I've noticed this as well. The function should return as soon as it is finished I 
believe. This could be a CURL issue or a PHP issue. I'm interested to hear what 
the dev's say since I've had all kinds of issues with curl_multi_select in newer 
PHP versions. I keep having to revert to 5.3.6.. I've tried 5.3.10 and using 
curl_multi_select within a loop checking for != -1 and it causes an infinite loop 
since it always returns -1 on Windows 7 x64/x86, PHP 5.3.10

I have the same problem white them.
Env: win7 + php5.4.0

Use the code as curl_multi-exec
http://cn2.php.net/manual/zh/function.curl-multi-exec.php
cause the final error: Fatal error: Maximum execution time of 30 seconds 
exceeded. But it be runing well in php5.3.6

In PHP5.4 , when i replace the under code
-----------------------------------
$active = null;
// 执行批处理句柄
do {
    $mrc = curl_multi_exec($mh, $active);
} while ($mrc == CURLM_CALL_MULTI_PERFORM);

while ($active && $mrc == CURLM_OK) {
    if (curl_multi_select($mh) != -1) {
        do {
            $mrc = curl_multi_exec($mh, $active);
        } while ($mrc == CURLM_CALL_MULTI_PERFORM);
    }
}
--------------------------------------
With

do {
	curl_multi_exec($hMultiCurl, $iRunning);
} while ($iRunning > 0);
-------------------------------------

the programe run ok

So the question is the curl_multi_select bug , cause the while infinite loop.

Possibly related to 61141 and 61240

This behavior is probably related to Bug #61141. Can you try this script 

$ch1 = curl_init();
curl_setopt_array($ch1, array(CURLOPT_URL=>"http://lxr.php.net/", 
CURLOPT_HEADER=>0, CURLOPT_RETURNTRANSFER=>1));
$mh = curl_multi_init();
curl_multi_add_handle($mh,$ch1);

$active = null;
do $mrc = curl_multi_exec($mh, $active);
while ($mrc == CURLM_CALL_MULTI_PERFORM);

$start_time = microtime(true);

while ($active && $mrc == CURLM_OK) {
    if (curl_multi_select($mh) == -1) { 
        usleep(100);
    }
    do $mrc = curl_multi_exec($mh, $active);
    while ($mrc == CURLM_CALL_MULTI_PERFORM);
}

curl_multi_remove_handle($mh, $ch1); curl_multi_close($mh);

And let me know if you still have your problem ?

Works for me!

// jlcooke - thanks to http://technosophos.com/content/connection-sharing-curl-
php-how-re-use-http-connections-knock-70-rest-network-time
// https://forums.aws.amazon.com/thread.jspa?messageID=397448
class RequestCore {
    public static $curl_multi_handle = null;
    public static function curlExecUsingMulti($curl_handle) {
		set_time_limit(1); //Test
        // Create a multi if necessary.
        if (empty(RequestCore::$curl_multi_handle)) {
            RequestCore::$curl_multi_handle = curl_multi_init();
        }

        // Add the handle to be processed.
        curl_multi_add_handle(RequestCore::$curl_multi_handle, $curl_handle);

        // Do all the processing.
        $active = NULL;
        do {
            $ret = curl_multi_exec(RequestCore::$curl_multi_handle, $active);
        } while ($ret == CURLM_CALL_MULTI_PERFORM);

        while ($active && $ret == CURLM_OK) {
			//FIX https://bugs.php.net/bug.php?id=60790&edit=1 by 
pierrick@php.net
			if (curl_multi_select(RequestCore::$curl_multi_handle) 
== -1) {
				usleep(100);
			}
            //if (curl_multi_select(RequestCore::$curl_multi_handle) != -1) {
                    do {
                            $mrc = 
curl_multi_exec(RequestCore::$curl_multi_handle, $active);
                    } while ($mrc == CURLM_CALL_MULTI_PERFORM);
            //}
        }


        // Remove the handle from the multi processor.
        curl_multi_remove_handle(RequestCore::$curl_multi_handle, $curl_handle);

        return curl_multi_getcontent($curl_handle);
    }
}

Thanks pierrick, marfil for answers.
But, your codes still dont work:(

I found the answer by putting the following code: 

...
while ($mrc == CURLM_CALL_MULTI_PERFORM);
#fix
if(strtoupper(substr(PHP_OS,0,3)) === 'WIN'){
  curl_multi_select($this->m_handle, 0.005);
  curl_multi_exec($this->m_handle, $active);
}
...

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