my %siteHash : shared;

my $thread = threads->new( 
    sub {
        my( $address, $hashref ) = @_;
        my $downloader = eval{ Downloader->new } or die $@;
        $downloader->fetch( $address, $hashref );
    }, 
    $address, \%siteHash 
) or die $!;

## do other stuff

$thread->join;