Thread lifetime for TLS

language design
7

The hard bit about thread-locals are destructors. What with achieves is a lazy re-initialization of thread-locals.

In other words, what's the semantics of the following program?

#[thread_local]
static A: S = S(0);

#[thread_local]
static B: S = S(1);

struct S(u32);
impl Drop for S {
  fn drop(&mut self) {
    println!("{:?}", (A.0, B.0));
  }
}

fn main() {
  std::thread::spawn(|| {
    (A.0, B.0);
  }).join().unwrap();
}