How do you build while loops?

This is more about understanding than a bug report/feature request.

I have successfully build a little dataflow program that runs a fixed number of iterations of a particular computation. It basically generates a loop_variable, does its thing, and connects the loop at the end. Now I would like to be able to express something like "do this until this particular condition is met" rather than "do this a hundred times".

So far I'm at a loss of how to do this. I suppose there is some complexity in making sure all workers are on the same page about the decision whether to stop or not. But I can't really see, how the API supports this kind of while loop to begin with.

PS: is there a support forum/chat of some kind or is it okay to ask questions like this as a GitHub issue?

No file, test, or entry point is named. Start by reading the existing loop-related dataflow API and its examples, then determine whether a condition-controlled loop is supported; done would require a documented, agreed approach or a clearly scoped implementation request.