1 #ifndef BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED
2 #define BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED
9 // boost/detail/atomic_count.hpp - thread/SMP safe reference counter
11 // Copyright (c) 2001, 2002 Peter Dimov and Multi Media Ltd.
13 // Permission to copy, use, modify, sell and distribute this software
14 // is granted provided this copyright notice appears in all copies.
15 // This software is provided "as is" without express or implied
16 // warranty, and with no claim as to its suitability for any purpose.
18 // typedef <implementation-defined> boost::detail::atomic_count;
22 // (n is convertible to long)
24 // Effects: Constructs an atomic_count with an initial value of n
28 // Returns: (long) the current value of a
32 // Effects: Atomically increments the value of a
37 // Effects: Atomically decrements the value of a
38 // Returns: (long) zero if the new value of a is zero,
39 // unspecified non-zero value otherwise (usually the new value)
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
45 // On Intel IA-32 (x86) memory is always synchronized, so this
48 // On many architectures the atomic instructions already act as
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.
56 // The destructor needs to have a synchronized view of the
57 // object to perform proper cleanup.
59 // Original example by Alexander Terekhov:
63 // - a mutable shared object OBJ;
64 // - two threads THREAD1 and THREAD2 each holding
65 // a private smart_ptr object pointing to that OBJ.
67 // t1: THREAD1 updates OBJ (thread-safe via some synchronization)
68 // and a few cycles later (after "unlock") destroys smart_ptr;
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...
75 // Note: atomic_count_linux.hpp has been disabled by default; see the
76 // comments inside for more info.
78 #include <boost/config.hpp>
80 #ifndef BOOST_HAS_THREADS
88 typedef long atomic_count;
94 #elif defined(BOOST_USE_ASM_ATOMIC_H)
95 # include <boost/detail/atomic_count_linux.hpp>
96 #elif defined(BOOST_AC_USE_PTHREADS)
97 # include <boost/detail/atomic_count_pthreads.hpp>
98 #elif defined(WIN32) || defined(_WIN32) || defined(__WIN32__)
99 # include <boost/detail/atomic_count_win32.hpp>
100 #elif defined(__GLIBCPP__)
101 # include <boost/detail/atomic_count_gcc.hpp>
102 #elif defined(BOOST_HAS_PTHREADS)
103 # define BOOST_AC_USE_PTHREADS
104 # include <boost/detail/atomic_count_pthreads.hpp>
107 // #warning Unrecognized platform, detail::atomic_count will not be thread safe
115 typedef long atomic_count;
123 #endif // #ifndef BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED