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diff --git a/core/includes/lock.inc b/core/includes/lock.inc
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--- a/core/includes/lock.inc
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-<?php
-
-/**
- * @file
- * A database-mediated implementation of a locking mechanism.
- */
-
-/**
- * @defgroup lock Locking mechanisms
- * @{
- * Functions to coordinate long-running operations across requests.
- *
- * In most environments, multiple Drupal page requests (a.k.a. threads or
- * processes) will execute in parallel. This leads to potential conflicts or
- * race conditions when two requests execute the same code at the same time. A
- * common example of this is a rebuild like menu_rebuild() where we invoke many
- * hook implementations to get and process data from all active modules, and
- * then delete the current data in the database to insert the new afterwards.
- *
- * This is a cooperative, advisory lock system. Any long-running operation
- * that could potentially be attempted in parallel by multiple requests should
- * try to acquire a lock before proceeding. By obtaining a lock, one request
- * notifies any other requests that a specific operation is in progress which
- * must not be executed in parallel.
- *
- * To use this API, pick a unique name for the lock. A sensible choice is the
- * name of the function performing the operation. A very simple example use of
- * this API:
- * @code
- * function mymodule_long_operation() {
- *   if (lock_acquire('mymodule_long_operation')) {
- *     // Do the long operation here.
- *     // ...
- *     lock_release('mymodule_long_operation');
- *   }
- * }
- * @endcode
- *
- * If a function acquires a lock it should always release it when the
- * operation is complete by calling lock_release(), as in the example.
- *
- * A function that has acquired a lock may attempt to renew a lock (extend the
- * duration of the lock) by calling lock_acquire() again during the operation.
- * Failure to renew a lock is indicative that another request has acquired
- * the lock, and that the current operation may need to be aborted.
- *
- * If a function fails to acquire a lock it may either immediately return, or
- * it may call lock_wait() if the rest of the current page request requires
- * that the operation in question be complete. After lock_wait() returns,
- * the function may again attempt to acquire the 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 automatically break (delete) a lock
- * whose duration has exceeded the timeout specified when it was acquired.
- *
- * Alternative implementations of this API (such as APC) may be substituted
- * by setting the 'lock_inc' variable to an alternate include filepath. Since
- * this is an API intended to support alternative implementations, code using
- * this API should never rely upon specific implementation details (for example
- * no code should look for or directly modify a lock in the {semaphore} table).
- */
-
-/**
- * Initialize the locking system.
- */
-function lock_initialize() {
-  global $locks;
-
-  $locks = array();
-}
-
-/**
- * Helper function to get this request's unique id.
- */
-function _lock_id() {
-  // Do not use drupal_static(). This identifier refers to the current
-  // client request, and must not be changed under any circumstances
-  // else the shutdown handler may fail to release our locks.
-  static $lock_id;
-
-  if (!isset($lock_id)) {
-    // Assign a unique id.
-    $lock_id = uniqid(mt_rand(), TRUE);
-    // We only register a shutdown function if a lock is used.
-    drupal_register_shutdown_function('lock_release_all', $lock_id);
-  }
-  return $lock_id;
-}
-
-/**
- * Acquire (or renew) a lock, but do not block if it fails.
- *
- * @param $name
- *   The name of the lock.
- * @param $timeout
- *   A number of seconds (float) before the lock expires (minimum of 0.001).
- *
- * @return
- *   TRUE if the lock was acquired, FALSE if it failed.
- */
-function lock_acquire($name, $timeout = 30.0) {
-  global $locks;
-
-  // Insure that the timeout is at least 1 ms.
-  $timeout = max($timeout, 0.001);
-  $expire = microtime(TRUE) + $timeout;
-  if (isset($locks[$name])) {
-    // Try to extend the expiration of a lock we already acquired.
-    $success = (bool) db_update('semaphore')
-      ->fields(array('expire' => $expire))
-      ->condition('name', $name)
-      ->condition('value', _lock_id())
-      ->execute();
-    if (!$success) {
-      // The lock was broken.
