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<!-- Module User's Guide -->

<chapter>
    
    <title>&adminguide;</title>
    
    <section>
	<title>Overview</title>
	<para>
		The mqueue module offers a generic message queue system in shared memory for
		inter-process communication using the config file. One example of usage is
		to send time consuming operations to one or several timer processes that consumes
		items in the queue, without affecting SIP message handling in the socket-listening 
		process.
	</para>
	<para>
		There can be many defined queues. Access to queued values is done via
		pseudo variables.
	</para>
    </section>
    <section>
	<title>Dependencies</title>
	<section>
	    <title>&kamailio; Modules</title>
	    <para>
		The following modules must be loaded before this module:
	    	<itemizedlist>
		    <listitem>
			<para>
			    <emphasis>None</emphasis>.
			</para>
		    </listitem>
	    	</itemizedlist>
	    </para>
	</section>
	<section>
	    <title>External Libraries or Applications</title>
	    <para>
		The following libraries or applications must be installed before running
		&kamailio; with this module loaded:
	    	<itemizedlist>
		    <listitem>
			<para>
			    <emphasis>None</emphasis>.
			</para>
		    </listitem>
	    	</itemizedlist>
	    </para>
	</section>
    </section>
    <section>
	<title>Parameters</title>

	<section id="mqueue.p.mqueue">
	    <title><varname>mqueue</varname> (string)</title>
	    <para>
		Definition of a memory queue
	    </para>
	    <para>
		<emphasis>
		    Default value is <quote>none</quote>.
		</emphasis>
	    </para>
		<para>
		Value must be a list of parameters: attr=value;... The attribute 'name'
		is mandatory, defining the name of the queue. Optional attribute 'size'
		specifies the maximum number of items in queue, if it is execeeded the
		oldest one is removed.
	    </para>
		<para>
		The parameter can be set many times, each holding the definition of one
		queue.
	    </para>
	    <example>
		<title>Set <varname>mqueue</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("mqueue", "mqueue", "name=myq;size=20;")
modparam("mqueue", "mqueue", "name=qaz")
...
</programlisting>
	    </example>
	</section>

	</section>
	
    <section>
	<title>Functions</title>
 	<section id="mqueue.f.mq_add">
	    <title>
		<function moreinfo="none">mq_add(queue, key, value)</function>
	    </title>
	    <para>
		Add a new item (key, value) in the queue. If max size of queue is
		exceeded, the oldest one is removed.
	    </para>
		<example>
		<title><function>mq_add</function> usage</title>
		<programlisting format="linespecific">
...
mq_add("myq", "$rU", "call from $fU");
...
</programlisting>
	    </example>
	</section>
	
 	<section id="mqueue.f.mq_fetch">
	    <title>
		<function moreinfo="none">mq_fetch(queue)</function>
	    </title>
	    <para>
		Take oldest item from queue and fill $mqk(queue) and
		$mqv(queue) pseudo variables.
	    </para>
	    <para>
		Return: true on success (1); false on failure (-1) or
		no item fetched (-2).
	    </para>
		<example>
		<title><function>mq_fetch</function> usage</title>
		<programlisting format="linespecific">
...
while(mq_fetch("myq"))
{
   xlog("$mqk(myq) - $mqv(myq)\n");
}
...
</programlisting>
	    </example>
	</section>
	
 	<section id="mqueue.f.mq_pv_free">
	    <title>
		<function moreinfo="none">mq_pv_free(queue)</function>
	    </title>
	    <para>
		Free the item fetched in pseudo-variables. It is optional, a new fetch
		frees the previous values.
	    </para>
		<example>
		<title><function>mq_pv_free</function> usage</title>
		<programlisting format="linespecific">
...
mq_pv_free("myq");
...
</programlisting>
	    </example>
	</section>

	<section id="mqueue.f.mq_size">
	    <title>
		<function moreinfo="none">mq_size(queue)</function>
	    </title>
	    <para>
		Returns the current number of elements in the mqueue.
	    </para>
	    <para>
	    If the mqueue is empty, the function returns -1. If the
	    mqueue is not found, the function returns -2.
	    </para>
		<example>
		<title><function>mq_size</function> usage</title>
		<programlisting format="linespecific">
...
$var(q_size) = mq_size("queue");
xlog("L_INFO", "Size of queue is: $var(q_size)\n");
...
</programlisting>
	    </example>
	</section>
	
    </section>

    <section>
	<title>Exported Pseudo-variables</title>
		<itemizedlist>
			<listitem>
				<emphasis>$mqv(mqueue)</emphasis> - the most recent item key fetched from the specified mqueue
			</listitem>
			<listitem>
				<emphasis>$mqv(mqueue)</emphasis> - the most recent item value fetched from the specified mqueue
			</listitem>
			<listitem>
				<emphasis>$mq_size(mqueue)</emphasis> - the size of the specified mqueue
			</listitem>
		</itemizedlist>
		<para>
		Exported pseudo-variables are documented at &kamwikilink;.
		</para>
    </section>

</chapter>

