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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
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<h1>luaposix 36.3</h1>
<ul>
<li><a href="../index.html">Index</a></li>
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<h2>Contents</h2>
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<li><a href="#Functions">Functions</a></li>
<li><a href="#Tables">Tables</a></li>
<li><a href="#Constants">Constants </a></li>
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<h2>Modules</h2>
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<li><a href="../modules/posix.stdio.html">posix.stdio</a></li>
<li><a href="../modules/posix.stdlib.html">posix.stdlib</a></li>
<li><strong>posix.sys.msg</strong></li>
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<h1>Module <code>posix.sys.msg</code></h1>
<p>Sys V Message Queue Operations.</p>
<p> Where supported by the underlying system, functions to send and receive
interprocess messages. If the module loads successfully, but there is
no system support, then <code>posix.sys.msg.version</code> will be set, but the
unsupported APIs wil be <code>nil</code>.</p>
<h2><a href="#Functions">Functions</a></h2>
<table class="function_list">
<tr>
<td class="name" nowrap><a href="#msgctl">msgctl (id, cmd)</a></td>
<td class="summary">
</td>
</tr>
<tr>
<td class="name" nowrap><a href="#msgget">msgget (key[, flags=0])</a></td>
<td class="summary">Get a message queue identifier</td>
</tr>
<tr>
<td class="name" nowrap><a href="#msgrcv">msgrcv (id, size, type[, flags=0])</a></td>
<td class="summary">Receive message from a message queue</td>
</tr>
<tr>
<td class="name" nowrap><a href="#msgsnd">msgsnd (id, type, message[, flags=0])</a></td>
<td class="summary">Send message to a message queue</td>
</tr>
</table>
<h2><a href="#Tables">Tables</a></h2>
<table class="function_list">
<tr>
<td class="name" nowrap><a href="#PosixMsqid">PosixMsqid</a></td>
<td class="summary">Message queue record.</td>
</tr>
</table>
<h2><a href="#Constants">Constants </a></h2>
<table class="function_list">
<tr>
<td class="name" nowrap><a href="#posix.sys.msg">posix.sys.msg</a></td>
<td class="summary">Message constants.</td>
</tr>
</table>
<br/>
<br/>
<h2 class="section-header "><a name="Functions"></a>Functions</h2>
<dl class="function">
<dt>
<a name = "msgctl"></a>
<strong>msgctl (id, cmd)</strong>
</dt>
<dd>
<h3>Parameters:</h3>
<ul>
<li><span class="parameter">id</span>
<span class="types"><span class="type">int</span></span>
message queue identifier returned by <a href="../modules/posix.sys.msg.html#msgget">msgget</a>
</li>
<li><span class="parameter">cmd</span>
<span class="types"><span class="type">int</span></span>
one of <code>IPC_STAT</code>, <code>IPC_SET</code> or <code>IPC_RMID</code>
</li>
</ul>
<h3>Returns:</h3>
<ol>
<span class="types"><a class="type" href="../modules/posix.sys.msg.html#PosixMsqid">PosixMsqid</a></span>
table for <em>id</em>, with <code>IPC_STAT</code>, if successful
</ol>
<h3>Or</h3>
<ol>
<span class="types"><span class="type">non-nil,</span></span>
with <code>IPC_SET</code> or <code>IPC_RMID</code>, if successful
</ol>
<h3>Or</h3>
<ol>
<li>
<span class="types"><span class="type">nil</span></span>
otherwise</li>
<li>
<span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.4">string</a></span>
error message</li>
<li>
<span class="types"><span class="type">int</span></span>
errnum</li>
</ol>
<h3>See also:</h3>
<ul>
<a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/msgctl.html">msgctl(2)</a>
</ul>
<h3>Usage:</h3>
<ul>
<pre class="example"><span class="keyword">local</span> sysvmsg = <span class="global">require</span> <span class="string">'posix.sys.msg'</span>
<span class="keyword">local</span> msq = sysvmsg.<span class="function-name">msgget</span>(sysvmsg.IPC_PRIVATE)
<span class="keyword">local</span> msqid, errmsg = sysvmsg.<span class="function-name">msgctl</span>(msq, sysvmsg.IPC_STAT)
<span class="global">assert</span>(msqid, errmsg)
<span class="global">assert</span>(sysvmsg.<span class="function-name">msgctl</span>(msq, sysvmsg.IPC_RMID))</pre>
