mqnotifysig5.c

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#include	"unpipc.h"

int		pipefd[2];
static void	sig_usr1(int);
/* $$.bp$$ */
int
main(int argc, char **argv)
{
	int		nfds;
	char	c;
	fd_set	rset;
	mqd_t	mqd;
	void	*buff;
	ssize_t	n;
	struct mq_attr	attr;
	struct sigevent	sigev;

	if (argc != 2)
		err_quit("usage: mqnotifysig5 <name>");

		/* 4open queue, get attributes, allocate read buffer */
	mqd = Mq_open(argv[1], O_RDONLY | O_NONBLOCK);
	Mq_getattr(mqd, &attr);
	buff = Malloc(attr.mq_msgsize);

	Pipe(pipefd);

		/* 4establish signal handler, enable notification */
	Signal(SIGUSR1, sig_usr1);
	sigev.sigev_notify = SIGEV_SIGNAL;
	sigev.sigev_signo = SIGUSR1;
	Mq_notify(mqd, &sigev);

	FD_ZERO(&rset);
	for ( ; ; ) {
		FD_SET(pipefd[0], &rset);
		nfds = Select(pipefd[0] + 1, &rset, NULL, NULL, NULL);

		if (FD_ISSET(pipefd[0], &rset)) {
			Read(pipefd[0], &c, 1);
			Mq_notify(mqd, &sigev);			/* reregister first */
			while ( (n = mq_receive(mqd, buff, attr.mq_msgsize, NULL)) >= 0) {
				printf("read %ld bytes\n", (long) n);
			}
			if (errno != EAGAIN)
				err_sys("mq_receive error");
		}
	}
	exit(0);
}

static void
sig_usr1(int signo)
{
	Write(pipefd[1], "", 1);	/* one byte of 0 */
	return;
}