Priorities don't help. They are only relevant if there are more runnable threads than CPUs. In my case I had lots of spare CPUs so both threads could run, regar

Priorities don't help. They are only relevant if there are more runnable threads than CPUs. In my case I had lots of spare CPUs so both threads could run, regardless of priority. A QOS does not directly help. The only thing I am aware of that can help is fair locks, or occasionally fair locks, so that the lock is given directly to the waiting thread, instead of being made available to all. I have yet to hear of any other solutions.