Thanks for your design input. As I mentioned in my previous reply to BrowserUk, I am tempted to walk away from event based programming for the task, at least for now.

But before I do I will give it a last try with your proposed structure. As I've learned from your post, redeclaring condvars over and over again seems to be okay to send the overall system into stop and start states, as I can use a cv only once.
I've already looked into the begin/end methods a bit, but so far did not need its "counter" mechanism. We'll see.

Again, thanks!