php如何实现异步调用

$fp = fsockopen("blog.maplemark.cn", 80, $errno, $errstr, 30);
if (!$fp) {
    echo "$errstr ($errno)<br />\n";
} else {
    $out = "GET /backend.php  / HTTP/1.1\r\n";
    $out .= "Host: blog.maplemark.cn\r\n";
    $out .= "Connection: Close\r\n\r\n";
    fwrite($fp, $out);
    /*忽略执行结果
    while (!feof($fp)) {
        echo fgets($fp, 128);
    }*/
    fclose($fp);
}