I'm not sure if this is an issue the way Queue is used in practice, but in general you have to be careful with this kind of circular flow because if your queue communicates backpressure (which it should) then circular flows can deadlock.

Nathaniel, would you be able to elaborate more on the issue of backpressure? I think a lot of people here are not really familiar with the concepts and its importance, and it changes how you have to think about queues and the like.