libstdc++-v3/include/ext/mt_allocator.h - gcc - Git at Google

 // MT-optimized allocator -*- C++ -*-

 // Copyright (C) 2003, 2004 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.

 /** @file ext/mt_allocator.h
  *  This file is a GNU extension to the Standard C++ Library.
  *  You should only include this header if you are using GCC 3 or later.
  */

 #ifndef _MT_ALLOCATOR_H
 #define _MT_ALLOCATOR_H 1

 #include <new>
 #include <cstdlib>
 #include <bits/functexcept.h>
 #include <bits/gthr.h>
 #include <bits/atomicity.h>

 namespace __gnu_cxx
 {
   /**
    *  This is a fixed size (power of 2) allocator which - when
    *  compiled with thread support - will maintain one freelist per
    *  size per thread plus a "global" one. Steps are taken to limit
    *  the per thread freelist sizes (by returning excess back to
    *  "global").
    *
    *  Further details:
    *  http://gcc.gnu.org/onlinedocs/libstdc++/ext/mt_allocator.html
    */
   template<typename _Tp>
     class __mt_alloc
     {
     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<typename _Tp1>
         struct rebind
         { typedef __mt_alloc<_Tp1> other; };

       __mt_alloc() throw()
       {
 	// XXX
       }

       __mt_alloc(const __mt_alloc&) throw()
       {
 	// XXX
       }

       template<typename _Tp1>
         __mt_alloc(const __mt_alloc<_Tp1>& obj) throw()
         {
 	  // XXX
 	}

       ~__mt_alloc() throw() { }

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

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

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

       // _GLIBCXX_RESOLVE_LIB_DEFECTS
       // 402. wrong new expression in [some_] allocator::construct
       void
       construct(pointer __p, const _Tp& __val)
       { ::new(__p) _Tp(__val); }

       void
       destroy(pointer __p) { __p->~_Tp(); }

       pointer
       allocate(size_type __n, const void* = 0);

       void
       deallocate(pointer __p, size_type __n);

       // Variables used to configure the behavior of the allocator,
       // assigned and explained in detail below.
       struct _Tune
       {
 	// Alignment needed.
 	// NB: In any case must be >= sizeof(_Block_record), that
 	// is 4 on 32 bit machines and 8 on 64 bit machines.
 	size_t  _M_align;

 	// Allocation requests (after round-up to power of 2) below
 	// this value will be handled by the allocator. A raw new/
 	// call will be used for requests larger than this value.
 	size_t	_M_max_bytes;

 	// Size in bytes of the smallest bin.
 	// NB: Must be a power of 2 and >= _M_align.
 	size_t  _M_min_bin;

 	// In order to avoid fragmenting and minimize the number of
 	// new() calls we always request new memory using this
 	// value. Based on previous discussions on the libstdc++
 	// mailing list we have choosen the value below.
 	// See http://gcc.gnu.org/ml/libstdc++/2001-07/msg00077.html
 	size_t 	_M_chunk_size;

 	// The maximum number of supported threads. Our Linux 2.4.18
 	// reports 4070 in /proc/sys/kernel/threads-max
 	size_t 	_M_max_threads;

 	// Each time a deallocation occurs in a threaded application
 	// we make sure that there are no more than
 	// _M_freelist_headroom % of used memory on the freelist. If
 	// the number of additional records is more than
 	// _M_freelist_headroom % of the freelist, we move these
 	// records back to the global pool.
 	size_t 	_M_freelist_headroom;

 	// Set to true forces all allocations to use new().
 	bool 	_M_force_new;

 	explicit
 	_Tune()
 	: _M_align(8), _M_max_bytes(128), _M_min_bin(8),
 	  _M_chunk_size(4096 - 4 * sizeof(void*)),
 	  _M_max_threads(4096), _M_freelist_headroom(10),
 	  _M_force_new(getenv("GLIBCXX_FORCE_NEW") ? true : false)
 	{ }

 	explicit
 	_Tune(size_t __align, size_t __maxb, size_t __minbin,
 	      size_t __chunk, size_t __maxthreads, size_t __headroom,
 	      bool __force)
 	: _M_align(__align), _M_max_bytes(__maxb), _M_min_bin(__minbin),
 	  _M_chunk_size(__chunk), _M_max_threads(__maxthreads),
 	  _M_freelist_headroom(__headroom), _M_force_new(__force)
 	{ }
       };

     private:
       // We need to create the initial lists and set up some variables
       // before we can answer to the first request for memory.
 #ifdef __GTHREADS
       static __gthread_once_t 		_S_once;
 #endif
       static bool 			_S_init;

       static void
       _S_initialize();

       // Configuration options.
       static _Tune 	       		_S_options;

       static const _Tune
       _S_get_options()
       { return _S_options; }

       static void
       _S_set_options(_Tune __t)
       {
 	if (!_S_init)
 	  _S_options = __t;
       }

       // Using short int as type for the binmap implies we are never
       // caching blocks larger than 65535 with this allocator
       typedef unsigned short int        _Binmap_type;
       static _Binmap_type* 		_S_binmap;

       // Each requesting thread is assigned an id ranging from 1 to
       // _S_max_threads. Thread id 0 is used as a global memory pool.
       // In order to get constant performance on the thread assignment
       // routine, we keep a list of free ids. When a thread first
       // requests memory we remove the first record in this list and
       // stores the address in a __gthread_key. When initializing the
       // __gthread_key we specify a destructor. When this destructor
       // (i.e. the thread dies) is called, we return the thread id to
       // the front of this list.
 #ifdef __GTHREADS
       struct _Thread_record
       {
         // Points to next free thread id record. NULL if last record in list.
         _Thread_record* volatile        _M_next;