</ul>
</dd>
<dt>
<a name = "msgget"></a>
<strong>msgget (key[, flags=0])</strong>
</dt>
<dd>
Get a message queue identifier
<h3>Parameters:</h3>
<ul>
<li><span class="parameter">key</span>
<span class="types"><span class="type">int</span></span>
message queue id, or <code>IPC_PRIVATE</code> for a new queue
</li>
<li><span class="parameter">flags</span>
<span class="types"><span class="type">int</span></span>
bitwise OR of zero or more from <code>IPC_CREAT</code> and <code>IPC_EXCL</code>,
and access permissions <code>S_IRUSR</code>, <code>S_IWUSR</code>, <code>S_IRGRP</code>, <code>S_IWGRP</code>, <code>S_IROTH</code>
and <code>S_IWOTH</code> (from <a href="../modules/posix.sys.stat.html#">posix.sys.stat</a>)
(<em>default</em> 0)
</li>
</ul>
<h3>Returns:</h3>
<ol>
<span class="types"><span class="type">int</span></span>
message queue identifier, if successful
</ol>
<h3>Or</h3>
<ol>
<li>
nil</li>
<li>
<span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.4">string</a></span>
error message</li>
<li>
<span class="types"><span class="type">int</span></span>
errnum</li>
</ol>
<h3>See also:</h3>
<ul>
<a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/msgget.html">msgget(2)</a>
</ul>
</dd>
<dt>
<a name = "msgrcv"></a>
<strong>msgrcv (id, size, type[, flags=0])</strong>
</dt>
<dd>
Receive message from a message queue
<h3>Parameters:</h3>
<ul>
<li><span class="parameter">id</span>
<span class="types"><span class="type">int</span></span>
message queue identifier returned by <a href="../modules/posix.sys.msg.html#msgget">msgget</a>
</li>
<li><span class="parameter">size</span>
<span class="types"><span class="type">int</span></span>
maximum message size
</li>
<li><span class="parameter">type</span>
<span class="types"><span class="type">int</span></span>
message type (optional, default - 0)
</li>
<li><span class="parameter">flags</span>
<span class="types"><span class="type">int</span></span>
bitwise OR of zero or more of <code>IPC_NOWAIT</code>, <code>MSG_EXCEPT</code>
and <code>MSG_NOERROR</code>
(<em>default</em> 0)
</li>
</ul>
<h3>Returns:</h3>
<ol>
<li>
<span class="types"><span class="type">int</span></span>
message type from <a href="../modules/posix.sys.msg.html#msgsnd">msgsnd</a></li>
<li>
<span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.4">string</a></span>
message text, if successful</li>
</ol>
<h3>Or</h3>
<ol>
<li>
nil</li>
<li>
<span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.4">string</a></span>
error message</li>
<li>
<span class="types"><span class="type">int</span></span>
errnum</li>
</ol>
<h3>See also:</h3>
<ul>
<a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/msgrcv.html">msgrcv(2)</a>
</ul>
</dd>
<dt>
<a name = "msgsnd"></a>
<strong>msgsnd (id, type, message[, flags=0])</strong>
</dt>
<dd>
Send message to a message queue
<h3>Parameters:</h3>
<ul>
<li><span class="parameter">id</span>
<span class="types"><span class="type">int</span></span>
message queue identifier returned by <a href="../modules/posix.sys.msg.html#msgget">msgget</a>
</li>
<li><span class="parameter">type</span>
<span class="types"><span class="type">int</span></span>
arbitrary message type
</li>
<li><span class="parameter">message</span>
<span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.4">string</a></span>
content
</li>
<li><span class="parameter">flags</span>
<span class="types"><span class="type">int</span></span>
optionally <code>IPC_NOWAIT</code>
(<em>default</em> 0)
</li>
</ul>
<h3>Returns:</h3>
<ol>
<span class="types"><span class="type">int</span></span>
<code>0</code>, if successful
</ol>
<h3>Or</h3>
<ol>
<li>
nil</li>
<li>
<span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.4">string</a></span>
error message</li>
<li>
<span class="types"><span class="type">int</span></span>
errnum</li>
</ol>
<h3>See also:</h3>
<ul>
<a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/msgsnd.html">msgsnd(2)</a>
</ul>
</dd>
</dl>
<h2 class="section-header "><a name="Tables"></a>Tables</h2>
<dl class="function">
<dt>
<a name = "PosixMsqid"></a>
<strong>PosixMsqid</strong>
</dt>
<dd>
Message queue record.
