Luv: deadlock sharing resources between domains?

[talex5]

There's a hang reported in mirage/ocaml-cohttp#953 when using the Luv backend with multiple domains. I only looked at it briefly, but I wonder if using multiple Luv event loops is a bad idea. Possibly we should run a single Luv event loop in a sys-thread and dispatch events to domains from that?

[talex5]

The problem is that libuv associates resources with event loops when they are created, not when they are used. See mirage/ocaml-cohttp#953 (comment) for an example of it going wrong.