functionrolling_curl($urls,$callback, $custom_options= null) {</p>

// make sure therolling window isn’t greater than the # of urls
$rolling_window= 5;
$rolling_window=(sizeof($urls)&lt;$rolling_window) ?sizeof($urls): $rolling_window;

$master=curl_multi_init();
$curl_arr=array();

// add additional curloptions here
$std_options=array(CURLOPT_RETURNTRANSFER=&gt;true,
CURLOPT_FOLLOWLOCATION=&gt;true,
CURLOPT_MAXREDIRS=&gt;5);
$options=($custom_options) ?($std_options +$custom_options) :$std_options;

// start the firstbatch of requests
for($i =; $i&lt;$rolling_window;$i++) {
$ch =curl_init();
$options[CURLOPT_URL]=$urls[$i];
curl_setopt_array($ch,$options);
curl_multi_add_handle($master,$ch);
}

do{
while(($execrun=curl_multi_exec($master,$running)) ==CURLM_CALL_MULTI_PERFORM);
if($execrun !=CURLM_OK)
break;
// a request was just completed — findout which one
while($done =curl_multi_info_read($master)){
$info =curl_getinfo($done[‘handle’]);
if($info[‘http_code’]== 200) {
$output=curl_multi_getcontent($done[‘handle’]);

// request successful. process output using the callbackfunction.
$callback($output);
//bug在这里，他会有一次空请求
// start a new request(it’s important to do this before removing the oldone)
$ch=curl_init();
$options[CURLOPT_URL]=$urls[$i++]; // increment i
curl_setopt_array($ch,$options);
curl_multi_add_handle($master,$ch);

// remove the curlhandle that just completed
curl_multi_remove_handle($master,$done[‘handle’]);
} else {
// request failed. add error handling.
}
}
}while($running);

curl_multi_close($master);
returntrue;
}</div> </div>