<h3>Fields:</h3>
<ul>
<li><span class="parameter">msg_qnum</span>
<span class="types"><span class="type">int</span></span>
number of messages on the queue
</li>
<li><span class="parameter">msg_qbytes</span>
<span class="types"><span class="type">int</span></span>
number of bytes allowed on the queue
</li>
<li><span class="parameter">msg_lspid</span>
<span class="types"><span class="type">int</span></span>
process id of last msgsnd
</li>
<li><span class="parameter">msg_lrpid</span>
<span class="types"><span class="type">int</span></span>
process id of last msgrcv
</li>
<li><span class="parameter">msg_stime</span>
<span class="types"><span class="type">int</span></span>
time of last msgsnd
</li>
<li><span class="parameter">msg_rtime</span>
<span class="types"><span class="type">int</span></span>
time of last msgrcv
</li>
<li><span class="parameter">msg_ctime</span>
<span class="types"><span class="type">int</span></span>
time of last change
</li>
</ul>
</dd>
</dl>
<h2 class="section-header "><a name="Constants"></a>Constants </h2>
<dl class="function">
<dt>
<a name = "posix.sys.msg"></a>
<strong>posix.sys.msg</strong>
</dt>
<dd>
Message constants.
Any constants not available in the underlying system will be <code>nil</code> valued.
<h3>Fields:</h3>
<ul>
<li><span class="parameter">IPC_STAT</span>
<span class="types"><span class="type">int</span></span>
return a Msqid table from msgctl
</li>
<li><span class="parameter">IPC_SET</span>
<span class="types"><span class="type">int</span></span>
set the Msqid fields from msgctl
</li>
<li><span class="parameter">IPC_RMID</span>
<span class="types"><span class="type">int</span></span>
remove a message queue with msgctl
</li>
<li><span class="parameter">IPC_CREAT</span>
<span class="types"><span class="type">int</span></span>
create entry if key does not exist
</li>
<li><span class="parameter">IPC_EXCL</span>
<span class="types"><span class="type">int</span></span>
fail if key exists
</li>
<li><span class="parameter">IPC_PRIVATE</span>
<span class="types"><span class="type">int</span></span>
private key
</li>
<li><span class="parameter">IPC_NOWAIT</span>
<span class="types"><span class="type">int</span></span>
error if request must wait
</li>
<li><span class="parameter">MSG_EXCEPT</span>
<span class="types"><span class="type">int</span></span>
read messages with differing type
</li>
<li><span class="parameter">MSG_NOERROR</span>
<span class="types"><span class="type">int</span></span>
truncate received message rather than erroring
</li>
</ul>
<h3>Usage:</h3>
<ul>
<pre class="example"><span class="comment">-- Print msg constants supported on this host.
</span><span class="keyword">for</span> name, value <span class="keyword">in</span> <span class="global">pairs</span> (<span class="global">require</span> <span class="string">"posix.sys.msg"</span>) <span class="keyword">do</span>
<span class="keyword">if</span> <span class="global">type</span> (value) == <span class="string">"number"</span> <span class="keyword">then</span>
<span class="global">print</span> (name, value)
<span class="keyword">end</span>
<span class="keyword">end</span></pre>
</ul>
</dd>
</dl>
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