 	// Thread id ranging from 1 to _S_max_threads.
         size_t                          _M_id;
       };

       static _Thread_record* volatile 	_S_thread_freelist_first;
       static __gthread_mutex_t 		_S_thread_freelist_mutex;
       static __gthread_key_t 		_S_thread_key;

       static void
       _S_destroy_thread_key(void* __freelist_pos);
 #endif

       static size_t
       _S_get_thread_id();

       union _Block_record
       {
 	// Points to the block_record of the next free block.
         _Block_record* volatile         _M_next;

 #ifdef __GTHREADS
 	// The thread id of the thread which has requested this block.
         size_t                          _M_thread_id;
 #endif
       };

       struct _Bin_record
       {
 	// An "array" of pointers to the first free block for each
 	// thread id. Memory to this "array" is allocated in _S_initialize()
 	// for _S_max_threads + global pool 0.
         _Block_record** volatile        _M_first;

 #ifdef __GTHREADS
 	// An "array" of counters used to keep track of the amount of
 	// blocks that are on the freelist/used for each thread id.
 	// Memory to these "arrays" is allocated in _S_initialize() for
 	// _S_max_threads + global pool 0.
         size_t* volatile                _M_free;
         size_t* volatile                _M_used;

 	// Each bin has its own mutex which is used to ensure data
 	// integrity while changing "ownership" on a block.  The mutex
 	// is initialized in _S_initialize().
         __gthread_mutex_t*              _M_mutex;
 #endif
       };

       // An "array" of bin_records each of which represents a specific
       // power of 2 size. Memory to this "array" is allocated in
       // _S_initialize().
       static _Bin_record* volatile     	_S_bin;

       // Actual value calculated in _S_initialize().
       static size_t 	       	     	_S_bin_size;
     };

   template<typename _Tp>
     typename __mt_alloc<_Tp>::pointer
     __mt_alloc<_Tp>::
     allocate(size_type __n, const void*)
     {
       // Although the test in __gthread_once() would suffice, we wrap
       // test of the once condition in our own unlocked check. This
       // saves one function call to pthread_once() (which itself only
       // tests for the once value unlocked anyway and immediately
       // returns if set)
       if (!_S_init)
 	{
 #ifdef __GTHREADS
 	  if (__gthread_active_p())
 	    __gthread_once(&_S_once, _S_initialize);
 #endif
 	  if (!_S_init)
 	    _S_initialize();
 	}

       // Requests larger than _M_max_bytes are handled by new/delete
       // directly.
       const size_t __bytes = __n * sizeof(_Tp);
       if (__bytes > _S_options._M_max_bytes || _S_options._M_force_new)
 	{
 	  void* __ret = ::operator new(__bytes);
 	  return static_cast<_Tp*>(__ret);
 	}

       // Round up to power of 2 and figure out which bin to use.
       const size_t __which = _S_binmap[__bytes];
       const size_t __thread_id = _S_get_thread_id();

       // Find out if we have blocks on our freelist.  If so, go ahead
       // and use them directly without having to lock anything.
       const _Bin_record& __bin = _S_bin[__which];
       _Block_record* __block = NULL;
       if (__bin._M_first[__thread_id] == NULL)
 	{
 	  // NB: For alignment reasons, we can't use the first _M_align
 	  // bytes, even when sizeof(_Block_record) < _M_align.
 	  const size_t __bin_size = ((_S_options._M_min_bin << __which)
 				     + _S_options._M_align);
 	  size_t __block_count = _S_options._M_chunk_size / __bin_size;

 	  // Are we using threads?
 	  // - Yes, check if there are free blocks on the global
 	  //   list. If so, grab up to __block_count blocks in one
 	  //   lock and change ownership. If the global list is
 	  //   empty, we allocate a new chunk and add those blocks
 	  //   directly to our own freelist (with us as owner).
 	  // - No, all operations are made directly to global pool 0
 	  //   no need to lock or change ownership but check for free
 	  //   blocks on global list (and if not add new ones) and
 	  //   get the first one.
 #ifdef __GTHREADS
 	  if (__gthread_active_p())
 	    {
 	      __gthread_mutex_lock(__bin._M_mutex);
 	      if (__bin._M_first[0] == NULL)
 		{
 		  // No need to hold the lock when we are adding a
 		  // whole chunk to our own list.
 		  __gthread_mutex_unlock(__bin._M_mutex);

 		  void* __v = ::operator new(_S_options._M_chunk_size);
 		  __bin._M_first[__thread_id] = static_cast<_Block_record*>(__v);
 		  __bin._M_free[__thread_id] = __block_count;

 		  --__block_count;
 		  __block = __bin._M_first[__thread_id];
 		  while (__block_count-- > 0)
 		    {
 		      char* __c = reinterpret_cast<char*>(__block) + __bin_size;
 		      __block->_M_next = reinterpret_cast<_Block_record*>(__c);
 		      __block = __block->_M_next;
 		    }
 		  __block->_M_next = NULL;
 		}
 	      else
 		{
 		  // Is the number of required blocks greater than or
 		  // equal to the number that can be provided by the
 		  // global free list?
 		  __bin._M_first[__thread_id] = __bin._M_first[0];
 		  if (__block_count >= __bin._M_free[0])
 		    {
 		      __bin._M_free[__thread_id] = __bin._M_free[0];
 		      __bin._M_free[0] = 0;
 		      __bin._M_first[0] = NULL;
 		    }
 		  else
 		    {
 		      __bin._M_free[__thread_id] = __block_count;
 		      __bin._M_free[0] -= __block_count;
 		      --__block_count;
 		      __block = __bin._M_first[0];
 		      while (__block_count-- > 0)
 			__block = __block->_M_next;
 		      __bin._M_first[0] = __block->_M_next;
 		      __block->_M_next = NULL;
 		    }
 		  __gthread_mutex_unlock(__bin._M_mutex);
 		}
 	    }
 	  else
 #endif
 	    {
 	      void* __v = ::operator new(_S_options._M_chunk_size);
 	      __bin._M_first[0] = static_cast<_Block_record*>(__v);

