Currently within the shutdown we generally just do something like

AtomicBoolean shutdown = new AutomaticBoolean(false);

public void shutdown()
{
while (still deployments)
removeDeployments();
shutdown.set(true);
}

public void deploy()
{
if (shutdown.get())
throw new IllegalStateException("Already shutdown");
}

This needs improving to
1) Have a prepareShutdown() so we can signal that new deployments are not allowed earlier
2) The IllegalStateException should be replaced with a ShutdownException such that the caller
can ignore such errors and deal with the shutdown more gracefully