PHP에서 비동기 GET 요청을 어떻게 만들 수 있나요?

$output = file_get_contents('http://www.example.com/');

function make_async_get($url) {
    $parts = parse_url($url);
    $fp = fsockopen($parts['host'],
        isset($parts['port']) ? $parts['port'] : 80,
        $errno, $errstr, 30);
    
    $out = "GET ".$parts['path']." HTTP/1.1\r\n";
    $out.= "Host: ".$parts['host']."\r\n";
    $out.= "Connection: Close\r\n\r\n";
    
    fwrite($fp, $out);
    fclose($fp);
}

make_async_get('http://www.externalsite.com/script1.php?variable=45');