Date: Sun, 1 Feb 2004 11:50:12 -0500 (EST) From: Daniel Eischen <eischen@vigrid.com> To: Craig Rodrigues <rodrigc@crodrigues.org> Cc: freebsd-threads@freebsd.org Subject: Re: pthread_create() blocks if maxthreads reached? Message-ID: <Pine.GSO.4.10.10402011132590.524-100000@pcnet5.pcnet.com> In-Reply-To: <20040201152105.GA2370@crodrigues.org>
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On Sun, 1 Feb 2004, Craig Rodrigues wrote:
> On Sat, Jan 31, 2004 at 11:27:39PM -0800, Julian Elischer wrote:
> > >
> > > If I link with -lpthread, the program seems to
> > > block in the pthread_create() call, instead of
> > > returning EAGAIN (to indicate that a new thread cannot
> > > be created due to hitting some system limit).
> >
> > is that what you expected?
>
>
> No that is not what I expected. I expected
> that pthread_create() should either:
> - if it creates the thread successfully, return 0
> - if it cannot create the thread, return EAGAIN
> if a resource limit is it, or EINVAL if bad parameters
> were passed down into the pthread_create() call
>
>
> I never expected that pthread_create() would block.
You're missing the point. pthread_create() doesn't block;
you're application blocks because it has consumed the limit
of kernel threads allowed. It just so happens that the
only runnable thread is making a lot of calls to
pthread_create(), but it could be doing anything and
it would still block.
#include <err.h>
#include <inttypes.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
static pthread_mutex_t sync_lock;
static void *
worker(void *arg)
{
pthread_mutex_lock(&sync_lock);
pthread_mutex_unlock(&sync_lock);
select(0, NULL, NULL, NULL, NULL);
return (NULL);
}
int
main(int argc, char** argv)
{
pthread_t *threads;
int i, n;
if (argc > 1) {
n = strtoimax(argv[1], NULL, 10);
printf("Using %d threads (parameter)\n", n);
} else {
n = 5;
printf("Using %d threads (default)\n", n);
}
threads = (pthread_t *)malloc(sizeof(pthread_t) * n);
pthread_mutex_init(&sync_lock, NULL);
pthread_mutex_lock(&sync_lock);
/* Create and start n threads. */
for (i = 0; i < n; i++) {
if (pthread_create(&threads[i], NULL, worker, NULL) != 0) {
err(1, NULL);
}
}
/* Let the threads loose. */
printf("Created %d threads; letting them loose.\n", i);
pthread_mutex_unlock(&sync_lock);
sleep(10);
printf("Main thread waking up after sleeping\n");
/* Join the threads. */
for (i = 0; i < n; i++) {
if (pthread_join(threads[i], NULL) != 0) {
err(1, NULL);
}
printf("Joined thread %d\n", i);
}
free(threads);
return (0);
}
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