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MQ_NOTIFY(3) FreeBSD Library Functions Manual MQ_NOTIFY(3) NAME mq_notify - notify process that a message is available (REALTIME) LIBRARY POSIX Real-time Library (librt, -lrt) SYNOPSIS #include <mqueue.h> int mq_notify(mqd_t mqdes, const struct sigevent *notification); DESCRIPTION If the argument notification is not NULL, this function will 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 will 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 fails. If notification is NULL and the process is currently registered for notification by the specified message queue, the existing registration will be removed. When the notification is sent to the registered process, its registration will be removed. The message queue will 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 will satisfy the appropriate mq_receive(). The resulting behavior is as if the message queue remains empty, and no notification will be sent. RETURN VALUES The mq_notify() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ERRORS The mq_notify() function fails if: [EBADF] The mqdes argument is not a valid message queue descriptor. [EBUSY] A process is already registered for notification by the message queue. SEE ALSO mq(3), sigevent(3) STANDARDS This function conforms to the IEEE Std 1003.1-2001 ("POSIX.1") standard. HISTORY This function first appeared in NetBSD 5.0. 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. FreeBSD 14.1-RELEASE-p8 June 7, 2010 FreeBSD 14.1-RELEASE-p8