| #ifndef NDNBOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_HPP_INCLUDED |
| #define NDNBOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_HPP_INCLUDED |
| |
| // MS compatible compilers support #pragma once |
| |
| #if defined(_MSC_VER) && (_MSC_VER >= 1020) |
| # pragma once |
| #endif |
| |
| // |
| // ndnboost/detail/atomic_count.hpp - thread/SMP safe reference counter |
| // |
| // Copyright (c) 2001, 2002 Peter Dimov and Multi Media Ltd. |
| // |
| // Distributed under the Boost Software License, Version 1.0. (See |
| // accompanying file LICENSE_1_0.txt or copy at |
| // http://www.boost.org/LICENSE_1_0.txt) |
| // |
| // typedef <implementation-defined> ndnboost::detail::atomic_count; |
| // |
| // atomic_count a(n); |
| // |
| // (n is convertible to long) |
| // |
| // Effects: Constructs an atomic_count with an initial value of n |
| // |
| // a; |
| // |
| // Returns: (long) the current value of a |
| // |
| // ++a; |
| // |
| // Effects: Atomically increments the value of a |
| // Returns: (long) the new value of a |
| // |
| // --a; |
| // |
| // Effects: Atomically decrements the value of a |
| // Returns: (long) the new value of a |
| // |
| // Important note: when --a returns zero, it must act as a |
| // read memory barrier (RMB); i.e. the calling thread must |
| // have a synchronized view of the memory |
| // |
| // On Intel IA-32 (x86) memory is always synchronized, so this |
| // is not a problem. |
| // |
| // On many architectures the atomic instructions already act as |
| // a memory barrier. |
| // |
| // This property is necessary for proper reference counting, since |
| // a thread can update the contents of a shared object, then |
| // release its reference, and another thread may immediately |
| // release the last reference causing object destruction. |
| // |
| // The destructor needs to have a synchronized view of the |
| // object to perform proper cleanup. |
| // |
| // Original example by Alexander Terekhov: |
| // |
| // Given: |
| // |
| // - a mutable shared object OBJ; |
| // - two threads THREAD1 and THREAD2 each holding |
| // a private smart_ptr object pointing to that OBJ. |
| // |
| // t1: THREAD1 updates OBJ (thread-safe via some synchronization) |
| // and a few cycles later (after "unlock") destroys smart_ptr; |
| // |
| // t2: THREAD2 destroys smart_ptr WITHOUT doing any synchronization |
| // with respect to shared mutable object OBJ; OBJ destructors |
| // are called driven by smart_ptr interface... |
| // |
| |
| #include <ndnboost/config.hpp> |
| #include <ndnboost/smart_ptr/detail/sp_has_sync.hpp> |
| |
| #ifndef NDNBOOST_HAS_THREADS |
| |
| namespace ndnboost |
| { |
| |
| namespace detail |
| { |
| |
| typedef long atomic_count; |
| |
| } |
| |
| } |
| |
| #elif defined(NDNBOOST_AC_USE_PTHREADS) |
| # include <ndnboost/smart_ptr/detail/atomic_count_pthreads.hpp> |
| |
| #elif defined( __GNUC__ ) && ( defined( __i386__ ) || defined( __x86_64__ ) ) |
| # include <ndnboost/smart_ptr/detail/atomic_count_gcc_x86.hpp> |
| |
| #elif defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(__CYGWIN__) |
| # include <ndnboost/smart_ptr/detail/atomic_count_win32.hpp> |
| |
| #elif defined( NDNBOOST_SP_HAS_SYNC ) |
| # include <ndnboost/smart_ptr/detail/atomic_count_sync.hpp> |
| |
| #elif defined(__GLIBCPP__) || defined(__GLIBCXX__) |
| # include <ndnboost/smart_ptr/detail/atomic_count_gcc.hpp> |
| |
| #elif defined(NDNBOOST_HAS_PTHREADS) |
| |
| # define NDNBOOST_AC_USE_PTHREADS |
| # include <ndnboost/smart_ptr/detail/atomic_count_pthreads.hpp> |
| |
| #else |
| |
| // Use #define NDNBOOST_DISABLE_THREADS to avoid the error |
| #error Unrecognized threading platform |
| |
| #endif |
| |
| #endif // #ifndef NDNBOOST_SMART_PTR_DETAIL_ATOMIC_COUNT_HPP_INCLUDED |