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

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

       #include <mqueue.h>

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

       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  mes-
       sage arrival at the specified message queue, subsequent attempts to register for that mes-
       sage 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

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

       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.





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

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				     MQ_NOTIFY(P)
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