Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.208
diff -u -3 -p -r1.208 bootstrap.inc
--- includes/bootstrap.inc	14 Apr 2008 17:48:33 -0000	1.208
+++ includes/bootstrap.inc	27 Apr 2008 10:50:49 -0000
@@ -71,31 +71,36 @@ define('DRUPAL_BOOTSTRAP_DATABASE', 2);
 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.
@@ -902,6 +907,7 @@ function drupal_anonymous_user($session 
  *     DRUPAL_BOOTSTRAP_EARLY_PAGE_CACHE: try to call a non-database cache fetch routine.
  *     DRUPAL_BOOTSTRAP_DATABASE: initialize database layer.
  *     DRUPAL_BOOTSTRAP_ACCESS: identify and reject banned hosts.
+ *     DRUPAL_BOOTSTRAP_LOCK: initialize locking system.
  *     DRUPAL_BOOTSTRAP_SESSION: initialize session handling.
  *     DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE: load bootstrap.inc and module.inc, start
  *       the variable system and try to serve a page from the cache.
@@ -910,7 +916,7 @@ function drupal_anonymous_user($session 
  *     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];
@@ -960,6 +966,11 @@ function _drupal_bootstrap($phase) {
       }
       break;
 
+    case DRUPAL_BOOTSTRAP_LOCK:
+      require_once variable_get('lock_inc', './includes/lock-db.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');
Index: includes/lock-apc.inc
===================================================================
RCS file: includes/lock-apc.inc
diff -N includes/lock-apc.inc
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ includes/lock-apc.inc	27 Apr 2008 10:50:49 -0000
@@ -0,0 +1,96 @@
+<?php
+// $Id $
+
+/**
+ * @file
+ * Lock handling for concurrent requests (apc-based)..
+ */
+
+/**
+ * Initialize the locking system.
+ */
+function lock_init() {
+  global $locks, $lock_id, $instance_id;
+  $locks = array();
+  // assign this request an unique id
+  $lock_id = md5(uniqid());
+  $instance_id = md5(conf_path());
+  register_shutdown_function('lock_release_all');
+}
+
+/**
+ * Acquire a lock, do not block if it fails.
+ *
+ * @param $name
+ *   The name of the lock.
+ * @return TRUE if the lock was acquired, FALSE if it failed.
+ */
+function lock_acquire($name) {
+  global $locks, $lock_id, $instance_id;
+  if (isset($locks[$name])) {
+    return TRUE;
+  }
+  else {
+    // try to acquire the lock
+    if (apc_add('lock:' . $instance_id . ':' . $name, $lock_id)) {
+      $locks[$name] = TRUE;
+      return TRUE;
+    }
+    else {
+      return FALSE;
+    }
+  }
+}
+
+/**
+ * Wait for a lock to be released.
+ *
+ * @param $name
+ *   The name of the lock.
+ * @param $timeout
+ *   The timeout to wait for the lock.
+ * @return TRUE if the lock was acquired, FALSE if it failed.
+ */
+function lock_wait($name, $timeout = 20) {
+  global $locks, $lock_id, $instance_id;
+  if (isset($locks[$name])) {
+    return TRUE;
+  }
+  else {
+    $wait = 0;
+    while (apc_fetch('lock:' . $instance_id . ':' . $name)) {
+      sleep(1);
+      if (++$wait == $timeout) {
+        return FALSE;
+      }
+    }
+    return TRUE;
+  }
+}
+
+/**
+ * Release a lock previously acquired by lock_acquire().
+ *
+ * @param $name
+ *   The name of the lock.
+ */
+function lock_release($name) {
+  global $locks, $lock_id, $instance_id;
+  if ($lock_id && isset($locks[$name])) {
+    apc_delete('lock:' . $instance_id . ':' . $name);
+    unset($locks[$name]);
+  }
+}
+
+/**
+ * Release all previously acquired locks.
