boost/boost/detail/lwm_win32.hpp

   1 #ifndef BOOST_DETAIL_LWM_WIN32_HPP_INCLUDED
   2 #define BOOST_DETAIL_LWM_WIN32_HPP_INCLUDED
   3
   4 #if _MSC_VER >= 1020
   5 #pragma once
   6 #endif
   7
   8 //
   9 //  boost/detail/lwm_win32.hpp
  10 //
  11 //  Copyright (c) 2002 Peter Dimov and Multi Media Ltd.
  12 //
  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.
  17 //
  18
  19 #include <boost/detail/winapi.hpp>
  20
  21 namespace boost
  22 {
  23
  24 namespace detail
  25 {
  26
  27 class lightweight_mutex
  28 {
  29 private:
  30
  31     long l_;
  32
  33     lightweight_mutex(lightweight_mutex const &);
  34     lightweight_mutex & operator=(lightweight_mutex const &);
  35
  36 public:
  37
  38     lightweight_mutex(): l_(0)
  39     {
  40     }
  41
  42     class scoped_lock;
  43     friend class scoped_lock;
  44
  45     class scoped_lock
  46     {
  47     private:
  48
  49         lightweight_mutex & m_;
  50
  51         scoped_lock(scoped_lock const &);
  52         scoped_lock & operator=(scoped_lock const &);
  53
  54     public:
  55
  56         explicit scoped_lock(lightweight_mutex & m): m_(m)
  57         {
  58             while( winapi::InterlockedExchange(&m_.l_, 1) )
  59             {
  60                 winapi::Sleep(0);
  61             }
  62         }
  63
  64         ~scoped_lock()
  65         {
  66             winapi::InterlockedExchange(&m_.l_, 0);
  67
  68             // Note: adding a Sleep(0) here will make
  69             // the mutex more fair and will increase the overall
  70             // performance of some applications substantially in
  71             // high contention situations, but will penalize the
  72             // low contention / single thread case up to 5x
  73         }
  74     };
  75 };
  76
  77 } // namespace detail
  78
  79 } // namespace boost
  80
  81 #endif // #ifndef BOOST_DETAIL_LWM_WIN32_HPP_INCLUDED