When I wanted this, I could not find what I was looking
for on CPAN. It may have been there, I just didn't see
it. For instance if you go browse for descriptions
on CPAN you will find that File::Flock and File::BasicFlock just are
more sophisticated versions of the flock() command. So
they do not implement the semantics that I wanted. The File::Lock module looked closer, but it had only a very simple OO interface that was not fired by destruction.
In general all of the things I saw on CPAN were wrappers around the idea, "let us give better/more detailed ways to lock stuff" while I wanted, "Gimme an incredibly easy 'get a lock' semantic that I won't mess up on."
However KM pointed out to me that the system call to "touch" is not the best approach if the file does not exist. I should really either do that in Perl or else use File::Flock.
FWIW I use this for wrapping a lot of complex operations. For instance if I want a set of processes to go in order, I just have them start in order and attempt to grab a lock. They will not succeed until the previous process drops the lock. I can then combine this in some processes with a timeout_limit argument and send a page if it does not succeed...