MDL-41019 improve language caching

Includes:
* no more hacky reloads, everything is written only once and kept until cache reset
* lang menu list is now cached in MUC
* both string and lang menu caches are compatible with local caches on cluster nodes
* config-dist.php cleanup

config-dist.php

@@ -365,25 +365,6 @@
 // Locking resolves race conditions and is strongly recommended for production servers.
 //     $CFG->preventfilelocking = false;
 //
-// If $CFG->langstringcache is enabled (which should always be in production
-// environment), Moodle keeps aggregated strings in its own internal format
-// optimised for performance. By default, this on-disk cache is created in
-// $CFG->cachedir/lang. In cluster environment, you may wish to specify
-// an alternative location of this cache so that each web server in the cluster
-// uses its own local cache and does not need to access the shared dataroot.
-// Make sure that the web server process has write permission to this location
-// and that it has permission to remove the folder, too (so that the cache can
-// be pruned).
-//
-//     $CFG->langcacheroot = '/var/www/moodle/htdocs/altcache/lang';
-//
-// If $CFG->langcache is enabled (which should always be in production
-// environment), Moodle stores the list of available languages in a cache file.
-// By default, the file $CFG->dataroot/languages is used. You may wish to
-// specify an alternative location of this cache file.
-//
-//     $CFG->langmenucachefile = '/var/www/moodle/htdocs/altcache/languages';
-//
 // Site default language can be set via standard administration interface. If you
 // want to have initial error messages for eventual database connection problems
 // localized too, you have to set your language code here.
@@ -488,7 +469,7 @@
 // Prevent JS caching
 // $CFG->jsrev = -1; // NOT FOR PRODUCTION SERVERS!
 //
-// Prevent core_string_manager on-disk cache
+// Prevent core_string_manager application caching
 // $CFG->langstringcache = false; // NOT FOR PRODUCTION SERVERS!
 //
 // When working with production data on test servers, no emails or other messages

lang/en/cache.php

@@ -46,6 +46,7 @@
 $string['cachedef_eventinvalidation'] = 'Event invalidation';
 $string['cachedef_groupdata'] = 'Course group information';
 $string['cachedef_htmlpurifier'] = 'HTML Purifier - cleaned content';
+$string['cachedef_langmenu'] = 'List of available languages';
 $string['cachedef_locking'] = 'Locking';
 $string['cachedef_observers'] = 'Event observers';
 $string['cachedef_plugininfo_base'] = 'Plugin info - base';

lib/classes/string_manager_install.php

@@ -107,7 +107,6 @@ public function get_string($identifier, $component = '', $a = null, $lang = null
                 if (isset($string['parentlanguage'])) {
                     $parent = $string['parentlanguage'];
                 }
-                unset($string);
             }
         }
 

lib/db/caches.php

@@ -29,8 +29,9 @@
 $definitions = array(
 
     // Used to store processed lang files.
-    // The keys used are the component of the string file.
+    // The keys used are the revision, lang and component of the string file.
     // The persistent max size has been based upon student access of the site.
+    // NOTE: this data may be safely stored in local caches on cluster nodes.
     'string' => array(
         'mode' => cache_store::MODE_APPLICATION,
         'simplekeys' => true,
@@ -39,6 +40,15 @@
         'persistentmaxsize' => 30
     ),
 
+    // Used to store cache of all available translations.
+    // NOTE: this data may be safely stored in local caches on cluster nodes.
+    'langmenu' => array(
+        'mode' => cache_store::MODE_APPLICATION,
+        'simplekeys' => true,
+        'simpledata' => true,
+        'persistent' => true,
+    ),
+
     // Used to store database meta information.
     // The database meta information includes information about tables and there columns.
     // Its keys are the table names.

lib/moodlelib.php

@@ -6635,14 +6635,7 @@ function get_string_manager($forcereload=false) {
                 $translist = explode(',', $CFG->langlist);
             }
 
-            if (empty($CFG->langmenucachefile)) {
-                $langmenucache = $CFG->cachedir . '/languages';
-            } else {
-                $langmenucache = $CFG->langmenucachefile;
-            }
-
-            $singleton = new core_string_manager_standard($CFG->langotherroot, $CFG->langlocalroot,
-                !empty($CFG->langstringcache), $translist, $langmenucache);
+            $singleton = new core_string_manager_standard($CFG->langotherroot, $CFG->langlocalroot, $translist);
 
         } else {
             $singleton = new core_string_manager_install();

lib/setuplib.php

@@ -529,8 +529,7 @@ function get_exception_info($ex) {
     // Remove some absolute paths from message and debugging info.
     $searches = array();
     $replaces = array();
-    $cfgnames = array('tempdir', 'cachedir', 'localcachedir', 'themedir',
-        'langmenucachefile', 'langcacheroot', 'dataroot', 'dirroot');
+    $cfgnames = array('tempdir', 'cachedir', 'localcachedir', 'themedir', 'dataroot', 'dirroot');
     foreach ($cfgnames as $cfgname) {
         if (property_exists($CFG, $cfgname)) {
             $searches[] = $CFG->$cfgname;

lib/upgrade.txt

@@ -13,6 +13,8 @@ information provided here is intended especially for developers.
 * New $CFG->localcachedir setting useful for cluster nodes. Admins have to update X-Sendfile aliases if used.
 * MS SQL Server drivers are now using NVARCHAR(MAX) instead of NTEXT and VARBINARY(MAX) instead of IMAGE,
   this change should be fully transparent and it should help significantly with add-on compatibility.
+* The string manager classes were renamed. Note that they should not be modified or used directly,
+  always use get_string_manager() to get instance of the string manager.
 
 DEPRECATIONS:
 Various previously deprecated functions have now been altered to throw DEBUG_DEVELOPER debugging notices

lib/weblib.php

@@ -3452,11 +3452,8 @@ function get_formatted_help_string($identifier, $component, $ajax = false) {
     global $CFG, $OUTPUT;
     $sm = get_string_manager();
 
-    if (!$sm->string_exists($identifier, $component) ||
-        !$sm->string_exists($identifier . '_help', $component)) {
-        // Strings in the on-disk cache may be dirty - try to rebuild it and check again.
-        $sm->load_component_strings($component, current_language(), true);
-    }
+    // Do not rebuild caches here!
+    // Devs need to learn to purge all caches after any change or disable $CFG->langstringcache.
 
     $data = new stdClass();