MQ_NOTIFY(P) POSIX Programmer's Manual MQ_NOTIFY(P)NAMEmq_notify - notify process that a message is available (REALTIME)
SYNOPSIS
#include <mqueue.h>
int mq_notify(mqd_t mqdes, const struct sigevent *notification);
DESCRIPTION
If the argument notification is not NULL, this function shall register
the calling process to be notified of message arrival at an empty mes‐
sage queue associated with the specified message queue descriptor,
mqdes. The notification specified by the notification argument shall 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 notifi‐
cation by a message queue. If the calling process or any other process
has already registered for notification of message arrival at the spec‐
ified message queue, subsequent attempts to register for that message
queue shall fail.
If notification is NULL and the process is currently registered for
notification by the specified message queue, the existing registration
shall be removed.
When the notification is sent to the registered process, its registra‐
tion shall be removed. The message queue shall 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 shall satisfy the appropriate mq_receive(). The resulting
behavior is as if the message queue remains empty, and no notification
shall be sent.
RETURN VALUE
Upon successful completion, the mq_notify() function shall return a
value of zero; otherwise, the function shall return a value of -1 and
set errno to indicate the error.
ERRORS
The mq_notify() function shall fail if:
EBADF The mqdes argument is not a valid message queue descriptor.
EBUSY A process is already registered for notification by the message
queue.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOmq_open() , mq_send() , mq_timedsend() , msgctl() , msgget() , msgrcv()
, msgsnd() , the Base Definitions volume of IEEE Std 1003.1-2001,
<mqueue.h>
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 .
IEEE/The Open Group 2003 MQ_NOTIFY(P)
