docs: public void unregisterAllTaskManagers() {
  		for(Instance instance: registeredHostsById.values()) {
  			deadHosts.add(instance.getTaskManagerID());
  
  			instance.markDead();
  
  			totalNumberOfAliveTaskSlots -= instance.getTotalNumberOfSlots();
  
  			notifyDeadInstance(instance);
  		}
  
  		registeredHostsById.clear();
  		registeredHostsByResource.clear();
  	}