prodcons2.c

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#include	"unpipc.h"

#define	NBUFF	 10

int		nitems;					/* read-only by producer and consumer */
struct {	/* data shared by producer and consumer */
  int	buff[NBUFF];
  sem_t	mutex, nempty, nstored;		/* semaphores, not pointers */
} shared;

void	*produce(void *), *consume(void *);

int
main(int argc, char **argv)
{
	pthread_t	tid_produce, tid_consume;

	if (argc != 2)
		err_quit("usage: prodcons2 <#items>");
	nitems = atoi(argv[1]);

		/* 4initialize three semaphores */
	Sem_init(&shared.mutex, 0, 1);
	Sem_init(&shared.nempty, 0, NBUFF);
	Sem_init(&shared.nstored, 0, 0);

	Set_concurrency(2);
	Pthread_create(&tid_produce, NULL, produce, NULL);
	Pthread_create(&tid_consume, NULL, consume, NULL);

	Pthread_join(tid_produce, NULL);
	Pthread_join(tid_consume, NULL);

	Sem_destroy(&shared.mutex);
	Sem_destroy(&shared.nempty);
	Sem_destroy(&shared.nstored);
	exit(0);
}

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

	for (i = 0; i < nitems; i++) {
		Sem_wait(&shared.nempty);	/* wait for at least 1 empty slot */
		Sem_wait(&shared.mutex);
		shared.buff[i % NBUFF] = i;	/* store i into circular buffer */
		Sem_post(&shared.mutex);
		Sem_post(&shared.nstored);	/* 1 more stored item */
	}
	return(NULL);
}

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

	for (i = 0; i < nitems; i++) {
		Sem_wait(&shared.nstored);		/* wait for at least 1 stored item */
		Sem_wait(&shared.mutex);
		if (shared.buff[i % NBUFF] != i)
			printf("buff[%d] = %d\n", i, shared.buff[i % NBUFF]);
		Sem_post(&shared.mutex);
		Sem_post(&shared.nempty);		/* 1 more empty slot */
	}
	return(NULL);
}