class WorkerThreadGroup implements WorkerThreadGroupCI {

	public synchronized void add_subgroup(WorkerThreadGroup wtg) {
		Ensure.not_null(wtg, "wtg == null");
		Ensure.is_true(wtg != this, "wtg == this");
		Ensure.is_false(m_subgroups.contains(wtg), "m_subgroups.contains(wtg)");
		Ensure.is_false(wtg.all_subgroups().contains(this),
				"wtg.all_subgroups().contains(this)");
		m_subgroups.add(wtg);
	}

	public  WorkerThreadGroup(String name);

}