217 lines
5.8 KiB
Groff
217 lines
5.8 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_SEND 2
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.Os
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.Sh NAME
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.Nm mq_send , mq_timedsend
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.Nd "send a message to message queue (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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.Fo mq_send
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.Fa "mqd_t mqdes"
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.Fa "const char *msg_ptr"
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.Fa "size_t msg_len"
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.Fa "unsigned msg_prio"
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.Fc
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.Ft int
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.Fo mq_timedsend
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.Fa "mqd_t mqdes"
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.Fa "const char *msg_ptr"
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.Fa "size_t msg_len"
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.Fa "unsigned msg_prio"
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.Fa "const struct timespec *abs_timeout"
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.Fc
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.Sh DESCRIPTION
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The
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.Fn mq_send
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system call adds the message pointed to by the argument
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.Fa msg_ptr
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to the message queue specified by
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.Fa mqdes .
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The
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.Fa msg_len
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argument specifies the length of the message, in bytes, pointed to by
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.Fa msg_ptr .
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The value of
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.Fa msg_len
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should be less than or equal to the
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.Va mq_msgsize
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attribute of the message queue, or
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.Fn mq_send
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will fail.
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.Pp
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If the specified message queue is not full,
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.Fn mq_send
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will behave as if the message is inserted into the message queue at
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the position indicated by the
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.Fa msg_prio
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argument.
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A message with a larger numeric value of
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.Fa msg_prio
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will be inserted before messages with lower values of
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.Fa msg_prio .
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A message will be inserted after other messages in the queue, if any,
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with equal
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.Fa msg_prio .
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The value of
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.Fa msg_prio
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should be less than
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.Brq Dv MQ_PRIO_MAX .
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.Pp
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If the specified message queue is full and
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.Dv O_NONBLOCK
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is not set in the message queue description associated with
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.Fa mqdes ,
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.Fn mq_send
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will block until space becomes available to enqueue the
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message, or until
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.Fn mq_send
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is interrupted by a signal.
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If more than one thread is
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waiting to send when space becomes available in the message queue and
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the Priority Scheduling option is supported, then the thread of the
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highest priority that has been waiting the longest will be unblocked
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to send its message.
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Otherwise, it is unspecified which waiting thread
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is unblocked.
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If the specified message queue is full and
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.Dv O_NONBLOCK
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is set in the message queue description associated with
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.Fa mqdes ,
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the message will not be queued and
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.Fn mq_send
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will return an error.
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.Pp
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The
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.Fn mq_timedsend
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system call will add a message to the message queue specified by
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.Fa mqdes
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in the manner defined for the
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.Fn mq_send
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system call.
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However, if the specified message queue is full and
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.Dv O_NONBLOCK
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is not set in the message queue description associated with
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.Fa mqdes ,
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the wait for sufficient room in the queue will be terminated when
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the specified timeout expires.
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If
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.Dv O_NONBLOCK
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is set in the message queue description, this system call is
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equivalent to
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.Fn mq_send .
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.Pp
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The timeout will expire when the absolute time specified by
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.Fa abs_timeout
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passes, as measured by the clock on which timeouts are based (that is,
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when the value of that clock equals or exceeds
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.Fa abs_timeout ) ,
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or if the absolute time specified by
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.Fa abs_timeout
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has already been passed at the time of the call.
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.Pp
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The timeout is based on the
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.Dv CLOCK_REALTIME
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clock.
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.Sh RETURN VALUES
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Upon successful completion, the
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.Fn mq_send
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and
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.Fn mq_timedsend
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system calls return a value of zero.
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Otherwise, no message will be
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enqueued, the system calls return \-1, and
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the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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The
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.Fn mq_send
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and
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.Fn mq_timedsend
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system calls
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The
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.Dv O_NONBLOCK
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flag is set in the message queue description associated with
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.Fa mqdes ,
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and the specified message queue is full.
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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 open for writing.
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.It Bq Er EINTR
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A signal interrupted the call to
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.Fn mq_send
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or
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.Fn mq_timedsend .
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.It Bq Er EINVAL
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The value of
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.Fa msg_prio
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was outside the valid range.
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.It Bq Er EINVAL
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The process or thread would have blocked, and the
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.Fa abs_timeout
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parameter specified a nanoseconds field value less than zero or greater
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than or equal to 1000 million.
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.It Bq Er EMSGSIZE
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The specified message length,
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.Fa msg_len ,
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exceeds the message size attribute of the message queue.
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.It Bq Er ETIMEDOUT
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The
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.Dv O_NONBLOCK
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flag was not set when the message queue was opened, but the timeout
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expired before the message could be added to the 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_receive 2 ,
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.Xr mq_setattr 2 ,
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.Xr mq_timedreceive 2
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.Sh STANDARDS
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The
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.Fn mq_send
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and
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.Fn mq_timedsend
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system calls conform 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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