gistfile1.txt

    pub fn lock(&self) -> Option<OnceMutexGuard<T>> {
        match state.load(SeqCst) {
            UNUSED => {
                state.store(LOCKED, SeqCst);
                Some(OnceMutexGuard::new(self))
            },
            // Other thread got here first or already locked.
            // Either way, no lock.
            _ => None
        }
    }