Are you remembering the (older) docs for signal handlers? E.g. quoting from the docs of Perl 5.6.1:

Do as little as you possibly can in your handler; notice how all we do is set a global variable and then raise an exception. That's because on most systems, libraries are not re-entrant; particularly, memory allocation and I/O routines are not. That means that doing nearly anything in your handler could in theory trigger a memory fault and subsequent core dump.

This was also the state of signal handling when Programming Perl 3rd edition was written - maybe that's where you read it?