Hah, sounds like a fun debugging session! Those are exactly the kinds of problems I've encountered with "too many processors for too few resources". At the wor

Hah, sounds like a fun debugging session! Those are exactly the kinds of problems I've encountered with "too many processors for too few resources". At the workplace where we used Java we used a library called Quasar which implements green threading resembling Rust async (it rewrites the bytecode into a state machine). I remember encountering a very similar deadlock, except the issue was caused by certain green threads "handing over" database connections to other green threads, and in the process yielding to the scheduler. Under high churn there was a chance that all connections ended up in the suspended set, causing a deadlock when other tasks were trying to allocate. It took a couple of days to track down because attaching a debugger and even printing caused the issue to go away. Your example is also a fun one, but to me it actually shows exactly why an unbounded/dynamic number of processing units are an issue. Coroutines are the extreme example where you are almost encouraged to launch as many tasks as you can.