When should a task be considered “long running”?

Question

When working with tasks, a rule of thumb appears to be that the thread pool - typically used by e.g. invoking Task.Run(), or Parallel.Invoke() - shoul

Answer 1

When working with tasks, a rule of thumb appears to be that the thread pool - typically used by e.g. invoking Task.Run(), or Parallel.Invoke() - should be used for relatively short operations. When working with long running operations, we are supposed to set the TaskCreationOptions.LongRunning to true in order to - as far as I understand it - avoid clogging the thread pool queue, i.e. to push work to a newly-created thread.

The vast majority of the time, you don't need to use LongRunning at all, because the thread pool will adjust to "losing" a thread to a long-running operation after 2 seconds.

The main problem with LongRunning is that it forces you to use the very dangerous StartNew API.

In other words, this appears to be a queuing and thread pool utilization optimization problem that should likely be solved case-by-case through testing, if at all. Am I correct?

Yes. You should never set LongRunning when first writing code. If you are seeing delays due to the thread pool injection rate, then you can carefully add LongRunning.