#define _XOPEN_SOURCE 600

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#include <time.h>
#include <assert.h>
#include <errno.h>
#include <signal.h>
#include <pthread.h>
#include <signal.h>

#define die(msg) {perror (msg); exit (EXIT_FAILURE); }

sem_t sem;
int stop;

void sig_handler (int sig)
{
	stop = sig;
}

void *thread1 (void *data)
{
	int t = (int) data;
	
	while (!stop)
	{
		while (sem_wait (&sem) == -1 && errno == EINTR)
			continue;
		printf ("My name is %d. thread %d\n", t, t);
		fflush (stdout);
		sem_post (&sem);
		sleep (1);
	}
	
	return NULL;
}

void *thread2 (void *data)
{
	int t = (int) data;
	
	while (!stop)
	{
		while (sem_wait (&sem) == -1 && errno == EINTR)
			continue;
		printf ("My name is %d. thread %d\n", t, t);
		fflush (stdout);
		sem_post (&sem);
		sleep (1);
	}
	
	return NULL;
}

void *thread3 (void *data)
{
	int t = (int) data;
	
	while (!stop)
	{
		while (sem_wait (&sem) == -1 && errno == EINTR)
			continue;
		printf ("My name is %d. thread %d\n", t, t);
		fflush (stdout);
		sem_post (&sem);
		sleep (1);
	}
	
	return NULL;
}

void *thread4 (void *data)
{
	int t = (int) data;
	
	while (!stop)
	{
		while (sem_wait (&sem) == -1 && errno == EINTR)
			continue;
		printf ("My name is %d. thread %d\n", t, t);
		fflush (stdout);
		sem_post (&sem);
		sleep (1);
	}
	
	return NULL;
}

int main (void)
{
	pthread_t p1, p2, p3, p4;
	
	signal (SIGINT, sig_handler);
	
	stop = 0;
	if (sem_init (&sem, 0, 0) == -1) die ("sem_init");
	
	pthread_create (&p1, NULL, thread1, (void *) 1);
	pthread_create (&p2, NULL, thread2, (void *) 2);
	pthread_create (&p3, NULL, thread3, (void *) 3);
	pthread_create (&p4, NULL, thread4, (void *) 4);
	
	while (!stop) 
	{
		printf ("main\n");
		fflush (stdout);
		sem_post (&sem);
		sleep (2);
	}
	
	sem_post (&sem);
	
	pthread_join (p1, NULL);
	pthread_join (p2, NULL);
	pthread_join (p3, NULL);
	pthread_join (p4, NULL);
	
	return 0;
}