Hmm… this code doesn’t work in the real world unless you only run it on a single machine. Perhaps a more interesting question is how to make a multi-node queue with max N concurrent requests.
“… it doesn't ever have to handle more than one request at once (at least from the same client, so we can assume this is a single-server per-client type of architecture).“
For sure a multithreaded async queue would be a very interesting interview, but if you started with the send system the interview is constructed around youd run out of time quickly.
These are multiple assumptions
"This queue is only on one machine and on one thread", what's the real world use-case here? Not saying there's none but make it clear. I wouldn't want to work for a company that has to think of some random precise question instead of e.g. "when would you not use mysql?"
