MQ_NOTIFY(3C)MQ_NOTIFY(3C)NAMEmq_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 pro‐
cesses 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 registra‐
tion.
When the notification is sent to the registered process, its registra‐
tion 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 notifica‐
tion 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 mes‐
sage queue.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬───────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼───────────────────┤
│Interface Stability │ Committed │
├────────────────────┼───────────────────┤
│MT-Level │ MT-Safe │
├────────────────────┼───────────────────┤
│Standard │ See standards(5). │
└────────────────────┴───────────────────┘
SEE ALSOmq_close(3C), mq_open(3C), mq_receive(3C), mq_send(3C),
mqueue.h(3HEAD), siginfo.h(3HEAD), signal.h(3HEAD), attributes(5),
standards(5)
Feb 5, 2008 MQ_NOTIFY(3C)
