#ifndef BOOST_DETAIL_QUICK_ALLOCATOR_HPP_INCLUDED

#define BOOST_DETAIL_QUICK_ALLOCATOR_HPP_INCLUDED



// MS compatible compilers support #pragma once



#if defined(_MSC_VER) && (_MSC_VER >= 1020)

# pragma once

#endif



//

//  detail/quick_allocator.hpp

//

//  Copyright (c) 2003 David Abrahams

//  Copyright (c) 2003 Peter Dimov

//

// Distributed under the Boost Software License, Version 1.0. (See

// accompanying file LICENSE_1_0.txt or copy at

// http://www.boost.org/LICENSE_1_0.txt)

//



#include <boost/config.hpp>



#include <boost/detail/lightweight_mutex.hpp>

#include <boost/type_traits/type_with_alignment.hpp>

#include <boost/type_traits/alignment_of.hpp>



#include <new>              // ::operator new, ::operator delete

#include <cstddef>          // std::size_t



namespace boost

{



namespace detail

{



template<unsigned size, unsigned align_> union freeblock

{

    typedef typename boost::type_with_alignment<align_>::type aligner_type;

    aligner_type aligner;

    char bytes[size];

    freeblock * next;

};



template<unsigned size, unsigned align_> struct allocator_impl

{

    typedef freeblock<size, align_> block;



    // It may seem odd to use such small pages.

    //

    // However, on a typical Windows implementation that uses

    // the OS allocator, "normal size" pages interact with the

    // "ordinary" operator new, slowing it down dramatically.

    //

    // 512 byte pages are handled by the small object allocator,

    // and don't interfere with ::new.

    //

    // The other alternative is to use much bigger pages (1M.)

    //

    // It is surprisingly easy to hit pathological behavior by

    // varying the page size. g++ 2.96 on Red Hat Linux 7.2,

    // for example, passionately dislikes 496. 512 seems OK.



#if defined(BOOST_QA_PAGE_SIZE)



    enum { items_per_page = BOOST_QA_PAGE_SIZE / size };



#else



    enum { items_per_page = 512 / size }; // 1048560 / size



#endif



#ifdef BOOST_HAS_THREADS



    static lightweight_mutex & mutex()

    {

        static lightweight_mutex m;

        return m;

    }



    static lightweight_mutex * mutex_init;



#endif



    static block * free;

    static block * page;

    static unsigned last;



    static inline void * alloc()

    {

#ifdef BOOST_HAS_THREADS

        lightweight_mutex::scoped_lock lock( mutex() );

#endif

        if(block * x = free)

        {

            free = x->next;

            return x;

        }

        else

        {

            if(last == items_per_page)

            {

                // "Listen to me carefully: there is no memory leak"

                // -- Scott Meyers, Eff C++ 2nd Ed Item 10

                page = ::new block[items_per_page];

                last = 0;

            }



            return &page[last++];

        }

    }



    static inline void * alloc(std::size_t n)

    {

        if(n != size) // class-specific new called for a derived object

        {

            return ::operator new(n);

        }

        else

        {

#ifdef BOOST_HAS_THREADS

            lightweight_mutex::scoped_lock lock( mutex() );

#endif

            if(block * x = free)

            {

                free = x->next;

                return x;

            }

            else

            {

                if(last == items_per_page)

                {

                    page = ::new block[items_per_page];

                    last = 0;

                }



                return &page[last++];

            }

        }

    }



    static inline void dealloc(void * pv)

    {

        if(pv != 0) // 18.4.1.1/13

        {

#ifdef BOOST_HAS_THREADS

            lightweight_mutex::scoped_lock lock( mutex() );

#endif

            block * pb = static_cast<block *>(pv);

            pb->next = free;

            free = pb;

        }

    }



    static inline void dealloc(void * pv, std::size_t n)

    {

        if(n != size) // class-specific delete called for a derived object

        {

            ::operator delete(pv);

        }

        else if(pv != 0) // 18.4.1.1/13

        {

#ifdef BOOST_HAS_THREADS

            lightweight_mutex::scoped_lock lock( mutex() );

#endif

            block * pb = static_cast<block *>(pv);

            pb->next = free;

            free = pb;

        }

    }

};



#ifdef BOOST_HAS_THREADS



template<unsigned size, unsigned align_>

  lightweight_mutex * allocator_impl<size, align_>::mutex_init = &allocator_impl<size, align_>::mutex();



#endif



template<unsigned size, unsigned align_>

  freeblock<size, align_> * allocator_impl<size, align_>::free = 0;



template<unsigned size, unsigned align_>

  freeblock<size, align_> * allocator_impl<size, align_>::page = 0;



template<unsigned size, unsigned align_>

  unsigned allocator_impl<size, align_>::last = allocator_impl<size, align_>::items_per_page;



template<class T>

struct quick_allocator: public allocator_impl< sizeof(T), boost::alignment_of<T>::value >

{

};



} // namespace detail



} // namespace boost



#endif  // #ifndef BOOST_DETAIL_QUICK_ALLOCATOR_HPP_INCLUDED

