diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index fd0ae33..0f4d6e8 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -226,6 +226,180 @@ define('REGISTRY_WRITE_LOOKUP_CACHE', 2);
 define('DRUPAL_PHP_FUNCTION_PATTERN', '[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*');
 
 /**
+ * Provides a caching wrapper to be used in place of large array structures.
+ *
+ * This class should be extended by systems that need to cache large amounts
+ * of data and have it represented as an array to calling functions. These
+ * arrays can become very large, so ArrayAccess is used to allow different
+ * strategies to be used for caching internally (lazy loading, building caches
+ * over time etc.). This can dramatically reduce the amount of data that needs
+ * to be loaded from cache backends on each request, and memory usage from
+ * static caches of that same data.
+ *
+ * Note that array_* functions do not work with ArrayAccess. Systems using
+ * DrupalCacheArray should use this only internally. If providing API functions
+ * that return the full array, this can be cached separately or returned
+ * directly. However since DrupalCacheArray holds partial content by design, it
+ * should be a normal PHP array or otherwise contain the full structure.
+ *
+ * By default, the class accounts for caches where calling functions might
+ * request keys in the array that won't exist even after a cache rebuild. This
+ * prevents situations where a cache rebuild would be triggered over and over
+ * due to a 'missing' item. These cases are stored internally as a value of
+ * NULL. This means that the offsetGet() and offsetExists() methods
+ * must be overridden if caching an array where the top level values can
+ * legitimately be NULL, and where $object->offsetExists() needs to correctly
+ * return (equivalent to array_key_exists() vs. isset()). This should not
+ * be necessary in the majority of cases.
+ *
+ * Classes extending this class must override at least the
+ * resolveCacheMiss() method to have a working implementation.
+ *
+ * offsetSet() is not overridden by this class by default. In practice this
+ * means that assigning an offset via arrayAccess will only apply while the
+ * object is in scope and will not be written back to the persistent cache.
+ * This follows a similar pattern to static vs. persistent caching in
+ * procedural code. Extending classes may wish to alter this behaviour, for
+ * example by overriding offsetSet() and adding an automatic call to persist().
+ *
+ * @see SchemaCache
+ */
+abstract class DrupalCacheArray implements ArrayAccess {
+
+  /**
+   * A cid to pass to cache_set() and cache_get().
+   */
+  private $cid;
+
+  /**
+   * A bin to pass to cache_set() and cache_get().
+   */
+  private $bin;
+
+  /**
+   * An array of keys to add to the cache at the end of the request.
+   */
+  protected $keysToPersist = array();
+
+  /**
+   * Storage for the data itself.
+   */
+  protected $storage = array();
+
+  /**
+   * Constructor.
+   *
+   * @param $cid
+   *   The cid for the array being cached.
+   * @param $bin
+   *   The bin to cache the array.
+   */
+  public function __construct($cid, $bin) {
+    $this->cid = $cid;
+    $this->bin = $bin;
+
+    if ($cached = cache_get($this->cid, $this->bin)) {
+     $this->storage = $cached->data;
+    }
+  }
+
+  public function offsetExists($offset) {
+    return $this->offsetGet($offset) !== NULL;
+  }
+
+  public function offsetGet($offset) {
+    if (isset($this->storage[$offset]) || array_key_exists($offset, $this->storage)) {
+      return $this->storage[$offset];
+    }
+    else {
+      return $this->resolveCacheMiss($offset);
+    }
+  }
+
+  public function offsetSet($offset, $value) {
+    $this->storage[$offset] = $value;
+  }
+
+  public function offsetUnset($offset) {
+    unset($this->storage[$offset]);
+  }
+
+  /**
+   * Flags an offset value to be written to the persistent cache.
+   *
+   * If a value is assigned to a cache object with offsetSet(), by default it
+   * will not be written to the persistent cache unless it is flagged with this
+   * method. This allows items to be cached for the duration of a request,
+   * without necessarily writing back to the persistent cache at the end.
+   *
+   * @param $offset
+   *   The array offset that was request.
+   * @param $persist
+   *   Optional boolean to specify whether the offset should be persisted or
+   *   not, defaults to TRUE. When called with $persist = FALSE the offset will
+   *   be unflagged so that it will not written at the end of the request.
+   */
+  protected function persist($offset, $persist = TRUE) {
+    $this->keysToPersist[$offset] = $persist;
+  }
+
+  /**
+   * Resolves a cache miss.
+   *
+   * When an offset is not found in the object, this is treated as a cache
+   * miss. This method allows classes implementing the interface to look up
+   * the actual value and allow it to be cached.
+   *
+   * @param $offset
+   *   The offset that was requested.
+   *
+   * @return
+   *   The value of the offset, or NULL if no value was found.
+   */
+  abstract protected function resolveCacheMiss($offset);
+
+  /**
+   * Immediately write a value to the persistent cache.
+   *
+   * @param $cid
+   *   The cache ID.
+   * @param $bin
+   *   The cache bin.
+   * @param $data
+   *   The data to write to the persistent cache.
+   * @param $lock
+   *   Whether to acquire a lock before writing to cache.
+   */
+  protected function set($cid, $data, $bin, $lock = TRUE) {
+    // Lock cache writes to help avoid stampedes.
+    // To implement locking for cache misses, override __construct().
+    $lock_name = $cid . ':' . $bin;
+    file_put_contents('/tmp/backtrace.txt', print_r(debug_backtrace(), 1), FILE_APPEND);
+    if (!$lock || lock_acquire($lock_name)) {
+      if ($cached = cache_get($cid, $bin)) {
+        $data = $cached->data + $data;
+      }
+      cache_set($cid, $data, $bin);
+      if ($lock) {
+        lock_release($lock_name);
+      }
+    }
+  }
+
+  public function __destruct() {
+    $data = array();
+    foreach ($this->keysToPersist as $offset => $persist) {
+      if ($persist) {
+        $data[$offset] = $this->storage[$offset];
+      }
+    }
+    if (!empty($data)) {
+      $this->set($this->cid, $data, $this->bin);
+    }
+  }
+}
+
+/**
  * Start the timer with the specified name. If you start and stop the same
  * timer multiple times, the measured intervals will be accumulated.
  *
diff --git a/includes/path.inc b/includes/path.inc
index db60537..ee14185 100644
--- a/includes/path.inc
+++ b/includes/path.inc
@@ -55,21 +55,13 @@ function drupal_lookup_path($action, $path = '', $path_language = NULL) {
     $cache = array(
       'map' => array(),
       'no_source' => array(),
-      'whitelist' => NULL,
+      'whitelist' => new PathAliasWhitelist('path_alias_whitelist', 'cache'),
       'system_paths' => array(),
       'no_aliases' => array(),
       'first_call' => TRUE,
     );
   }
 
