I need to use flock to prevent two processes from attempting to read/write a GDBM file at the same time. Following this example: http://www.nntp.perl.org/group/perl.beginners/2001/09/msg11124.html and this one: http://docstore.mik.ua/orelly/perl/cookbook/ch14_06.htm I wrote the following code:

use strict;
use GDBM_File;
use Carp qw(confess);
use Fcntl qw(:flock);

my %term_doc_count;
my $db = tie(%term_doc_count, 'GDBM_File', "resources/term_docCount", 
+GDBM_READER, 0666)
    or confess("Unable to tie GDBM db : $!");

my $fd = $db->fd();
open(DB_FH, "<&=$fd") or confess "Could not open file: $!";
unless (flock (DB_FH, LOCK_SH | LOCK_NB)) {
       print "$$: CONTENTION; can't read during write update!
                  Waiting for read lock ($!) ....        \n";
       unless (flock (DB_FH, LOCK_SH)) { die "flock: $!" }
   }
print "$$: Read lock granted\n";
untie %term_doc_count;
close(DB_FH);
flock(DB_FH, LOCK_UN);
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However, I am getting the following error: fd is not a valid GDBM_File macro at test.pl line 12

I can't tell from the GDBM_file documentation here: http://search.cpan.org/~flora/perl-5.14.2/ext/GDBM_File/GDBM_File.pm, how I can get the file descriptor. Please, any ideas?