code: public boolean hasDeadlock(List<? extends PlanNode> sinks) {
  		this.g = new DeadlockGraph();
  		
  		for(PlanNode s : sinks) {
  			s.accept(this);
  		}
  		
  		if(g.hasCycle()) {
  			return true;
  		} else {
  			return false;
  		}
  	}
docs: Creates new DeadlockGraph from plan and checks for cycles
  
  @param plan
  @return