132 lines
4.1 KiB
Groff
132 lines
4.1 KiB
Groff
.\" Copyright (c) 2005 David Xu <davidxu@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), this list of conditions and the following disclaimer in
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.\" the documentation and/or other materials provided with the
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.\" distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
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.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd November 29, 2005
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.Dt MQ_NOTIFY 2
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.Os
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.Sh NAME
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.Nm mq_notify
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.Nd "notify process that a message is available (REALTIME)"
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In mqueue.h
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.Ft int
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.Fn mq_notify "mqd_t mqdes" "const struct sigevent *notification"
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.Sh DESCRIPTION
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If the argument notification is not
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.Dv NULL ,
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this system call will register the calling process to be notified of message
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arrival at an empty message queue associated with the specified message
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queue descriptor,
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.Fa mqdes .
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The notification specified by the
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.Fa notification
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argument will be sent to
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the process when the message queue transitions from empty to non-empty.
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At any time, only one process may be registered for notification by a
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message queue.
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If the calling process or any other process has already
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registered for notification of message arrival at the specified message
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queue, subsequent attempts to register for that message queue will fail.
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.Pp
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The
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.Fa notification
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argument points to a
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.Vt sigevent
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structure that defines how the calling process will be notified.
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If
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.Fa notification->sigev_notify
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is
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.Dv SIGEV_NONE ,
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then no signal will be posted, but the error status and the return status
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for the operation will be set appropriately.
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If
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.Fa notification->sigev_notify
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is
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.Dv SIGEV_SIGNAL ,
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then the signal specified in
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.Fa notification->sigev_signo
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will be sent to the process.
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The signal will be queued to the process and the value specified in
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.Fa notification->sigev_value
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will be the
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.Va si_value
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component of the generated signal.
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.Pp
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If
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.Fa notification
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is
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.Dv NULL
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and the process is currently registered for notification by the specified
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message queue, the existing registration will be removed.
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.Pp
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When the notification is sent to the registered process, its registration
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is removed.
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The message queue then is available for registration.
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.Pp
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If a process has registered for notification of message arrival at a
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message queue and some thread is blocked in
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.Fn mq_receive
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waiting to receive a message when a message arrives at the queue, the
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arriving message will satisfy the appropriate
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.Fn mq_receive .
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The resulting behavior is as if the message queue remains empty, and no
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notification will be sent.
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.Sh RETURN VALUES
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.Rv -std
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.Sh ERRORS
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The
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.Fn mq_notify
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system call
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa mqdes
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argument is not a valid message queue descriptor.
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.It Bq Er EBUSY
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Process is already registered for notification by the message queue.
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.El
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.Sh SEE ALSO
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.Xr mq_open 2 ,
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.Xr mq_send 2 ,
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.Xr mq_timedsend 2 ,
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.Xr siginfo 3
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.Sh STANDARDS
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The
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.Fn mq_notify
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system call conforms to
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.St -p1003.1-2004 .
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.Sh HISTORY
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Support for
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.Tn POSIX
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message queues first appeared in
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.Fx 7.0 .
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