 	      --__block_count;
 	      __block = __bin._M_first[0];
 	      while (__block_count-- > 0)
 		{
 		  char* __c = reinterpret_cast<char*>(__block) + __bin_size;
 		  __block->_M_next = reinterpret_cast<_Block_record*>(__c);
 		  __block = __block->_M_next;
 		}
 	      __block->_M_next = NULL;
 	    }
 	}

       __block = __bin._M_first[__thread_id];
       __bin._M_first[__thread_id] = __bin._M_first[__thread_id]->_M_next;
 #ifdef __GTHREADS
       if (__gthread_active_p())
 	{
 	  __block->_M_thread_id = __thread_id;
 	  --__bin._M_free[__thread_id];
 	  ++__bin._M_used[__thread_id];
 	}
 #endif

       char* __c = reinterpret_cast<char*>(__block) + _S_options._M_align;
       return static_cast<_Tp*>(static_cast<void*>(__c));
     }

   template<typename _Tp>
     void
     __mt_alloc<_Tp>::
     deallocate(pointer __p, size_type __n)
     {
       // Requests larger than _M_max_bytes are handled by operators
       // new/delete directly.
       const size_t __bytes = __n * sizeof(_Tp);
       if (__bytes > _S_options._M_max_bytes || _S_options._M_force_new)
 	{
 	  ::operator delete(__p);
 	  return;
 	}

       // Round up to power of 2 and figure out which bin to use.
       const size_t __which = _S_binmap[__bytes];
       const _Bin_record& __bin = _S_bin[__which];

       char* __c = reinterpret_cast<char*>(__p) - _S_options._M_align;
       _Block_record* __block = reinterpret_cast<_Block_record*>(__c);

 #ifdef __GTHREADS
       if (__gthread_active_p())
 	{
 	  // Calculate the number of records to remove from our freelist:
 	  // in order to avoid too much contention we wait until the
 	  // number of records is "high enough".
 	  const size_t __thread_id = _S_get_thread_id();

 	  long __remove = ((__bin._M_free[__thread_id]
 			    * _S_options._M_freelist_headroom)
 			   - __bin._M_used[__thread_id]);
 	  if (__remove > static_cast<long>(100 * (_S_bin_size - __which)
 					   * _S_options._M_freelist_headroom)
 	      && __remove > static_cast<long>(__bin._M_free[__thread_id]))
 	    {
 	      _Block_record* __tmp = __bin._M_first[__thread_id];
 	      _Block_record* __first = __tmp;
 	      __remove /= _S_options._M_freelist_headroom;
 	      const long __removed = __remove;
 	      --__remove;
 	      while (__remove-- > 0)
 		__tmp = __tmp->_M_next;
 	      __bin._M_first[__thread_id] = __tmp->_M_next;
 	      __bin._M_free[__thread_id] -= __removed;

 	      __gthread_mutex_lock(__bin._M_mutex);
 	      __tmp->_M_next = __bin._M_first[0];
 	      __bin._M_first[0] = __first;
 	      __bin._M_free[0] += __removed;
 	      __gthread_mutex_unlock(__bin._M_mutex);
 	    }

 	  // Return this block to our list and update counters and
 	  // owner id as needed.
 	  --__bin._M_used[__block->_M_thread_id];

 	  __block->_M_next = __bin._M_first[__thread_id];
 	  __bin._M_first[__thread_id] = __block;

 	  ++__bin._M_free[__thread_id];
 	}
       else
 #endif
 	{
 	  // Single threaded application - return to global pool.
 	  __block->_M_next = __bin._M_first[0];
 	  __bin._M_first[0] = __block;
 	}
     }

   template<typename _Tp>
     void
     __mt_alloc<_Tp>::
     _S_initialize()
     {
       // This method is called on the first allocation (when _S_init is still
       // false) to create the bins.

       // Ensure that the static initialization of _S_options has
       // happened.  This depends on (a) _M_align == 0 being an invalid
       // value that is only present at startup, and (b) the real
       // static initialization that happens later not actually
       // changing anything.
       if (_S_options._M_align == 0)
         new (&_S_options) _Tune;

       // _M_force_new must not change after the first allocate(),
       // which in turn calls this method, so if it's false, it's false
       // forever and we don't need to return here ever again.
       if (_S_options._M_force_new)
 	{
 	  _S_init = true;
 	  return;
 	}

       // Calculate the number of bins required based on _M_max_bytes.
       // _S_bin_size is statically-initialized to one.
       size_t __bin_size = _S_options._M_min_bin;
       while (_S_options._M_max_bytes > __bin_size)
 	{
 	  __bin_size <<= 1;
 	  ++_S_bin_size;
 	}

       // Setup the bin map for quick lookup of the relevant bin.
       const size_t __j = (_S_options._M_max_bytes + 1) * sizeof(_Binmap_type);
       _S_binmap = static_cast<_Binmap_type*>(::operator new(__j));

       _Binmap_type* __bp = _S_binmap;
       _Binmap_type __bin_max = _S_options._M_min_bin;
       _Binmap_type __bint = 0;
       for (_Binmap_type __ct = 0; __ct <= _S_options._M_max_bytes; ++__ct)
         {
           if (__ct > __bin_max)
             {
               __bin_max <<= 1;
               ++__bint;
             }
           *__bp++ = __bint;
         }

       // Initialize _S_bin and its members.
       void* __v = ::operator new(sizeof(_Bin_record) * _S_bin_size);
       _S_bin = static_cast<_Bin_record*>(__v);

       // If __gthread_active_p() create and initialize the list of
       // free thread ids. Single threaded applications use thread id 0
       // directly and have no need for this.
 #ifdef __GTHREADS
       if (__gthread_active_p())
         {
 	  const size_t __k = sizeof(_Thread_record) * _S_options._M_max_threads;
 	  __v = ::operator new(__k);
           _S_thread_freelist_first = static_cast<_Thread_record*>(__v);

