#ifndef BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED

 #define BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED

 // MS compatible compilers support #pragma once

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

 # pragma once

 #endif

 //

 //  boost/detail/atomic_count.hpp - thread/SMP safe reference counter

 //

 //  Copyright (c) 2001, 2002 Peter Dimov and Multi Media Ltd.

 //

 // 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)

 //

 //  typedef <implementation-defined> boost::detail::atomic_count;

 //

 //  atomic_count a(n);

 //

 //    (n is convertible to long)

 //

 //    Effects: Constructs an atomic_count with an initial value of n

 //

 //  a;

 //

 //    Returns: (long) the current value of a

 //

 //  ++a;

 //

 //    Effects: Atomically increments the value of a

 //    Returns: nothing

 //

 //  --a;

 //

 //    Effects: Atomically decrements the value of a

 //    Returns: (long) zero if the new value of a is zero,

 //      unspecified non-zero value otherwise (usually the new value)

 //

 //    Important note: when --a returns zero, it must act as a

 //      read memory barrier (RMB); i.e. the calling thread must

 //      have a synchronized view of the memory

 //

 //    On Intel IA-32 (x86) memory is always synchronized, so this

 //      is not a problem.

 //

 //    On many architectures the atomic instructions already act as

 //      a memory barrier.

 //

 //    This property is necessary for proper reference counting, since

 //      a thread can update the contents of a shared object, then

 //      release its reference, and another thread may immediately

 //      release the last reference causing object destruction.

 //

 //    The destructor needs to have a synchronized view of the

 //      object to perform proper cleanup.

 //

 //    Original example by Alexander Terekhov:

 //

 //    Given:

 //

 //    - a mutable shared object OBJ;

 //    - two threads THREAD1 and THREAD2 each holding 

 //      a private smart_ptr object pointing to that OBJ.

 //

 //    t1: THREAD1 updates OBJ (thread-safe via some synchronization)

 //      and a few cycles later (after "unlock") destroys smart_ptr;

 //

 //    t2: THREAD2 destroys smart_ptr WITHOUT doing any synchronization 

 //      with respect to shared mutable object OBJ; OBJ destructors

 //      are called driven by smart_ptr interface...

 //

 #include <boost/config.hpp>

 #ifndef BOOST_HAS_THREADS

 namespace boost

 {

 namespace detail

 {

 typedef long atomic_count;

 }

 }

 #elif defined(BOOST_AC_USE_PTHREADS)

 #  include <boost/detail/atomic_count_pthreads.hpp>

 #elif defined(WIN32) || defined(_WIN32) || defined(__WIN32__)

 #  include <boost/detail/atomic_count_win32.hpp>

 #elif defined(__GLIBCPP__) || defined(__GLIBCXX__)

 #  include <boost/detail/atomic_count_gcc.hpp>

 #elif defined(BOOST_HAS_PTHREADS)

 #  define BOOST_AC_USE_PTHREADS

 #  include <boost/detail/atomic_count_pthreads.hpp>

 #else

 // Use #define BOOST_DISABLE_THREADS to avoid the error

 #error Unrecognized threading platform

 #endif

 #endif // #ifndef BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED