- Patch #331611 by sun, joshmiller, TheRec, Rob Loach, Damien Tournoud: add a poormanscron-like feature to core.

CHANGELOG.txt

@@ -32,6 +32,8 @@ Drupal 7.0, xxxx-xx-xx (development version)
       now be achieved with Field API.
     * Added additional features to the default install profile, and implemented
       a "slimmed down" install profile designed for developers.
+    * Added a built-in, automated cron run feature, which is triggered by site
+      visitors.
     * Added an administrator role which is assigned all permisions for
       installed modules automatically.
     * Image toolkits are now provided by modules (rather than requiring a manual

INSTALL.txt

@@ -231,9 +231,18 @@ INSTALLATION
    maintenance task, including search module (to build and update the index
    used for keyword searching), aggregator module (to retrieve feeds from other
    sites), and system module (to perform routine maintenance and pruning on
-   system tables). To activate these tasks, visit the page "cron.php", which
-   executes maintenance tasks on behalf of installed modules. The URL of the
-   cron.php page requires a "cron key" to protect against unauthorized access.
+   system tables).
+
+   For most sites, the built-in, automated cron feature should be sufficient.
+   Note, however, that cron tasks will only be executed when there are site
+   visitors. You can enable the built-in cron feature at:
+
+          Administer > Configuration and modules > Development > Maintenance mode
+
+   Advanced users may want to ensure that cron tasks are executed periodically.
+   To do this, visit the page "cron.php", which executes maintenance tasks on
+   behalf of installed modules. The URL of the cron.php page requires a "cron
+   key" to protect against unauthorized access.
    Each cron key is automatically generated during installation and is specific
    to your site. The full URL of the page, with cron key, is available in the
    "Cron maintenance tasks" section of the "Status report page" at:

modules/system/system.admin.inc

@@ -1313,7 +1313,16 @@ 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', DRUPAL_CRON_DEFAULT_THRESHOLD),
+    '#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';
+  $form['#submit'][] = 'system_site_information_settings_submit';
 
   return system_settings_form($form);
 }
@@ -1333,6 +1342,18 @@ function system_site_information_settings_validate($form, &$form_state) {
   }
 }
 
+/**
+ * Form submit handler for the site-information form.
+ */
+function system_site_information_settings_submit($form, &$form_state) {
+  // Clear caches when the cron threshold is changed to ensure that the cron
+  // image is not contained in cached pages.
+  $cron_threshold = variable_get('cron_safe_threshold', DRUPAL_CRON_DEFAULT_THRESHOLD);
+  if (($cron_threshold > 0 && $form_state['input']['cron_safe_threshold'] == 0) || ($cron_threshold == 0 && $form_state['input']['cron_safe_threshold'] > 0)) {
+    cache_clear_all();
+  }
+}
+
 /**
  * Form builder; Configure error reporting settings.
  *

modules/system/system.module

@@ -41,6 +41,11 @@ define('DRUPAL_MINIMUM_PGSQL',  '8.3');
  */
 define('DRUPAL_MAXIMUM_TEMP_FILE_AGE', 21600);
 
+/**
+ * Default interval for automatic cron executions in seconds.
+ */
+define('DRUPAL_CRON_DEFAULT_THRESHOLD', 10800);
+
 /**
  * New users will be set to the default time zone at registration.
  */
@@ -196,6 +201,9 @@ function system_theme() {
       'arguments' => array('version' => NULL),
     ),
     'system_compact_link' => array(),
+    'system_run_cron_image' => array(
+      'arguments' => array('image_path' => NULL),
+    ),
   ));
 }
 
@@ -496,6 +504,12 @@ function system_menu() {
     '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,
+  );
   $items['admin'] = array(
     'title' => 'Administer',
     'access arguments' => array('access administration pages'),
@@ -2968,3 +2982,104 @@ function system_retrieve_file($url, $destination = NULL, $overwrite = TRUE) {
   
