01 [
02   [[0, 0], [0, 1], [0, 2], [0, 3]],
03   [[1, 0], [1, 1], [1, 2], [1, 3]],
04   [[2, 0], [2, 1], [2, 2], [2, 3]],
05   [[3, 0], [3, 1], [3, 2], [3, 3]],
06 ]
<code>

@queue should perhaps better been named @rows. Then:
<code>
01 my $queue = Thread::Queue->new();
02 $queue->enqueue(\@rows);
03 my @threads = map { threads->create( \&process, $queue ); } 1 .. 4;
04 ...