So do I understand correctly that there is no cross platform method of accomplishing this, portable to Linux?

I don't know enough about Linux to comment authoratively. I have read that traditional signals do not mix well with Perl.

In their raw form, as used prior to 5.8.0, they could interupt individual Perl opcodes part way through execution, and so leave Perl's fat datastructures in an incomplete or unstable state. Mostly okay for exceptional purposes where the code was to die anyway, but not so good for pure IPC purposes, where the code interupted needed to continue.

In their 'safe-signals' form, this problem is avoided by ensuring that the signal does not interupt the user's (perl) code until the interpreter is 'between' opcodes. This makes continuaton more reliable, but renders the immediacy of signals somewhat dented. Unlike a C program, where a single cpu-level opcode can rarely take more than a few milliseconds, a single Perl opcode can be doing a great deal (sorting a huge datastructure for example).

There are the IPC::SysV & IPC::Semaphore stuff, but from what I read these are not even that dependable on systems that claim SysV compatibility, and probably do nothing at all on many non-*nix based patforms.

Take all that with a pinch of salt as I'm really relating what I have read, not talking from experience.