280 lines
9.9 KiB
HTML
280 lines
9.9 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>msgrcv</title>
|
|
</head>
|
|
<body bgcolor="white">
|
|
<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
|
|
</script>
|
|
|
|
<basefont size="3"> <a name="msgrcv"></a> <a name="tag_03_395"></a><!-- msgrcv -->
|
|
<!--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_395_01"></a>NAME</h4>
|
|
|
|
<blockquote>msgrcv - XSI message receive operation</blockquote>
|
|
|
|
<h4><a name="tag_03_395_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>
|
|
ssize_t msgrcv(int</tt> <i>msqid</i><tt>, void *</tt><i>msgp</i><tt>, size_t</tt> <i>msgsz</i><tt>, long</tt>
|
|
<i>msgtyp</i><tt>,<br>
|
|
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_395_03"></a>DESCRIPTION</h4>
|
|
|
|
<blockquote>
|
|
<p>The <i>msgrcv</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>msgrcv</i>() function shall read a message from the queue associated with the message queue identifier specified by
|
|
<i>msqid</i> and place it in the user-defined buffer pointed to by <i>msgp</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 the received message's type as specified by the sending process.</p>
|
|
|
|
<p>The structure member <i>mtext</i> is the text of the message.</p>
|
|
|
|
<p>The argument <i>msgsz</i> specifies the size in bytes of <i>mtext</i>. The received message shall be truncated to <i>msgsz</i>
|
|
bytes if it is larger than <i>msgsz</i> and (<i>msgflg</i> & MSG_NOERROR) is non-zero. The truncated part of the message shall
|
|
be lost and no indication of the truncation shall be given to the calling process.</p>
|
|
|
|
<p>If the value of <i>msgsz</i> is greater than {SSIZE_MAX}, the result is implementation-defined.</p>
|
|
|
|
<p>The argument <i>msgtyp</i> specifies the type of message requested as follows:</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>If <i>msgtyp</i> is 0, the first message on the queue shall be received.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>If <i>msgtyp</i> is greater than 0, the first message of type <i>msgtyp</i> shall be received.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>If <i>msgtyp</i> is less than 0, the first message of the lowest type that is less than or equal to the absolute value of
|
|
<i>msgtyp</i> shall be received.</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>The argument <i>msgflg</i> specifies the action to be taken if a message of the desired type is not on the queue. These are as
|
|
follows:</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>If (<i>msgflg</i> & IPC_NOWAIT) is non-zero, the calling thread shall return immediately with a return value of -1 and
|
|
<i>errno</i> set to [ENOMSG].</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>A message of the desired type is placed on the queue.</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 a message is not received 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>:</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p><b>msg_qnum</b> shall be decremented by 1.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p><b>msg_lrpid</b> shall be set equal to the process ID of the calling process.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p><b>msg_rtime</b> shall be set equal to the current time.</p>
|
|
</li>
|
|
</ul>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_395_04"></a>RETURN VALUE</h4>
|
|
|
|
<blockquote>
|
|
<p>Upon successful completion, <i>msgrcv</i>() shall return a value equal to the number of bytes actually placed into the buffer
|
|
<i>mtext</i>. Otherwise, no message shall be received, <i>msgrcv</i>() shall return (<b>ssize_t</b>)-1, and <i>errno</i> shall be
|
|
set to indicate the error.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_395_05"></a>ERRORS</h4>
|
|
|
|
<blockquote>
|
|
<p>The <i>msgrcv</i>() function shall fail if:</p>
|
|
|
|
<dl compact>
|
|
<dt>[E2BIG]</dt>
|
|
|
|
<dd>The value of <i>mtext</i> is greater than <i>msgsz</i> and (<i>msgflg</i> & MSG_NOERROR) is 0.</dd>
|
|
|
|
<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>[EIDRM]</dt>
|
|
|
|
<dd>The message queue identifier <i>msqid</i> is removed from the system.</dd>
|
|
|
|
<dt>[EINTR]</dt>
|
|
|
|
<dd>The <i>msgrcv</i>() function was interrupted by a signal.</dd>
|
|
|
|
<dt>[EINVAL]</dt>
|
|
|
|
<dd><i>msqid</i> is not a valid message queue identifier.</dd>
|
|
|
|
<dt>[ENOMSG]</dt>
|
|
|
|
<dd>The queue does not contain a message of the desired type and (<i>msgflg</i> & IPC_NOWAIT) is non-zero.</dd>
|
|
</dl>
|
|
</blockquote>
|
|
|
|
<hr>
|
|
<div class="box"><em>The following sections are informative.</em></div>
|
|
|
|
<h4><a name="tag_03_395_06"></a>EXAMPLES</h4>
|
|
|
|
<blockquote>
|
|
<h5><a name="tag_03_395_06_01"></a>Receiving a Message</h5>
|
|
|
|
<p>The following example receives the first message on the queue (based on the value of the <i>msgtyp</i> argument, 0). The queue
|
|
is identified by the <i>msqid</i> argument (assuming that the value has previously been set). This call specifies that an error
|
|
should be reported if no message is available, but not if the message is too large. 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;
|
|
long msgtyp = 0;
|
|
...
|
|
result = msgrcv(msqid, (void *) &msg, sizeof(msg.text),
|
|
msgtyp, MSG_NOERROR | IPC_NOWAIT);
|
|
</tt>
|
|
</pre>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_395_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_395_08"></a>RATIONALE</h4>
|
|
|
|
<blockquote>
|
|
<p>None.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_395_09"></a>FUTURE DIRECTIONS</h4>
|
|
|
|
<blockquote>
|
|
<p>None.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_395_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="msgsnd.html"><i>msgsnd</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_395_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_395_12"></a>Issue 5</h4>
|
|
|
|
<blockquote>
|
|
<p>The type of the return value is changed from <b>int</b> to <b>ssize_t</b>, and a warning is added to the DESCRIPTION about
|
|
values of <i>msgsz</i> larger the {SSIZE_MAX}.</p>
|
|
|
|
<p>The note about use of POSIX Realtime Extension IPC routines has been moved from FUTURE DIRECTIONS to the APPLICATION USAGE
|
|
section.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_395_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>
|
|
|