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)