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

From: Victor A. Wagner, Jr. (vawjr_at_[hidden])
Date: 2003-03-01 13:48:17

What is there to fix?  Of course yield only yields to equal priority 
threads (one hopes that higher priority threads have already pre-empted).

At Tuesday 2003/02/25 08:26, you wrote:

>Russell Hind said:
> > 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)
>
>I'll look into this and fix it.  Thanks.
>
>--
>William E. Kempf
>
>
>_______________________________________________
>Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost

Victor A. Wagner Jr.      http://rudbek.com
The five most dangerous words in the English language:
               "There oughta be a law"