PHP - curl_multi_exec never completes

As a comment says at http://php.net/manual/en/function.curl-multi-init.php#115055, there's a problem on the official document. So the class of example 2 should look something like this. Changed the first while loop

class ParallelGet
{
  function __construct($urls)
  {
    // Create get requests for each URL
    $mh = curl_multi_init();
    foreach($urls as $i => $url)
    {
      $ch[$i] = curl_init($url);
      curl_setopt($ch[$i], CURLOPT_RETURNTRANSFER, 1);
      curl_multi_add_handle($mh, $ch[$i]);
    }

    // Start performing the request
    do {
        $execReturnValue = curl_multi_exec($mh, $runningHandles);
    } while ($execReturnValue == CURLM_CALL_MULTI_PERFORM);

    // Loop and continue processing the request
    while ($runningHandles && $execReturnValue == CURLM_OK) {

      // !!!!! changed this if and the next do-while !!!!!

      if (curl_multi_select($mh) != -1) {
        usleep(100);
      }

      do {
        $execReturnValue = curl_multi_exec($mh, $runningHandles);
      } while ($execReturnValue == CURLM_CALL_MULTI_PERFORM);

    }

    // Check for any errors
    if ($execReturnValue != CURLM_OK) {
      trigger_error("Curl multi read error $execReturnValue\n", E_USER_WARNING);
    }

    // Extract the content
    foreach($urls as $i => $url)
    {
      // Check for errors
      $curlError = curl_error($ch[$i]);
      if($curlError == "") {
        $res[$i] = curl_multi_getcontent($ch[$i]);
      } else {
        print "Curl error on handle $i: $curlError\n";
      }
      // Remove and close the handle
      curl_multi_remove_handle($mh, $ch[$i]);
      curl_close($ch[$i]);
    }
    // Clean up the curl_multi handle
    curl_multi_close($mh);

    // Print the response data
    print_r($res);
  }
}