williamr@2: #ifndef BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED
williamr@2: #define BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED
williamr@2: 
williamr@2: // MS compatible compilers support #pragma once
williamr@2: 
williamr@2: #if defined(_MSC_VER) && (_MSC_VER >= 1020)
williamr@2: # pragma once
williamr@2: #endif
williamr@2: 
williamr@2: //
williamr@2: //  boost/detail/atomic_count.hpp - thread/SMP safe reference counter
williamr@2: //
williamr@2: //  Copyright (c) 2001, 2002 Peter Dimov and Multi Media Ltd.
williamr@2: //
williamr@2: // Distributed under the Boost Software License, Version 1.0. (See
williamr@2: // accompanying file LICENSE_1_0.txt or copy at
williamr@2: // http://www.boost.org/LICENSE_1_0.txt)
williamr@2: //
williamr@2: //  typedef <implementation-defined> boost::detail::atomic_count;
williamr@2: //
williamr@2: //  atomic_count a(n);
williamr@2: //
williamr@2: //    (n is convertible to long)
williamr@2: //
williamr@2: //    Effects: Constructs an atomic_count with an initial value of n
williamr@2: //
williamr@2: //  a;
williamr@2: //
williamr@2: //    Returns: (long) the current value of a
williamr@2: //
williamr@2: //  ++a;
williamr@2: //
williamr@2: //    Effects: Atomically increments the value of a
williamr@2: //    Returns: nothing
williamr@2: //
williamr@2: //  --a;
williamr@2: //
williamr@2: //    Effects: Atomically decrements the value of a
williamr@2: //    Returns: (long) zero if the new value of a is zero,
williamr@2: //      unspecified non-zero value otherwise (usually the new value)
williamr@2: //
williamr@2: //    Important note: when --a returns zero, it must act as a
williamr@2: //      read memory barrier (RMB); i.e. the calling thread must
williamr@2: //      have a synchronized view of the memory
williamr@2: //
williamr@2: //    On Intel IA-32 (x86) memory is always synchronized, so this
williamr@2: //      is not a problem.
williamr@2: //
williamr@2: //    On many architectures the atomic instructions already act as
williamr@2: //      a memory barrier.
williamr@2: //
williamr@2: //    This property is necessary for proper reference counting, since
williamr@2: //      a thread can update the contents of a shared object, then
williamr@2: //      release its reference, and another thread may immediately
williamr@2: //      release the last reference causing object destruction.
williamr@2: //
williamr@2: //    The destructor needs to have a synchronized view of the
williamr@2: //      object to perform proper cleanup.
williamr@2: //
williamr@2: //    Original example by Alexander Terekhov:
williamr@2: //
williamr@2: //    Given:
williamr@2: //
williamr@2: //    - a mutable shared object OBJ;
williamr@2: //    - two threads THREAD1 and THREAD2 each holding 
williamr@2: //      a private smart_ptr object pointing to that OBJ.
williamr@2: //
williamr@2: //    t1: THREAD1 updates OBJ (thread-safe via some synchronization)
williamr@2: //      and a few cycles later (after "unlock") destroys smart_ptr;
williamr@2: //
williamr@2: //    t2: THREAD2 destroys smart_ptr WITHOUT doing any synchronization 
williamr@2: //      with respect to shared mutable object OBJ; OBJ destructors
williamr@2: //      are called driven by smart_ptr interface...
williamr@2: //
williamr@2: 
williamr@2: #include <boost/config.hpp>
williamr@2: 
williamr@2: #ifndef BOOST_HAS_THREADS
williamr@2: 
williamr@2: namespace boost
williamr@2: {
williamr@2: 
williamr@2: namespace detail
williamr@2: {
williamr@2: 
williamr@2: typedef long atomic_count;
williamr@2: 
williamr@2: }
williamr@2: 
williamr@2: }
williamr@2: 
williamr@2: #elif defined(BOOST_AC_USE_PTHREADS)
williamr@2: #  include <boost/detail/atomic_count_pthreads.hpp>
williamr@2: #elif defined(WIN32) || defined(_WIN32) || defined(__WIN32__)
williamr@2: #  include <boost/detail/atomic_count_win32.hpp>
williamr@2: #elif defined(__GLIBCPP__) || defined(__GLIBCXX__)
williamr@2: #  include <boost/detail/atomic_count_gcc.hpp>
williamr@2: #elif defined(BOOST_HAS_PTHREADS)
williamr@2: #  define BOOST_AC_USE_PTHREADS
williamr@2: #  include <boost/detail/atomic_count_pthreads.hpp>
williamr@2: #else
williamr@2: 
williamr@2: // Use #define BOOST_DISABLE_THREADS to avoid the error
williamr@2: #error Unrecognized threading platform
williamr@2: 
williamr@2: #endif
williamr@2: 
williamr@2: #endif // #ifndef BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED