HP-UX Reference (11i v1 05/09) - 2 System Calls (vol 5)

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mq_notify(2) mq_notify(2)

NAME

mq_notify - register/cancel a notiﬁcation request with a message queue

SYNOPSIS

#include <sys/mqueue.h>

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

DESCRIPTION

If the argument notiﬁcation is not

NULL, the mq_notify() system call 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 the notiﬁcation argument will be sent to the process when the message

queue transitions from the empty state to the non-empty state. At any time, only one process can be

registered for notiﬁcation with a message queue. If the calling process, or any other process has already

registered for notiﬁcation with the speciﬁed message queue, subsequent attempts to register with that

queue will fail.

If notiﬁcation is

NULL and the process is currently registered for notiﬁcation with the speciﬁed message

queue, the existing registration is canceled.

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

then available for registration.

If there is some process blocked in

mq_receive() waiting to receive a message from a message queue,

the arrival of a message on the queue will satisfy the mq_receive() , even if the queue has a registered

notiﬁcation request. The resulting behavior is as if the message queue remains empty, and no notiﬁcation is

sent.

RETURN VALUE

mq_notify() returns the following values:

0 Successful completion.

-1 Failure. errno is set to indicate the error.

ERRORS

If mq_notify() fails, errno is set to one of the following values:

[EAGAIN] The system lacks sufﬁcient signal queuing resources to honor the request.

[EBADF] The mqdes argument is not a valid message queue descriptor.

[EBUSY] A process is already registered for notiﬁcation with the message queue.

[EINVAL] An attempt was made to cancel a non-existent notiﬁcation request, or notiﬁcation

points to an invalid address.

[ENOSYS]

mq_notify() is not supported by the implementation.