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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<chapter id="backend-dbus">
<title>DBUS Backends</title>
<para>
Backend helpers communicating over standard out and standard
error are easy to write, but can have some performance
problems.
For instance, if your packages system has to do a lot of work when it
starts up and shuts down, performance in the UI may suffer.
In these cases, you can use a persistant backend daemon that
communicates to the C backend over DBUS.
</para>
<para>
Your daemon will be started by DBUS, and should be responsible
for it's own thread management.
It should receive an <literal>Init()</literal> method call when the C
backend starts, and an <literal>Exit()</literal> method call before it
exits.
You should also consider adding a timeout value to your daemon so that
it will exit after a set time with no activity from the C backend.
That way the daemon will still exit even if the C backend crashes for
some reason.
</para>
<para>
Again, like the helper backends described above, a compiled
backend stub is needed. An example of a DBUS backend written
in python can be found in <literal>backends/apt</literal>,
along with a compiled stub written in C.
</para>
</chapter>
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