Index: includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.1279
diff -u -p -r1.1279 common.inc
--- includes/common.inc	21 Dec 2010 19:16:31 -0000	1.1279
+++ includes/common.inc	31 Dec 2010 17:08:17 -0000
@@ -2326,15 +2326,15 @@ function l($text, $path, array $options 
     // rendering.
     if (variable_get('theme_link', TRUE)) {
       drupal_theme_initialize();
-      $registry = theme_get_registry();
+      $hook_info = theme_get_hook('link');
       // We don't want to duplicate functionality that's in theme(), so any
       // hint of a module or theme doing anything at all special with the 'link'
       // theme hook should simply result in theme() being called. This includes
       // the overriding of theme_link() with an alternate function or template,
       // the presence of preprocess or process functions, or the presence of
       // include files.
-      $use_theme = !isset($registry['link']['function']) || ($registry['link']['function'] != 'theme_link');
-      $use_theme = $use_theme || !empty($registry['link']['preprocess functions']) || !empty($registry['link']['process functions']) || !empty($registry['link']['includes']);
+      $use_theme = !$hook_info['function'] || ($hook_info['function'] != 'theme_link');
+      $use_theme = $use_theme || !empty($hook_info['preprocess functions']) || !empty($hook_info['process functions']) || !empty($hook_info['includes']);
     }
     else {
       $use_theme = FALSE;
Index: includes/theme.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/theme.inc,v
retrieving revision 1.626
diff -u -p -r1.626 theme.inc
--- includes/theme.inc	11 Dec 2010 02:06:25 -0000	1.626
+++ includes/theme.inc	31 Dec 2010 17:08:20 -0000
@@ -736,7 +736,7 @@ function list_themes($refresh = FALSE) {
  *   An HTML string representing the themed output.
  */
 function theme($hook, $variables = array()) {
-  static $hooks = NULL;
+  static $initialized;
 
   // If called before all modules are loaded, we do not necessarily have a full
   // theme registry to work with, and therefore cannot process the theme
@@ -744,17 +744,16 @@ function theme($hook, $variables = array
   if (!module_load_all(NULL) && !defined('MAINTENANCE_MODE')) {
     throw new Exception(t('theme() may not be called until all modules are loaded.'));
   }
-
-  if (!isset($hooks)) {
+  if (!isset($initialized)) {
     drupal_theme_initialize();
-    $hooks = theme_get_registry();
+    $initialized = TRUE;
   }
 
   // If an array of hook candidates were passed, use the first one that has an
   // implementation.
   if (is_array($hook)) {
     foreach ($hook as $candidate) {
-      if (isset($hooks[$candidate])) {
+      if (theme_get_hook($candidate)) {
         break;
       }
     }
@@ -763,16 +762,16 @@ function theme($hook, $variables = array
 
   // If there's no implementation, check for more generic fallbacks. If there's
   // still no implementation, log an error and return an empty string.
-  if (!isset($hooks[$hook])) {
+  if (!theme_get_hook($hook)) {
     // Iteratively strip everything after the last '__' delimiter, until an
     // implementation is found.
     while ($pos = strrpos($hook, '__')) {
       $hook = substr($hook, 0, $pos);
-      if (isset($hooks[$hook])) {
+      if (theme_get_hook($hook)) {
         break;
       }
     }
-    if (!isset($hooks[$hook])) {
+    if (!theme_get_hook($hook)) {
       // Only log a message when not trying theme suggestions ($hook being an
       // array).
       if (!isset($candidate)) {
@@ -782,7 +781,7 @@ function theme($hook, $variables = array
     }
   }
 
-  $info = $hooks[$hook];
+  $info = theme_get_hook($hook);
   global $theme_path;
   $temp = $theme_path;
   // point path_to_theme() to the currently used theme path:
@@ -827,7 +826,7 @@ function theme($hook, $variables = array
   // be used unless overridden by a variable processor function.
   if (isset($info['base hook'])) {
     $base_hook = $info['base hook'];
-    $base_hook_info = $hooks[$base_hook];
+    $base_hook_info = theme_get_hook($base_hook);
     if (isset($base_hook_info['preprocess functions']) || isset($base_hook_info['process functions'])) {
       $variables['theme_hook_suggestion'] = $hook;
       $hook = $base_hook;
@@ -930,6 +929,44 @@ function theme($hook, $variables = array
 }
 
 /**
+ * Find the theme definition for a hook.
+ *
+ * This function maintains a cached subset of the theme registry which is built
+ * during calls to theme. To avoid loading the entire theme registry on every
+ * request for hooks which may not be called during normal site usage.
+ *
+ * @param $hook
+ *   The theme hook being requested.
+ * @return
+ *   The registry entry for the hook, or FALSE if none was found.
+ */
+function theme_get_hook($hook) {
+  global $theme;
+  static $hooks = array();
+  if (empty($hooks)) {
+    if ($cached = cache_get("theme_registry:hooks:$theme")) {
+      $hooks = $cached->data;
+    }
+  }
+  if (isset($hooks[$hook])) {
+    return $hooks[$hook];
+  }
+  else {
+    $registry = theme_get_registry();
+    if (isset($registry[$hook])) {
+      $hooks[$hook] = $registry[$hook];
+      cache_set("theme_registry:hooks:$theme", $hooks);
+      return $hooks[$hook];
+    }
+    else {
+      $hooks[$hook] = FALSE;
+      cache_set("theme_registry:hooks:$theme", $hooks);
+    }
+  }
+  return FALSE;
+}
+
+/**
  * Return the path to the current themed element.
  *
  * It can point to the active theme or the module handling a themed implementation.
Index: modules/contextual/contextual.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/contextual/contextual.module,v
retrieving revision 1.9
diff -u -p -r1.9 contextual.module
--- modules/contextual/contextual.module	31 Oct 2010 03:56:46 -0000	1.9
+++ modules/contextual/contextual.module	31 Dec 2010 17:08:20 -0000
@@ -83,24 +83,19 @@ function contextual_element_info() {
  * @see contextual_pre_render_links()
  */
 function contextual_preprocess(&$variables, $hook) {
-  static $hooks;
-
   // Nothing to do here if the user is not permitted to access contextual links.
   if (!user_access('access contextual links')) {
     return;
   }
-
-  if (!isset($hooks)) {
-    $hooks = theme_get_registry();
-  }
+  $hook_info = theme_get_hook($hook);
 
   // Determine the primary theme function argument.
-  if (!empty($hooks[$hook]['variables'])) {
-    $keys = array_keys($hooks[$hook]['variables']);
+  if (!empty($hook_info['variables'])) {
+    $keys = array_keys($hook_info['variables']);
     $key = $keys[0];
   }
-  elseif (!empty($hooks[$hook]['render element'])) {
-    $key = $hooks[$hook]['render element'];
+  elseif (!empty($hook_info['render element'])) {
+    $key = $hook_info['render element'];
   }
   if (!empty($key) && isset($variables[$key])) {
     $element = $variables[$key];