/*
 ***************************************************
 *
	Print the 5th.
 *	One thread reads numbers from the keyboard.
 *	One of two other threads outputs every 5th number.
 *
 *	Silvia Figueira -- Winter 09
 *
 ***************************************************
 */

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


/*
 *	global variables
 */
int		number = 0;
int		counter = 0;
int		flag = 0;
pthread_mutex_t	mp = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t	cp = PTHREAD_COND_INITIALIZER;


/*
 *	functions
 */
void *read_number(void *arg);
void *print_number(void *arg);


/*
 *	main
 */
int
main()
{
	int		i;
	pthread_t	th1, th2, th3;

	pthread_mutex_init (&mp, NULL);
	pthread_cond_init (&cp, NULL);

	pthread_create (&th1, NULL, read_number, (void *)NULL);
	pthread_create (&th2, NULL, print_number, (void *) (void *)2);
	pthread_create (&th3, NULL, print_number, (void *) (void *)3);

	pthread_join (th1, NULL); 
	pthread_join (th2, NULL); 
	pthread_join (th3, NULL); 
}


/*
 *	read numbers
 */
void
*read_number (void *arg)
{
	int	lnumber;

	while (1)
	{
		scanf ("%d", &lnumber);

		pthread_mutex_lock (&mp);

		counter++;
		number = lnumber;
		if ((counter % 5) == 0)
			flag = 1;

		pthread_mutex_unlock (&mp);

		if ((counter % 5) == 0)
			pthread_cond_signal (&cp);
	}
}


/*
 *	print numbers
 */
void *
print_number (void *arg)
{
	int id = (int)arg;

	while (1)
	{
		printf ("Waiting...\n");

		pthread_mutex_lock (&mp);

		/*
		 *	Use the flag to make sure only one thread prints
		 */
		while (!flag)
		{
			pthread_cond_wait (&cp, &mp);
		}
			
		flag = 0;
		printf  ("Thread %d: %d ==> %d\n", id, counter, number);

		pthread_mutex_unlock (&mp);
	}
}