Time and clocks about turmoil

[marcbowes]

I'm struggling to understand how things work right now.

1. When the sim runs, it ticks 1ms forward

   turmoil/src/sim.rs

   Lines 152 to 161 in 2dd03ad

   	let tick = self.config.tick;
   	loop {
   	let mut is_finished = true;
   	for (&addr, rt) in self.rts.iter() {
   	// Set the current host
   	self.world.borrow_mut().current = Some(addr);
   	let now = World::enter(&self.world, || rt.tick(tick));

2. When a message is received, it is only delivered based on whether wallclock now has advanced.

.. presumably this means that for fast tests (i.e. ticks are < 1ms) the code lands up waiting for realtime to advance?

on the recv path (https://github.com/tokio-rs/turmoil/blob/main/src/io.rs#L20) it looks like we will wait for a notification, which (I think) is triggered when the host ticks past the wallclock-now of the message delivery time (which is based on fake time on the send host - which also seems busted to me)

[marcbowes]

which is based on fake time on the send host - which also seems busted to me

I take that back. Host::send is actually called on the receiving host. So the method name is just confusing.

[marcbowes]

There is some magic (through globals, my favorite) going on that makes this more or less work out the way it should. I'm not sure it's 100% yet, so I plan on digging more before closing this out. Hopefully I can add some comments to help explain how it all works.

[carllerche]

You can schedule some time with me and I can walk you through it. Short version is that it uses Tokio’s Instant::now which can be made virtual.

[marcbowes]

See #23