sl@0: #ifndef BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED
sl@0: #define BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED
sl@0: 
sl@0: // MS compatible compilers support #pragma once
sl@0: 
sl@0: #if defined(_MSC_VER) && (_MSC_VER >= 1020)
sl@0: # pragma once
sl@0: #endif
sl@0: 
sl@0: //
sl@0: //  boost/detail/atomic_count.hpp - thread/SMP safe reference counter
sl@0: //
sl@0: //  Copyright (c) 2001, 2002 Peter Dimov and Multi Media Ltd.
sl@0: //
sl@0: // Distributed under the Boost Software License, Version 1.0. (See
sl@0: // accompanying file LICENSE_1_0.txt or copy at
sl@0: // http://www.boost.org/LICENSE_1_0.txt)
sl@0: //
sl@0: //  typedef <implementation-defined> boost::detail::atomic_count;
sl@0: //
sl@0: //  atomic_count a(n);
sl@0: //
sl@0: //    (n is convertible to long)
sl@0: //
sl@0: //    Effects: Constructs an atomic_count with an initial value of n
sl@0: //
sl@0: //  a;
sl@0: //
sl@0: //    Returns: (long) the current value of a
sl@0: //
sl@0: //  ++a;
sl@0: //
sl@0: //    Effects: Atomically increments the value of a
sl@0: //    Returns: nothing
sl@0: //
sl@0: //  --a;
sl@0: //
sl@0: //    Effects: Atomically decrements the value of a
sl@0: //    Returns: (long) zero if the new value of a is zero,
sl@0: //      unspecified non-zero value otherwise (usually the new value)
sl@0: //
sl@0: //    Important note: when --a returns zero, it must act as a
sl@0: //      read memory barrier (RMB); i.e. the calling thread must
sl@0: //      have a synchronized view of the memory
sl@0: //
sl@0: //    On Intel IA-32 (x86) memory is always synchronized, so this
sl@0: //      is not a problem.
sl@0: //
sl@0: //    On many architectures the atomic instructions already act as
sl@0: //      a memory barrier.
sl@0: //
sl@0: //    This property is necessary for proper reference counting, since
sl@0: //      a thread can update the contents of a shared object, then
sl@0: //      release its reference, and another thread may immediately
sl@0: //      release the last reference causing object destruction.
sl@0: //
sl@0: //    The destructor needs to have a synchronized view of the
sl@0: //      object to perform proper cleanup.
sl@0: //
sl@0: //    Original example by Alexander Terekhov:
sl@0: //
sl@0: //    Given:
sl@0: //
sl@0: //    - a mutable shared object OBJ;
sl@0: //    - two threads THREAD1 and THREAD2 each holding 
sl@0: //      a private smart_ptr object pointing to that OBJ.
sl@0: //
sl@0: //    t1: THREAD1 updates OBJ (thread-safe via some synchronization)
sl@0: //      and a few cycles later (after "unlock") destroys smart_ptr;
sl@0: //
sl@0: //    t2: THREAD2 destroys smart_ptr WITHOUT doing any synchronization 
sl@0: //      with respect to shared mutable object OBJ; OBJ destructors
sl@0: //      are called driven by smart_ptr interface...
sl@0: //
sl@0: 
sl@0: #include <boost/config.hpp>
sl@0: 
sl@0: #ifndef BOOST_HAS_THREADS
sl@0: 
sl@0: namespace boost
sl@0: {
sl@0: 
sl@0: namespace detail
sl@0: {
sl@0: 
sl@0: typedef long atomic_count;
sl@0: 
sl@0: }
sl@0: 
sl@0: }
sl@0: 
sl@0: #elif defined(BOOST_AC_USE_PTHREADS)
sl@0: #  include <boost/detail/atomic_count_pthreads.hpp>
sl@0: #elif defined(WIN32) || defined(_WIN32) || defined(__WIN32__)
sl@0: #  include <boost/detail/atomic_count_win32.hpp>
sl@0: #elif defined(__GLIBCPP__) || defined(__GLIBCXX__)
sl@0: #  include <boost/detail/atomic_count_gcc.hpp>
sl@0: #elif defined(BOOST_HAS_PTHREADS)
sl@0: #  define BOOST_AC_USE_PTHREADS
sl@0: #  include <boost/detail/atomic_count_pthreads.hpp>
sl@0: #else
sl@0: 
sl@0: // Use #define BOOST_DISABLE_THREADS to avoid the error
sl@0: #error Unrecognized threading platform
sl@0: 
sl@0: #endif
sl@0: 
sl@0: #endif // #ifndef BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED