Issue #2367609: Warn on misconfiguration of stampede protection with core locking

README.txt

@@ -106,7 +106,7 @@ The memcache-lock.inc file included with this module can be used as a drop-in
 replacement for the database-mediated locking mechanism provided by Drupal
 core. To enable, define the following in your settings.php:
 
-$conf['lock_inc'] = 'sites/all/modules/memcache/memcache-lock.inc';
+  $conf['lock_inc'] = 'sites/all/modules/memcache/memcache-lock.inc';
 
 Locks are written in the 'semaphore' table, which will map to the 'default'
 memcache cluster unless you explicitly configure a 'semaphore' cluster.
@@ -116,11 +116,12 @@ memcache cluster unless you explicitly configure a 'semaphore' cluster.
 Memcache includes stampede protection for rebuilding expired and invalid cache
 items.  To enable stampede protection, define the following in settings.php:
 
-$conf['memcache_stampede_protection'] = TRUE;
+  $conf['memcache_stampede_protection'] = TRUE;
 
 To avoid lock stampedes, it is important that you enable the memacache lock
 implementation when enabling stampede protection -- enabling stampede protection
-without enabling the Memache lock implementation can cause worse performance.
+without enabling the Memache lock implementation can cause worse performance and
+can result in dropped locks due to key-length truncation.
 
 Memcache stampede protection is primarily designed to benefit the following
 caching pattern: a miss on a cache_get() for a specific cid is immediately

memcache.install

@@ -142,6 +142,12 @@ function memcache_requirements($phase) {
         // An unexpected exception occurred.
         $errors[] = $t('Unexpected failure when testing memcache configuration.');
       }
+      // Core's lock implementation can cause worse performance together with
+      // stampede protection. Plus, long keys will be truncated resulting in
+      // dropped locks.
+      if (variable_get('memcache_stampede_protection', FALSE) && strpos(variable_get('lock_inc', 'includes/lock.inc'), 'includes/lock.inc') !== FALSE) {
+        $warnings[] = $t('Drupal\'s core lock implementation (%core) is not supported by memcache stampede protection. Enable the memcache lock implementation (%memcache) or disable memcache stampede protection.', array('%core' => 'includes/lock.inc', '%memcache' => drupal_get_path('module', 'memcache') . "/memcache-lock.inc"));
+      }
     }
 
     if (!empty($errors)) {
@@ -150,11 +156,11 @@ function memcache_requirements($phase) {
       $errors = array_merge($errors, $warnings);
       unset($warnings);
       $requirements['memcache_extension']['severity'] = REQUIREMENT_ERROR;
-      $requirements['memcache_extension']['description'] = $t('There is a problem with your memcache configuration, check the Drupal logs for additional errors. Please review %readme for help resolving the following !issue: !errors', array('%readme' => 'README.txt', '!issue' => format_plural(count($errors), 'issue', 'issues'), '!errors' => '<ul><li>' . implode('<li>', $errors)));
+      $requirements['memcache_extension']['description'] = $t('There is a problem with your memcache configuration, check the Drupal logs for additional errors. Please review %readme for help resolving the following !issue: !errors', array('%readme' => drupal_get_path('module', 'memcache') . '/' . 'README.txt', '!issue' => format_plural(count($errors), 'issue', 'issues'), '!errors' => '<ul><li>' . implode('<li>', $errors)));
     }
     elseif (!empty($warnings)) {
       $requirements['memcache_extension']['severity'] = REQUIREMENT_WARNING;
-      $requirements['memcache_extension']['description'] = $t('There is a problem with your memcache configuration. Please review %readme for help resolving the following !issue: !warnings', array('%readme' => 'README.txt', '!issue' => format_plural(count($warnings), 'issue', 'issues'), '!warnings' => '<ul><li>' . implode('<li>', $warnings)));
+      $requirements['memcache_extension']['description'] = $t('There is a problem with your memcache configuration. Please review %readme for help resolving the following !issue: !warnings', array('%readme' => drupal_get_path('module', 'memcache') . '/' . 'README.txt', '!issue' => format_plural(count($warnings), 'issue', 'issues'), '!warnings' => '<ul><li>' . implode('<li>', $warnings)));
     }
     else {
       $requirements['memcache_extension']['severity'] = REQUIREMENT_OK;