mq_notify(3p) [centos man page]

MQ_NOTIFY(3P)						     POSIX Programmer's Manual						     MQ_NOTIFY(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       mq_notify - notify process that a message is available (REALTIME)

SYNOPSIS

       #include <mqueue.h>

       int mq_notify(mqd_t mqdes, const struct sigevent *notification);

DESCRIPTION

       If the argument notification is not NULL, this function shall register the calling process to be notified of message arrival  at  an  empty
       message	queue associated with the specified message queue descriptor, mqdes. The notification specified by the notification argument shall
       be sent to the process when the message queue transitions from empty to non-empty. At any time, only one  process  may  be  registered  for
       notification  by a message queue. If the calling process or any other process has already registered for notification of message arrival at
       the specified message queue, subsequent attempts to register for that message queue shall fail.

       If notification is NULL and the process is currently registered for notification by the specified message queue, the existing  registration
       shall be removed.

       When  the  notification is sent to the registered process, its registration shall be removed. The message queue shall then be available for
       registration.

       If a process has registered for notification of message arrival at a message queue and some thread is blocked in  mq_receive()  waiting	to
       receive	a  message  when  a  message arrives at the queue, the arriving message shall satisfy the appropriate mq_receive().  The resulting
       behavior is as if the message queue remains empty, and no notification shall be sent.

RETURN VALUE

       Upon successful completion, the mq_notify() function shall return a value of zero; otherwise, the function shall return a value of  -1  and
       set errno to indicate the error.

ERRORS

       The mq_notify() function shall fail if:

       EBADF  The mqdes argument is not a valid message queue descriptor.

       EBUSY  A process is already registered for notification by the message queue.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       mq_open(),  mq_send(),  mq_timedsend(),	msgctl(),  msgget(),  msgrcv(),  msgsnd(),  the  Base  Definitions volume of IEEE Std 1003.1-2001,
       <mqueue.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
       and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003							     MQ_NOTIFY(3P)

MQ_NOTIFY(3P)						     POSIX Programmer's Manual						     MQ_NOTIFY(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       mq_notify -- notify process that a message is available (REALTIME)

SYNOPSIS

       #include <mqueue.h>

       int mq_notify(mqd_t mqdes, const struct sigevent *notification);

DESCRIPTION

       If the argument notification is not NULL, this function shall register the calling process to be notified of message arrival  at  an  empty
       message queue associated with the specified message queue descriptor, mqdes.  The notification specified by the notification argument shall
       be sent to the process when the message queue transitions from empty to non-empty. At any time, only one  process  may  be  registered  for
       notification  by a message queue. If the calling process or any other process has already registered for notification of message arrival at
       the specified message queue, subsequent attempts to register for that message queue shall fail.

       If notification is NULL and the process is currently registered for notification by the specified message queue, the existing  registration
       shall be removed.

       When  the  notification is sent to the registered process, its registration shall be removed. The message queue shall then be available for
       registration.

       If a process has registered for notification of message arrival at a message queue and some thread is blocked in mq_receive()  or  mq_time-
       dreceive()  waiting  to	receive  a  message  when  a  message  arrives	at  the  queue, the arriving message shall satisfy the appropriate
       mq_receive() or mq_timedreceive(), respectively. The resulting behavior is as if the message queue remains empty, and no notification shall
       be sent.

RETURN VALUE

       Upon  successful  completion, the mq_notify() function shall return a value of zero; otherwise, the function shall return a value of -1 and
       set errno to indicate the error.

ERRORS

       The mq_notify() function shall fail if:

       EBADF  The mqdes argument is not a valid message queue descriptor.

       EBUSY  A process is already registered for notification by the message queue.

       The mq_notify() function may fail if:

       EINVAL The notification argument is NULL and the process is currently not registered.

       The following sections are informative.

EXAMPLES

       The following program registers a notification request for the message queue named in its command-line argument. Notification is  performed
       by creating a thread. The thread executes a function which reads one message from the queue and then terminates the process.

	   #include <pthread.h>
	   #include <mqueue.h>
	   #include <assert.h>
	   #include <stdio.h>
	   #include <stdlib.h>
	   #include <unistd.h>

	   static void			   /* Thread start function */
	   tfunc(union sigval sv)
	   {
	       struct mq_attr attr;
	       ssize_t nr;
	       void *buf;
	       mqd_t mqdes = *((mqd_t *) sv.sival_ptr);

	       /* Determine maximum msg size; allocate buffer to receive msg */

	       if (mq_getattr(mqdes, &attr) == -1) {
		   perror("mq_getattr");
		   exit(EXIT_FAILURE);
	       }
	       buf = malloc(attr.mq_msgsize);

	       if (buf == NULL) {
		   perror("malloc");
		   exit(EXIT_FAILURE);
	       }

	       nr = mq_receive(mqdes, buf, attr.mq_msgsize, NULL);
	       if (nr == -1) {
		   perror("mq_receive");
		   exit(EXIT_FAILURE);
	       }

	       printf("Read %ld bytes from message queue
", (long) nr);
	       free(buf);
	       exit(EXIT_SUCCESS);	   /* Terminate the process */
	   }

	   int
	   main(int argc, char *argv[])
	   {
	       mqd_t mqdes;
	       struct sigevent not;

	       assert(argc == 2);

	       mqdes = mq_open(argv[1], O_RDONLY);
	       if (mqdes == (mqd_t) -1) {
		   perror("mq_open");
		   exit(EXIT_FAILURE);
	       }

	       not.sigev_notify = SIGEV_THREAD;
	       not.sigev_notify_function = tfunc;
	       not.sigev_notify_attributes = NULL;
	       not.sigev_value.sival_ptr = &mqdes;   /* Arg. to thread func. */
	       if (mq_notify(mqdes, &not) == -1) {
		   perror("mq_notify");
		   exit(EXIT_FAILURE);
	       }

	       pause();    /* Process will be terminated by thread function */
	   }

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       mq_open(), mq_send(), mq_receive(), msgctl(), msgget(), msgrcv(), msgsnd()

       The Base Definitions volume of POSIX.1-2008, <mqueue.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C)  2013  by	the  Institute	of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013							     MQ_NOTIFY(3P)