263 lines
9.0 KiB
HTML
263 lines
9.0 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
|
<html>
|
|
<head>
|
|
<meta name="generator" content="HTML Tidy, see www.w3.org">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
|
|
<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
|
|
<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
|
|
<title>msgsnd</title>
|
|
</head>
|
|
<body bgcolor="white">
|
|
<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
|
|
</script>
|
|
|
|
<basefont size="3"> <a name="msgsnd"></a> <a name="tag_03_396"></a><!-- msgsnd -->
|
|
<!--header start-->
|
|
<center><font size="2">The Open Group Base Specifications Issue 6<br>
|
|
IEEE Std 1003.1-2001<br>
|
|
Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
|
|
|
|
<!--header end-->
|
|
<hr size="2" noshade>
|
|
<h4><a name="tag_03_396_01"></a>NAME</h4>
|
|
|
|
<blockquote>msgsnd - XSI message send operation</blockquote>
|
|
|
|
<h4><a name="tag_03_396_02"></a>SYNOPSIS</h4>
|
|
|
|
<blockquote class="synopsis">
|
|
<div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
|
|
"[Option Start]" border="0"> #include <<a href="../basedefs/sys/msg.h.html">sys/msg.h</a>><br>
|
|
<br>
|
|
int msgsnd(int</tt> <i>msqid</i><tt>, const void *</tt><i>msgp</i><tt>, size_t</tt> <i>msgsz</i><tt>, int</tt> <i>msgflg</i><tt>);
|
|
<img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
|
|
|
|
<tt><br>
|
|
</tt></blockquote>
|
|
|
|
<h4><a name="tag_03_396_03"></a>DESCRIPTION</h4>
|
|
|
|
<blockquote>
|
|
<p>The <i>msgsnd</i>() function operates on XSI message queues (see the Base Definitions volume of IEEE Std 1003.1-2001,
|
|
<a href="../basedefs/xbd_chap03.html#tag_03_224">Section 3.224, Message Queue</a>). It is unspecified whether this function
|
|
interoperates with the realtime interprocess communication facilities defined in <a href=
|
|
"xsh_chap02_08.html#tag_02_08"><i>Realtime</i></a> .</p>
|
|
|
|
<p>The <i>msgsnd</i>() function shall send a message to the queue associated with the message queue identifier specified by
|
|
<i>msqid</i>.</p>
|
|
|
|
<p>The application shall ensure that the argument <i>msgp</i> points to a user-defined buffer that contains first a field of type
|
|
<b>long</b> specifying the type of the message, and then a data portion that holds the data bytes of the message. The structure
|
|
below is an example of what this user-defined buffer might look like:</p>
|
|
|
|
<pre>
|
|
<tt>struct mymsg {
|
|
long mtype; /* Message type. */
|
|
char mtext[1]; /* Message text. */
|
|
}
|
|
</tt>
|
|
</pre>
|
|
|
|
<p>The structure member <i>mtype</i> is a non-zero positive type <b>long</b> that can be used by the receiving process for message
|
|
selection.</p>
|
|
|
|
<p>The structure member <i>mtext</i> is any text of length <i>msgsz</i> bytes. The argument <i>msgsz</i> can range from 0 to a
|
|
system-imposed maximum.</p>
|
|
|
|
<p>The argument <i>msgflg</i> specifies the action to be taken if one or more of the following is true:</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>The number of bytes already on the queue is equal to <b>msg_qbytes</b>; see <a href=
|
|
"../basedefs/sys/msg.h.html"><i><sys/msg.h></i></a>.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>The total number of messages on all queues system-wide is equal to the system-imposed limit.</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>These actions are as follows:</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>If (<i>msgflg</i> & IPC_NOWAIT) is non-zero, the message shall not be sent and the calling thread shall return
|
|
immediately.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>If (<i>msgflg</i> & IPC_NOWAIT) is 0, the calling thread shall suspend execution until one of the following occurs:</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>The condition responsible for the suspension no longer exists, in which case the message is sent.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>The message queue identifier <i>msqid</i> is removed from the system; when this occurs, <i>errno</i> shall be set equal to
|
|
[EIDRM] and -1 shall be returned.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>The calling thread receives a signal that is to be caught; in this case the message is not sent and the calling thread resumes
|
|
execution in the manner prescribed in <a href="sigaction.html"><i>sigaction</i>()</a> .</p>
|
|
</li>
|
|
</ul>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>Upon successful completion, the following actions are taken with respect to the data structure associated with <i>msqid</i>; see
|
|
<a href="../basedefs/sys/msg.h.html"><i><sys/msg.h></i></a>:</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p><b>msg_qnum</b> shall be incremented by 1.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p><b>msg_lspid</b> shall be set equal to the process ID of the calling process.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p><b>msg_stime</b> shall be set equal to the current time.</p>
