mq_notify(3)						     Library Functions Manual						      mq_notify(3)

NAME

       mq_notify - Attaches a request for asynchronous signal notification to a message queue (P1003.1b)

LIBRARY

       Realtime Library (librt.so, librt.a)

SYNOPSIS

       #include <mqueue.h>

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

PARAMETERS

       mqdes	      Specifies a message queue descriptor.

       *notification  Specifies  a  signal  to	be sent when the specified queue accepts a message.  If the notification argument is NULL, and the
		      process has previously attached a notification request to the message queue  with  this  mqdes  argument,  the  notification
		      request is detached and the queue is available for another process to attach a notification request.

DESCRIPTION

       The  mq_notify  function  attaches  a request for asynchronous signal notification to a message queue for the calling process.  Following a
       call to this function, the specified signal is sent to the calling process when the queue transitions from empty to non-empty.  Two or more
       processes cannot attach notification requests to the same queue at the same time.

       If  a process has attached a notification request and any process is blocked in the execution of the mq_receive function waiting to receive
       a message when a message arrives at the queue, then the appropriate mq_receive function is completed and the notification remains pending.

       When the notification has been sent, the registration is canceled.  In effect, it is a one-shot notification and must be  re-registered	if
       required.

       Note  that  the	POSIX  IPC  functions are not reentrant with respect to signals.  For example, if your application were to use a signal to
       notify it that a queue has become non-empty and then attempt to call mq_receive from the signal handler, the signal handler must reside	in
       a thread other than the tread that called mq_send.  Otherwise, a deadlock on internal locks would occur.

RETURN VALUES

       On  successful completion, the function returns the value 0 (zero); otherwise, the function returns the value -1 and sets errno to indicate
       the error.

ERRORS

       The mq_notify function fails under the following conditions:

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

       [EBUSY]	      A process has already attached to this message queue for asynchronous notification, or the calling process attempted to can-
		      cel a request that was attached by another process.

       [EINVAL]       The requested signo is invalid, or the sigev_notify field of the notification structure does not equal SIGEV_SIGNAL.

RELATED INFORMATION

       Functions: mq_open(3), mq_send(3)

       Guide to Realtime Programming delim off

																      mq_notify(3)