 	  // NOTE! The first assignable thread id is 1 since the
 	  // global pool uses id 0
           size_t __i;
           for (__i = 1; __i < _S_options._M_max_threads; ++__i)
             {
 	      _Thread_record& __tr = _S_thread_freelist_first[__i - 1];
               __tr._M_next = &_S_thread_freelist_first[__i];
               __tr._M_id = __i;
             }

           // Set last record.
           _S_thread_freelist_first[__i - 1]._M_next = NULL;
           _S_thread_freelist_first[__i - 1]._M_id = __i;

 	  // Make sure this is initialized.
 #ifndef __GTHREAD_MUTEX_INIT
 	  __GTHREAD_MUTEX_INIT_FUNCTION(&_S_thread_freelist_mutex);
 #endif
           // Initialize per thread key to hold pointer to
           // _S_thread_freelist.
           __gthread_key_create(&_S_thread_key, _S_destroy_thread_key);

 	  const size_t __max_threads = _S_options._M_max_threads + 1;
 	  for (size_t __n = 0; __n < _S_bin_size; ++__n)
 	    {
 	      _Bin_record& __bin = _S_bin[__n];
 	      __v = ::operator new(sizeof(_Block_record*) * __max_threads);
 	      __bin._M_first = static_cast<_Block_record**>(__v);

 	      __v = ::operator new(sizeof(size_t) * __max_threads);
               __bin._M_free = static_cast<size_t*>(__v);

 	      __v = ::operator new(sizeof(size_t) * __max_threads);
               __bin._M_used = static_cast<size_t*>(__v);

 	      __v = ::operator new(sizeof(__gthread_mutex_t));
               __bin._M_mutex = static_cast<__gthread_mutex_t*>(__v);

 #ifdef __GTHREAD_MUTEX_INIT
               {
                 // Do not copy a POSIX/gthr mutex once in use.
                 __gthread_mutex_t __tmp = __GTHREAD_MUTEX_INIT;
                 *__bin._M_mutex = __tmp;
               }
 #else
               { __GTHREAD_MUTEX_INIT_FUNCTION(__bin._M_mutex); }
 #endif

 	      for (size_t __threadn = 0; __threadn < __max_threads;
 		   ++__threadn)
 		{
 		  __bin._M_first[__threadn] = NULL;
 		  __bin._M_free[__threadn] = 0;
 		  __bin._M_used[__threadn] = 0;
 		}
 	    }
 	}
       else
 #endif
 	for (size_t __n = 0; __n < _S_bin_size; ++__n)
 	  {
 	    _Bin_record& __bin = _S_bin[__n];
 	    __v = ::operator new(sizeof(_Block_record*));
 	    __bin._M_first = static_cast<_Block_record**>(__v);
 	    __bin._M_first[0] = NULL;
 	  }

       _S_init = true;
     }

   template<typename _Tp>
     size_t
     __mt_alloc<_Tp>::
     _S_get_thread_id()
     {
 #ifdef __GTHREADS
       // If we have thread support and it's active we check the thread
       // key value and return its id or if it's not set we take the
       // first record from _S_thread_freelist and sets the key and
       // returns it's id.
       if (__gthread_active_p())
         {
           _Thread_record* __freelist_pos =
 	    static_cast<_Thread_record*>(__gthread_getspecific(_S_thread_key));
 	  if (__freelist_pos == NULL)
             {
 	      // Since _S_options._M_max_threads must be larger than
 	      // the theoretical max number of threads of the OS the
 	      // list can never be empty.
               __gthread_mutex_lock(&_S_thread_freelist_mutex);
               __freelist_pos = _S_thread_freelist_first;
               _S_thread_freelist_first = _S_thread_freelist_first->_M_next;
               __gthread_mutex_unlock(&_S_thread_freelist_mutex);

               __gthread_setspecific(_S_thread_key,
 				    static_cast<void*>(__freelist_pos));
             }
           return __freelist_pos->_M_id;
         }
 #endif
       // Otherwise (no thread support or inactive) all requests are
       // served from the global pool 0.
       return 0;
     }

 #ifdef __GTHREADS
   template<typename _Tp>
     void
     __mt_alloc<_Tp>::
     _S_destroy_thread_key(void* __freelist_pos)
     {
       // Return this thread id record to front of thread_freelist.
       __gthread_mutex_lock(&_S_thread_freelist_mutex);
       _Thread_record* __tr = static_cast<_Thread_record*>(__freelist_pos);
       __tr->_M_next = _S_thread_freelist_first;
       _S_thread_freelist_first = __tr;
       __gthread_mutex_unlock(&_S_thread_freelist_mutex);
     }
 #endif

   template<typename _Tp>
     inline bool
     operator==(const __mt_alloc<_Tp>&, const __mt_alloc<_Tp>&)
     { return true; }

   template<typename _Tp>
     inline bool
     operator!=(const __mt_alloc<_Tp>&, const __mt_alloc<_Tp>&)
     { return false; }

   template<typename _Tp>
     bool __mt_alloc<_Tp>::_S_init = false;

   template<typename _Tp>
     typename __mt_alloc<_Tp>::_Tune __mt_alloc<_Tp>::_S_options;

   template<typename _Tp>
     typename __mt_alloc<_Tp>::_Binmap_type* __mt_alloc<_Tp>::_S_binmap;

   template<typename _Tp>
     typename __mt_alloc<_Tp>::_Bin_record* volatile __mt_alloc<_Tp>::_S_bin;

   template<typename _Tp>
     size_t __mt_alloc<_Tp>::_S_bin_size = 1;

   // Actual initialization in _S_initialize().
 #ifdef __GTHREADS
   template<typename _Tp>
     __gthread_once_t __mt_alloc<_Tp>::_S_once = __GTHREAD_ONCE_INIT;

   template<typename _Tp>
     typename __mt_alloc<_Tp>::_Thread_record*
     volatile __mt_alloc<_Tp>::_S_thread_freelist_first = NULL;

   template<typename _Tp>
     __gthread_key_t __mt_alloc<_Tp>::_S_thread_key;

   template<typename _Tp>
     __gthread_mutex_t
 #ifdef __GTHREAD_MUTEX_INIT
     __mt_alloc<_Tp>::_S_thread_freelist_mutex = __GTHREAD_MUTEX_INIT;
 #else
     __mt_alloc<_Tp>::_S_thread_freelist_mutex;
 #endif
 #endif
 } // namespace __gnu_cxx

 #endif
	// MT-optimized allocator -- C++ --

	// Copyright (C) 2003, 2004 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.

