Function wait_generation 

pub fn wait_generation(
    layout: &Layout,
    last: u64,
    poll_ms: u64,
    timeout_ms: u64,
) -> Result<u64>

Block until the generation passes last, or the timeout expires. Returns the generation either way; the caller compares it against last to tell which happened. A timeout_ms of 0 is a peek: it never sleeps.

Errors

The signature is Result to match the other event verbs. This path does not fail.