? includes/handlers.inc
? modules/system/system.path_lazy.inc
? modules/system/system.path_precache.inc
Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.278
diff -u -p -r1.278 bootstrap.inc
--- includes/bootstrap.inc	30 Apr 2009 16:15:44 -0000	1.278
+++ includes/bootstrap.inc	4 May 2009 02:07:59 -0000
@@ -1407,6 +1407,8 @@ function _drupal_bootstrap($phase) {
       }
 
       // Prepare for non-cached page workflow.
+      require_once DRUPAL_ROOT . '/' . variable_get('lock_inc', 'includes/lock.inc');
+      lock_init();
 
       // If the session has not already been started and output buffering is
       // not enabled, the HTTP headers must be sent now, including the session
Index: includes/lock.inc
===================================================================
RCS file: includes/lock.inc
diff -N includes/lock.inc
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ includes/lock.inc	4 May 2009 02:08:00 -0000
@@ -0,0 +1,201 @@
+<?php
+// $Id$
+
+/**
+ * @file
+ * A database-mediated implementation of a locking mechanism.
+ */
+
+/**
+ * @defgroup locks Lock acquire and release functions
+ * @{
+ * Functions to coordinate long-running operations across requests.
+ *
+ * This is a cooperative, advisory lock system. Any long-running
+ * operation which could potentially be attempted in parallel by multiple
+ * requests should try to acquire a lock before proceeding.  For example,
+ * functions doing a large number of database inserts after building new
+ * data based on a drupal variable's state.  If a function fails to acquire
+ * a lock it should either immediately return, or call lock_wait() if the
+ * rest of the page request requires that the operation in question be
+ * complete.  After lock_wait() returns, the function may again attempt to
+ * acquire a lock, or may simply allow the page request to proceed on the
+ * assumption that a parallel request completed the operation.
+ *
+ * lock_acquire() and lock_wait() will break stale locks, so that they do
+ * not persist.
+ *
+ * A function that has acquired a lock may attempt to renew the lock one
+ * or more times during the operation in order to extend the lifetime of the
+ * lock. Failure to renew a lock is indicative that another request has
+ * acquired the lock, and that the current operation may need to be aborted.
+ *
+ * Alternative implementations of this API (such as APC) my be substituted
+ * by setting the 'lock_inc' variable to an alternate include filepath.
+ */
+
+/**
+ * Initialize the locking system.
+ */
+function lock_init() {
+  global $locks;
+
+  $locks = array();
+}
+
+/**
+ * Helper function to get this request's unique id.
+ */
+function _lock_id() {
+  $lock_id = &drupal_static(__FUNCTION__);
+
+  if (!isset($lock_id)) {
+    // Assign a unique id.
+    $lock_id = uniqid(mt_rand(), TRUE);
+    // We only register a shutdown function if a lock is used.
+    register_shutdown_function('lock_release_all', $lock_id);
+  }
+  return $lock_id;
+}
+
+/**
+ * Acquire a lock, but do not block if it fails.
+ *
+ * @param $name
+ *   The name of the lock.
+ * @param $timeout
+ *   A number of seconds (float) before the lock expires.
+ * @return TRUE if the lock was acquired, FALSE if it failed.
+ */
+function lock_acquire($name, $timeout = 20.0) {
+  global $locks;
+
+  if (isset($locks[$name])) {
+    // We acquired a lock before, so check whether our lock is intact.
+    if (!db_query("SELECT 1 FROM {semaphore} WHERE name = :name AND value = :value", array(':name' => $name, ':value' => _lock_id()))->fetchField()) {
+      // The lock was broken.
+      unset($locks[$name]);
+    }
+  }
+  elseif (lock_may_be_available($name)) {
+    // Try to acquire the lock.
+    $expire = microtime(TRUE) + $timeout;
+    try {
+      db_insert('semaphore')
+        ->fields(array(
+          'name' => $name,
+          'value' => _lock_id(),
+          'expire' => $expire,
+        ))
+        ->execute();
+      $locks[$name] = TRUE;
+    }
+    catch (PDOException $e) {
+      // Suppress the error.
+    }
+  }
+  return isset($locks[$name]);
+}
+
+/**
+ * Try to renew (extend) a lock previously acquired.
+ *
+ * @param $name
+ *   The name of the lock.
+ * @param $timeout
+ *   A number of seconds (float) before the lock expires.
+ * @return TRUE if the lock was renewed, FALSE if it failed.
+ */
