Implementation of async url fetching using curl (with laravel Cache-facade caching)

lara_multi_url_to_html.php

<?php

function urlToHtml(string ...$urls)
{
    $cache = array_map('sha1', $urls);
    $ttl = array_fill(0, count($urls), null);
    $res = [];
    $ch = [];
    $mh = curl_multi_init();
    $options = [
        CURLOPT_FOLLOWLOCATION => true,
        CURLOPT_RETURNTRANSFER => true,
    ];

    foreach ($urls as $i => $url) {
        if (Cache::has($cache[$i])) {
            $res[$i] = Cache::get($cache[$i]);
        } else {
            $ch[$i] = curl_init($url);
            curl_setopt_array($ch[$i], $options);
            curl_multi_add_handle($mh, $ch[$i]);
        }
    }

    do {
        if (curl_multi_select($mh) !== -1) {
            usleep(100);
        }

        do {
            $execReturnValue = curl_multi_exec($mh, $runningHandles);
        } while ($execReturnValue === CURLM_CALL_MULTI_PERFORM);
    } while ($runningHandles && $execReturnValue === CURLM_OK);

    if ($execReturnValue != CURLM_OK) {
        trigger_error("Curl multi read error $execReturnValue\n", E_USER_WARNING);
    }

    foreach ($urls as $i => $url) {
        if (!array_key_exists($i, $ch)) {
            continue;
        }
        $curlError = curl_error($ch[$i]);
        if ($curlError === '') {
            $responseContent = curl_multi_getcontent($ch[$i]);
            $res[$i] = $responseContent;
            Cache::put($cache[$i], $responseContent, $ttl[$i]);
        } else {
            trigger_error("Curl error on handle $i: $curlError\n", E_USER_WARNING);
        }
        curl_multi_remove_handle($mh, $ch[$i]);
        curl_close($ch[$i]);
    }

    curl_multi_close($mh);
    return count($urls) === 1 ? reset($res) : $res;
}