#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