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 #ifdef __BORLANDC__
  22 # pragma warn -8027     // Functions containing while are not expanded inline
  23 #endif
  24
  25 namespace boost
  26 {
  27
  28 namespace detail
  29 {
  30
  31 class lightweight_mutex
  32 {
  33 private:
  34
  35     long l_;
  36
  37     lightweight_mutex(lightweight_mutex const &);
  38     lightweight_mutex & operator=(lightweight_mutex const &);
  39
  40 public:
  41
  42     lightweight_mutex(): l_(0)
  43     {
  44     }
  45
  46     class scoped_lock;
  47     friend class scoped_lock;
  48
  49     class scoped_lock
  50     {
  51     private:
  52
  53         lightweight_mutex & m_;
  54
  55         scoped_lock(scoped_lock const &);
  56         scoped_lock & operator=(scoped_lock const &);
  57
  58     public:
  59
  60         explicit scoped_lock(lightweight_mutex & m): m_(m)
  61         {
  62             while( winapi::InterlockedExchange(&m_.l_, 1) )
  63             {
  64                 // Note: changed to Sleep(1) from Sleep(0).
  65                 // According to MSDN, Sleep(0) will never yield
  66                 // to a lower-priority thread, whereas Sleep(1)
  67                 // will. Performance seems not to be affected.
  68
  69                 winapi::Sleep(1);
  70             }
  71         }
  72
  73         ~scoped_lock()
  74         {
  75             winapi::InterlockedExchange(&m_.l_, 0);
  76
  77             // Note: adding a yield here will make
  78             // the spinlock more fair and will increase the overall
  79             // performance of some applications substantially in
  80             // high contention situations, but will penalize the
  81             // low contention / single thread case up to 5x
  82         }
  83     };
  84 };
  85
  86 } // namespace detail
  87
  88 } // namespace boost
  89
  90 #ifdef __BORLANDC__
  91 # pragma warn .8027     // Functions containing while are not expanded inline
  92 #endif
  93
  94 #endif // #ifndef BOOST_DETAIL_LWM_WIN32_HPP_INCLUDED