Index: system.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.admin.inc,v
retrieving revision 1.158
diff -u -r1.158 system.admin.inc
--- modules/system/system.admin.inc	19 Jun 2009 20:35:05 -0000	1.158
+++ modules/system/system.admin.inc	29 Jun 2009 10:34:43 -0000
@@ -1241,6 +1241,14 @@
     '#description' => t('Render all blocks on the default 404 (not found) page. Disabling blocks can help with performance but might leave users with a less functional site.'),
     '#default_value' => variable_get('site_404_blocks', 0)
   );
+  $form['cron_safe_threshold'] = array(
+    '#type' => 'select',
+    '#title' => t('Automatically run cron'),
+    '#default_value' => variable_get('cron_safe_threshold', DRUPAL_DEFAULT_CRON_THRESHOLD),
+    '#options' => array(0 => t('Never')) + drupal_map_assoc(array(1,3600, 10800, 21600, 43200, 86400, 604800), 'format_interval'),
+    '#description' => t('When enabled, the site will check whether cron has been run in the configured interval and automatically run it upon the next page request. For more information visit the <a href="@status-report-url">status report page</a>.', array('@status-report-url' => url('admin/reports/status'))),
+  );
+
   $form['#validate'][] = 'system_site_information_settings_validate';
 
   return system_settings_form($form);
Index: system.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.module,v
retrieving revision 1.716
diff -u -r1.716 system.module
--- modules/system/system.module	28 Jun 2009 12:52:57 -0000	1.716
+++ modules/system/system.module	29 Jun 2009 13:00:24 -0000
@@ -42,6 +42,11 @@
 define('DRUPAL_MAXIMUM_TEMP_FILE_AGE', 21600);
 
 /**
+ * Default interval between automatically ran cron task in seconds.
+ */
+define('DRUPAL_DEFAULT_CRON_THRESHOLD', 10800);
+
+/**
  * New users will be set to the default time zone at registration.
  */
 define('DRUPAL_USER_TIMEZONE_DEFAULT', 0);
@@ -476,6 +481,12 @@
     'access callback' => TRUE,
     'type' => MENU_CALLBACK,
   );
+  $items['system/run-cron-image'] = array(
+    'title' => 'Execute cron',
+    'page callback' => 'system_run_cron_image',
+    'access callback' => '_system_run_cron_image_access',
+    'type' => MENU_CALLBACK,
+  );
   $items['admin'] = array(
     'title' => 'Administer',
     'access arguments' => array('access administration pages'),
@@ -2569,3 +2580,42 @@
   }
   return $local;
 }
+
+/**
+ * Implement hook_footer().
+ *
+ * Add a transparent 1x1 image in the closure of the page when the cron needs
+ * to run.
+ */
+function system_footer() {
+  // Display the image only when it is possible to access it.
+  if (_system_run_cron_image_access()) {
+    return '<div><img src="' . url('system/run-cron-image').'" alt="" /></div>';
+  }
+}
+
+/**
+ * Menu page callback; executes the cron via an image callback.
+ */
+function system_run_cron_image() {
+  // Output a transparent 1x1 image to the browser.
+  drupal_set_header('Content-Type: image/gif');
+  echo "\x47\x49\x46\x38\x39\x61\x1\x0\x1\x0\x80\xff\x0\xc0\xc0\xc0\x0\x0\x0\x21\xf9\x4\x1\x0\x0\x0\x0\x2c\x0\x0\x0\x0\x1\x0\x1\x0\x0\x2\x2\x44\x1\x0\x3b";
+  
+  drupal_cron_run();
+  exit;
+}
+
+/**
+ * Checks if the cron needs to run automatically.
+ * 
+ * Also used as a menu access callback for this feature.
+ * 
+ * @return
+ *   TRUE if the cron threshold is enable and crossed, FALSE otherwise.
+ */
+function _system_run_cron_image_access() {
+  $cron_last = variable_get('cron_last', NULL);
+  $cron_threshold = variable_get('cron_safe_threshold', DRUPAL_DEFAULT_CRON_THRESHOLD);
+  return $cron_threshold > 0 && (!isset($cron_last) || (REQUEST_TIME - $cron_last > $cron_threshold));
+}
\ No newline at end of file