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Re: starvation in pthread_once?
- From: Ross Johnson <rpj at callisto dot canberra dot edu dot au>
- To: Pthreads-Win32 list <pthreads-win32 at sources dot redhat dot com>
- Date: Sat, 05 Mar 2005 10:18:29 +1100
- Subject: Re: starvation in pthread_once?
- References: <email@example.com>
On Thu, 2005-03-03 at 04:32 -0500, Gottlob Frege wrote:
> I'm concerned about the Sleep(0) in pthread_once:
Thanks. It looks like this routine needs to be redesigned.
> if (!once_control->done)
> if (InterlockedIncrement (&(once_control->started)) == 0)
> * First thread to increment the started variable
> (*init_routine) ();
> once_control->done = PTW32_TRUE;
> * Block until other thread finishes executing the onceRoutine
> while (!(once_control->done))
> * The following gives up CPU cycles without pausing
> * unnecessarily
> Sleep (0);
> IIRC, Sleep(0) does not relinquish time slices to lower priority
> threads. (Sleep(n) for n != 0 does, but 0 does not). So, if a lower
> priority thread is first in, followed closely by a higher priority
> one, the higher priority thread will spin on Sleep(0) *forever*
> because the lower, first thread will never get a chance to set done.
> So even Sleep(10) should be good enough. In theory, there could be
> enough higher priority threads in the system that the first thread
> still doesn't get in (ever?!), but unlikely. And that would probably
> mean a general design flaw of the calling code, not pthread_once.