1.\" $NetBSD: mq_notify.3,v 1.2 2010/06/07 07:21:52 jruoho Exp $ 2.\" 3.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 4.\" 5.Dd June 7, 2010 6.Dt MQ_NOTIFY 3 7.Os 8.Sh NAME 9.Nm mq_notify 10.Nd notify process that a message is available (REALTIME) 11.Sh LIBRARY 12.Lb librt 13.Sh SYNOPSIS 14.In mqueue.h 15.Ft int 16.Fn mq_notify "mqd_t mqdes" "const struct sigevent *notification" 17.Sh DESCRIPTION 18If the argument 19.Fa notification 20is not 21.Dv NULL , 22this function will register the calling process to be notified of 23message arrival at an empty message queue associated with the 24specified message queue descriptor, 25.Fa mqdes . 26The notification specified by the 27.Fa notification 28argument will be sent to the process when the message queue 29transitions from empty to non-empty. 30At any time, only one process may be registered for notification 31by a message queue. 32If the calling process or any other process has already registered 33for notification of message arrival at the specified message queue, 34subsequent attempts to register for that message queue fails. 35.Pp 36If 37.Fa notification 38is 39.Dv NULL 40and the process is currently registered for notification by the 41specified message queue, the existing registration will be removed. 42.Pp 43When the notification is sent to the registered process, 44its registration will be removed. 45The message queue will then be available for registration. 46.Pp 47If a process has registered for notification of message arrival 48at a message queue and some thread is blocked in 49.Fn mq_receive 50waiting to receive a message when a message arrives at the queue, 51the arriving message will satisfy the appropriate 52.Fn mq_receive . 53The resulting behavior is as if the message queue remains empty, 54and no notification will be sent. 55.Sh RETURN VALUES 56.Rv -std mq_notify 57.Sh ERRORS 58The 59.Fn mq_notify 60function fails if: 61.Bl -tag -width Er 62.It Bq Er EBADF 63The 64.Fa mqdes 65argument is not a valid message queue descriptor. 66.It Bq Er EBUSY 67A process is already registered for notification by the message queue. 68.El 69.Sh SEE ALSO 70.Xr mq 3 , 71.Xr sigevent 3 72.Sh STANDARDS 73This function conforms to the 74.St -p1003.1-2001 75standard. 76.Sh HISTORY 77This function first appeared in 78.Nx 5.0 . 79.Sh COPYRIGHT 80Portions of this text are reprinted and reproduced in electronic form 81from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology 82-- Portable Operating System Interface (POSIX), The Open Group Base 83Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of 84Electrical and Electronics Engineers, Inc and The Open Group. 85In the 86event of any discrepancy between this version and the original IEEE and 87The Open Group Standard, the original IEEE and The Open Group Standard 88is the referee document. 89The original Standard can be obtained online at 90http://www.opengroup.org/unix/online.html . 91