Index: modules/system/system.api.php
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.api.php,v
retrieving revision 1.65
diff -u -r1.65 system.api.php
--- modules/system/system.api.php	26 Aug 2009 03:09:12 -0000	1.65
+++ modules/system/system.api.php	26 Aug 2009 07:48:53 -0000
@@ -365,21 +365,19 @@
  * certain library also depend on the API of a certain library version.
  *
  * @param $libraries
- *   The JavaScript/CSS libraries provided by $module. Keyed by internal library
- *   name and passed by reference.
- * @param $module
- *   The name of the module that registered the libraries.
+ *   The registered JavaScript/CSS libraries. An array of libraries, keyed by
+ *   the name of the module that registers the libraries. Passed by reference.
  *
  * @see hook_library()
  */
-function hook_library_alter(&$libraries, $module) {
+function hook_library_alter(&$libraries) {
   // Update Farbtastic to version 2.0.
-  if ($module == 'system' && isset($libraries['farbtastic'])) {
+  if (isset($libraries['system']['farbtastic'])) {
     // Verify existing version is older than the one we are updating to.
-    if (version_compare($libraries['farbtastic']['version'], '2.0', '<')) {
+    if (version_compare($libraries['system']['farbtastic']['version'], '2.0', '<')) {
       // Update the existing Farbtastic to version 2.0.
-      $libraries['farbtastic']['version'] = '2.0';
-      $libraries['farbtastic']['js'] = array(
+      $libraries['system']['farbtastic']['version'] = '2.0';
+      $libraries['system']['farbtastic']['js'] = array(
         drupal_get_path('module', 'farbtastic_update') . '/farbtastic-2.0.js' => array(),
       );
     }
Index: modules/simpletest/tests/common_test.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/simpletest/tests/common_test.module,v
retrieving revision 1.2
diff -u -r1.2 common_test.module
--- modules/simpletest/tests/common_test.module	4 Jul 2009 18:26:42 -0000	1.2
+++ modules/simpletest/tests/common_test.module	26 Aug 2009 07:48:53 -0000
@@ -27,12 +27,12 @@
 /**
  * Implementation of hook_library_alter().
  */
-function common_test_library_alter(&$libraries, $module) {
-  if ($module == 'system' && isset($libraries['farbtastic'])) {
+function common_test_library_alter(&$libraries) {
+  if (isset($libraries['system']['farbtastic'])) {
     // Change the title of Farbtastic to "Farbtastic: Altered Library".
-    $libraries['farbtastic']['title'] = 'Farbtastic: Altered Library';
+    $libraries['system']['farbtastic']['title'] = 'Farbtastic: Altered Library';
     // Make Farbtastic depend on jQuery Form to test library dependencies.
-    $libraries['farbtastic']['dependencies'][] = array('system', 'form');
+    $libraries['system']['farbtastic']['dependencies'][] = array('system', 'form');
   }
 }
 
Index: includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.975
diff -u -r1.975 common.inc
--- includes/common.inc	25 Aug 2009 21:53:47 -0000	1.975
+++ includes/common.inc	26 Aug 2009 07:48:53 -0000
@@ -3234,41 +3234,52 @@
  *   without conflicts in case the libraries are loaded on certain pages only.
  *
  * @param $module
- *   The name of a module that registered a library.
+ *   (optional) The name of a module that registered a library.
  * @param $library
- *   The name of a registered library.
+ *   (optional) The name of a registered library.
  * @return
- *   The definition of the requested library, if existent, or FALSE.
+ *   The definition of the requested library, if existent, or FALSE. If no
+ *   library is requested, will return the full registry.
  *
  * @see drupal_add_library()
  * @see hook_library()
  * @see hook_library_alter()
- *
- * @todo The purpose of drupal_get_*() is completely different to other page
- *   requisite API functions; find and use a different name.
  */
-function drupal_get_library($module, $name) {
+function drupal_get_library($module = NULL, $name = NULL) {
   $libraries = &drupal_static(__FUNCTION__, array());
 
-  if (!array_key_exists($module, $libraries)) {
-    // Retrieve all libraries associated with the module.
-    $module_libraries = module_invoke($module, 'library');
-
-    // Allow modules to alter the module's registered libraries.
-    if (!empty($module_libraries)) {
-      drupal_alter('library', $module_libraries, $module);
-    }
-    $libraries[$module] = $module_libraries;
-  }
-  if (!empty($libraries[$module][$name]) && is_array($libraries[$module][$name])) {
-    // Add default elements to allow for easier processing.
-    $libraries[$module][$name] += array('dependencies' => array(), 'js' => array(), 'css' => array());
+  if (empty($libraries)) {
+    if ($cache = cache_get('drupal_get_library')) {
+      $libraries = $cache->data;
+    }
+    else {
+      // Retrieve all libraries associated with each module, namespaced by the
+      // module name to avoid version compatibility issues.
+      foreach (module_implements('library') as $modulelibrary) {
+        $libraries[$modulelibrary] = module_invoke($modulelibrary, 'library');
+
+        // Add default elements to allow for easier processing.
+        foreach ($libraries[$modulelibrary] as $libraryname => $library) {
+          $libraries[$modulelibrary][$libraryname] += array(
+            'dependencies' => array(),
+            'js' => array(),
+            'css' => array(),
+          );
+        }
+      }
+
+      // Allow modules to alter the registered libraries and save in the cache.
+      drupal_alter('library', $libraries);
+      cache_set('drupal_get_library', $libraries);
+    }
+  }
+
+  if (isset($module) && isset($name)) {
+    return isset($libraries[$module][$name]) ? $libraries[$module][$name] : FALSE;
   }
   else {
-    $libraries[$module][$name] = FALSE;
+    return $libraries;
   }
-
-  return $libraries[$module][$name];
 }
 
 /**