MQ_NOTIFY(3C) Standard C Library Functions MQ_NOTIFY(3C)

NAME

mq_notify - notify process (or thread) that a message is available on a
queue

SYNOPSIS

#include <mqueue.h>

int mq_notify(mqd_t mqdes, const struct sigevent *notification);

DESCRIPTION

The mq_notify() function provides an asynchronous mechanism for processes
to receive notice that messages are available in a message queue, rather
than synchronously blocking (waiting) in mq_receive(3C).


If notification is not NULL, this function registers the calling process
to be notified of message arrival at an empty message queue associated
with the message queue descriptor, mqdes. The notification specified by
notification will be sent to the process when the message queue
transitions from empty to non-empty. See signal.h(3HEAD). At any time,
only one process may be registered for notification by a specific 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.


If notification is NULL and the process is currently registered for
notification by the specified message queue, the existing registration is
removed. The message queue is then available for future registration.


When the notification is sent to the registered process, its registration
is removed. The message queue is then available for registration.


If a process has registered for notification of message arrival at a
message queue and some processes is blocked in mq_receive(3C) waiting to
receive a message when a message arrives at the queue, the arriving
message will be received by the appropriate mq_receive(3C), and no
notification will be sent to the registered process. The resulting
behavior is as if the message queue remains empty, and this notification
will not be sent until the next arrival of a message at this queue.


Any notification registration is removed if the calling process either
closes the message queue or exits.

RETURN VALUES

Upon successful completion, mq_notify() returns 0; otherwise, it returns
-1 and sets errno to indicate the error.

ERRORS

The mq_notify() function will 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.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|MT-Level | MT-Safe |
+--------------------+-------------------+
|Standard | See standards(7). |
+--------------------+-------------------+

SEE ALSO

mq_close(3C), mq_open(3C), mq_receive(3C), mq_send(3C), mqueue.h(3HEAD),
siginfo.h(3HEAD), signal.h(3HEAD), attributes(7), standards(7)

February 5, 2008 MQ_NOTIFY(3C)