[boost] Question about boost::thread::yield for Win32

From: Russell Hind (rhind_at_[hidden])
Date: 2003-02-25 08:06:52

Is yield intended to always yield to another thread if one can run? 
Because  the code for yield is

void thread::yield()
{
#if defined(BOOST_HAS_WINTHREADS)
     Sleep(0);
#elif defined(BOOST_HAS_PTHREADS)
#   if defined(BOOST_HAS_SCHED_YIELD)
     int res = 0;
     res = sched_yield();
     assert(res == 0);
#   elif defined(BOOST_HAS_PTHREAD_YIELD)
     int res = 0;
     res = pthread_yield();
     assert(res == 0);
#   else
     xtime xt;
     xtime_get(&xt, TIME_UTC);
     sleep(xt);
#   endif
#elif defined(BOOST_HAS_MPTASKS)
     MPYield();
#endif
}

Taken from the main CVS.

Sleep(0) on Win32 will only yield to another thread of equal or higher 
priority, not to lower priority threads.

In boost::detail::lightweight_mutex::scoped_lock, it is mentioned that 
Sleep(1) will get around.  Is the behaviour of Sleep(0) the intended use 
of yield?

         explicit scoped_lock(lightweight_mutex & m): m_(m)
         {
             while( InterlockedExchange(&m_.l_, 1) )
             {
                 // Note: changed to Sleep(1) from Sleep(0).
                 // According to MSDN, Sleep(0) will never yield
                 // to a lower-priority thread, whereas Sleep(1)
                 // will. Performance seems not to be affected.

                 Sleep(1);
             }
         }

(I don't actually use yield yet, so currently have no preference for 
either, but just wondered what the intended use of yield was)

Thanks

Russell