incr3.c

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#include	"unpipc.h"

struct shared {
  sem_t	mutex;		/* the mutex: a Posix memory-based semaphore */
  int	count;		/* and the counter */
} shared;

int
main(int argc, char **argv)
{
	int		fd, i, nloop;
	struct shared 	*ptr;

	if (argc != 3)
		err_quit("usage: incr3 <pathname> <#loops>");
	nloop = atoi(argv[2]);

		/* 4open file, initialize to 0, map into memory */
	fd = Open(argv[1], O_RDWR | O_CREAT, FILE_MODE);
	Write(fd, &shared, sizeof(struct shared));
	ptr = Mmap(NULL, sizeof(struct shared), PROT_READ | PROT_WRITE,
			   MAP_SHARED, fd, 0);
	Close(fd);

		/* 4initialize semaphore that is shared between processes */
	Sem_init(&ptr->mutex, 1, 1);

	setbuf(stdout, NULL);	/* stdout is unbuffered */
	if (Fork() == 0) {		/* child */
		for (i = 0; i < nloop; i++) {
			Sem_wait(&ptr->mutex);
			printf("child: %d\n", ptr->count++);
			Sem_post(&ptr->mutex);
		}
		exit(0);
	}

		/* 4parent */
	for (i = 0; i < nloop; i++) {
		Sem_wait(&ptr->mutex);
		printf("parent: %d\n", ptr->count++);
		Sem_post(&ptr->mutex);
	}
	exit(0);
}