   return $local;
 }
+
+/**
+ * Implement hook_page_alter().
+ */
+function system_page_alter(&$page) {
+  // Automatic cron runs.
+  // @see system_run_cron_image()
+  if (system_run_cron_image_access()) {
+    $page['page_bottom']['run_cron'] = array(
+      // Trigger cron run via AJAX.
+      '#attached_js' => array(
+        '(function($){ $.get(' . drupal_to_js(url('system/run-cron-image')) . '); })(jQuery);' => array('type' => 'inline', 'scope' => 'header'),
+      ),
+      // Trigger cron run for clients not supporting JavaScript (fall-back).
+      '#markup' => theme('system_run_cron_image', 'system/run-cron-image'),
+    );
+  }
+}
+
+/**
+ * Menu callback; executes cron via an image callback.
+ *
+ * This callback runs cron in a separate HTTP request to prevent "mysterious"
+ * slow-downs of regular HTTP requests. It is either invoked via an AJAX request
+ * (if the client's browser supports JavaScript) or by an IMG tag directly in
+ * the page output (for clients not supporting JavaScript). For the latter case,
+ * we need to output a transparent 1x1 image, so the browser does not render the
+ * image's alternate text or a 'missing image placeholder'. The AJAX request
+ * does not process the returned output.
+ *
+ * @see system_page_alter()
+ * @see theme_system_run_cron_image()
+ * @see system_run_cron_image_access()
+ */
+function system_run_cron_image() {
+  drupal_page_is_cacheable(FALSE);
+
+  // Output a transparent 1x1 image to the browser; required for clients not
+  // supporting JavaScript.
+  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";
+
+  // Cron threshold semaphore is used to avoid errors every time the image
+  // callback is displayed when a previous cron is still running.
+  $threshold_semaphore = variable_get('cron_threshold_semaphore', FALSE);
+  if ($threshold_semaphore) {
+    if (REQUEST_TIME - $threshold_semaphore > 3600) {
+      // Either cron has been running for more than an hour or the semaphore
+      // was not reset due to a database error.
+      watchdog('cron', 'Cron has been running for more than an hour and is most likely stuck.', array(), WATCHDOG_ERROR);
+
+      // Release the cron threshold semaphore.
+      variable_del('cron_threshold_semaphore');
+    }
+  }
+  else {
+    // Run cron automatically if it has never run or threshold was crossed.
+    $cron_last = variable_get('cron_last', NULL);
+    $cron_threshold = variable_get('cron_safe_threshold', DRUPAL_CRON_DEFAULT_THRESHOLD);
+    if (!isset($cron_last) || (REQUEST_TIME - $cron_last > $cron_threshold)) {
+      // Lock cron threshold semaphore.
+      variable_set('cron_threshold_semaphore', REQUEST_TIME);
+      drupal_cron_run();
+      // Release the cron threshold semaphore.
+      variable_del('cron_threshold_semaphore');
+    }
+  }
+
+  exit;
+}
+
+/**
+ * Checks if the feature to automatically run cron is enabled.
+ *
+ * Also used as a menu access callback for this feature.
+ *
+ * @return
+ *   TRUE if cron threshold is enabled, FALSE otherwise.
+ *
+ * @see system_run_cron_image()
+ * @see system_page_alter()
+ */
+function system_run_cron_image_access() {
+  return variable_get('cron_safe_threshold', DRUPAL_CRON_DEFAULT_THRESHOLD) > 0;
+}
+
+/**
+ * Display image used to run cron automatically.
+ *
+ * Renders an image pointing to the automatic cron run menu callback for
+ * graceful degradation when Javascript is not available. The wrapping NOSCRIPT
+ * tag ensures that only browsers not supporting JavaScript render the image.
+ *
+ * @see system_page_alter()
+ * @see system_run_cron_image()
+ * @ingroup themeable
+ */
+function theme_system_run_cron_image($image_path) {
+  return '<noscript><div id="system-cron-image">' . theme('image', $image_path, '', '', array(), FALSE) . '</div></noscript>';
+}
+

modules/system/system.test

@@ -372,6 +372,7 @@ class CronRunTestCase extends DrupalWebTestCase {
    */
   function testCronRun() {
     global $base_url;
+
     // Run cron anonymously without any cron key.
     $this->drupalGet($base_url . '/cron.php', array('external' => TRUE));
     $this->assertResponse(403);
@@ -390,14 +391,58 @@ class CronRunTestCase extends DrupalWebTestCase {
     $this->assertTrue(drupal_cron_run(), t('Cron ran successfully.'));
   }
 
+  /**
+   * Follow every image paths in the previously retrieved content.
+   */
+  function drupalGetAllImages() {
+    foreach ($this->xpath('//img') as $image) {
+      $this->drupalGet($this->getAbsoluteUrl($image['src']));
+    }
+  }
+
+  /**
+   * Ensure that the cron image callback to run it automatically is working.
+   *
+   * In these tests we do not use REQUEST_TIME to track start time, because we
+   * need the exact time when cron is triggered.
+   */
+  function testCronThreshold() {
+    // Ensure cron does not run when the cron threshold is enabled and was
+    // not passed.
+    $start_cron_last = time();
+    variable_set('cron_last', $start_cron_last);
+    variable_set('cron_safe_threshold', 10);
+    $this->drupalGet('');
+    // Follow every image path on the page.
+    $this->drupalGetAllImages();
+    $this->assertTrue($start_cron_last == variable_get('cron_last', NULL), t('Cron does not run when the cron threshold is not passed.'));
+
+    // Test if cron runs when the cron threshold was passed.
+    $start_cron_last = time() - 15;
+    variable_set('cron_last', $start_cron_last);
+    $this->drupalGet('');
+    // Follow every image path on the page.
+    $this->drupalGetAllImages();
+    $this->assertTrue(variable_get('cron_last', NULL) > $start_cron_last, t('Cron runs when the cron threshold is passed.'));
+
+    // Test if cron does not run when the cron threshold was is disabled.
+    $start_cron_last = time() - 15;
+    variable_set('cron_safe_threshold', 0);
+    variable_set('cron_last', $start_cron_last);
+    $this->drupalGet('');
+    // Follow every image path on the page.
+    $this->drupalGetAllImages();
+    $this->assertTrue($start_cron_last == variable_get('cron_last', NULL), t('Cron does not run when the cron threshold is disabled.'));
+  }
+
   /**
    * Ensure that temporary files are removed.
+   *
+   * Create files for all the possible combinations of age and status. We are
+   * using UPDATE statments rather than file_save() because it would set the
+   * timestamp.
    */
   function testTempFileCleanup() {
-    // Create files for all the possible combinations of age and status. We're
-    // using UPDATE statments rather than file_save() because it would set the
-    // timestamp.
-
     // Temporary file that is older than DRUPAL_MAXIMUM_TEMP_FILE_AGE.
     $temp_old = file_save_data('');
     db_update('file')