	/** @file ext/mt_allocator.h
	* This file is a GNU extension to the Standard C++ Library.
	* You should only include this header if you are using GCC 3 or later.
	*/

	#ifndef _MT_ALLOCATOR_H
	#define _MT_ALLOCATOR_H 1

	#include <new>
	#include <cstdlib>
	#include <bits/functexcept.h>
	#include <bits/gthr.h>
	#include <bits/atomicity.h>

	namespace __gnu_cxx
	{
	/**
	* This is a fixed size (power of 2) allocator which - when
	* compiled with thread support - will maintain one freelist per
	* size per thread plus a "global" one. Steps are taken to limit
	* the per thread freelist sizes (by returning excess back to
	* "global").
	*
	* Further details:
	* http://gcc.gnu.org/onlinedocs/libstdc++/ext/mt_allocator.html
	*/
	template<typename _Tp>
	class __mt_alloc
	{
	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<typename _Tp1>
	struct rebind
	{ typedef __mt_alloc<_Tp1> other; };

	__mt_alloc() throw()
	{
	// XXX
	}

	__mt_alloc(const __mt_alloc&) throw()
	{
	// XXX
	}

	template<typename _Tp1>
	__mt_alloc(const __mt_alloc<_Tp1>& obj) throw()
	{
	// XXX
	}

	~__mt_alloc() throw() { }

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

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

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

	// _GLIBCXX_RESOLVE_LIB_DEFECTS
	// 402. wrong new expression in [some_] allocator::construct
	void
	construct(pointer __p, const _Tp& __val)
	{ ::new(__p) _Tp(__val); }

	void
	destroy(pointer __p) { __p->~_Tp(); }

	pointer
	allocate(size_type __n, const void* = 0);

	void
	deallocate(pointer __p, size_type __n);

	// Variables used to configure the behavior of the allocator,
	// assigned and explained in detail below.
	struct _Tune
	{
	// Alignment needed.
	// NB: In any case must be >= sizeof(_Block_record), that
	// is 4 on 32 bit machines and 8 on 64 bit machines.
	size_t _M_align;

	// Allocation requests (after round-up to power of 2) below
	// this value will be handled by the allocator. A raw new/
	// call will be used for requests larger than this value.
	size_t _M_max_bytes;

	// Size in bytes of the smallest bin.
	// NB: Must be a power of 2 and >= _M_align.
	size_t _M_min_bin;

	// In order to avoid fragmenting and minimize the number of
	// new() calls we always request new memory using this
	// value. Based on previous discussions on the libstdc++
	// mailing list we have choosen the value below.
	// See http://gcc.gnu.org/ml/libstdc++/2001-07/msg00077.html
	size_t _M_chunk_size;

	// The maximum number of supported threads. Our Linux 2.4.18
	// reports 4070 in /proc/sys/kernel/threads-max
	size_t _M_max_threads;

	// Each time a deallocation occurs in a threaded application
	// we make sure that there are no more than
	// _M_freelist_headroom % of used memory on the freelist. If
	// the number of additional records is more than
	// _M_freelist_headroom % of the freelist, we move these
	// records back to the global pool.
	size_t _M_freelist_headroom;

	// Set to true forces all allocations to use new().
	bool _M_force_new;

	explicit
	_Tune()
	: _M_align(8), _M_max_bytes(128), _M_min_bin(8),
	_M_chunk_size(4096 - 4 * sizeof(void*)),
	_M_max_threads(4096), _M_freelist_headroom(10),
	_M_force_new(getenv("GLIBCXX_FORCE_NEW") ? true : false)
	{ }

	explicit
	_Tune(size_t __align, size_t __maxb, size_t __minbin,
	size_t __chunk, size_t __maxthreads, size_t __headroom,
	bool __force)
	: _M_align(__align), _M_max_bytes(__maxb), _M_min_bin(__minbin),
	_M_chunk_size(__chunk), _M_max_threads(__maxthreads),
	_M_freelist_headroom(__headroom), _M_force_new(__force)
	{ }
	};

	private:
	// We need to create the initial lists and set up some variables
	// before we can answer to the first request for memory.
	#ifdef __GTHREADS
	static __gthread_once_t _S_once;
	#endif
	static bool _S_init;

	static void
	_S_initialize();

	// Configuration options.
	static _Tune _S_options;

	static const _Tune
	_S_get_options()
	{ return _S_options; }

	static void
	_S_set_options(_Tune __t)
	{
	if (!_S_init)
	_S_options = __t;
	}

	// Using short int as type for the binmap implies we are never
	// caching blocks larger than 65535 with this allocator
	typedef unsigned short int _Binmap_type;
	static _Binmap_type* _S_binmap;

	// Each requesting thread is assigned an id ranging from 1 to
	// _S_max_threads. Thread id 0 is used as a global memory pool.
	// In order to get constant performance on the thread assignment
	// routine, we keep a list of free ids. When a thread first
	// requests memory we remove the first record in this list and
	// stores the address in a __gthread_key. When initializing the
	// __gthread_key we specify a destructor. When this destructor
	// (i.e. the thread dies) is called, we return the thread id to
	// the front of this list.
	#ifdef __GTHREADS
	struct _Thread_record
	{
	// Points to next free thread id record. NULL if last record in list.
	_Thread_record* volatile _M_next;

