mirror of https://github.com/mkerrisk/man-pages
160 lines
4.4 KiB
Groff
160 lines
4.4 KiB
Groff
'\" t
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH MQ_SEND 3 2006-02-25 "Linux" "Linux Programmer's Manual"
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.SH NAME
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mq_send, mq_timedsend \- send a message to a message queue
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.SH SYNOPSIS
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.nf
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.B #include <mqueue.h>
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.sp
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.BI "mqd_t mq_send(mqd_t " mqdes ", const char *" msg_ptr ,
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.BI " size_t " msg_len ", unsigned " msg_prio );
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.sp
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.B #define _XOPEN_SOURCE 600
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.B #include <time.h>
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.B #include <mqueue.h>
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.sp
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.BI "mqd_t mq_timedsend(mqd_t " mqdes ", const char *" msg_ptr ,
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.BI " size_t " msg_len ", unsigned " msg_prio ,
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.BI " const struct timespec *" abs_timeout );
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.fi
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.sp
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Link with \fI\-lrt\fP.
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.SH DESCRIPTION
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.BR mq_send ()
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adds the message pointed to by
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.I msg_ptr
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to the message queue referred to by the descriptor
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.IR mqdes .
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The
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.I msg_len
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argument specifies the length of the message pointed to by
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.IR msg_ptr ;
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this length must be less than or equal to the queue's
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.I mq_msgsize
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attribute.
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Zero-length messages are allowed.
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The
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.I msg_prio
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argument is a non-negative integer that specifies the priority
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of this message.
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Messages are placed on the queue in decreasing order of priority,
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with newer messages of the same priority being placed after
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older messages with the same priority.
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If the message queue is already full
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(i.e., the number of messages on the queue equals the queue's
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.I mq_maxmsg
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attribute), then, by default,
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.BR mq_send ()
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blocks until sufficient space becomes available to allow the message
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to be queued, or until the call is interrupted by a signal handler.
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If the
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.B O_NONBLOCK
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flag is enabled for the message queue description,
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then the call instead fails immediately with the error
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.BR EAGAIN .
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.BR mq_timedsend ()
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behaves just like
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.BR mq_send (),
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except that if the queue is full and the
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.B O_NONBLOCK
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flag is not enabled for the message queue description, then
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.I abs_timeout
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points to a structure which specifies a ceiling on the time for which
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the call will block.
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This ceiling is an absolute timeout in seconds and nanoseconds
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since the Epoch (midnight on the morning of 1 January 1970),
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specified in the following structure:
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.sp
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.in +4n
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.nf
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struct timespec {
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time_t tv_sec; /* seconds */
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long tv_nsec; /* nanoseconds */
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};
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.fi
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.in
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If the message queue is full,
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and the timeout has already expired by the time of the call,
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.BR mq_timedsend ()
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returns immediately.
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.SH RETURN VALUE
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On success,
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.BR mq_send ()
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and
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.BR mq_timedsend ()
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return zero; on error, \-1 is returned, with
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.I errno
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set to indicate the error.
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.SH ERRORS
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.TP
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.B EAGAIN
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The queue was empty, and the
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.B O_NONBLOCK
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flag was set for the message queue description referred to by
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.IR mqdes .
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.TP
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.B EBADF
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The descriptor specified in
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.I mqdes
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was invalid.
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.TP
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.B EINTR
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The call was interrupted by a signal handler.
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.TP
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.B EINVAL
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The call would have blocked, and
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.I abs_timeout
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was invalid, either because
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.I tv_sec
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was less than zero, or because
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.I tv_nsec
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was less than zero or greater than 1000 million.
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.TP
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.B EMSGSIZE
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.I msg_len
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was greater than the
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.I mq_msgsize
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attribute of the message queue.
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.TP
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.B ETIMEDOUT
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The call timed out before a message could be transferred.
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.SH CONFORMING TO
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POSIX.1-2001.
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.SH "SEE ALSO"
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.BR mq_close (3),
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.BR mq_getattr (3),
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.BR mq_notify (3),
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.BR mq_open (3),
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.BR mq_receive (3),
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.BR mq_unlink (3),
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.BR feature_test_macros (7),
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.BR mq_overview (7)
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