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<section version="5.0"
         xml:id="other-miscellaneous-topics-performance-and-thread-safety"
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    <title>Performance and thread-safety</title>

    <para>The JAXBContext class is thread safe, but the Marshaller,
    Unmarshaller, and Validator classes are not thread safe.</para>

    <para>For example, suppose you have a multi-thread server application that
    processes incoming XML documents by JAXB. In this case, for the best
    performance you should have just one instance of JAXBContext in your whole
    application like this:</para>

    <example>
        <title>Singleton JAXBContext</title>

        <programlisting language="java"><![CDATA[class MyServlet extends HttpServlet {
    static final JAXBContext context = initContext();

    private static JAXBContext initContext() {
        return JAXBContext.newInstance(Foo.class,Bar.class);
    }
}]]></programlisting>
    </example>

    <para>And each time you need to unmarshal/marshal/validate a document.
    Just create a new Unmarshaller/Marshaller/Validator from this context,
    like this:</para>

    <example>
        <title>Thread local Unmarshaller</title>

        <programlisting language="java"><![CDATA[    public void doGet( HttpServletRequest req, HttpServletResponse ) {
        Unmarshaller u = context.createUnmarshaller();
        u.unmarshal(...);
    }]]></programlisting>
    </example>

    <para>This is the simplest safe way to use the JAXB RI from multi-threaded
    applications.</para>

    <para>If you really care about the performance, and/or your application is
    going to read a lot of small documents, then creating Unmarshaller could
    be relatively an expensive operation. In that case, consider pooling
    Unmarshaller objects. Different threads may reuse one Unmarshaller
    instance, as long as you don't use one instance from two threads at the
    same time.</para>
</section>
