#![feature(thread_local)] #[thread_local] static S: &str = "before"; fn set_s() { S = "after"; } fn main() { println!("{}", S); set_s(); println!("{}", S); }

On rustc 1.31.0-nightly (b2d6ea9 2018-10-07) and x86_64-unknown-linux-gnu, we see the following surprising behavior:

$ cargo run # as expected before after $ cargo run --release before before

In release mode it seems the write has not happened in the place that it should.

Mentioning thread_local tracking issue: rust-lang/rust#29594.