/*
 ********************************************************
 *
 *	Two threads alternate synchronously.
 *	Silvia Figueira -- Winter 09
 *
 ********************************************************
 */

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


/*
 *	global variables
 */
pthread_mutex_t	mp;
pthread_cond_t	cp1;
pthread_cond_t	cp2;
pthread_t	th1;
pthread_t	th2;


/*
 *	functions
 */
void *ping_pong(void *arg);


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


	pthread_mutex_init (&mp, NULL);

	pthread_cond_init (&cp1, NULL);
	pthread_cond_init (&cp2, NULL);

	pthread_create (&th1, NULL, ping_pong, (void *) 1);
	pthread_create (&th2, NULL, ping_pong, (void *) 2);

	pthread_join (th1, NULL);
	pthread_join (th2, NULL);
}


/*
 *	ping_pong
 */
void *ping_pong (void *arg)
{
	int	th_id = (int)arg;
	char	dummy;

	if (th_id == 1)
	{
		printf ("Start!\n");
		scanf ("%c", &dummy);
	}

	while (1)
	{
		if (th_id == 1)
		{
			/*
			 *	thread 1 - executes first
			 */
			printf ("Thread %d\n", th_id);
			sleep (3);
			pthread_cond_signal (&cp2);

			pthread_mutex_lock (&mp);
			pthread_cond_wait (&cp1, &mp);
			pthread_mutex_unlock (&mp);
		}
		else
		{
			/*
			 *	thread 2 - executes second
			 */
			pthread_mutex_lock (&mp);
			pthread_cond_wait (&cp2, &mp);
			pthread_mutex_unlock (&mp);

			printf ("Thread %d\n", th_id);
			sleep (3);
			pthread_cond_signal (&cp1);
		}
	}
}