Re: Instability with signals and threads

[Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>]

On Wed, 19 Nov 2014, Mikulas Patocka wrote:

> Hi
> 
> I have a program that sets a repetitive timer with setitimer and spawns 
> several threads.
> 
> The program is very unstable on cygwin, it locks up in few minutes.

This is a simplified example that triggers the lockup very quicky.

When I change remove_tls so that it always acquires the lock, it reduces 
the probability of the lockup, but doesn't eliminate it entirely - so 
there must be some other bug.

Mikulas



#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <sys/time.h>
#include <pthread.h>

static volatile sig_atomic_t events;

static void signal_handler(int sig)
{
	events++;
}

static void *thread_func(void *ptr)
{
	return NULL;
}

#define N_THREADS	12

static pthread_t threads[N_THREADS];

int main(void)
{
	int i, r;
	struct sigaction sa;
	struct itimerval timer;

	memset(&sa, 0, sizeof sa);
	sa.sa_handler = signal_handler;
	sigemptyset(&sa.sa_mask);
	sa.sa_flags |= SA_RESTART;
	r = sigaction(SIGALRM, &sa, NULL);
	if (r) perror("sigaction"), exit(1);

	timer.it_interval.tv_sec = 0;
	timer.it_interval.tv_usec = 1000;
	timer.it_value = timer.it_interval;
	r = setitimer(ITIMER_REAL, &timer, NULL);
	if (r) perror("setitimer"), exit(1);

	while (1) {
		for (i = 0; i < N_THREADS; i++) {
			r = pthread_create(&threads[i], NULL, thread_func, NULL);
			if (r) fprintf(stderr, "pthread_create: %s", strerror(r));
		}
		for (i = 0; i < N_THREADS; i++) {
			r = pthread_join(threads[i], NULL);
			if (r) fprintf(stderr, "pthread_create: %s", strerror(r));
		}
		printf("events: %d\n", events);
	}
}

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