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119 lines
3.3 KiB
119 lines
3.3 KiB
#ifndef BOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_HPP_INCLUDED |
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#define BOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_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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// boost/detail/atomic_count.hpp - thread/SMP safe reference counter |
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// |
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// Copyright (c) 2001, 2002 Peter Dimov and Multi Media Ltd. |
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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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// typedef <implementation-defined> boost::detail::atomic_count; |
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// |
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// atomic_count a(n); |
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// |
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// (n is convertible to long) |
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// |
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// Effects: Constructs an atomic_count with an initial value of n |
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// |
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// a; |
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// |
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// Returns: (long) the current value of a |
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// |
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// ++a; |
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// |
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// Effects: Atomically increments the value of a |
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// Returns: (long) the new value of a |
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// |
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// --a; |
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// |
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// Effects: Atomically decrements the value of a |
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// Returns: (long) the new value of a |
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// |
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// Important note: when --a returns zero, it must act as a |
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// read memory barrier (RMB); i.e. the calling thread must |
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// have a synchronized view of the memory |
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// |
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// On Intel IA-32 (x86) memory is always synchronized, so this |
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// is not a problem. |
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// |
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// On many architectures the atomic instructions already act as |
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// a memory barrier. |
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// |
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// This property is necessary for proper reference counting, since |
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// a thread can update the contents of a shared object, then |
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// release its reference, and another thread may immediately |
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// release the last reference causing object destruction. |
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// |
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// The destructor needs to have a synchronized view of the |
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// object to perform proper cleanup. |
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// |
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// Original example by Alexander Terekhov: |
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// |
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// Given: |
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// |
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// - a mutable shared object OBJ; |
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// - two threads THREAD1 and THREAD2 each holding |
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// a private smart_ptr object pointing to that OBJ. |
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// |
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// t1: THREAD1 updates OBJ (thread-safe via some synchronization) |
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// and a few cycles later (after "unlock") destroys smart_ptr; |
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// |
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// t2: THREAD2 destroys smart_ptr WITHOUT doing any synchronization |
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// with respect to shared mutable object OBJ; OBJ destructors |
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// are called driven by smart_ptr interface... |
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// |
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#include <boost/config.hpp> |
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#include <boost/smart_ptr/detail/sp_has_sync.hpp> |
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#ifndef BOOST_HAS_THREADS |
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namespace boost |
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{ |
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namespace detail |
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{ |
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typedef long atomic_count; |
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} |
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} |
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#elif defined(BOOST_AC_USE_PTHREADS) |
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# include <boost/smart_ptr/detail/atomic_count_pthreads.hpp> |
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#elif defined( __GNUC__ ) && ( defined( __i386__ ) || defined( __x86_64__ ) ) |
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# include <boost/smart_ptr/detail/atomic_count_gcc_x86.hpp> |
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#elif defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(__CYGWIN__) |
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# include <boost/smart_ptr/detail/atomic_count_win32.hpp> |
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#elif defined( BOOST_SP_HAS_SYNC ) |
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# include <boost/smart_ptr/detail/atomic_count_sync.hpp> |
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#elif defined(__GLIBCPP__) || defined(__GLIBCXX__) |
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# include <boost/smart_ptr/detail/atomic_count_gcc.hpp> |
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#elif defined(BOOST_HAS_PTHREADS) |
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# define BOOST_AC_USE_PTHREADS |
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# include <boost/smart_ptr/detail/atomic_count_pthreads.hpp> |
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#else |
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// Use #define BOOST_DISABLE_THREADS to avoid the error |
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#error Unrecognized threading platform |
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#endif |
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#endif // #ifndef BOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_HPP_INCLUDED
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