Function pump 

pub(crate) fn pump(ml: &mut Mainloop, timeout_us: u64) -> bool

Run one bounded iteration of a PulseAudio standard mainloop: prepare(timeout_us) → poll → dispatch. Returns false if any stage errors.

The timeout_us bound is what makes a pending stop observable within ~20 ms even when the audio source delivers nothing, since every loop that calls this re-checks stop_pending() between pumps.