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    use crate::env;
    use crate::sync::atomic::{self, Ordering};
    use crate::sys::thread as imp;

    pub fn min_stack() -> usize {
        static MIN: atomic::AtomicUsize = atomic::AtomicUsize::new(0);
        match MIN.load(Ordering::SeqCst) {
            0 => {}
            n => return n - 1,
        }
        let amt = env::var("RUST_MIN_STACK").ok().and_then(|s| s.parse().ok());
        let amt = amt.unwrap_or(imp::DEFAULT_MIN_STACK_SIZE);

        // 0 is our sentinel value, so ensure that we'll never see 0 after
        // initialization has run
        MIN.store(amt + 1, Ordering::SeqCst);
        amt
    }