|
|
</li>
|
|
</ul>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_396_04"></a>RETURN VALUE</h4>
|
|
|
|
<blockquote>
|
|
<p>Upon successful completion, <i>msgsnd</i>() shall return 0; otherwise, no message shall be sent, <i>msgsnd</i>() shall return
|
|
-1, and <i>errno</i> shall be set to indicate the error.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_396_05"></a>ERRORS</h4>
|
|
|
|
<blockquote>
|
|
<p>The <i>msgsnd</i>() function shall fail if:</p>
|
|
|
|
<dl compact>
|
|
<dt>[EACCES]</dt>
|
|
|
|
<dd>Operation permission is denied to the calling process; see <a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess
|
|
Communication</i></a> .</dd>
|
|
|
|
<dt>[EAGAIN]</dt>
|
|
|
|
<dd>The message cannot be sent for one of the reasons cited above and (<i>msgflg</i> & IPC_NOWAIT) is non-zero.</dd>
|
|
|
|
<dt>[EIDRM]</dt>
|
|
|
|
<dd>The message queue identifier <i>msgid</i> is removed from the system.</dd>
|
|
|
|
<dt>[EINTR]</dt>
|
|
|
|
<dd>The <i>msgsnd</i>() function was interrupted by a signal.</dd>
|
|
|
|
<dt>[EINVAL]</dt>
|
|
|
|
<dd>The value of <i>msqid</i> is not a valid message queue identifier, or the value of <i>mtype</i> is less than 1; or the value of
|
|
<i>msgsz</i> is less than 0 or greater than the system-imposed limit.</dd>
|
|
</dl>
|
|
</blockquote>
|
|
|
|
<hr>
|
|
<div class="box"><em>The following sections are informative.</em></div>
|
|
|
|
<h4><a name="tag_03_396_06"></a>EXAMPLES</h4>
|
|
|
|
<blockquote>
|
|
<h5><a name="tag_03_396_06_01"></a>Sending a Message</h5>
|
|
|
|
<p>The following example sends a message to the queue identified by the <i>msqid</i> argument (assuming that value has previously
|
|
been set). This call specifies that an error should be reported if no message is available. The message size is calculated directly
|
|
using the <i>sizeof</i> operator.</p>
|
|
|
|
<pre>
|
|
<tt>#include <sys/msg.h>
|
|
...
|
|
int result;
|
|
int msqid;
|
|
struct message {
|
|
long type;
|
|
char text[20];
|
|
} msg;
|
|
<br>
|
|
msg.type = 1;
|
|
strcpy(msg.text, "This is message 1");
|
|
...
|
|
result = msgsnd(msqid, (void *) &msg, sizeof(msg.text), IPC_NOWAIT);
|
|
</tt>
|
|
</pre>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_396_07"></a>APPLICATION USAGE</h4>
|
|
|
|
<blockquote>
|
|
<p>The POSIX Realtime Extension defines alternative interfaces for interprocess communication (IPC). Application developers who
|
|
need to use IPC should design their applications so that modules using the IPC routines described in <a href=
|
|
"xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> can be easily modified to use the alternative
|
|
interfaces.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_396_08"></a>RATIONALE</h4>
|
|
|
|
<blockquote>
|
|
<p>None.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_396_09"></a>FUTURE DIRECTIONS</h4>
|
|
|
|
<blockquote>
|
|
<p>None.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_396_10"></a>SEE ALSO</h4>
|
|
|
|
<blockquote>
|
|
<p><a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> , <a href=
|
|
"xsh_chap02_08.html#tag_02_08"><i>Realtime</i></a> , <a href="mq_close.html"><i>mq_close</i>()</a> , <a href=
|
|
"mq_getattr.html"><i>mq_getattr</i>()</a> , <a href="mq_notify.html"><i>mq_notify</i>()</a> , <a href=
|
|
"mq_open.html"><i>mq_open</i>()</a> , <a href="mq_receive.html"><i>mq_receive</i>()</a> , <a href=
|
|
"mq_send.html"><i>mq_send</i>()</a> , <a href="mq_setattr.html"><i>mq_setattr</i>()</a> , <a href=
|
|
"mq_unlink.html"><i>mq_unlink</i>()</a> , <a href="msgctl.html"><i>msgctl</i>()</a> , <a href="msgget.html"><i>msgget</i>()</a> ,
|
|
<a href="msgrcv.html"><i>msgrcv</i>()</a> , <a href="sigaction.html"><i>sigaction</i>()</a> , the Base Definitions volume of
|
|
IEEE Std 1003.1-2001, <a href="../basedefs/sys/msg.h.html"><i><sys/msg.h></i></a></p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_396_11"></a>CHANGE HISTORY</h4>
|
|
|
|
<blockquote>
|
|
<p>First released in Issue 2. Derived from Issue 2 of the SVID.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_396_12"></a>Issue 5</h4>
|
|
|
|
<blockquote>
|
|
<p>The note about use of POSIX Realtime Extension IPC routines has been moved from FUTURE DIRECTIONS to a new APPLICATION USAGE
|
|
section.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_396_13"></a>Issue 6</h4>
|
|
|
|
<blockquote>
|
|
<p>The DESCRIPTION is updated to avoid use of the term "must" for application requirements.</p>
|
|
</blockquote>
|
|
|
|
<div class="box"><em>End of informative text.</em></div>
|
|
|
|
<hr>
|
|
<hr size="2" noshade>
|
|
<center><font size="2"><!--footer start-->
|
|
UNIX ® is a registered Trademark of The Open Group.<br>
|
|
POSIX ® is a registered Trademark of The IEEE.<br>
|
|
[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
|
|
"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
|
|
]</font></center>
|
|
|
|
<!--footer end-->
|
|
<hr size="2" noshade>
|
|
</body>
|
|
</html>
|
|
|