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MQ_NOTIFY(3)               Library Functions Manual               MQ_NOTIFY(3)

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

     POSIX Real-time Library (librt, -lrt)

     #include <mqueue.h>

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

     If the argument notification is not NULL, this function 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
     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 fails.

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

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

     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 will satisfy the appropriate mq_receive().  The resulting
     behavior is as if the message queue remains empty, and no notification
     will be sent.

     The mq_notify() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the

     The mq_notify() function fails if:

     [EBADF]            The mqdes argument is not a valid message queue

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

     mq(3), sigevent(3)

     This function conforms to the IEEE Std 1003.1-2001 ("POSIX.1") standard.

     This function first appeared in NetBSD 5.0.

     Portions of this text are reprinted and reproduced in electronic form
     from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
     -- 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

NetBSD 9.99                      June 7, 2010                      NetBSD 9.99