Setting AsyncAutoResetEvent after used in Task.WhenAny

[kakkamstrup]

    AsyncAutoResetEvent runEvent = new();
    await Task.WhenAny(runEvent.WaitAsync(), Task.Delay(TimeSpan.FromSeconds(1)));
    runEvent.Set(); // This doesn't set runEvent.IsSet to true and the following line doesn't return immediately
    await Task.WhenAny(runEvent.WaitAsync(), Task.Delay(TimeSpan.FromSeconds(5)));

[StephenCleary]

This is how auto-reset events work: when they become set, they release all waiters and immediately become unset again. Did you perhaps want to use a manual-reset event?

[kakkamstrup]

I think I know how auto-reset events work, but I guess I don't know Task.WhenAny.
When the task from WhenAny completes because of Task.Delay, the runEvent.WaitAsync()-task is alive, but "abandoned" and it's the abandoned task that gets signaled.
I think I get it now. Thank you for your response.

[StephenCleary]

Ah. Yes, your description is correct: the task previously returned from WaitAsync is completed (but is ignored by the calling code).