mq_notify
- notify process that a message is available (REALTIME)
LIBRARY
Lb librt
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,
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.
If
Fa notification->sigev_notify
is
SIGEV_SIGNAL
then the signal specified in
Fa notification->sigev_signo
will be sent to the process.
The signal will be queued to the process and the value specified in
Fa notification->sigev_value
will be the
si_value
component of the generated signal.
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
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
Rv -std
ERRORS
The
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.
The
mq_notify ();
system call conforms to
St -p1003.1-2004 .
HISTORY
Support for
POSIX
message queues first appeared in
Fx 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.
