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   1  <?php
   2  // $Id: throttle.module,v 1.83 2007/12/14 18:08:49 goba Exp $
   3  
   4  /**
   5   * @file
   6   * Allows configuration of congestion control auto-throttle mechanism.
   7   */
   8  
   9  function throttle_menu() {
  10    $items['admin/settings/throttle'] = array(
  11      'title' => 'Throttle',
  12      'description' => 'Control how your site cuts out content during heavy load.',
  13      'page callback' => 'drupal_get_form',
  14      'page arguments' => array('throttle_admin_settings'),
  15      'access arguments' => array('administer site configuration'),
  16      'file' => 'throttle.admin.inc',
  17    );
  18    return $items;
  19  }
  20  
  21  /**
  22   * Determine the current load on the site.
  23   *
  24   * Call the throttle_status() function from your own modules, themes, blocks,
  25   * etc. as follows:
  26   *
  27   *   $throttle = module_invoke('throttle', 'status');
  28   *
  29   * to determine the current throttle status. Use module_invoke() so the
  30   * call will still work if the throttle module is disabled. For example, in
  31   * your theme you might choose to disable pictures when your site is too busy
  32   * (reducing bandwidth), or in your modules you might choose to disable
  33   * some complicated logic when your site is too busy (reducing CPU utilization).
  34   *
  35   * @return
  36   *   0 or 1. 0 means that the throttle is currently disabled. 1 means that
  37   *   the throttle is currently enabled. When the throttle is enabled, CPU
  38   *   and bandwidth intensive functionality should be disabled.
  39   */
  40  function throttle_status() {
  41    return variable_get('throttle_level', 0);
  42  }
  43  
  44  /**
  45   * Implementation of hook_exit().
  46   *
  47   * Changes the current throttle level based on page hits.
  48   */
  49  function throttle_exit() {
  50    // The following logic determines what the current throttle level should
  51    //  be, and can be disabled by the admin. If enabled, the mt_rand() function
  52    //  returns a number between 0 and N, N being specified by the admin. If
  53    //  0 is returned, the throttle logic is run, adding two additional database
  54    //  queries. Otherwise, the following logic is skipped. This mechanism is
  55    //  referred to in the admin page as the 'probability limiter', roughly
  56    //  limiting throttle related database calls to 1 in N.
  57    if (!mt_rand(0, variable_get('throttle_probability_limiter', 9))) {
  58  
  59      // Count users with activity in the past n seconds.
  60      // This value is defined in the user module Who's Online block.
  61      $time_period = variable_get('user_block_seconds_online', 900);
  62  
  63      // When determining throttle status in your own module or theme, use
  64      // $throttle = module_invoke('throttle', 'status');
  65      // as that will still work when throttle.module is disabled.
  66      // Clearly here the module is enabled so we call throttle_status() directly.
  67      $throttle = throttle_status();
  68  
  69      if ($max_guests = variable_get('throttle_anonymous', 0)) {
  70        $guests = sess_count(time() - $time_period, TRUE);
  71      }
  72      else {
  73        $guests = 0;
  74      }
  75      if ($max_users = variable_get('throttle_user', 0)) {
  76        $users = sess_count(time() - $time_period, FALSE);
  77      }
  78      else {
  79        $users = 0;
  80      }
  81  
  82      // update the throttle status
  83      $message = '';
  84      if ($max_users && $users > $max_users) {
  85        if (!$throttle) {
  86          variable_set('throttle_level', 1);
  87          $message = format_plural($users,
  88                                   '1 user accessing site; throttle enabled.',
  89                                   '@count users accessing site; throttle enabled.');
  90        }
  91      }
  92      elseif ($max_guests && $guests > $max_guests) {
  93        if (!$throttle) {
  94          variable_set('throttle_level', 1);
  95          $message = format_plural($guests,
  96                                   '1 guest accessing site; throttle enabled.',
  97                                   '@count guests accessing site; throttle enabled.');
  98        }
  99      }
 100      else {
 101        if ($throttle) {
 102          variable_set('throttle_level', 0);
 103          // Note: unorthodox format_plural() usage due to Gettext plural limitations.
 104          $message = format_plural($users, '1 user', '@count users') .', ';
 105          $message .= format_plural($guests, '1 guest accessing site; throttle disabled', '@count guests accessing site; throttle disabled');
 106        }
 107      }
 108      if ($message) {
 109        cache_clear_all();
 110        watchdog('throttle', 'Throttle: %message', array('%message' => $message));
 111      }
 112    }
 113  }
 114  
 115  /**
 116   * Implementation of hook_help().
 117   */
 118  function throttle_help($path, $arg) {
 119    switch ($path) {
 120      case 'admin/help#throttle':
 121        $output = '<p>'. t('The throttle module provides a congestion control mechanism that automatically adjusts to a surge in incoming traffic. If your site is referenced by a popular website, or experiences a "Denial of Service" (DoS) attack, your webserver might become overwhelmed. The throttle mechanism is utilized by modules to temporarily disable CPU-intensive functionality, increasing performance. For instance, via the throttle module, modules may choose to disable resource-intensive blocks or the code within the site theme may temporarily disable user pictures in posts.') .'</p>';
 122        $output .= '<p>'. t('The congestion control throttle can be automatically enabled when the number of anonymous or authenticated users currently visiting the site exceeds a specified threshold.') .'</p>';
 123        $output .= '<p>'. t('For more information, see the online handbook entry for <a href="@throttle">Throttle module</a>.', array('@throttle' => 'http://drupal.org/handbook/modules/throttle/')) .'</p>';
 124        return $output;
 125      case 'admin/settings/throttle':
 126        return '<p>'. t('The throttle module provides a congestion control mechanism that automatically adjusts to a surge in incoming traffic. If your site is referenced by a popular website, or experiences a "Denial of Service" (DoS) attack, your webserver might become overwhelmed. The throttle mechanism is utilized by modules to temporarily disable CPU-intensive functionality, increasing performance.') .'</p>';
 127    }
 128  }