Asynchronous PHP with Background Process

bgp-async.php

<?php

// Fetch main feed.
// Main feed at /items.json
// Individual item feeds at /item/<id>.json

$url = 'http://example.com/items.json';
$result = drupal_http_request($url);
$data = drupal_json_decode($result->data);

// Subfetch subitems for each json item in main json feed.
// Subitems only available via single item fetch.
$processes = array();
foreach ($data['response'] as &$response) {
  // Generate URL and headers
  $url = 'http://example.com/item/' . $response['id'] . '.json';

  // Postpone request polling and set callback.
  $options = array(
    'postpone' => TRUE,
    'callback' => function ($result) use (&$response) {
      $item = drupal_json_decode($result->data);
      $response['subitems'] = $item['response']['subitems'];
    }
  );

  // Add request object to our polling pool.
  $processes[] = background_process_http_request($url, $options);
}

// Wait for processes to finish, max 10 concurrent requests at a time.
background_process_http_request_process($processes, array('limit' => 10));

// $data is now populated.