Method lock

tests/wast.rs:328–336

(&self)

    impl MyState {
        fn lock(&self) -> impl Drop + '_ {
            let state = self.lock.lock().unwrap();
            let mut state = self
                .waiters
                .wait_while(state, |cnt| *cnt >= MAX_CONCURRENT_POOLING)
                .unwrap();
            *state += 1;
            LockGuard { state: self }
        }
    }

    struct LockGuard<'a> {