#!/usr/local/bin/perl
use Fcntl qw(LOCK_EX LOCK_UN LOCK_NB);


# This opens a file in a lexcially scoped file handle, and flocks it.
# It will close and unlock when that variable goes out of scope.
sub fn {
    my $fn = "FOO";
    open my $F, ">$fn";
    flock($F, LOCK_EX) or die "no lock";
    
    return $fn;
}

# In this case, for some reason $F above isn't destroyed until after
# the for loop completes.
for my $fn (fn()) {
    open my $G, $fn;
    flock($G, LOCK_EX|LOCK_NB) or warn "no lock 2";
}