run-with-timer vs run-with-idle-timer

[João Távora]

Hi

I suspect this one has been asked before, but still, why does this
return after 1 second:

  (catch 'done
    (run-with-timer 1 nil (lambda () (throw 'done nil)))
    (while t (accept-process-output nil 0.1)))

And this never returns?

  (catch 'done
    (run-with-idle-timer 1 nil (lambda () (throw 'done nil)))
    (while t (accept-process-output nil 0.1)))

Is it because accept-process-output means emacs isn't really idle?
Because it also fails with sleep-for and sit-for...

I need this because this (while t..) spin is a common way to wait for
async conditions (in this case the async condition is flymake kicking
in).

João