Method lock

tests/relacy/relacy/example/ws_deque2/ws_deque.cpp:53–59

    }

    void lock()
    {
        std::atomic_thread_fence($)(std::memory_order_seq_cst);

        assert(th[rl::ctx().threadx_->index_] == defer_limit);
        th[rl::ctx().threadx_->index_] = pos;
    }

    void unlock()
    {