odd problem(s) with libthr and libkse

Christopher Sedore cmsedore at maxwell.syr.edu
Mon Oct 13 13:36:22 PDT 2003

On Sat, 11 Oct 2003, Daniel Eischen wrote:

> On Sat, 11 Oct 2003, Christopher M. Sedore wrote:
> > I have a multithreaded program that I've built to run under libc_r, libthr,
> > and libkse.  I use the libc_r build for debugging and the others for actual
> > work (the program is disk/network io intensive and I want the disk io
> > concurrency from thr or kse).
> >  Anyway, here is the issue I'm seeing.  It may be the same or a related
> > problem for both, or may not be.
> >  When running under libthr, everything works fine for an indeterminate
> > period, usually between 10 seconds and 30 minutes.  Eventually, all program
> > function stops.  If I watch in top, threads get stuck in "sigwai".  First
> > one, then a couple, then all.
> >  When running under kse, the program pauses periodically.  I have one thread
> > that prints out a heartbeat once per second, and prints debug info.  I get
> > pauses of up to 5 seconds between my heartbeat:
> sigwait() may not be behaving as you'd expect in libkse.
> It is slightly different than in libc_r, but should be
> POSIX compliant nonetheless.

The strange thing is that I don't call sigwait().

> I use the following to test libkse for I/O intensive applications:
>   http://people.freebsd.org/~deischen/kse/crew.c
>   http://people.freebsd.org/~deischen/kse/sched_bug.c
> The latter test may be similar to what you are describing.
> It spawns a bunch of threads to perform disk I/O and one thread
> that just sleeps and prints an incrementing number once a
> second.
> Use the first test as "crew node /usr/src" and it will spawn
> worker threads to search for the string "node" in all files
> in /usr/src.  It is one of Butenhof's tests.

Thanks, I'll try these and see if I get similar behaviour.

> Other than that, you'll need to give more info.  SCHED_4BSD
> or SCHED_ULE?  SMP or UP?  scope system threads or scope
> process threads?  Sample program to demonstrate the problem?

4BSD, SMP.   I'm running with default parameters, which I assume is scope
process threads (I'd like to take advantage of M:N threading...).

I've peaked out around 15 threads, so I don't think I should be bumping
any limits.

I can try to boil the program down to a sample.  At this point it is too
large (~6600 lines :-).


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