pthreads example

threads.c

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <sys/sysinfo.h>

#define UBOUND	1000000000

void *tfunc(void *arg);

int main(int argc, char *argv[])
{
	int i;
	int cpus = get_nprocs();
	int nthreads;
	int (*vals)[2];
	pthread_t *threads;

	nthreads = cpus;
	printf("num CPUs: %d\n", cpus);
	printf("num threads: %d\n", nthreads);
	threads = malloc((nthreads-1) * sizeof(pthread_t));
	vals = malloc(nthreads * sizeof(int[2]));
	for (i=0; i<nthreads-1; ++i) {
		vals[i+1][0] = i+1;
		vals[i+1][1] = 0;
		pthread_create(threads+i, NULL, tfunc, vals+i+1);
	}

	vals[0][0] = 0;
	for (; vals[0][1] < UBOUND; ++vals[0][1]);
	printf("thread %d: val == %d\n", vals[0][0], vals[0][1]);

	for (i=0; i<cpus-1; ++i)
		if (pthread_join(threads[i], NULL)) {
			fprintf(stderr, "error joining thread #%d\n", i+1);
			return 2;
		}

	printf("done\n");
	free(vals);
	free(threads);
	return 0;
}

void *tfunc(void *arg)
{
	int (*arr)[2] = arg;
	int *val = *arr + 1;

	for (; *val < UBOUND; ++*val);
	printf("thread %d: val == %d\n", (*arr)[0], *val);

	return NULL;
}