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 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
       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, 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 http://www.opengroup.org/unix/online.html .