Is my use of curl_multi() still serial? If so, how can I parallelize?

I got a hint from someone today that my curl_multi() code is actually working in serial, when my hope was to parallelize the cURL requests.

Is my code still serial? If so, how I can parallelize?

Here's the relevant code:

  /**
   * Returns the cURL responses given multiple target URLs
   * @param array $targetUrls Array of target URLs for cURL
   *
   * @return array cURL Responses
   */
  private function getCurlMultiResponses($targetUrls)
  {
    // Cache the count
    $count = count($targetUrls);

    // Create the multiple cURL handles
    for($i = 0; $i < $count; $i++) {
      $ch[$i] = curl_init($targetUrls[$i]);
      curl_setopt($ch[$i], CURLOPT_POST, FALSE);
      curl_setopt($ch[$i], CURLOPT_SSL_VERIFYPEER, FALSE);
      curl_setopt($ch[$i], CURLOPT_RETURNTRANSFER, TRUE);
    }

    // Initialize the multiple cURL handle
    $mh = curl_multi_init();

    // Add the handles to the curl_multi handle
    for($i = 0; $i < $count开发者_运维知识库; $i++) {
      curl_multi_add_handle($mh, $ch[$i]);
    }

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

    $responses = array();

    // Remove the handles and return the response
    for($i = 0; $i < $count; $i++) {
      curl_multi_remove_handle($mh, $ch[$i]);

      $responses[$i] = curl_multi_getcontent($ch[$i]);
    }

    // Close the multiple cURL handle
    curl_multi_close($mh);

    return $responses;
  }

The manual certainly suggests it's a parallel operation:

Allows the processing of multiple cURL handles in parallel.

There's a good tutorial here.