gistfile1.php

<?

require 'parallelcurl.php';

$pc = new ParallelCurl(5);

// Bind $callback and $pc using "use()" construct, because we'll use them inside the closure
$callback = function($content, $url, $ch, $userParams) use (&$callback, $pc) {
  // Print status of finished request
  $i = $userParams['i'];
  $httpcode = curl_getinfo($ch, CURLINFO_HTTP_CODE);    
  echo "Request index {$i}, got http code: $httpcode\n";

  if ($i == 20) {
    // That's enough
    echo "Finished!\n";
    return;
  }

  // Continue with next request
  $pc->startRequest('example.com', $callback, ['i' => $i + 1]);
};

// Queue our first request
$pc->startRequest('example.com', $callback, ['i' => 1]);

// Start actually processing requests, until request queue is empty
$pc->finishAllRequests();