From the docs on https://doc.rust-lang.org/stable/std/thread/struct.Scope.htm...,
> If the join handle is dropped, the spawned thread will implicitly joined at the end of the scope.
Plus the comment says
> // We can even mutably borrow `x` here, // because no other threads are using it.
Which doesn’t line up with another thread having a read-only borrow on it.
Anyway not at my machine to test right now, I could be wrong.
"end of scope" here refers to the end of the closure, after the second thread is spawned.
You can trivially show that the threads exist in parallel by adding waits.
