.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "MQ_SEND" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" mq_send 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
mq_send, mq_timedsend \- send a message to a message queue (\fBREALTIME\fP)
.SH SYNOPSIS
.LP
\fB#include <mqueue.h>
.br
.sp
int mq_send(mqd_t\fP \fImqdes\fP\fB, const char *\fP\fImsg_ptr\fP\fB,
size_t\fP \fImsg_len\fP\fB,
.br
\ \ \ \ \ \  unsigned\fP \fImsg_prio\fP\fB); \fP
\fB
.br
.sp
\fP 
.LP
\fB
.br
#include <mqueue.h>
.br
#include <time.h>
.br
int mq_timedsend(mqd_t\fP \fImqdes\fP\fB, const char *\fP\fImsg_ptr\fP\fB,
size_t\fP \fImsg_len\fP\fB,
.br
\ \ \ \ \ \  unsigned\fP \fImsg_prio\fP\fB, const struct timespec
*\fP\fIabs_timeout\fP\fB); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fImq_send\fP() function shall add the message pointed to by the
argument \fImsg_ptr\fP to the message queue specified by
\fImqdes\fP. The \fImsg_len\fP argument specifies the length of the
message, in bytes, pointed to by \fImsg_ptr\fP. The value of
\fImsg_len\fP shall be less than or equal to the \fImq_msgsize\fP
attribute of the message queue, or \fImq_send\fP() shall
fail.
.LP
If the specified message queue is not full, \fImq_send\fP() shall
behave as if the message is inserted into the message queue
at the position indicated by the \fImsg_prio\fP argument. A message
with a larger numeric value of \fImsg_prio\fP shall be
inserted before messages with lower values of \fImsg_prio\fP. A message
shall be inserted after other messages in the queue, if
any, with equal \fImsg_prio\fP. The value of \fImsg_prio\fP shall
be less than {MQ_PRIO_MAX}.
.LP
If the specified message queue is full and O_NONBLOCK is not set in
the message queue description associated with \fImqdes\fP,
\fImq_send\fP() shall block until space becomes available to enqueue
the message, or until \fImq_send\fP() is interrupted by a
signal. If more than one thread is waiting to send when space becomes
available in the message queue and the Priority Scheduling
option is supported, then the thread of the highest priority that
has been waiting the longest shall be unblocked to send its
message. Otherwise, it is unspecified which waiting thread is unblocked.
If the specified message queue is full and O_NONBLOCK is
set in the message queue description associated with \fImqdes\fP,
the message shall not be queued and \fImq_send\fP() shall
return an error.
.LP
The \fImq_timedsend\fP() function shall add a message to the message
queue specified by \fImqdes\fP in the manner defined for the
\fImq_send\fP() function. However, if the specified message queue
is full and O_NONBLOCK is not set in the message queue
description associated with \fImqdes\fP, the wait for sufficient room
in the queue shall be terminated when the specified timeout
expires. If O_NONBLOCK is set in the message queue description, this
function shall be equivalent to \fImq_send\fP().
.LP
The timeout shall expire when the absolute time specified by \fIabs_timeout\fP
passes, as measured by the clock on which
timeouts are based (that is, when the value of that clock equals or
exceeds \fIabs_timeout\fP), or if the absolute time specified
by \fIabs_timeout\fP has already been passed at the time of the call.
.LP
If the Timers option is supported, the timeout shall be based on the
CLOCK_REALTIME clock; if the Timers option is not
supported, the timeout shall be based on the system clock as returned
by the \fItime\fP()
function. 
.LP
The resolution of the timeout shall be the resolution of the clock
on which it is based. The \fItimespec\fP argument is defined in
the \fI<time.h>\fP header.
.LP
Under no circumstance shall the operation fail with a timeout if there
is sufficient room in the queue to add the message
immediately. The validity of the \fIabs_timeout\fP parameter need
not be checked when there is sufficient room in the queue. 
.SH RETURN VALUE
.LP
Upon successful completion, the \fImq_send\fP()  and \fImq_timedsend\fP()
functions shall return a value of zero. Otherwise, no message shall
be enqueued, the functions shall
return -1, and \fIerrno\fP shall be set to indicate the error.
.SH ERRORS
.LP
The \fImq_send\fP()  and \fImq_timedsend\fP() 
functions shall fail if:
.TP 7
.B EAGAIN
The O_NONBLOCK flag is set in the message queue description associated
with \fImqdes\fP, and the specified message queue is
full.
.TP 7
.B EBADF
The \fImqdes\fP argument is not a valid message queue descriptor open
for writing.
.TP 7
.B EINTR
A signal interrupted the call to \fImq_send\fP()  or \fImq_timedsend\fP().
.TP 7
.B EINVAL
The value of \fImsg_prio\fP was outside the valid range.
.TP 7
.B EINVAL
The process or thread would have blocked, and the \fIabs_timeout\fP
parameter specified a nanoseconds field value less than zero
or greater than or equal to 1000 million. 
.TP 7
.B EMSGSIZE
The specified message length, \fImsg_len\fP, exceeds the message size
attribute of the message queue.
.TP 7
.B ETIMEDOUT
The O_NONBLOCK flag was not set when the message queue was opened,
but the timeout expired before the message could be added to the
queue. 
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
The value of the symbol {MQ_PRIO_MAX} limits the number of priority
levels supported by the application. Message priorities
range from 0 to {MQ_PRIO_MAX}-1.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fImq_open\fP(), \fImq_receive\fP(), \fImq_setattr\fP(), \fImq_timedreceive\fP(),
\fItime\fP(), the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
\fI<mqueue.h>\fP, \fI<time.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .