96 lines
2.8 KiB
Groff
96 lines
2.8 KiB
Groff
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.\" $NetBSD: mq_notify.3,v 1.1 2009/01/05 21:19:49 rmind Exp $
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.\"
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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.\"
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.Dd January 5, 2009
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.Dt MQ_NOTIFY 3
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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 librt
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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
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.Fa notification
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is not
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.Dv NULL ,
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this function will register the calling process to be notified of
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message arrival at an empty message queue associated with the
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specified message 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 the process when the message queue
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transitions from empty to non-empty.
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At any time, only one process may be registered for notification
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by a message queue.
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If the calling process or any other process has already registered
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for notification of message arrival at the specified message queue,
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subsequent attempts to register for that message queue fails.
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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
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specified 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,
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its registration will be removed.
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The message queue will then be available for registration.
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.Pp
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If a process has registered for notification of message arrival
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at a 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,
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the 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,
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and no notification will be sent.
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.Sh RETURN VALUES
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.Rv -std mq_notify
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.Sh ERRORS
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The
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.Fn mq_notify
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function fails 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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A 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_close 3 ,
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.Xr mq_getattr 3 ,
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.Xr mq_open 3 ,
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.Xr mq_receive 3 ,
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.Xr mq_send 3 ,
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.Xr mq_setattr 3 ,
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.Xr mq_unlink 3
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.Sh STANDARDS
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This function conforms to the
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.St -p1003.1-2001
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standard.
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.Sh HISTORY
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This function first appeared in
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.Nx 5.0 .
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.Sh COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group.
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In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document.
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The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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