Yeah doing something else on the main interpreter loop, BEFORE checking the signal flag, is what what I meant. The "something else" could be long-running C extension code, or a blocking syscall. (I realize the original signal will interrupt a syscall, but there could be another one after that.)

In either case, the signal handler doesn't get run for an arbitrary period of time. And another signal could occur.

I didn't trace through the code to see how this is handled... but it seems like it is hard to handle simply and correctly (you're kind of recapitulating the problems of signals to begin with, in a higher level language).

Any docs / clarity on this would be interesting to me, as I will probably implement this in my own language soon.