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MQ_NOTIFY(2)		    BSD	System Calls Manual		  MQ_NOTIFY(2)

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

LIBRARY
     POSIX Real-time Library (librt, -lrt)

SYNOPSIS
     #include <mqueue.h>

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

DESCRIPTION
     If	the argument notification is not NULL, this system call	will 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 will 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	mes-
     sage queue.  If the calling process or any	other process has already reg-
     istered for notification of message arrival at the	specified message
     queue, subsequent attempts	to register for	that message queue will	fail.

     The notification argument points to a sigevent structure that defines how
     the calling process will be notified.  If notification-_sigev_notify is
     SIGEV_NONE, then no signal	will be	posted,	but the	error status and the
     return status for the operation will be set appropriately.	 For
     SIGEV_SIGNO and SIGEV_THREAD_ID notifications, the	signal specified in
     notification-_sigev_signo will be sent to the calling process
     (SIGEV_SIGNO) or to the thread whose LWP ID is
     notification-_sigev_notify_thread_id (SIGEV_THREAD_ID).  The information
     for the queued signal will	include:

     Member	 Value
     si_code	 SI_MESGQ
     si_value	 the value stored in notification-_sigev_value
     si_mqd	 mqdes

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

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

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

RETURN VALUES
     Upon successful completion, the value 0 is	returned; otherwise the
     value -1 is returned and the global variable errno	is set to indicate the
     error.

ERRORS
     The mq_notify() system call will fail if:

     [EBADF]		The mqdes argument is not a valid message queue	de-
			scriptor.

     [EBUSY]		Process	is already registered for notification by the
			message	queue.

     [EINVAL]		The asynchronous notification method in
			notification-_sigev_notify is invalid or not sup-
			ported.

SEE ALSO
     mq_open(2), mq_send(2), mq_timedsend(2), sigevent(3), siginfo(3)

STANDARDS
     The mq_notify() system call conforms to IEEE Std 1003.1-2004 ("POSIX.1").

HISTORY
     Support for POSIX message queues first appeared in	FreeBSD	7.0.

COPYRIGHT
     Portions of this text are reprinted and reproduced	in electronic form
     from IEEE Std 1003.1, 2004	Edition, Standard for Information Technology
     --	Portable Operating System Interface (POSIX), The Open Group Base Spec-
     ifications	Issue 6, Copyright (C) 2001-2004 by the	Institute of Electri-
     cal 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 ref-
     eree document.  The original Standard can be obtained online at
     http://www.opengroup.org/unix/online.html.

BSD				 July 15, 2016				   BSD

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY | COPYRIGHT

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