Copyright (c) 2005 David Xu <davidxu@FreeBSD.org> All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice(s), this list of conditions and the following disclaimer as the first lines of this file unmodified other than the possible addition of one or more copyright notices. 2. Redistributions in b...
NAMEmq_notify - notify process that a message is available (REALTIME)
SYNOPSISIn mqueue.h Ft int Fn mq_notify mqd_t mqdes const struct sigevent *notification
DESCRIPTIONIf 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, Fa mqdes . The notification specified by the Fa 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 will fail.
The Fa notification argument points to a Vt sigevent structure that defines how the calling process will be notified. If Fa 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 Fa notification->sigev_signo will be sent to the calling process (SIGEV_SIGNO ) or to the thread whose LWP ID is Fa notification->sigev_notify_thread_id (SIGEV_THREAD_ID ) The information for the queued signal will include:
- Member Ta Value
- si_code Ta SI_MESGQ
- si_value Ta the value stored in
- Fa notification->sigev_value
- si_mqd Ta Fa mqdes
If Fa 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 is removed. The message queue then is available for registration.
If a process has registered for notification of message arrival at a message queue and some thread is blocked in Fn mq_receive waiting to receive a message when a message arrives at the queue, the arriving message will satisfy the appropriate Fn mq_receive . The resulting behavior is as if the message queue remains empty, and no notification will be sent.
RETURN VALUESRv -std
ERRORSThe Fn mq_notify system call will fail if:
- Bq Er EBADF
- The Fa mqdes argument is not a valid message queue descriptor.
- Bq Er EBUSY
- Process is already registered for notification by the message queue.
- Bq Er EINVAL
- The asynchronous notification method in Fa notification->sigev_notify is invalid or not supported.