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MQ_NOTIFY(2)             DragonFly 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 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 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 fails.

     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
     will be removed.  The message queue will then be available for registra-
     tion.

     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

     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
     error.


ERRORS

     The mq_notify() function fails if:

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

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


SEE ALSO

     mq_close(2), mq_getattr(2), mq_open(2), mq_receive(2), mq_send(2),
     mq_setattr(2), mq_unlink(2)


STANDARDS

     This function conforms to the IEEE Std 1003.1-2001 (``POSIX.1'') stan-
     dard.


HISTORY

     This function first appeared in DragonFly 2.5.


COPYRIGHT

     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 Spec-
     ifications Issue 6, Copyright (C) 2001-2003 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 .

DragonFly 3.5                   August 19, 2009                  DragonFly 3.5

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