diff -ur includes/bootstrap.inc includes/bootstrap.inc
--- includes/bootstrap.inc	2008-12-08 03:49:48.000000000 -0800
+++ includes/bootstrap.inc	2009-01-13 22:39:30.000000000 -0800
@@ -71,31 +71,36 @@
 define('DRUPAL_BOOTSTRAP_ACCESS', 3);
 
 /**
- * Fifth bootstrap phase: initialize session handling.
+ * Fifth bootstrap phase: initialize locking system.
  */
-define('DRUPAL_BOOTSTRAP_SESSION', 4);
+define('DRUPAL_BOOTSTRAP_LOCK', 4);
 
 /**
- * Sixth bootstrap phase: load bootstrap.inc and module.inc, start
+ * Sixth bootstrap phase: initialize session handling.
+ */
+define('DRUPAL_BOOTSTRAP_SESSION', 5);
+
+/**
+ * Seventh bootstrap phase: load bootstrap.inc and module.inc, start
  * the variable system and try to serve a page from the cache.
  */
-define('DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE', 5);
+define('DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE', 6);
 
 /**
- * Seventh bootstrap phase: find out language of the page.
+ * Eighth bootstrap phase: find out language of the page.
  */
-define('DRUPAL_BOOTSTRAP_LANGUAGE', 6);
+define('DRUPAL_BOOTSTRAP_LANGUAGE', 7);
 
 /**
- * Eighth bootstrap phase: set $_GET['q'] to Drupal path of request.
+ * Nineth bootstrap phase: set $_GET['q'] to Drupal path of request.
  */
-define('DRUPAL_BOOTSTRAP_PATH', 7);
+define('DRUPAL_BOOTSTRAP_PATH', 8);
 
 /**
  * Final bootstrap phase: Drupal is fully loaded; validate and fix
  * input data.
  */
-define('DRUPAL_BOOTSTRAP_FULL', 8);
+define('DRUPAL_BOOTSTRAP_FULL', 9);
 
 /**
  * Role ID for anonymous users; should match what's in the "role" table.
@@ -945,6 +950,7 @@
  *     DRUPAL_BOOTSTRAP_EARLY_PAGE_CACHE: try to call a non-database cache fetch routine.
  *     DRUPAL_BOOTSTRAP_DATABASE: initialize database layer.
  *     DRUPAL_BOOTSTRAP_ACCESS: identify and reject banned hosts.
+ *     DRUPAL_BOOTSTRAP_LOCK: initialize locking system.
  *     DRUPAL_BOOTSTRAP_SESSION: initialize session handling.
  *     DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE: load bootstrap.inc and module.inc, start
  *       the variable system and try to serve a page from the cache.
@@ -953,7 +959,7 @@
  *     DRUPAL_BOOTSTRAP_FULL: Drupal is fully loaded, validate and fix input data.
  */
 function drupal_bootstrap($phase) {
-  static $phases = array(DRUPAL_BOOTSTRAP_CONFIGURATION, DRUPAL_BOOTSTRAP_EARLY_PAGE_CACHE, DRUPAL_BOOTSTRAP_DATABASE, DRUPAL_BOOTSTRAP_ACCESS, DRUPAL_BOOTSTRAP_SESSION, DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE, DRUPAL_BOOTSTRAP_LANGUAGE, DRUPAL_BOOTSTRAP_PATH, DRUPAL_BOOTSTRAP_FULL), $phase_index = 0;
+  static $phases = array(DRUPAL_BOOTSTRAP_CONFIGURATION, DRUPAL_BOOTSTRAP_EARLY_PAGE_CACHE, DRUPAL_BOOTSTRAP_DATABASE, DRUPAL_BOOTSTRAP_ACCESS, DRUPAL_BOOTSTRAP_LOCK, DRUPAL_BOOTSTRAP_SESSION, DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE, DRUPAL_BOOTSTRAP_LANGUAGE, DRUPAL_BOOTSTRAP_PATH, DRUPAL_BOOTSTRAP_FULL), $phase_index = 0;
 
   while ($phase >= $phase_index && isset($phases[$phase_index])) {
     $current_phase = $phases[$phase_index];
@@ -1003,6 +1009,11 @@
       }
       break;
 
+    case DRUPAL_BOOTSTRAP_LOCK:
+      require_once variable_get('lock_inc', './includes/lock.inc');
+      lock_init();
+      break;
+
     case DRUPAL_BOOTSTRAP_SESSION:
       require_once variable_get('session_inc', './includes/session.inc');
       session_set_save_handler('sess_open', 'sess_close', 'sess_read', 'sess_write', 'sess_destroy_sid', 'sess_gc');
Only in includes: lock.inc
diff -ur includes/menu.inc includes/menu.inc
--- includes/menu.inc	2008-11-10 09:30:39.000000000 -0800
+++ includes/menu.inc	2009-01-13 22:41:37.000000000 -0800
@@ -1651,6 +1651,9 @@
  * is different and leaves stale data in the menu tables.
  */
 function menu_rebuild() {
+  if (!lock_acquire('menu_rebuild')) {
+    return FALSE;
+  }
   variable_del('menu_rebuild_needed');
   menu_cache_clear_all();
   $menu = menu_router_build(TRUE);
@@ -1660,6 +1663,7 @@
   if (defined('MAINTENANCE_MODE')) {
     variable_set('menu_rebuild_needed', TRUE);
   }
+  lock_release('menu_rebuild');
 }
 
 /**
@@ -1667,7 +1671,6 @@
  */
 function menu_router_build($reset = FALSE) {
   static $menu;
-
   if (!isset($menu) || $reset) {
     if (!$reset && ($cache = cache_get('router:', 'cache_menu')) && isset($cache->data)) {
       $menu = $cache->data;
diff -ur modules/locale/locale.module modules/locale/locale.module
--- modules/locale/locale.module	2008-10-20 02:31:06.000000000 -0700
+++ modules/locale/locale.module	2009-01-13 22:40:07.000000000 -0800
@@ -357,14 +357,17 @@
         $locale_t[$langcode] = $cache->data;
       }
       else {
-        // Refresh database stored cache of translations for given language.
-        // We only store short strings used in current version, to improve
-        // performance and consume less memory.
-        $result = db_query("SELECT s.source, t.translation, t.language FROM {locales_source} s LEFT JOIN {locales_target} t ON s.lid = t.lid AND t.language = '%s' WHERE s.textgroup = 'default' AND s.version = '%s' AND LENGTH(s.source) < 75", $langcode, VERSION);
-        while ($data = db_fetch_object($result)) {
-          $locale_t[$langcode][$data->source] = (empty($data->translation) ? TRUE : $data->translation);
+        if (lock_acquire('locale_cache_' . $langcode)) {
+          // Refresh database stored cache of translations for given language.
+          // We only store short strings used in current version, to improve
+          // performance and consume less memory.
+          $result = db_query("SELECT s.source, t.translation, t.language FROM {locales_source} s LEFT JOIN {locales_target} t ON s.lid = t.lid AND t.language = '%s' WHERE s.textgroup = 'default' AND s.version = '%s' AND LENGTH(s.source) < 75", $langcode, VERSION);
+          while ($data = db_fetch_object($result)) {
+            $locale_t[$langcode][$data->source] = (empty($data->translation) ? TRUE : $data->translation);
+          }
+          cache_set('locale:'. $langcode, $locale_t[$langcode]);
+          lock_release('locale_cache_' . $langcode);
         }
-        cache_set('locale:'. $langcode, $locale_t[$langcode]);
       }
     }
   }