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#ifndef BOOST_DETAIL_QUICK_ALLOCATOR_HPP_INCLUDED
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#define BOOST_DETAIL_QUICK_ALLOCATOR_HPP_INCLUDED
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// MS compatible compilers support #pragma once
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#if defined(_MSC_VER) && (_MSC_VER >= 1020)
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# pragma once
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#endif
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//
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// detail/quick_allocator.hpp
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//
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// Copyright (c) 2003 David Abrahams
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// Copyright (c) 2003 Peter Dimov
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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#include <boost/config.hpp>
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#include <boost/detail/lightweight_mutex.hpp>
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#include <boost/type_traits/type_with_alignment.hpp>
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#include <boost/type_traits/alignment_of.hpp>
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#include <new> // ::operator new, ::operator delete
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#include <cstddef> // std::size_t
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namespace boost
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{
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namespace detail
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{
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template<unsigned size, unsigned align_> union freeblock
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{
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typedef typename boost::type_with_alignment<align_>::type aligner_type;
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aligner_type aligner;
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char bytes[size];
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freeblock * next;
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};
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template<unsigned size, unsigned align_> struct allocator_impl
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{
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typedef freeblock<size, align_> block;
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// It may seem odd to use such small pages.
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//
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// However, on a typical Windows implementation that uses
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// the OS allocator, "normal size" pages interact with the
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// "ordinary" operator new, slowing it down dramatically.
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//
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// 512 byte pages are handled by the small object allocator,
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// and don't interfere with ::new.
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//
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// The other alternative is to use much bigger pages (1M.)
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//
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// It is surprisingly easy to hit pathological behavior by
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// varying the page size. g++ 2.96 on Red Hat Linux 7.2,
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// for example, passionately dislikes 496. 512 seems OK.
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#if defined(BOOST_QA_PAGE_SIZE)
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enum { items_per_page = BOOST_QA_PAGE_SIZE / size };
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#else
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enum { items_per_page = 512 / size }; // 1048560 / size
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#endif
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#ifdef BOOST_HAS_THREADS
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static lightweight_mutex & mutex()
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{
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static lightweight_mutex m;
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return m;
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}
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static lightweight_mutex * mutex_init;
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#endif
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static block * free;
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static block * page;
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static unsigned last;
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static inline void * alloc()
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{
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#ifdef BOOST_HAS_THREADS
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lightweight_mutex::scoped_lock lock( mutex() );
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#endif
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if(block * x = free)
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{
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free = x->next;
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return x;
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}
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else
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{
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if(last == items_per_page)
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{
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// "Listen to me carefully: there is no memory leak"
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// -- Scott Meyers, Eff C++ 2nd Ed Item 10
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page = ::new block[items_per_page];
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last = 0;
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}
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return &page[last++];
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}
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}
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static inline void * alloc(std::size_t n)
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{
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if(n != size) // class-specific new called for a derived object
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{
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return ::operator new(n);
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}
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else
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{
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#ifdef BOOST_HAS_THREADS
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lightweight_mutex::scoped_lock lock( mutex() );
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#endif
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if(block * x = free)
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{
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free = x->next;
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return x;
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}
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else
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{
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if(last == items_per_page)
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{
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page = ::new block[items_per_page];
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last = 0;
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}
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return &page[last++];
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}
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}
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}
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static inline void dealloc(void * pv)
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{
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if(pv != 0) // 18.4.1.1/13
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{
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#ifdef BOOST_HAS_THREADS
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lightweight_mutex::scoped_lock lock( mutex() );
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#endif
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block * pb = static_cast<block *>(pv);
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pb->next = free;
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free = pb;
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}
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}
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static inline void dealloc(void * pv, std::size_t n)
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{
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if(n != size) // class-specific delete called for a derived object
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{
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::operator delete(pv);
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}
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else if(pv != 0) // 18.4.1.1/13
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{
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#ifdef BOOST_HAS_THREADS
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lightweight_mutex::scoped_lock lock( mutex() );
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#endif
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block * pb = static_cast<block *>(pv);
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pb->next = free;
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free = pb;
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}
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}
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};
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#ifdef BOOST_HAS_THREADS
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template<unsigned size, unsigned align_>
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lightweight_mutex * allocator_impl<size, align_>::mutex_init = &allocator_impl<size, align_>::mutex();
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#endif
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template<unsigned size, unsigned align_>
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freeblock<size, align_> * allocator_impl<size, align_>::free = 0;
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template<unsigned size, unsigned align_>
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freeblock<size, align_> * allocator_impl<size, align_>::page = 0;
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template<unsigned size, unsigned align_>
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unsigned allocator_impl<size, align_>::last = allocator_impl<size, align_>::items_per_page;
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template<class T>
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struct quick_allocator: public allocator_impl< sizeof(T), boost::alignment_of<T>::value >
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{
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};
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} // namespace detail
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} // namespace boost
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#endif // #ifndef BOOST_DETAIL_QUICK_ALLOCATOR_HPP_INCLUDED
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