<?php

// $Id: throttle.module,v 1.83 2007/12/14 18:08:49 goba Exp $

/**

 * @file

 * Allows configuration of congestion control auto-throttle mechanism.

 */

function throttle_menu() {

  $items['admin/settings/throttle'] = array(

    'title' => 'Throttle',

    'description' => 'Control how your site cuts out content during heavy load.',

    'page callback' => 'drupal_get_form',

    'page arguments' => array('throttle_admin_settings'),

    'access arguments' => array('administer site configuration'),

    'file' => 'throttle.admin.inc',

  );

  return $items;

}

/**

 * Determine the current load on the site.

 *

 * Call the throttle_status() function from your own modules, themes, blocks,

 * etc. as follows:

 *

 *   $throttle = module_invoke('throttle', 'status');

 *

 * to determine the current throttle status. Use module_invoke() so the

 * call will still work if the throttle module is disabled. For example, in

 * your theme you might choose to disable pictures when your site is too busy

 * (reducing bandwidth), or in your modules you might choose to disable

 * some complicated logic when your site is too busy (reducing CPU utilization).

 *

 * @return

 *   0 or 1. 0 means that the throttle is currently disabled. 1 means that

 *   the throttle is currently enabled. When the throttle is enabled, CPU

 *   and bandwidth intensive functionality should be disabled.

 */

function throttle_status() {

  return variable_get('throttle_level', 0);

}

/**

 * Implementation of hook_exit().

 *

 * Changes the current throttle level based on page hits.

 */

function throttle_exit() {

  // The following logic determines what the current throttle level should

  //  be, and can be disabled by the admin. If enabled, the mt_rand() function

  //  returns a number between 0 and N, N being specified by the admin. If

  //  0 is returned, the throttle logic is run, adding two additional database

  //  queries. Otherwise, the following logic is skipped. This mechanism is

  //  referred to in the admin page as the 'probability limiter', roughly

  //  limiting throttle related database calls to 1 in N.

  if (!mt_rand(0, variable_get('throttle_probability_limiter', 9))) {

    // Count users with activity in the past n seconds.

    // This value is defined in the user module Who's Online block.

    $time_period = variable_get('user_block_seconds_online', 900);

    // When determining throttle status in your own module or theme, use

    // $throttle = module_invoke('throttle', 'status');

    // as that will still work when throttle.module is disabled.

    // Clearly here the module is enabled so we call throttle_status() directly.

    $throttle = throttle_status();

    if ($max_guests = variable_get('throttle_anonymous', 0)) {

      $guests = sess_count(time() - $time_period, TRUE);

    }

    else {

      $guests = 0;

    }

    if ($max_users = variable_get('throttle_user', 0)) {

      $users = sess_count(time() - $time_period, FALSE);

    }

    else {

      $users = 0;

    }

    // update the throttle status

    $message = '';

    if ($max_users && $users > $max_users) {

      if (!$throttle) {

        variable_set('throttle_level', 1);

        $message = format_plural($users,

                                 '1 user accessing site; throttle enabled.',

                                 '@count users accessing site; throttle enabled.');

      }

    }

    elseif ($max_guests && $guests > $max_guests) {

      if (!$throttle) {

        variable_set('throttle_level', 1);

        $message = format_plural($guests,

                                 '1 guest accessing site; throttle enabled.',

                                 '@count guests accessing site; throttle enabled.');

      }

    }

    else {

      if ($throttle) {

        variable_set('throttle_level', 0);

        // Note: unorthodox format_plural() usage due to Gettext plural limitations.

        $message = format_plural($users, '1 user', '@count users') .', ';

        $message .= format_plural($guests, '1 guest accessing site; throttle disabled', '@count guests accessing site; throttle disabled');

      }

    }

    if ($message) {

      cache_clear_all();

      watchdog('throttle', 'Throttle: %message', array('%message' => $message));

    }

  }

}

/**

 * Implementation of hook_help().

 */

function throttle_help($path, $arg) {

  switch ($path) {

    case 'admin/help#throttle':

      $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>';

      $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>';

      $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>';

      return $output;

    case 'admin/settings/throttle':

      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>';

  }

}