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 mq_notify(2)							mq_notify(2)

      mq_notify - register/cancel a notification request with a message

      #include <&lt&lt&lt;sys/mqueue.h>&gt&gt&gt;

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

      If the argument notification is not NULL, the mq_notify() system call
      registers the calling process to be notified of message arrival at an
      empty message queue associated with the message queue descriptor
      mqdes.  The notification specified by the notification argument will
      be sent to the process when the message queue transitions from the
      empty state to the non-empty state. At any time, only one process can
      be registered for notification with a message queue. If the calling
      process, or any other process has already registered for notification
      with the specified message queue, subsequent attempts to register with
      that queue will fail.

      If notification is NULL and the process is currently registered for
      notification with the specified message queue, the existing
      registration is canceled.

      When the notification is sent to the registered process, its
      registration is removed. The message queue is then available for

      If there is some process blocked in mq_receive() waiting to receive a
      message from a message queue, the arrival of a message on the queue
      will satisfy the mq_receive(), even if the queue has a registered
      notification request. The resulting behavior is as if the message
      queue remains empty, and no notification is sent.

      mq_notify() returns the following values:

	   0	Successful completion.

	   -1	Failure.  errno is set to indicate the error.

      If mq_notify() fails, errno is set to one of the following values:

	   [EAGAIN]	  The system lacks sufficient signal queuing
			  resources to honor the request.

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

 Hewlett-Packard Company	    - 1 -   HP-UX Release 11i: November 2000

 mq_notify(2)							mq_notify(2)

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

	   [EINVAL]	  An attempt was made to cancel a non-existent
			  notification request, or notification points to an
			  invalid address.

	   [ENOSYS]	  mq_notify() is not supported by the

      mq_open(2), mq_send(2).

      mq_notify(): POSIX 1003.1b

 Hewlett-Packard Company	    - 2 -   HP-UX Release 11i: November 2000