Session Listeners
Definition
The application session listeners are objects instantiated at server startup and are notified when a client session invokes the application for the first time and when the client disconnects. We need a session listener to remove the subscription for disconnected clients: 
public class SubscriptionCleanup implements ISessionListener
{
    /**
     * Does nothing.
     *
     * @since 1.0
     */
    public void init() throws InitSessionListenerException
    {
        // initialize the session listener
    }

    /**
     * Does nothing.
     *
     * @since 1.0
     */
    public void sessionOpened( IConnectionContext connection )
    {
        // allocate session data, for example create an empty shopping cart
    }

    /**
     * Removes the session subscription when closed.
     *
     * @see com.accendia.iris.server.IConnectionContext
     *
     * @since 1.0
     */
    public void sessionClosed( IConnectionContext connection )
    {
        SubscriptionManager.instance().removeSubscription( connection );
    }
}

Session Listener Declaration
The session listener must be declared in the application.properties file: 
Application.session_listener=cleanup
Application.session_listener.cleanup=com.accendia.datasynch.server.SubscriptionCleanup
Application.session_listener.cleanup.enabled=true
The listener name is not used by the application code but is useful in self documenting the application.properties file.