Subj : Re: threads do not get cpa
To   : comp.programming.threads,comp.sys.sgi.misc
From : azb123
Date : Mon Aug 08 2005 01:29 am

> Also note that some implementations of drand48() require a mutex to
> protect the internal state of the random number generator.  Others
> have the generator per-thread, but there's not any easy way to
> tell the difference.

Thanks, this was exactly the problem! I replaced drand48() by erand48()
which has a pointer to a buffer for the internal state as a command
line argument, and now I get the desired speed-up. Seems that the
internal state was mutex protected and that resulted in a contention
problem.

However, the original question still remains: the number of processors
the program runs on seems unpredictable (at least to me), even after I
have added the pthread_setconcurrency() call. When I create 3 threads,
the program sometimes gets 3 processors, and sometimes just 1 (the SGI
is still mostly empty).

Is there anything known about the way the number of processors to be
used is determined under IRIX 6.5.24m?

Markus

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