Why does `notify_one_slow` return true even if threads were only requeued, and not unparked?

[Brian Merchant]

This is a conceptual question.

In notify_one_slow on Condvar, we have:

parking_lot/src/condvar.rs

Line 174 in 4adcfdd

 res.unparked_threads + res.requeued_threads != 0 

Suppose res.unparked_threads == 0, but res.requeued_threads > 0, then should notify_one_slow return true?

[Amanieu d'Antras]

notify_one returns true if a thread was waiting on the condvar and has now been woken up. It doesn't matter whether this was done by waking it up directly or requeuing it to the mutex so that it will be woken up when the mutex is unlocked.

[Brian Merchant]

@Amanieu Thank you, that makes sense!