	// Thread id ranging from 1 to _S_max_threads.
	size_t _M_id;
	};

	static _Thread_record* volatile _S_thread_freelist_first;
	static __gthread_mutex_t _S_thread_freelist_mutex;
	static __gthread_key_t _S_thread_key;

	static void
	_S_destroy_thread_key(void* __freelist_pos);
	#endif

	static size_t
	_S_get_thread_id();

	union _Block_record
	{
	// Points to the block_record of the next free block.
	_Block_record* volatile _M_next;

	#ifdef __GTHREADS
	// The thread id of the thread which has requested this block.
	size_t _M_thread_id;
	#endif
	};

	struct _Bin_record
	{
	// An "array" of pointers to the first free block for each
	// thread id. Memory to this "array" is allocated in _S_initialize()
	// for _S_max_threads + global pool 0.
	_Block_record** volatile _M_first;

	#ifdef __GTHREADS
	// An "array" of counters used to keep track of the amount of
	// blocks that are on the freelist/used for each thread id.
	// Memory to these "arrays" is allocated in _S_initialize() for
	// _S_max_threads + global pool 0.
	size_t* volatile _M_free;
	size_t* volatile _M_used;

	// Each bin has its own mutex which is used to ensure data
	// integrity while changing "ownership" on a block. The mutex
	// is initialized in _S_initialize().
	__gthread_mutex_t* _M_mutex;
	#endif
	};

	// An "array" of bin_records each of which represents a specific
	// power of 2 size. Memory to this "array" is allocated in
	// _S_initialize().
	static _Bin_record* volatile _S_bin;

	// Actual value calculated in _S_initialize().
	static size_t _S_bin_size;
	};

	template<typename _Tp>
	typename __mt_alloc<_Tp>::pointer
	__mt_alloc<_Tp>::
	allocate(size_type __n, const void*)
	{
	// Although the test in __gthread_once() would suffice, we wrap
	// test of the once condition in our own unlocked check. This
	// saves one function call to pthread_once() (which itself only
	// tests for the once value unlocked anyway and immediately
	// returns if set)
	if (!_S_init)
	{
	#ifdef __GTHREADS
	if (__gthread_active_p())
	__gthread_once(&_S_once, _S_initialize);
	#endif
	if (!_S_init)
	_S_initialize();
	}

	// Requests larger than _M_max_bytes are handled by new/delete
	// directly.
	const size_t __bytes = __n * sizeof(_Tp);
	if (__bytes > _S_options._M_max_bytes \|\| _S_options._M_force_new)
	{
	void* __ret = ::operator new(__bytes);
	return static_cast<_Tp*>(__ret);
	}

	// Round up to power of 2 and figure out which bin to use.
	const size_t __which = _S_binmap[__bytes];
	const size_t __thread_id = _S_get_thread_id();

	// Find out if we have blocks on our freelist. If so, go ahead
	// and use them directly without having to lock anything.
	const _Bin_record& __bin = _S_bin[__which];
	_Block_record* __block = NULL;
	if (__bin._M_first[__thread_id] == NULL)
	{
	// NB: For alignment reasons, we can't use the first _M_align
	// bytes, even when sizeof(_Block_record) < _M_align.
	const size_t __bin_size = ((_S_options._M_min_bin << __which)
	+ _S_options._M_align);
	size_t __block_count = _S_options._M_chunk_size / __bin_size;

	// Are we using threads?
	// - Yes, check if there are free blocks on the global
	// list. If so, grab up to __block_count blocks in one
	// lock and change ownership. If the global list is
	// empty, we allocate a new chunk and add those blocks
	// directly to our own freelist (with us as owner).
	// - No, all operations are made directly to global pool 0
	// no need to lock or change ownership but check for free
	// blocks on global list (and if not add new ones) and
	// get the first one.
	#ifdef __GTHREADS
	if (__gthread_active_p())
	{
	__gthread_mutex_lock(__bin._M_mutex);
	if (__bin._M_first[0] == NULL)
	{
	// No need to hold the lock when we are adding a
	// whole chunk to our own list.
	__gthread_mutex_unlock(__bin._M_mutex);

	void* __v = ::operator new(_S_options._M_chunk_size);
	__bin._M_first[__thread_id] = static_cast<_Block_record*>(__v);
	__bin._M_free[__thread_id] = __block_count;

	--__block_count;
	__block = __bin._M_first[__thread_id];
	while (__block_count-- > 0)
	{
	char* __c = reinterpret_cast<char*>(__block) + __bin_size;
	__block->_M_next = reinterpret_cast<_Block_record*>(__c);
	__block = __block->_M_next;
	}
	__block->_M_next = NULL;
	}
	else
	{
	// Is the number of required blocks greater than or
	// equal to the number that can be provided by the
	// global free list?
	__bin._M_first[__thread_id] = __bin._M_first[0];
	if (__block_count >= __bin._M_free[0])
	{
	__bin._M_free[__thread_id] = __bin._M_free[0];
	__bin._M_free[0] = 0;
	__bin._M_first[0] = NULL;
	}
	else
	{
	__bin._M_free[__thread_id] = __block_count;
	__bin._M_free[0] -= __block_count;
	--__block_count;
	__block = __bin._M_first[0];
	while (__block_count-- > 0)
	__block = __block->_M_next;
	__bin._M_first[0] = __block->_M_next;
	__block->_M_next = NULL;
	}
	__gthread_mutex_unlock(__bin._M_mutex);
	}
	}
	else
	#endif
	{
	void* __v = ::operator new(_S_options._M_chunk_size);
	__bin._M_first[0] = static_cast<_Block_record*>(__v);

