1 #ifndef BOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_HPP_INCLUDED 2 #define BOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_HPP_INCLUDED 3 4 // MS compatible compilers support #pragma once 5 6 #if defined(_MSC_VER) && (_MSC_VER >= 1020) 7 # pragma once 8 #endif 9 10 // 11 // boost/detail/atomic_count.hpp - thread/SMP safe reference counter 12 // 13 // Copyright (c) 2001, 2002 Peter Dimov and Multi Media Ltd. 14 // 15 // Distributed under the Boost Software License, Version 1.0. (See 16 // accompanying file LICENSE_1_0.txt or copy at 17 // http://www.boost.org/LICENSE_1_0.txt) 18 // 19 // typedef <implementation-defined> boost::detail::atomic_count; 20 // 21 // atomic_count a(n); 22 // 23 // (n is convertible to long) 24 // 25 // Effects: Constructs an atomic_count with an initial value of n 26 // 27 // a; 28 // 29 // Returns: (long) the current value of a 30 // 31 // ++a; 32 // 33 // Effects: Atomically increments the value of a 34 // Returns: (long) the new value of a 35 // 36 // --a; 37 // 38 // Effects: Atomically decrements the value of a 39 // Returns: (long) the new value of a 40 // 41 // Important note: when --a returns zero, it must act as a 42 // read memory barrier (RMB); i.e. the calling thread must 43 // have a synchronized view of the memory 44 // 45 // On Intel IA-32 (x86) memory is always synchronized, so this 46 // is not a problem. 47 // 48 // On many architectures the atomic instructions already act as 49 // a memory barrier. 50 // 51 // This property is necessary for proper reference counting, since 52 // a thread can update the contents of a shared object, then 53 // release its reference, and another thread may immediately 54 // release the last reference causing object destruction. 55 // 56 // The destructor needs to have a synchronized view of the 57 // object to perform proper cleanup. 58 // 59 // Original example by Alexander Terekhov: 60 // 61 // Given: 62 // 63 // - a mutable shared object OBJ; 64 // - two threads THREAD1 and THREAD2 each holding 65 // a private smart_ptr object pointing to that OBJ. 66 // 67 // t1: THREAD1 updates OBJ (thread-safe via some synchronization) 68 // and a few cycles later (after "unlock") destroys smart_ptr; 69 // 70 // t2: THREAD2 destroys smart_ptr WITHOUT doing any synchronization 71 // with respect to shared mutable object OBJ; OBJ destructors 72 // are called driven by smart_ptr interface... 73 // 74 75 #include <boost/config.hpp> 76 #include <boost/smart_ptr/detail/sp_has_sync.hpp> 77 78 #ifndef BOOST_HAS_THREADS 79 80 namespace boost 81 { 82 83 namespace detail 84 { 85 86 typedef long atomic_count; 87 88 } 89 90 } 91 92 #elif defined(BOOST_AC_USE_PTHREADS) 93 # include <boost/smart_ptr/detail/atomic_count_pthreads.hpp> 94 95 #elif defined( __GNUC__ ) && ( defined( __i386__ ) || defined( __x86_64__ ) ) 96 # include <boost/smart_ptr/detail/atomic_count_gcc_x86.hpp> 97 98 #elif defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(__CYGWIN__) 99 # include <boost/smart_ptr/detail/atomic_count_win32.hpp> 100 101 #elif defined( BOOST_SP_HAS_SYNC ) 102 # include <boost/smart_ptr/detail/atomic_count_sync.hpp> 103 104 #elif defined(__GLIBCPP__) || defined(__GLIBCXX__) 105 # include <boost/smart_ptr/detail/atomic_count_gcc.hpp> 106 107 #elif defined(BOOST_HAS_PTHREADS) 108 109 # define BOOST_AC_USE_PTHREADS 110 # include <boost/smart_ptr/detail/atomic_count_pthreads.hpp> 111 112 #else 113 114 // Use #define BOOST_DISABLE_THREADS to avoid the error 115 #error Unrecognized threading platform 116 117 #endif 118 119 #endif // #ifndef BOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_HPP_INCLUDED 120