boost/boost/detail/lwm_gcc.hpp

   1 #ifndef BOOST_DETAIL_LWM_GCC_HPP_INCLUDED
   2 #define BOOST_DETAIL_LWM_GCC_HPP_INCLUDED
   3
   4 //
   5 //  boost/detail/lwm_gcc.hpp
   6 //
   7 //  lightweight_mutex for GNU libstdc++ v3
   8 //
   9 //  http://gcc.gnu.org/onlinedocs/porting/Thread-safety.html
  10 //
  11 //  Copyright (c) 2002 Peter Dimov and Multi Media Ltd.
  12 //  Copyright (c) 2002 Lars Gullik Bjønnes <larsbj@lyx.org>
  13 //
  14 //  Permission to copy, use, modify, sell and distribute this software
  15 //  is granted provided this copyright notice appears in all copies.
  16 //  This software is provided "as is" without express or implied
  17 //  warranty, and with no claim as to its suitability for any purpose.
  18 //
  19
  20 #include <bits/atomicity.h>
  21 #include <sched.h>
  22
  23 namespace boost
  24 {
  25
  26 namespace detail
  27 {
  28
  29 class lightweight_mutex
  30 {
  31 private:
  32
  33     _Atomic_word a_;
  34
  35     lightweight_mutex(lightweight_mutex const &);
  36     lightweight_mutex & operator=(lightweight_mutex const &);
  37
  38 public:
  39
  40     lightweight_mutex(): a_(1)
  41     {
  42     }
  43
  44     class scoped_lock;
  45     friend class scoped_lock;
  46
  47     class scoped_lock
  48     {
  49     private:
  50
  51         lightweight_mutex & m_;
  52
  53         scoped_lock(scoped_lock const &);
  54         scoped_lock & operator=(scoped_lock const &);
  55
  56     public:
  57
  58         explicit scoped_lock(lightweight_mutex & m): m_(m)
  59         {
  60             while( !__exchange_and_add(&m_.a_, -1) )
  61             {
  62                 __atomic_add(&m_.a_, 1);
  63                 sched_yield();
  64             }
  65         }
  66
  67         ~scoped_lock()
  68         {
  69             __atomic_add(&m_.a_, 1);
  70         }
  71     };
  72 };
  73
  74 } // namespace detail
  75
  76 } // namespace boost
  77
  78 #endif // #ifndef BOOST_DETAIL_LWM_GCC_HPP_INCLUDED