	--__block_count;
	__block = __bin._M_first[0];
	while (__block_count-- > 0)
	{
	char* __c = reinterpret_cast<char*>(__block) + __bin_size;
	__block->_M_next = reinterpret_cast<_Block_record*>(__c);
	__block = __block->_M_next;
	}
	__block->_M_next = NULL;
	}
	}

	__block = __bin._M_first[__thread_id];
	__bin._M_first[__thread_id] = __bin._M_first[__thread_id]->_M_next;
	#ifdef __GTHREADS
	if (__gthread_active_p())
	{
	__block->_M_thread_id = __thread_id;
	--__bin._M_free[__thread_id];
	++__bin._M_used[__thread_id];
	}
	#endif

	char* __c = reinterpret_cast<char*>(__block) + _S_options._M_align;
	return static_cast<_Tp>(static_cast<void>(__c));
	}

	template<typename _Tp>
	void
	__mt_alloc<_Tp>::
	deallocate(pointer __p, size_type __n)
	{
	// Requests larger than _M_max_bytes are handled by operators
	// new/delete directly.
	const size_t __bytes = __n * sizeof(_Tp);
	if (__bytes > _S_options._M_max_bytes \|\| _S_options._M_force_new)
	{
	::operator delete(__p);
	return;
	}

	// Round up to power of 2 and figure out which bin to use.
	const size_t __which = _S_binmap[__bytes];
	const _Bin_record& __bin = _S_bin[__which];

	char* __c = reinterpret_cast<char*>(__p) - _S_options._M_align;
	_Block_record* __block = reinterpret_cast<_Block_record*>(__c);

	#ifdef __GTHREADS
	if (__gthread_active_p())
	{
	// Calculate the number of records to remove from our freelist:
	// in order to avoid too much contention we wait until the
	// number of records is "high enough".
	const size_t __thread_id = _S_get_thread_id();

	long __remove = ((__bin._M_free[__thread_id]
	* _S_options._M_freelist_headroom)
	- __bin._M_used[__thread_id]);
	if (__remove > static_cast<long>(100 * (_S_bin_size - __which)
	* _S_options._M_freelist_headroom)
	&& __remove > static_cast<long>(__bin._M_free[__thread_id]))
	{
	_Block_record* __tmp = __bin._M_first[__thread_id];
	_Block_record* __first = __tmp;
	__remove /= _S_options._M_freelist_headroom;
	const long __removed = __remove;
	--__remove;
	while (__remove-- > 0)
	__tmp = __tmp->_M_next;
	__bin._M_first[__thread_id] = __tmp->_M_next;
	__bin._M_free[__thread_id] -= __removed;

	__gthread_mutex_lock(__bin._M_mutex);
	__tmp->_M_next = __bin._M_first[0];
	__bin._M_first[0] = __first;
	__bin._M_free[0] += __removed;
	__gthread_mutex_unlock(__bin._M_mutex);
	}

	// Return this block to our list and update counters and
	// owner id as needed.
	--__bin._M_used[__block->_M_thread_id];

	__block->_M_next = __bin._M_first[__thread_id];
	__bin._M_first[__thread_id] = __block;

	++__bin._M_free[__thread_id];
	}
	else
	#endif
	{
	// Single threaded application - return to global pool.
	__block->_M_next = __bin._M_first[0];
	__bin._M_first[0] = __block;
	}
	}

	template<typename _Tp>
	void
	__mt_alloc<_Tp>::
	_S_initialize()
	{
	// This method is called on the first allocation (when _S_init is still
	// false) to create the bins.

	// Ensure that the static initialization of _S_options has
	// happened. This depends on (a) _M_align == 0 being an invalid
	// value that is only present at startup, and (b) the real
	// static initialization that happens later not actually
	// changing anything.
	if (_S_options._M_align == 0)
	new (&_S_options) _Tune;

	// _M_force_new must not change after the first allocate(),
	// which in turn calls this method, so if it's false, it's false
	// forever and we don't need to return here ever again.
	if (_S_options._M_force_new)
	{
	_S_init = true;
	return;
	}

	// Calculate the number of bins required based on _M_max_bytes.
	// _S_bin_size is statically-initialized to one.
	size_t __bin_size = _S_options._M_min_bin;
	while (_S_options._M_max_bytes > __bin_size)
	{
	__bin_size <<= 1;
	++_S_bin_size;
	}

	// Setup the bin map for quick lookup of the relevant bin.
	const size_t __j = (_S_options._M_max_bytes + 1) * sizeof(_Binmap_type);
	_S_binmap = static_cast<_Binmap_type*>(::operator new(__j));

	_Binmap_type* __bp = _S_binmap;
	_Binmap_type __bin_max = _S_options._M_min_bin;
	_Binmap_type __bint = 0;
	for (_Binmap_type __ct = 0; __ct <= _S_options._M_max_bytes; ++__ct)
	{
	if (__ct > __bin_max)
	{
	__bin_max <<= 1;
	++__bint;
	}
	*__bp++ = __bint;
	}

	// Initialize _S_bin and its members.
	void* __v = ::operator new(sizeof(_Bin_record) * _S_bin_size);
	_S_bin = static_cast<_Bin_record*>(__v);

	// If __gthread_active_p() create and initialize the list of
	// free thread ids. Single threaded applications use thread id 0
	// directly and have no need for this.
	#ifdef __GTHREADS
	if (__gthread_active_p())
	{
	const size_t __k = sizeof(_Thread_record) * _S_options._M_max_threads;
	__v = ::operator new(__k);
	_S_thread_freelist_first = static_cast<_Thread_record*>(__v);

	// NOTE! The first assignable thread id is 1 since the
	// global pool uses id 0
	size_t __i;
	for (__i = 1; __i < _S_options._M_max_threads; ++__i)
	{
	_Thread_record& __tr = _S_thread_freelist_first[__i - 1];
	__tr._M_next = &_S_thread_freelist_first[__i];
	__tr._M_id = __i;
	}

