MDL-22015 core_string_manager: caching and performance logging improved

The results of merged en + en_local + parentlang + parentlang_local +
lang + lang_local are now saved into disk cache in dataroot/cache/lang/.
The number of get_string() calls, and number of mem cache and disk cache
hits are part of performance logging.
Disk cache must be removed whenever the language packs or their local
customizations are deleted. Disk cache is rebuilt automatically.

lib/moodlelib.php

@@ -5848,8 +5848,6 @@ interface string_manager {
 /**
  * Standard string_manager implementation
  *
- * TODO: implement lang precompilation
- *
  * @package    moodlecore
  * @copyright  2010 Petr Skoda (http://skodak.org)
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
@@ -5859,19 +5857,28 @@ class core_string_manager implements string_manager {
     protected $otherroot;
     /** @var string location of all lang pack local modifications */
     protected $localroot;
-
+    /** @var string location of on-disk cache of merged strings */
+    protected $cacheroot;
     /** @var array lang string cache - it will be optimised more later */
     protected $cache = array();
-
+    /** @var int get_string() counter */
+    protected $countgetstring = 0;
+    /** @var int in-memory cache hits counter */
+    protected $countmemcache = 0;
+    /** @var int on-disk cache hits counter */
+    protected $countdiskcache = 0;
     /**
-     * Crate new instance of amos string manager
+     * Crate new instance of string manager
      *
      * @param string $otherroot location of downlaoded lang packs - usually $CFG->dataroot/lang
      * @param string $localroot usually the same as $otherroot
      */
     public function __construct($otherroot, $localroot) {
+        global $CFG;
+
         $this->otherroot  = $otherroot;
         $this->localroot  = $localroot;
+        $this->cacheroot  = "$CFG->dataroot/cache/lang";
     }
 
     /**
@@ -5908,15 +5915,26 @@ class core_string_manager implements string_manager {
         global $CFG;
 
         list($plugintype, $pluginname) = normalize_component($component);
-
-        if (!isset($this->cache[$lang])) {
-            $this->cache[$lang] = array();
+        if ($plugintype == 'core' and is_null($pluginname)) {
+            $component = 'core';
+        } else {
+            $component = $plugintype . '_' . $pluginname;
         }
 
-        if (isset($this->cache[$lang][$plugintype.$pluginname])) {
-            return $this->cache[$lang][$plugintype.$pluginname];
+        // try in-memory cache first
+        if (isset($this->cache[$lang][$component])) {
+            $this->countmemcache++;
+            return $this->cache[$lang][$component];
         }
 
+        // try on-disk cache then
+        if (file_exists($this->cacheroot . "/$lang/$component")) {
+            $this->countdiskcache++;
+            eval('$this->cache[$lang][$component] = ' . file_get_contents($this->cacheroot . "/$lang/$component") . ';');
+            return $this->cache[$lang][$component];
+        }
+
+        // no cache found - let us merge all possible sources of the strings
         if ($plugintype === 'core') {
             $file = $pluginname;
             if ($file === null) {
@@ -5988,8 +6006,11 @@ class core_string_manager implements string_manager {
         // we do not want any extra strings from other languages - everything must be in en lang pack
         $string = array_intersect_key($string, $originalkeys);
 
-        $this->cache[$lang][$plugintype.$pluginname] = $string;
-
+        // now we have a list of strings from all possible sources. put it into both in-memory and on-disk
+        // caches so we do not need to do all this merging and dependecies resolving again
+        $this->cache[$lang][$component] = $string;
+        check_dir_exists($this->cacheroot . '/' . $lang, true, true);
+        file_put_contents($this->cacheroot . "/$lang/$component", var_export($string, true));
         return $string;
     }
 
@@ -6026,6 +6047,7 @@ class core_string_manager implements string_manager {
      * @return string The String !
      */
     public function get_string($identifier, $component = '', $a = NULL, $lang = NULL) {
+        $this->countgetstring++;
         // there are very many uses of these time formating strings without the 'langconfig' component,
         // it would not be reasonable to expect that all of them would be converted during 2.0 migration
         static $langconfigstrs = array(
@@ -6101,6 +6123,22 @@ class core_string_manager implements string_manager {
         return $string;
     }
 
+    /**
+     * Returns information about the string_manager performance
+     * @return array
+     */
+    public function get_performance_summary() {
+        return array(array(
+            'langcountgetstring' => $this->countgetstring,
+            'langcountmemcache' => $this->countmemcache,
+            'langcountdiskcache' => $this->countdiskcache,
+        ), array(
+            'langcountgetstring' => 'get_string calls',
+            'langcountmemcache' => 'strings mem cache hits',
+            'langcountdiskcache' => 'strings disk cache hits',
+        ));
+    }
+
     /**
      * Returns a localised list of all country names, sorted by localised name.
      *
@@ -9055,6 +9093,16 @@ function get_performance_info() {
         }
     }
 
+    $stringmanager = get_string_manager();
+    if (method_exists($stringmanager, 'get_performance_summary')) {
+        list($filterinfo, $nicenames) = $stringmanager->get_performance_summary();
+        $info = array_merge($filterinfo, $info);
+        foreach ($filterinfo as $key => $value) {
+            $info['html'] .= "<span class='$key'>$nicenames[$key]: $value </span> ";
+            $info['txt'] .= "$key: $value ";
+        }
+    }
+
     if (!empty($PERF->logwrites)) {
         $info['logwrites'] = $PERF->logwrites;
         $info['html'] .= '<span class="logwrites">Log DB writes '.$info['logwrites'].'</span> ';
@@ -9667,4 +9715,4 @@ function get_home_page() {
         }
     }
     return HOMEPAGE_SITE;
-}
+}