What becomes non-deterministic with async is the order in which operations are executed (depending on how long the previous processes took) possibly creating ra

What becomes non-deterministic with async is the order in which operations are executed (depending on how long the previous processes took) possibly creating race conditions that can sometimes become very hard to debug. However if you work with immutable objects like Scala or Haskell encourages you to do, this shouldn't become much a problem.