|MQ_NOTIFY(2)||System Calls Manual||MQ_NOTIFY(2)|
LIBRARY¶POSIX Real-time Library (librt, -lrt)
mqdes, const struct
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 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 notification argument points to a
sigevent structure that defines how the calling
process will be notified. If
SIGEV_NONE, then no signal will be posted, but the
error status and the return status for the operation will be set
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:
|si_value||the value stored in notification->sigev_value|
If notification is
NULL and the process is currently registered for
notification by the specified message queue, the existing registration will
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
mq_receive() waiting to receive a message when a
message arrives at the queue, the arriving message will satisfy the
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.
mq_notify() system call will fail if:
SEE ALSO¶mq_open(2), mq_send(2), mq_timedsend(2), sigevent(3), siginfo(3)
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 Specifications Issue 6, Copyright (C) 2001-2004 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.
|July 15, 2016||Linux 4.9.0-9-amd64|