#331611 by Damien Tournoud: Add poorman's cron-like feature to core.

From: damz <damz@damz-dev.local>


---
 system/system.admin.inc |    8 ++++++++
 system/system.module    |   39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 0 deletions(-)

diff --git modules/system/system.admin.inc modules/system/system.admin.inc
index 3aa003c..b612cdc 100644
--- modules/system/system.admin.inc
+++ modules/system/system.admin.inc
@@ -1241,6 +1241,14 @@ function system_site_information_settings() {
     '#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', 10800),
+    '#options' => array(0 => t('Never')) + drupal_map_assoc(array(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);
diff --git modules/system/system.module modules/system/system.module
index 7389341..1bb2f9b 100644
--- modules/system/system.module
+++ modules/system/system.module
@@ -476,6 +476,13 @@ function system_menu() {
     'access callback' => TRUE,
     'type' => MENU_CALLBACK,
   );
+  $items['system/cron/%'] = array(
+    'title' => 'Execute cron',
+    'page callback' => 'system_execute_cron',
+    'page arguments' => array(2),
+    'access callback' => TRUE,
+    'type' => MENU_CALLBACK,
+  );
   $items['admin'] = array(
     'title' => 'Administer',
     'access arguments' => array('access administration pages'),
@@ -2569,3 +2576,35 @@ function system_retrieve_file($path) {
   }
   return $local;
 }
+
+/**
+ * Implement hook_footer().
+ *
+ * Add a transparent 1x1 image in the closure of the page when the cron needs
+ * to run.
+ */
+function system_footer() {
+  if ($cron_treshold = variable_get('cron_safe_threshold', 10800)) {
+    $cron_last = variable_get('cron_last', NULL);
+    if (!isset($cron_last) || (REQUEST_TIME - $cron_last > $cron_treshold)) {
+      return '<img src="' . url('system/cron/' . drupal_get_token($cron_last)) . '" alt=""/>';
+    }
+  }
+}
+
+/**
+ * Menu callback; execute the cron via an image callback.
+ */
+function system_execute_cron($token) {
+  $cron_last = variable_get('cron_last', NULL);
+  if (drupal_valid_token($token, $cron_last)) {
+    // 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";
+
+    // Execute the code.
+    drupal_cron_run();
+
+    exit;
+  }
+}