&gt; For the benefit of any who are not sure what you are talking about, could you please elaborate on what some of these &quot;better ways to handle that&quot; are?<p>While I am not certain what the GP specifically references, I can say that about 40 years ago the Actor model[1] was officially documented.  The literature documenting benefits of an Actor model over a callback approach are easily found.  For understanding the pain which callback-based systems often produce, a person can familiarize themselves with the Win32 API (disclaimer: this is a masochistic exercise not recommended for anyone).<p>1 - <a href="https:&#x2F;&#x2F;www.cypherpunks.to&#x2F;erights&#x2F;history&#x2F;actors&#x2F;AIM-410.pdf" rel="nofollow">https:&#x2F;&#x2F;www.cypherpunks.to&#x2F;erights&#x2F;history&#x2F;actors&#x2F;AIM-410.pd...</a>