-process machines.
	    __i = __size;
            for (; __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) 
		  {
		    *__my_free_list = __p -> _M_free_list_link;
		    _S_start_free = (char*)__p;
                    _S_end_free = _S_start_free + __i;
                    return(_S_chunk_alloc(__size, __nobjs));
                    // Any leftover piece will eventually make it to the
                    // right free list.
		  }
	      }
	    _S_end_free = 0;	// In case of exception.
            _S_start_free = (char*)__mem_interface::allocate(__bytes_to_get);
            // This should either throw an exception or remedy the situation.
            // Thus we assume it succeeded.
	  }
        _S_heap_size += __bytes_to_get;
        _S_end_free = _S_start_free + __bytes_to_get;
        return(_S_chunk_alloc(__size, __nobjs));
      }
}


// Returns an object of size __n, and optionally adds to "size __n"'s free list.
// We assume that __n is properly aligned.  We hold the allocation lock.
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* 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);
}

template <bool __threads, int __inst>
  _STL_mutex_lock
  __default_alloc_template<__threads, __inst>::_S_node_allocator_lock
    __STL_MUTEX_INITIALIZER;

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* volatile
__default_alloc_template<__threads, __inst> ::_S_free_list[
    __default_alloc_template<__threads, __inst>::_NFREELISTS ];


typedef __default_alloc_template<true, 0>    __alloc;
typedef __default_alloc_template<false, 0>   __single_client_alloc;


#endif /* ! __USE_MALLOC */


/**
 *  This is a "standard" allocator, as per [20.4].  The private _Alloc is
 *  "SGI" style.  (See comments at the top of stl_alloc.h.)
 *
 *  The underlying allocator behaves as follows.
 *  - if __USE_MALLOC then
 *    - thread safety depends on malloc and is entirely out of our hands
 *    - __malloc_alloc_template is used for memory requests
 *  - else (the default)
 *    - __default_alloc_template is used via two typedefs
 *    - "__single_client_alloc" typedef does no locking for threads
 *    - "__alloc" typedef is threadsafe via the locks
 *    - __new_alloc is used for memory requests
 *
 *  (See @link Allocators allocators info @endlink for more.)
*/
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() throw() {}
  allocator(const allocator&) throw() {}
  template <class _Tp1> allocator(const allocator<_Tp1>&) throw() {}
  ~allocator() throw() {}

  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 throw() 
    { 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;
}


/**
 *  @maint
 *  Allocator adaptor to turn an "SGI" style allocator (e.g., __alloc,
 *  __malloc_alloc_template) 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>.
 *  @endmaint
 *  (See @link Allocators allocators info @endlink for more.)
*/
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() throw() {}
  __allocator(const __allocator& __a) throw()
    : __underlying_alloc(__a.__underlying_alloc) {}
  template <class _Tp1> 
  __allocator(const __allocator<_Tp1, _Alloc>& __a) throw()
    : __underlying_alloc(__a.__underlying_alloc) {}
  ~__allocator() throw() {}

  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 throw() 
    { 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;
}

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;
}


//@{
/** Comparison operators for all of the predifined SGI-style allocators.
 *  This ensures that __allocator<malloc_alloc> (for example) will work
 *  correctly.  As required, all allocators compare equal.
*/
template <int inst>
inline bool operator==(const __malloc_alloc_template<inst>&,
                       const __malloc_alloc_template<inst>&)
{
  return true;
}

template <int __inst>
inline bool operator!=(const __malloc_alloc_template<__inst>&,
                       const __malloc_alloc_template<__inst>&)
{
  return false;
}

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

template <class _Alloc>
inline bool operator!=(const __debug_alloc<_Alloc>&,
                       const __debug_alloc<_Alloc>&) {
  return false;
}
//@}


/**
 *  @maint
 *  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" allocators.  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.  For examples of use, see stl_vector.h, etc, or
 *  any of the other classes derived from this one.
 *
 *  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 size_t parameters are "standard" style (see top of stl_alloc.h) in
 *  that they take counts, not sizes.
 *
 *  @endmaint
 *  (See @link Allocators allocators info @endlink for more.)
*/
//@{
// The fully general version.
template <class _Tp, class _Allocator>
struct _Alloc_traits
{
  static const bool _S_instanceless = false;
  typedef typename _Allocator::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.
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;
};

#ifndef __USE_MALLOC
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;
};
#endif

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;
};

#ifndef __USE_MALLOC
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;
};
#endif

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;
};
//@}

} // namespace std

#endif /* __GLIBCPP_INTERNAL_ALLOC_H */

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