use Data::Dumper;
 
$copy=1; #what you want?
 
%threads=(
      keyA => [ 2, 6, 8 ],
      keyB => [ 3, 5, 10, 14, 18 ],
     );
 
$tnum=0;
foreach $thread (keys %threads) {
    $tsub[$tnum]      = $thread;    
    $tlist[$tnum]     = $threads{$thread}    unless $copy;
    @{$tlist[$tnum]}  = @{$threads{$thread}} if $copy;
    $tsize[$tnum]     = @{$tlist[$tnum]};    
    $tnum++;
}
 
print Dumper \@tsub,\@tlist,\@tsize;
[download]

# OUTPUT

$VAR1 = [
          'keyB',
          'keyA'
        ];
$VAR2 = [
          [
            '3',
            '5',
            '10',
            '14',
            '18'
          ],
          [
            '2',
            '6',
            '8'
          ]
        ];
$VAR3 = [
          5,
          3
        ];
[download]

there are more elegant ways using arrayslices but I think you should first start to understand perlref

UPDATE: Who cares, here a solution with slices (no copy)

@tsub2   = keys %threads;
@tlist2  = @threads{@tsub2};
@tsize2  = map { scalar @{$_} } @tlist2;
 
print Dumper \@tsub2,\@tlist2,\@tsize2;
[download]

hmmm that solution without slices is even simpler, I wasn't sure that the order of keys and values are guarantied, but it's documented so, as long as the hash isn't modified.