Signals and perl don't mix very well.

In perls < 5.8 (?), your signal could get caught in the middle of an opcode execution, so your signal handler could wind up "reentering" a non-reentrant part of the perl core, like the regex engine.

In perls after 5.8, your signal will be deferred until the current op completes, but it could still interrupt system calls, and not restart them, I believe.
--
Mike