foreach $thread (keys %threads) {
    $tsub[$tnum] = $thread;    
    $tlist[$tnum] = $threads{$thread};
    $tsize[$tnum] = @{$tlist[$tnum]};
    $tnum++;
}

print "\n\nThe Thread Arrays\n\n";
for ($i=0;$i<$tnum ;$i++) {
    print "\n$tsub[$i], size=$tsize[$i], @{$tlist[$i]}";
}

##</code><code>##

# Define the arrays as lexical vars. 
# So you are sure they are not conflicting with other vars in the program
my @tsub;
my @tlist;
foreach $thread (keys %threads) {
    # using push you don't need the counter
    push(@tsub, $thread);
    push(@tlist, $threads{$thread}); 
}

print "\n\nThe Thread Arrays\n\n";
for ($i=0;$i<@tsub ;$i++) {
    # compute tsize only when you need it, another array is useless
    my $tsize=@{$tlist[$i]};
    print "\n$tsub[$i], size=$tsize, @{$tlist[$i]}";
}