Green threads can share memory while Erlang processes cannot, they are strictly forbidden to do it.
Also Erlang scheduler is highly optimized to work as a soft real-time platform, so they never run for infinite amount of time, they never block and never (at least that's the goal) bring down the entire application, the worst thing that can happen is that everything slows down but it's still functional and responsive.
I don't know about Tokio.
So message passing is the only way to communicate between proccesses? I guess that makes sense with elixir being a fp language. This was not clear in the article:
> Lunatic takes the same approach as Go, Erlang and the earlier implementation of Rust based on green threads.
There are escape hatches. Obviously, you can do something really heavy like open a network port or open a file descriptor, but it also provides you with use ets, which is basically "really fast redis for intra-vm stuff" and you can transact over shared memory if you drop down to FFI.
each process also has a receive() block where you essentially listen to everything that ends up in your mailbox and pattern match on it to take action.