Here is what I would do , partition the url list upfront into different storable files, so when you fork you're only sharing a single filename, then later the parent process unifies the results of the child process ... only parent partitions jobs because only parent spawns children

#!/usr/bin/perl --
## 
## 
## 
## perltidy -olq  -csc -csci=3 -cscl="sub : BEGIN END " -otr -opr -ce 
+-nibc -i=4 -pt=0   "-nsak=*"
## perltidy -olq  -csc -csci=10 -cscl="sub : BEGIN END if " -otr -opr 
+-ce -nibc -i=4 -pt=0   "-nsak=*"
## perltidy -olq  -csc -csci=10 -cscl="sub : BEGIN END if while " -otr
+ -opr -ce -nibc -i=4 -pt=0   "-nsak=*"
#!/usr/bin/perl --
use strict;
use warnings;
use Data::Dump qw/ dd /;

Main( @ARGV );
exit( 0 );

sub Main {
    my @files = StorePartitionUrls( GetInitialUniqueUrls() );
    ForkThisStuff( @files );
    UnifyChildResults( 'Ohmy-unique-hostname-urls-storable', @files );
} ## end sub Main

sub GetInitialUniqueUrls {
    my @urls;
    ...
    return \@urls;
} ## end sub GetInitialUniqueUrls

sub ForkThisStuff { ## spawn kids with one file, wait, whatever
    for my $file ( @files ) {
        EachChildGetsItsOwn( $file );
    }
} ## end sub ForkThisStuff

sub ForkThisStuff {
    for my $file( @files ){
## something forking here
        EachChildGetsItsOwn( $file );
    }
}

sub StorePartitionUrls {
    my( $urls , $partition , $fnamet, ) = @_;
    $partition ||= 100;
    $fnamet    ||= 'Ohmy-candidate-urls-%d-%d-storable';
    my @files;
    while( @$urls ){
        my @hundred = splice @$urls, 0, $partition ;
#~         my $file    = "Ohmy-".int( @$urls ).'-'.int( @hundred ).'-s
+torable';
        my $file    = sprintf $fnamet, int( @$urls ), int( @hundred );
        lock_store \@hundred, $file;
        push @files, $file;
    }
    return @files;
} ## end sub StorePartitionUrls

__END__
[download]

As jellisi2 said, this script will not work, and also will makes the script more difficult to run because maybe it will crawl a single page many many times.