title: Genuinely test std::atomic is lock-free or not
body: <p>Since <code>std::atomic::is_lock_free()</code> may not genuinely reflect the reality [<a href="https://stackoverflow.com/q/49816855/1348273">ref</a>], I'm considering writing a genuine runtime test instead. However, when I got down to it, I found that it's not a trivial task I thought it to be. I'm wondering whether there is some clever idea that could do it.</p>