Imprecise elapsed simulation time

[nickgian]

sim_elapsed provides the simulation time elapsed as perceived by a host without a skew, by offsetting the host's time by the time the simulation started. However, when a host crashes time "freezes" for it and it remains skewed forever.
My title might be inaccurate - I am not sure if this is the desired behavior (to test impact of clock skew), but having a way for hosts to keep track of the simulation time elapsed (a global clock) simplifies testing global properties and debugging.

The example below demonstrates this:

   #[test]
    fn elapsed_time_across_crashes() -> Result {
        let tick_ms = 5;
        let mut sim = Builder::new()
            .tick_duration(Duration::from_millis(tick_ms))
            .build();


        sim.host("host", move || {
            async move {
                loop {
                    tokio::time::sleep(Duration::from_millis(1)).await;
                    println!("Time elapsed according to host: {}", sim_elapsed().unwrap().as_millis());
                }
            }
        });

        sim.host("host2", move || {
            async move {
                loop {
                    tokio::time::sleep(Duration::from_millis(1)).await;
                    println!("Time elapsed according to host2: {}", sim_elapsed().unwrap().as_millis());
                }
            }
        });

        println!("First run");
        sim.run()?;
        sim.crash("host");
        println!("Crashed host 1");
        sim.run()?;
        sim.bounce("host");
        println!("Bounced host 1");
        sim.run()?;

        Ok(())
    }

will output

First run
Time elapsed according to host: 1
Time elapsed according to host: 2
Time elapsed according to host: 3
Time elapsed according to host: 4
Time elapsed according to host2: 1
Time elapsed according to host2: 2
Time elapsed according to host2: 3
Time elapsed according to host2: 4
Crashed host 1
Time elapsed according to host2: 5
Time elapsed according to host2: 6
Time elapsed according to host2: 7
Time elapsed according to host2: 8
Time elapsed according to host2: 9
Bounced host 1
Time elapsed according to host: 6
Time elapsed according to host: 7
Time elapsed according to host: 8
Time elapsed according to host: 9
Time elapsed according to host2: 10
Time elapsed according to host2: 11
Time elapsed according to host2: 12
Time elapsed according to host2: 13
Time elapsed according to host2: 14