quote

lock

lock THING

This function places an advisory lock on a shared variable, or referenced object contained in THING until the lock goes out of scope.

lock() is a "weak keyword" : this means that if you've defined a function by this name (before any calls to it), that function will be called instead. (However, if you've said use threads, lock() is always a keyword.) See threads.

unquote

Which would mean that you could lock a FILEHANDLE but it is not the same functionality as flock. Update Or because it is a weak function as simonm pointed out below if the require calls are after its use instead of before it will use the internal lock functin instead of the user defined lock function.