epoc32/include/stdapis/boost/detail/atomic_count.hpp
author William Roberts <williamr@symbian.org>
Wed, 31 Mar 2010 12:33:34 +0100
branchSymbian3
changeset 4 837f303aceeb
permissions -rw-r--r--
Current Symbian^3 public API header files (from PDK 3.0.h)
This is the epoc32/include tree with the "platform" subtrees removed, and
all but a selected few mbg and rsg files removed.
     1 #ifndef BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED
     2 #define BOOST_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: nothing
    35 //
    36 //  --a;
    37 //
    38 //    Effects: Atomically decrements the value of a
    39 //    Returns: (long) zero if the new value of a is zero,
    40 //      unspecified non-zero value otherwise (usually the new value)
    41 //
    42 //    Important note: when --a returns zero, it must act as a
    43 //      read memory barrier (RMB); i.e. the calling thread must
    44 //      have a synchronized view of the memory
    45 //
    46 //    On Intel IA-32 (x86) memory is always synchronized, so this
    47 //      is not a problem.
    48 //
    49 //    On many architectures the atomic instructions already act as
    50 //      a memory barrier.
    51 //
    52 //    This property is necessary for proper reference counting, since
    53 //      a thread can update the contents of a shared object, then
    54 //      release its reference, and another thread may immediately
    55 //      release the last reference causing object destruction.
    56 //
    57 //    The destructor needs to have a synchronized view of the
    58 //      object to perform proper cleanup.
    59 //
    60 //    Original example by Alexander Terekhov:
    61 //
    62 //    Given:
    63 //
    64 //    - a mutable shared object OBJ;
    65 //    - two threads THREAD1 and THREAD2 each holding 
    66 //      a private smart_ptr object pointing to that OBJ.
    67 //
    68 //    t1: THREAD1 updates OBJ (thread-safe via some synchronization)
    69 //      and a few cycles later (after "unlock") destroys smart_ptr;
    70 //
    71 //    t2: THREAD2 destroys smart_ptr WITHOUT doing any synchronization 
    72 //      with respect to shared mutable object OBJ; OBJ destructors
    73 //      are called driven by smart_ptr interface...
    74 //
    75 
    76 #include <boost/config.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/detail/atomic_count_pthreads.hpp>
    94 #elif defined(WIN32) || defined(_WIN32) || defined(__WIN32__)
    95 #  include <boost/detail/atomic_count_win32.hpp>
    96 #elif defined(__GLIBCPP__) || defined(__GLIBCXX__)
    97 #  include <boost/detail/atomic_count_gcc.hpp>
    98 #elif defined(BOOST_HAS_PTHREADS)
    99 #  define BOOST_AC_USE_PTHREADS
   100 #  include <boost/detail/atomic_count_pthreads.hpp>
   101 #else
   102 
   103 // Use #define BOOST_DISABLE_THREADS to avoid the error
   104 #error Unrecognized threading platform
   105 
   106 #endif
   107 
   108 #endif // #ifndef BOOST_DETAIL_ATOMIC_COUNT_HPP_INCLUDED