#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>

volatile int counter = 0;
int loops;

sem_t mysem;

void* worker(void* arg) {
	int i;

	sem_wait(&mysem);
	for (i = 0; i < loops; i++) {
		counter++;
	}
	sem_post(&mysem);
	return NULL;
}

int main(int argc, char* argv[]) {

	if (argc != 2) {
		fprintf(stderr, "usage: threads <value>\n");
		exit(1);
	}
	loops = atoi(argv[1]);
	
	sem_init(&mysem, 0, 1);

	pthread_t p1, p2;
	printf("Initial value : %d\n", counter);
	pthread_create(&p1, NULL, worker, NULL);
	pthread_create(&p2, NULL, worker, NULL);
	pthread_join(p1, NULL);
	pthread_join(p2, NULL);
	printf("Final value   : %d\n", counter);
	return 0;
}