	// Set last record.
	_S_thread_freelist_first[__i - 1]._M_next = NULL;
	_S_thread_freelist_first[__i - 1]._M_id = __i;

	// Make sure this is initialized.
	#ifndef __GTHREAD_MUTEX_INIT
	__GTHREAD_MUTEX_INIT_FUNCTION(&_S_thread_freelist_mutex);
	#endif
	// Initialize per thread key to hold pointer to
	// _S_thread_freelist.
	__gthread_key_create(&_S_thread_key, _S_destroy_thread_key);

	const size_t __max_threads = _S_options._M_max_threads + 1;
	for (size_t __n = 0; __n < _S_bin_size; ++__n)
	{
	_Bin_record& __bin = _S_bin[__n];
	__v = ::operator new(sizeof(_Block_record) __max_threads);
	__bin._M_first = static_cast<_Block_record**>(__v);

	__v = ::operator new(sizeof(size_t) * __max_threads);
	__bin._M_free = static_cast<size_t*>(__v);

	__v = ::operator new(sizeof(size_t) * __max_threads);
	__bin._M_used = static_cast<size_t*>(__v);

	__v = ::operator new(sizeof(__gthread_mutex_t));
	__bin._M_mutex = static_cast<__gthread_mutex_t*>(__v);

	#ifdef __GTHREAD_MUTEX_INIT
	{
	// Do not copy a POSIX/gthr mutex once in use.
	__gthread_mutex_t __tmp = __GTHREAD_MUTEX_INIT;
	*__bin._M_mutex = __tmp;
	}
	#else
	{ __GTHREAD_MUTEX_INIT_FUNCTION(__bin._M_mutex); }
	#endif

	for (size_t __threadn = 0; __threadn < __max_threads;
	++__threadn)
	{
	__bin._M_first[__threadn] = NULL;
	__bin._M_free[__threadn] = 0;
	__bin._M_used[__threadn] = 0;
	}
	}
	}
	else
	#endif
	for (size_t __n = 0; __n < _S_bin_size; ++__n)
	{
	_Bin_record& __bin = _S_bin[__n];
	__v = ::operator new(sizeof(_Block_record*));
	__bin._M_first = static_cast<_Block_record**>(__v);
	__bin._M_first[0] = NULL;
	}

	_S_init = true;
	}

	template<typename _Tp>
	size_t
	__mt_alloc<_Tp>::
	_S_get_thread_id()
	{
	#ifdef __GTHREADS
	// If we have thread support and it's active we check the thread
	// key value and return its id or if it's not set we take the
	// first record from _S_thread_freelist and sets the key and
	// returns it's id.
	if (__gthread_active_p())
	{
	_Thread_record* __freelist_pos =
	static_cast<_Thread_record*>(__gthread_getspecific(_S_thread_key));
	if (__freelist_pos == NULL)
	{
	// Since _S_options._M_max_threads must be larger than
	// the theoretical max number of threads of the OS the
	// list can never be empty.
	__gthread_mutex_lock(&_S_thread_freelist_mutex);
	__freelist_pos = _S_thread_freelist_first;
	_S_thread_freelist_first = _S_thread_freelist_first->_M_next;
	__gthread_mutex_unlock(&_S_thread_freelist_mutex);

	__gthread_setspecific(_S_thread_key,
	static_cast<void*>(__freelist_pos));
	}
	return __freelist_pos->_M_id;
	}
	#endif
	// Otherwise (no thread support or inactive) all requests are
	// served from the global pool 0.
	return 0;
	}

	#ifdef __GTHREADS
	template<typename _Tp>
	void
	__mt_alloc<_Tp>::
	_S_destroy_thread_key(void* __freelist_pos)
	{
	// Return this thread id record to front of thread_freelist.
	__gthread_mutex_lock(&_S_thread_freelist_mutex);
	_Thread_record* __tr = static_cast<_Thread_record*>(__freelist_pos);
	__tr->_M_next = _S_thread_freelist_first;
	_S_thread_freelist_first = __tr;
	__gthread_mutex_unlock(&_S_thread_freelist_mutex);
	}
	#endif

	template<typename _Tp>
	inline bool
	operator==(const __mt_alloc<_Tp>&, const __mt_alloc<_Tp>&)
	{ return true; }

	template<typename _Tp>
	inline bool
	operator!=(const __mt_alloc<_Tp>&, const __mt_alloc<_Tp>&)
	{ return false; }

	template<typename _Tp>
	bool __mt_alloc<_Tp>::_S_init = false;

	template<typename _Tp>
	typename __mt_alloc<_Tp>::_Tune __mt_alloc<_Tp>::_S_options;

	template<typename _Tp>
	typename __mt_alloc<_Tp>::_Binmap_type* __mt_alloc<_Tp>::_S_binmap;

	template<typename _Tp>
	typename __mt_alloc<_Tp>::_Bin_record* volatile __mt_alloc<_Tp>::_S_bin;

	template<typename _Tp>
	size_t __mt_alloc<_Tp>::_S_bin_size = 1;

	// Actual initialization in _S_initialize().
	#ifdef __GTHREADS
	template<typename _Tp>
	__gthread_once_t __mt_alloc<_Tp>::_S_once = __GTHREAD_ONCE_INIT;

	template<typename _Tp>
	typename __mt_alloc<_Tp>::_Thread_record*
	volatile __mt_alloc<_Tp>::_S_thread_freelist_first = NULL;

	template<typename _Tp>
	__gthread_key_t __mt_alloc<_Tp>::_S_thread_key;

	template<typename _Tp>
	__gthread_mutex_t
	#ifdef __GTHREAD_MUTEX_INIT
	__mt_alloc<_Tp>::_S_thread_freelist_mutex = __GTHREAD_MUTEX_INIT;
	#else
	__mt_alloc<_Tp>::_S_thread_freelist_mutex;
	#endif
	#endif
	} // namespace __gnu_cxx

	#endif