Description:
------------
At the curl_multi_init there is an example that says:

$running=null;
//execute the handles
do {
    curl_multi_exec($mh,$running);
} while ($running > 0);

This causes a *very* tight loop while curl requests the files, as a result an 
almost 100% cpu usage.

My suggestion is to put a usleep() with a 10ms delay inside the loop:

$running=null;
//execute the handles
do {
    usleep(10000);
    curl_multi_exec($mh,$running);
} while ($running > 0);