Function release_host_inflight 

pub(crate) fn release_host_inflight(
    host: Option<&HostSession>,
    cap: &mut WlCapture,
    display_id: u32,
    all: bool,
)

Hand back to the host the frames its compositor blitted that a zero-copy encode no longer reads: each once the encode thread is done with every frame published from it, or all of them (all) where the capture is going away.