208 lines
5.3 KiB
Groff
208 lines
5.3 KiB
Groff
.\" $NetBSD: mq_send.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_SEND 3
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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 a message queue (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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.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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.In mqueue.h
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.In time.h
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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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function will add 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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will be less than or equal to the
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.Fa 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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behaves as if the message is inserted into the message queue at the
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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,
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if any, 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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will 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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blocks until space becomes available to enqueue the 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 waiting to send when space becomes available
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in the message queue, then the thread of the highest priority that has
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been waiting the longest will be unblocked to send its message.
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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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function 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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function.
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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
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when 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 function will be 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 resolution of the timeout is based on the CLOCK_REALTIME clock.
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The
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.Fa timespec
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argument is defined in the
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.Aq time.h
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header.
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.Pp
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Under no circumstance will the operation fail with a timeout if there is
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sufficient room in the queue to add the message immediately.
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The validity of the
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.Fa abs_timeout
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parameter need not be checked when there is sufficient room in the queue.
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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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functions return a value of zero.
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Otherwise, no message will be enqueued,
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the functions will return \-1, and the global variable
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.Va errno
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will be 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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functions 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, or
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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
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or greater 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,
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but the timeout 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_close 3 ,
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.Xr mq_getattr 3 ,
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.Xr mq_notify 3 ,
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.Xr mq_open 3 ,
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.Xr mq_receive 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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These functions are expected to conform 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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The
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.Fn mq_send
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and
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.Fn mq_timedsend
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functions 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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