-      unset($locks[$name]);
-    }
-    return $success;
-  }
-  else {
-    // Optimistically try to acquire the lock, then retry once if it fails.
-    // The first time through the loop cannot be a retry.
-    $retry = FALSE;
-    // We always want to do this code at least once.
-    do {
-      try {
-        db_insert('semaphore')
-          ->fields(array(
-            'name' => $name,
-            'value' => _lock_id(),
-            'expire' => $expire,
-          ))
-          ->execute();
-        // We track all acquired locks in the global variable.
-        $locks[$name] = TRUE;
-        // We never need to try again.
-        $retry = FALSE;
-      }
-      catch (PDOException $e) {
-        // Suppress the error. If this is our first pass through the loop,
-        // then $retry is FALSE. In this case, the insert must have failed
-        // meaning some other request acquired the lock but did not release it.
-        // We decide whether to retry by checking lock_may_be_available()
-        // Since this will break the lock in case it is expired.
-        $retry = $retry ? FALSE : lock_may_be_available($name);
-      }
-      // We only retry in case the first attempt failed, but we then broke
-      // an expired lock.
-    } while ($retry);
-  }
-  return isset($locks[$name]);
-}
-
-/**
- * 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;
-  }
-  $expire = (float) $lock['expire'];
-  $now = microtime(TRUE);
-  if ($now > $expire) {
-    // We check two conditions to prevent a race condition where another
-    // request acquired the lock and set a new expire time. We add a small
-    // number to $expire to avoid errors with float to string conversion.
-    return (bool) db_delete('semaphore')
-      ->condition('name', $name)
-      ->condition('value', $lock['value'])
-      ->condition('expire', 0.0001 + $expire, '<=')
-      ->execute();
-  }
-  return FALSE;
-}
-
-/**
- * Wait for a lock to be available.
- *
- * This function may be called in a request that fails to acquire a desired
- * lock. This will block further execution until the lock is available or the
- * specified delay in seconds is reached. This should not be used with locks
- * that are acquired very frequently, since the lock is likely to be acquired
- * again by a different request while waiting.
- *
- * @param $name
- *   The name of the lock.
- * @param $delay
- *   The maximum number of seconds to wait, as an integer.
- *
- * @return
- *   TRUE if the lock holds, FALSE if it is available.
- */
-function lock_wait($name, $delay = 30) {
-  // Pause the process for short periods between calling
-  // lock_may_be_available(). This prevents hitting the database with constant
-  // database queries while waiting, which could lead to performance issues.
-  // However, if the wait period is too long, there is the potential for a
-  // large number of processes to be blocked waiting for a lock, especially
-  // if the item being rebuilt is commonly requested. To address both of these
-  // concerns, begin waiting for 25ms, then add 25ms to the wait period each
-  // time until it reaches 500ms. After this point polling will continue every
-  // 500ms until $delay is reached.
-
-  // $delay is passed in seconds, but we will be using usleep(), which takes
-  // microseconds as a parameter. Multiply it by 1 million so that all
-  // further numbers are equivalent.
-  $delay = (int) $delay * 1000000;
-
-  // Begin sleeping at 25ms.
-  $sleep = 25000;
-  while ($delay > 0) {
-    // This function should only be called by a request that failed to get a
-    // lock, so we sleep first to give the parallel request a chance to finish
-    // and release the lock.
-    usleep($sleep);
-    // After each sleep, increase the value of $sleep until it reaches
-    // 500ms, to reduce the potential for a lock stampede.
-    $delay = $delay - $sleep;
-    $sleep = min(500000, $sleep + 25000, $delay);
-    if (lock_may_be_available($name)) {
-      // No longer need to wait.
-      return FALSE;
-    }
-  }
-  // The caller must still wait longer to get the lock.
-  return TRUE;
-}
-
-/**
- * Release a lock previously acquired by lock_acquire().
- *
- * This will release the named lock if it is still held by the current request.
- *
- * @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 lock".
- */