-  // Retrieve the path alias whitelist.
-  if (!isset($cache['whitelist'])) {
-    $cache['whitelist'] = variable_get('path_alias_whitelist', NULL);
-    if (!isset($cache['whitelist'])) {
-      $cache['whitelist'] = drupal_path_alias_whitelist_rebuild();
-    }
-  }
-
   // If no language is explicitly specified we default to the current URL
   // language. If we used a language different from the one conveyed by the
   // requested URL, we might end up being unable to check if there is a path
@@ -355,6 +347,16 @@ function current_path() {
   return $_GET['q'];
 }
 
+class PathAliasWhitelist extends DrupalCacheArray {
+  function resolveCacheMiss($offset) {
+    $exists = (bool) db_query_range('SELECT 1 FROM {url_alias} WHERE source LIKE :path', 0, 1, array(':path' => $offset . '%'))->fetchField();
+    $value = $exists ? TRUE : NULL;
+    $this->storage[$offset] = $value;
+    $this->persist($offset);
+    return $value;
+  }
+}
+
 /**
  * Rebuild the path alias white list.
  *
@@ -362,27 +364,19 @@ function current_path() {
  *   An optional system path for which an alias is being inserted.
  *
  * @return
- *   An array containing a white list of path aliases.
+ *   An instance of the PathAliasWhitelist class.
  */
 function drupal_path_alias_whitelist_rebuild($source = NULL) {
   // When paths are inserted, only rebuild the whitelist if the system path
   // has a top level component which is not already in the whitelist.
   if (!empty($source)) {
-    $whitelist = variable_get('path_alias_whitelist', NULL);
+    $whitelist = new PathAliasWhitelist('path_alias_whitelist', 'cache');
     if (isset($whitelist[strtok($source, '/')])) {
       return $whitelist;
     }
   }
-  // For each alias in the database, get the top level component of the system
-  // path it corresponds to. This is the portion of the path before the first
-  // '/', if present, otherwise the whole path itself.
-  $whitelist = array();
-  $result = db_query("SELECT DISTINCT SUBSTRING_INDEX(source, '/', 1) AS path FROM {url_alias}");
-  foreach ($result as $row) {
-    $whitelist[$row->path] = TRUE;
-  }
-  variable_set('path_alias_whitelist', $whitelist);
-  return $whitelist;
+  cache_clear_all('path_alias_whitelist', 'cache');
+  return new PathAliasWhitelist('path_alias_whitelist', 'cache');
 }
 
 /**
diff --git a/modules/simpletest/drupal_web_test_case.php b/modules/simpletest/drupal_web_test_case.php
index 5c39cfc..b2a7bf1 100644
--- a/modules/simpletest/drupal_web_test_case.php
+++ b/modules/simpletest/drupal_web_test_case.php
@@ -1238,6 +1238,10 @@ class DrupalWebTestCase extends DrupalTestCase {
       ->condition('test_id', $this->testId)
       ->execute();
 
+    // Reset all statics and variables to perform tests in a clean environment.
+    $conf = array();
+    drupal_static_reset();
+
     // Clone the current connection and replace the current prefix.
     $connection_info = Database::getConnectionInfo('default');
     Database::renameConnection('default', 'simpletest_original_default');
@@ -1285,10 +1289,6 @@ class DrupalWebTestCase extends DrupalTestCase {
     ini_set('log_errors', 1);
     ini_set('error_log', $public_files_directory . '/error.log');
 
-    // Reset all statics and variables to perform tests in a clean environment.
-    $conf = array();
-    drupal_static_reset();
-
     // Set the test information for use in other parts of Drupal.
     $test_info = &$GLOBALS['drupal_test_info'];
     $test_info['test_run_id'] = $this->databasePrefix;
diff --git a/modules/simpletest/tests/theme.test b/modules/simpletest/tests/theme.test
index f1e1bd5..2529e8d 100644
--- a/modules/simpletest/tests/theme.test
+++ b/modules/simpletest/tests/theme.test
@@ -194,7 +194,7 @@ class ThemeItemListUnitTest extends DrupalWebTestCase {
 /**
  * Unit tests for theme_links().
  */
-class ThemeLinksUnitTest extends DrupalUnitTestCase {
+class ThemeLinksTest extends DrupalWebTestCase {
   public static function getInfo() {
     return array(
       'name' => 'Links',