+function lock_renew($name, $timeout = 20.0) {
+  global $locks;
+
+  if (isset($locks[$name])) {
+    $expire = microtime(TRUE) + $timeout;
+    return (bool)db_update('semaphore')
+      ->fields(array('expire' => $expire))
+      ->condition('name', $name)
+      ->condition('value', _lock_id())
+      ->execute();
+  }
+  return FALSE;
+}
+
+/**
+ * Check if lock acquired by a different process may be available.
+ *
+ * If an existing lock has expired, it is removed.
+ *
+ * @param $name
+ *   The name of the lock.
+ *
+ * @return TRUE if there is no lock or it was removed, FALSE otherwise.
+ */
+function lock_may_be_available($name) {
+  $lock = db_query("SELECT expire, value FROM {semaphore} WHERE name = :name", array(':name' => $name))->fetchAssoc();
+  if (!$lock) {
+    return TRUE;
+  }
+  $now = microtime(TRUE);
+  if ($now > $lock['expire']) {
+    return (bool)db_delete('semaphore')
+      ->condition('name', $name)
+      ->condition('value', $lock['value'])
+      ->condition('expire', $lock['expire'])
+      ->execute();
+  }
+  return FALSE;
+}
+
+/**
+ * Wait for a lock to be released.
+ *
+ * @param $name
+ *   The name of the lock.
+ * @param $delay
+ *   The maximum number of seconds to wait.
+ * @return TRUE if the lock holds, FALSE if it is available.
+ */
+function lock_wait($name, $delay = 30) {
+  while ($delay--) {
+    sleep(1);
+    if (lock_may_be_available($name)) {
+      return FALSE;
+    }
+  }
+  return TRUE;
+}
+
+/**
+ * Release a lock previously acquired by lock_acquire().
+ *
+ * @param $name
+ *   The name of the lock.
+ */
+function lock_release($name) {
+  global $locks;
+
+  unset($locks[$name]);
+  db_delete('semaphore')
+    ->condition('name', $name)
+    ->condition('value', _lock_id())
+    ->execute();
+}
+
+/**
+ * Release all previously acquired locks.
+ */
+function lock_release_all($lock_id = NULL) {
+  global $locks;
+
+  $locks = array();
+  if (empty($lock_id)) {
+    $lock_id = _lock_id();
+  }
+  db_delete('semaphore')
+    ->condition('value', $lock_id)
+    ->execute();
+}
+
+/**
+ * @} End of "defgroup locks".
+ */
Index: includes/menu.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/menu.inc,v
retrieving revision 1.322
diff -u -p -r1.322 menu.inc
--- includes/menu.inc	25 Apr 2009 15:19:12 -0000	1.322
+++ includes/menu.inc	4 May 2009 02:08:00 -0000
@@ -1818,16 +1818,28 @@ function menu_cache_clear_all() {
  * is different and leaves stale data in the menu tables.
  */
 function menu_rebuild() {
-  variable_del('menu_rebuild_needed');
+  if (!lock_acquire('menu_rebuild')) {
+    // Wait for another request that is already doing this work.
+    lock_wait('menu_rebuild');
+    return FALSE;
+  }
+
   list($menu, $masks) = menu_router_build();
   _menu_router_save($menu, $masks);
-  _menu_navigation_links_rebuild($menu);
-  menu_cache_clear_all();
-  // Clear the page and block caches.
-  _menu_clear_page_cache();
+  if (lock_renew('menu_rebuild')) {
+    _menu_navigation_links_rebuild($menu);
+    // Clear the menu, page and block caches.
+    menu_cache_clear_all();
+    _menu_clear_page_cache();
+  }
   if (defined('MAINTENANCE_MODE')) {
     variable_set('menu_rebuild_needed', TRUE);
   }
+  else {
+    variable_del('menu_rebuild_needed');
+  }
+  lock_release('menu_rebuild');
+  return TRUE;
 }
 
 /**
Index: modules/locale/locale.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/locale/locale.module,v
retrieving revision 1.238
diff -u -p -r1.238 locale.module
--- modules/locale/locale.module	31 Mar 2009 02:02:21 -0000	1.238
+++ modules/locale/locale.module	4 May 2009 02:08:00 -0000
@@ -372,7 +372,7 @@ function locale($string = NULL, $langcod
       if ($cache = cache_get('locale:' . $langcode, 'cache')) {
         $locale_t[$langcode] = $cache->data;
       }
-      else {
+      elseif (lock_acquire('locale_cache_' . $langcode)) {
         // Refresh database stored cache of translations for given language.
         // We only store short strings used in current version, to improve
         // performance and consume less memory.
@@ -381,6 +381,7 @@ function locale($string = NULL, $langcod
           $locale_t[$langcode][$data->source] = (empty($data->translation) ? TRUE : $data->translation);
         }
         cache_set('locale:' . $langcode, $locale_t[$langcode]);
+        lock_release('locale_cache_' . $langcode);
       }
     }
   }