+ */
+function lock_release_all() {
+  global $locks, $lock_id, $instance_id;
+  if ($lock_id && count($locks)) {
+    foreach($locks as $lock_name => $v) {
+      apc_delete('lock:' . $instance_id . ':' . $lock_name);
+    }
+    $locks = array();
+  }
+}
Index: includes/lock-db.inc
===================================================================
RCS file: includes/lock-db.inc
diff -N includes/lock-db.inc
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ includes/lock-db.inc	27 Apr 2008 10:50:49 -0000
@@ -0,0 +1,93 @@
+<?php
+// $Id $
+
+/**
+ * @file
+ * Lock handling for concurrent requests (database-based)..
+ */
+
+/**
+ * Initialize the locking system.
+ */
+function lock_init() {
+  global $locks, $lock_id;
+  $locks = array();
+  // assign this request an unique id
+  $lock_id = md5(uniqid());
+  register_shutdown_function('lock_release_all');
+}
+
+/**
+ * Acquire a lock, do not block if it fails.
+ *
+ * @param $name
+ *   The name of the lock.
+ * @return TRUE if the lock was acquired, FALSE if it failed.
+ */
+function lock_acquire($name) {
+  global $locks, $lock_id;
+  if (isset($locks[$name])) {
+    return TRUE;
+  }
+  else {
+    // try to acquire the lock
+    if (@db_query("INSERT INTO {variable} (name, value) VALUES ('%s', '%s')", 'lock:' . $name, $lock_id)) {
+      $locks[$name] = TRUE;
+      return TRUE;
+    }
+    else {
+      return FALSE;
+    }
+  }
+}
+
+/**
+ * Wait for a lock to be released.
+ *
+ * @param $name
+ *   The name of the lock.
+ * @param $timeout
+ *   The timeout to wait for the lock.
+ * @return TRUE if the lock was acquired, FALSE if it failed.
+ */
+function lock_wait($name, $timeout = 20) {
+  global $locks, $lock_id;
+  if (isset($locks[$name])) {
+    return TRUE;
+  }
+  else {
+    $wait = 0;
+    while (db_result(db_query("SELECT name FROM {variable} WHERE name = '%s'", 'lock:' . $name))) {
+      sleep(1);
+      if (++$wait == $timeout) {
+        return FALSE;
+      }
+    }
+    return TRUE;
+  }
+}
+
+/**
+ * Release a lock previously acquired by lock_acquire().
+ *
+ * @param $name
+ *   The name of the lock.
+ */
+function lock_release($name) {
+  global $locks, $lock_id;
+  if ($lock_id && isset($locks[$name])) {
+    db_query("DELETE FROM {variable} WHERE name = '%s'", 'lock:' . $name);
+    unset($locks[$name]);
+  }
+}
+
+/**
+ * Release all previously acquired locks.
+ */
+function lock_release_all() {
+  global $locks, $lock_id;
+  if ($lock_id && count($locks)) {
+    db_query("DELETE FROM {variable} WHERE name LIKE 'lock:%%' AND value = '%s'", $lock_id);
+    $locks = array();
+  }
+}
Index: includes/menu.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/menu.inc,v
retrieving revision 1.269
diff -u -3 -p -r1.269 menu.inc
--- includes/menu.inc	23 Apr 2008 20:01:47 -0000	1.269
+++ includes/menu.inc	27 Apr 2008 10:50:51 -0000
@@ -1636,6 +1636,11 @@ function menu_cache_clear_all() {
  * is different and leaves stale data in the menu tables.
  */
 function menu_rebuild() {
+  if (!lock_acquire('menu_rebuild')) {
+    // Wait for the other request to do our work
+    lock_wait('menu_rebuild');
+    return;
+  }
   variable_del('menu_rebuild_needed');
   menu_cache_clear_all();
   $menu = menu_router_build(TRUE);
@@ -1645,6 +1650,7 @@ function menu_rebuild() {
   if (defined('MAINTENANCE_MODE')) {
     variable_set('menu_rebuild_needed', TRUE);
   }
+  lock_release('menu_rebuild');
 }
 
 /**
Index: modules/locale/locale.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/locale/locale.module,v
retrieving revision 1.217
diff -u -3 -p -r1.217 locale.module
--- modules/locale/locale.module	23 Apr 2008 20:01:52 -0000	1.217
+++ modules/locale/locale.module	27 Apr 2008 10:50:53 -0000
@@ -360,14 +360,17 @@ function locale($string = NULL, $langcod
         $locale_t[$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]);
       }
     }
   }