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MQ_NOTIFY(2) BSD System Calls Manual MQ_NOTIFY(2) 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 system call 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 mes- sage queue. If the calling process or any other process has already reg- istered for notification of message arrival at the specified message queue, subsequent attempts to register for that message queue will fail. The notification argument points to a sigevent structure that defines how the calling process will be notified. If notification-_sigev_notify is SIGEV_NONE, then no signal will be posted, but the error status and the return status for the operation will be set appropriately. For SIGEV_SIGNO and SIGEV_THREAD_ID notifications, the signal specified in notification-_sigev_signo will be sent to the calling process (SIGEV_SIGNO) or to the thread whose LWP ID is notification-_sigev_notify_thread_id (SIGEV_THREAD_ID). The information for the queued signal will include: Member Value si_code SI_MESGQ si_value the value stored in notification-_sigev_value si_mqd mqdes If notification is NULL and the process is currently registered for noti- fication by the specified message queue, the existing registration will be removed. When the notification is sent to the registered process, its registration is removed. The message queue then is available for registration. If a process has registered for notification of message arrival at a mes- sage 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 Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ERRORS The mq_notify() system call will fail if: [EBADF] The mqdes argument is not a valid message queue de- scriptor. [EBUSY] Process is already registered for notification by the message queue. [EINVAL] The asynchronous notification method in notification-_sigev_notify is invalid or not sup- ported. SEE ALSO mq_open(2), mq_send(2), mq_timedsend(2), sigevent(3), siginfo(3) STANDARDS The mq_notify() system call conforms to IEEE Std 1003.1-2004 ("POSIX.1"). HISTORY Support for POSIX message queues first appeared in FreeBSD 7.0. COPYRIGHT Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Spec- ifications Issue 6, Copyright (C) 2001-2004 by the Institute of Electri- cal 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 ref- eree document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html. BSD July 15, 2016 BSD
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY | COPYRIGHT
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