title: What constitutes asynchronous-safeness
body: <p>It is said that you should only call <strong>asynchronous-safe</strong> functions inside a signal handler. My question is, what constitutes <strong>asynchronous-safeness</strong>? A function which is both <em>reentrant</em> and <em>thread safe</em> is <strong>asynchronous-safe</strong> I guess? Or No?</p>