I think we are getting off-track here. The non-deterministic nature is about concurrent programs, not about scheduler. Scheduler is just one source causing no

I think we are getting off-track here. The non-deterministic nature is about concurrent programs, not about scheduler. Scheduler is just one source causing non-deterministic execution order of threads. There are other non-deterministic causing sources. Imagine you spin off 10 threads waiting for network requests where one thread per client machine. It cannot be deterministically decided which thread will run first and which will run next. It depends on which client connects to which thread first. That's the non-deterministic nature of the program. Concurrency is the discipline to deal with that problem.