[zbentley]

Interesting that it’s temporal (according to the article, you have around 10 microseconds before the signal-based preempter kicks in). How bad is performance if the load on the host is so high that double-preempting is common, I wonder? Or am I missing something and that question is not meaningful?

[lcof]

No it’s an interesting comment. This is not really about load, but about control flow: if goroutine is just spinning wild without going through any function prologue, it won’t even be aware of the synchronous preemption request. Asynchronous preemption (signal-based) is mainly (I say “mainly” because I am not sure I can say “only”) for this kind of situation.

I don’t have the link ready, but twitch had this kind of issue with base64 decoding in some kind of servers. The GC would try to STW, but there would always be one or a few goroutines decoding base64 in a tight loop for the time STW was attempted, delaying it again and again.

Asynchronous preemption is a solution to this kind of issue. Load is not the issue here, as long as you go through the runtime often enough.

[jerf]

You'll actually see that's a general concurrency pattern, and I mean, far beyond Go. It is certainly ideal to trigger off of some signal (in a very, very generic sense of the term, not OS signal) in order to trigger some other process (again in a very generic sense), but in general if you're programming concurrent code you should always have some sort of time-based fallback for any wait you are doing, because you will hit it out in the field. It's all kinds of no fun to have processes that will wait forever. (Unless you're really sure you need it.)