@Override
    public void enableService(final boolean enabled, final boolean persistent) {
        if (isServiceEnabled() == enabled) {
            // Do nothing if the service status has not changed
            return;
        }
        if (!enabled) {
            // Stop the service/module
            stop();
        }
        if (persistent) {
            MUCPersistenceManager.setProperty(chatServiceName, "enabled", Boolean.toString(enabled));
        }
        serviceEnabled = enabled;
        if (enabled) {
            // Start the service/module
            start();
        }
    }
Accessor uses the "double-check idiom" for proper lazy instantiation.
@return An Archiver instance, never null.
xmppserver/src/main/java/org/jivesoftware/openfire/muc/spi/MultiUserChatServiceImpl.java