php二维数组排序方法(array_multisort usort)

$users = array(
    array('name' => 'tom', 'age' => 20)
    , array('name' => 'anny', 'age' => 18)
    , array('name' => 'jack', 'age' => 22)
);

$ages = array();
foreach ($users as $user) {
    $ages[] = $user['age'];
}
array_multisort($ages, SORT_ASC, $users);

array_multisort($ages, SORT_ASC, $names, SORT_ASC, $users);

usort($users, function($a, $b) {
            $al = strlen($a['name']);
            $bl = strlen($b['name']);
            if ($al == $bl)
                return 0;
            return ($al > $bl) ? -1 : 1;
        });