Date: Sun, 16 Jan 2000 22:08:53 -0700 From: Wes Peters <wes@softweyr.com> To: Daniel Eischen <eischen@vigrid.com> Cc: archer@lucky.net, hackers@FreeBSD.ORG Subject: Re: Preemptiveness of FreeBSD threads Message-ID: <3882A3E5.2ABD9EBF@softweyr.com> References: <200001170423.XAA10093@pcnet1.pcnet.com>
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Daniel Eischen wrote:
>
> Alexander Litvin wrote:
> > First, I must say that this all concernes quite current
> > CURRENT (Jan 9 or so). I don't know if the same holds for
> > older versions.
> >
> > I'm kind of puzzled.
> >
> > I've a simple sample program (see at the bottom). It creates 10
> > threads with start function start_my_thread(), and then runs the
> > same function in main(). So, we have 11 threads doing the same job.
> >
> > Function start_my_thread() just increments indefinitely counters
> > (each thread has its own counter).
> >
> > Program, when killed with SIGINT, prints all counters and exits.
> >
> > Now, as I understand, userspace threads in FreeBSD are preemptive.
> > So, though my 11 threads are all computational and do not do
> > any syscalls, sleeps, sched_yield, whatever -- newertheless,
> > the program should not be stuck in one thread. And it seems to
> > be sometimes true. But only sometimes!
> >
> > Depending on the phase of the moon (it seems) sometimes my
> > program gives (after ^C):
> >
> > ^C
> > Thread 0x00: 0
> > Thread 0x01: 0
> > Thread 0x02: 0
> > Thread 0x03: 0
> > Thread 0x04: 0
> > Thread 0x05: 0
> > Thread 0x06: 0
> > Thread 0x07: 0
> > Thread 0x08: 0
> > Thread 0x09: 0
> > Thread 0x0a: 488133092
>
> Hmm, I can't get this to occur with your test program. I've tried
> it several times and the threads seem to be scheduled properly.
> If you figure out how to repeat this without relying on phases of
> the moon, I'd be interested in hearing how.
It does it every time for me, on 3.3-RELEASE. On 3.4-STABLE as of Dec 20,
it never does it (over a very small sample period). The machines are located
about 25 miles apart; the phase of the moon should be significantly the same
for both. ;^)
--
"Where am I, and what am I doing in this handbasket?"
Wes Peters Softweyr LLC
wes@softweyr.com http://softweyr.com/
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