mq_setattr.c

让你了解Unix进程间的通信是如何实现的

/* include mq_setattr */
#include	"unpipc.h"
#include	"mqueue.h"

int
mymq_setattr(mymqd_t mqd, const struct mymq_attr *mqstat,
			 struct mymq_attr *omqstat)
{
	int		n;
	struct mymq_hdr	*mqhdr;
	struct mymq_attr	*attr;
	struct mymq_info	*mqinfo;

	mqinfo = mqd;
	if (mqinfo->mqi_magic != MQI_MAGIC) {
		errno = EBADF;
		return(-1);
	}
	mqhdr = mqinfo->mqi_hdr;
	attr = &mqhdr->mqh_attr;
	if ( (n = pthread_mutex_lock(&mqhdr->mqh_lock)) != 0) {
		errno = n;
		return(-1);
	}

	if (omqstat != NULL) {
		omqstat->mq_flags = mqinfo->mqi_flags;	/* previous attributes */
		omqstat->mq_maxmsg = attr->mq_maxmsg;
		omqstat->mq_msgsize = attr->mq_msgsize;
		omqstat->mq_curmsgs = attr->mq_curmsgs;	/* and current status */
	}

	if (mqstat->mq_flags & O_NONBLOCK)
		mqinfo->mqi_flags |= O_NONBLOCK;
	else
		mqinfo->mqi_flags &= ~O_NONBLOCK;

	pthread_mutex_unlock(&mqhdr->mqh_lock);
	return(0);
}
/* end mq_setattr */

void
Mymq_setattr(mymqd_t mqd, const struct mymq_attr *mqstat,
			 struct mymq_attr *omqstat)
{
	if (mymq_setattr(mqd, mqstat, omqstat) == -1)
		err_sys("mymq_setattr error");
}