alarm "works" since (I think) 5.8. On Windows, it's simulated using a timer message (WM_TIMER), but I think that "unsafe signals" do not look at whether that timer message has been received. So an alarm call can only interrupt the Perl interpreter when it is in the runloop, and not when it spends time in XS (or a system call, or a database operation).

The above is from memory - a closer look at win32_alarm in win32.c will likely be enlightening. It seems that alarm() could be made to "work" with unsafe signals (as far as unsafe signals can ever be called to "work") by having the WM_TIMER message trigger a callback, just like SIG_ALRM would under some unixish OS.

In reply to Re^3: Alarms with ActivePerl do not work properly by Corion
in thread Alarms with ActivePerl do not work properly by heiermann

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