如何用curl_multi_init将单线程curl请求改写成多线程并行处理？

function post($url, $data = '', $head = 'application/x-www-form-urlencoded')
{
    $ch = curl_init();
    curl_setopt($ch, curlopt_url, $url);
    curl_setopt($ch, curlopt_httpheader, array("content-type:{$head};charset=utf-8;"));
    curl_setopt($ch, curlopt_timeout, 30);
    curl_setopt($ch, curlopt_returntransfer, 1);  
    curl_setopt($ch, curlopt_header, 0);
    if (!empty($data)) {
        curl_setopt($ch, curlopt_post, 1);
        curl_setopt($ch, curlopt_postfields, $data);
    }
    $output = curl_exec($ch);
    curl_close($ch);
    return $output;
}

$url = 'http://localhost/test.php';
$res = [];
//模拟100条数据
for ($i=0; $i < 100; $i++) { 
    $res[$key] = post($url, 'key='.$i);
}
var_dump($res);

$newData = array_chunk($data, 10, true);
foreach ($newData as $k => $tmp) {
    $mh = curl_multi_init();
    $chs = [];
    foreach ($tmp as $key => $url) {
        $ch = curl_init();
        $chs[$key] = $ch;
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-type:application/x-www-form-urlencoded;charset=utf-8;'));
        curl_setopt($ch, CURLOPT_TIMEOUT, 30);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch, CURLOPT_HEADER, 0);
        curl_setopt($ch, CURLOPT_POST, 1);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $tmp);
        curl_multi_add_handle($mh, $ch);
    }
    $active = null;
    do {
        $mrc = curl_multi_exec($mh, $active);
    } while ($mrc == CURLM_CALL_MULTI_PERFORM);
    while ($active && $mrc == CURLM_OK) {
        if (curl_multi_select($mh) != -1) {
            do {
                $mrc = curl_multi_exec($mh, $active);
            } while ($mrc == CURLM_CALL_MULTI_PERFORM);
        }
    }
    foreach ($chs as $key => $ch) {
        $res[$k][$key] = curl_multi_getcontent($ch);
        curl_multi_remove_handle($mh, $ch);
    }

    curl_multi_close($mh);
}
var_dump($res);