If you would like to make life more simple, you should use either IO::File or Filehandle or Symbol::gensym, as in the following.

use IO::File ();

# assuming LOCK_FILE is a constant with the filename

my $fh = IO::File->new( LOCK_FILE, 'w' );
# now you can pass $fh directly to your sub
# as in code_lock( $fh );
# sub code_lock { my $fh = shift(); }
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You could also create the same sort of thing with Filehandle or with the following code.

use Symbol();
my $fh = Symbol::gensym();
open($fh,">".LOCK_FILE);
# pass it as in the above
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