"But alarm sends a signal to the process that called alarm, not the child process, right? Even if it sent it to the child, the child process would need a signal handler for that process."

Although I've caused all manner of consternation with doing process stuff with Windows (including killing off sub-procs), I've found that Perl is weird when talking processes/threads with that OS. "Processes", I've managed (mostly, but with difficulty), but threads, I'd definitely need advice from our experts.

Perhaps you could lay out at least some pseudo-code (or minimal working/broken problematic example) of what you've got, so the experts can see if they can help sort out a solution?