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 (con-
       sult the corresponding 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  speci-
       fied  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 Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                 MQ_NOTIFY(3P)