I've got the signal handler operational, but I'm still a little puzzled by what was going on...only discovered by dropping deep into the debugger! What I thought was the process hitting the sleep was actually the process disappearing into an Oracle DBI call and not coming out as there was a format conversion error in the SQL . DBI didn't return an error - it just hung and was uninterruptible, and I'm now guessing that the Oracle DBD module was resetting the signal handlers so my signals were ignored. Either way, correcting the SQL has resulted in a process that not only runs and produces required outcome but stops when asked!