How to make asynchronous HTTP requests in PHP

Is there a way in PHP to make asynchronous HTTP calls? I don't care about the response, I just want to do something like file_get_contents(), but not wait for the request to finish before executing the rest of my code. This would be super useful for setting off "events" of a sort in my application, or triggering long processes.

Any ideas?

Answer

The answer I'd previously accepted didn't work. It still waited for responses. This does work though, taken from How do I make an asynchronous GET request in PHP?

function post_without_wait($url, $params)
{
    foreach ($params as $key => &$val) {
      if (is_array($val)) $val = implode(',', $val);
        $post_params[] = $key.'='.urlencode($val);

    }
    $post_string = implode('&', $post_params);

    $parts=parse_url($url);

    $fp = fsockopen($parts['host'],
        isset($parts['port'])?$parts['port']:80,
        $errno, $errstr, 30);

    $out = "POST ".$parts['path']." HTTP/1.1\r\n";

    $out.= "Host: ".$parts['host']."\r\n";
    $out.= "Content-Type: application/x-www-form-urlencoded\r\n";
    $out.= "Content-Length: ".strlen($post_string)."\r\n";
    $out.= "Connection: Close\r\n\r\n";
    if (isset($post_string)) $out.= $post_string;

    fwrite($fp, $out);
    fclose($fp);
}