From bcf7f9f36f37c10cdb8737ea88cce365522e37cf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20=C5=A0koda?= <commits@skodak.org>
Date: Sat, 30 Jun 2012 09:50:18 +0200
Subject: [PATCH] MDL-34057 improve styles_debug concurrency

Please note style debugging is not intended for busy production sites!
---
 lib/outputlib.php | 48 +++++++++++++++++++++++++++--------------------
 1 file changed, 28 insertions(+), 20 deletions(-)

diff --git a/lib/outputlib.php b/lib/outputlib.php
index 7d963f30198..0cf29d8fef8 100644
--- a/lib/outputlib.php
+++ b/lib/outputlib.php
@@ -626,30 +626,38 @@ class theme_config {
             if (!defined('THEME_DESIGNER_CACHE_LIFETIME')) {
                 define('THEME_DESIGNER_CACHE_LIFETIME', 4); // this can be also set in config.php
             }
-            // Prepare the CSS optimiser if it is to be used
-            $optimiser = null;
-            $candidatesheet = "$CFG->cachedir/theme/$this->name/designer.ser";
-            if (!empty($CFG->enablecssoptimiser) && $this->supportscssoptimisation) {
-                require_once($CFG->dirroot.'/lib/csslib.php');
-                $optimiser = new css_optimiser;
-            }
-            if (!file_exists($candidatesheet)) {
-                $css = $this->css_content($optimiser);
-                check_dir_exists(dirname($candidatesheet));
-                file_put_contents($candidatesheet, serialize($css));
-
-            } else if (filemtime($candidatesheet) > time() - THEME_DESIGNER_CACHE_LIFETIME) {
+            $candidatedir = "$CFG->cachedir/theme/$this->name";
+            $candidatesheet = "$candidatedir/designer.ser";
+            $rebuild = true;
+            if (file_exists($candidatesheet) and filemtime($candidatesheet) > time() - THEME_DESIGNER_CACHE_LIFETIME) {
                 if ($css = file_get_contents($candidatesheet)) {
                     $css = unserialize($css);
-                } else {
-                    unlink($candidatesheet);
-                    $css = $this->css_content($optimiser);
+                    if (is_array($css)) {
+                        $rebuild = false;
+                    }
+                }
+            }
+            if ($rebuild) {
+                // Prepare the CSS optimiser if it is to be used,
+                // please note that it may be very slow and is therefore strongly discouraged in theme designer mode.
+                $optimiser = null;
+                if (!empty($CFG->enablecssoptimiser) && $this->supportscssoptimisation) {
+                    require_once($CFG->dirroot.'/lib/csslib.php');
+                    $optimiser = new css_optimiser;
                 }
-
-            } else {
-                unlink($candidatesheet);
                 $css = $this->css_content($optimiser);
-                file_put_contents($candidatesheet, serialize($css));
+
+                // We do not want any errors here because this may fail easily because of the concurrent access.
+                $prevabort = ignore_user_abort(true);
+                check_dir_exists($candidatedir);
+                $tempfile = tempnam($candidatedir, 'tmpdesigner');
+                file_put_contents($tempfile, serialize($css));
+                $reporting = error_reporting(0);
+                chmod($tempfile, $CFG->filepermissions);
+                unlink($candidatesheet); // Do not rely on rename() deleting original, they may decide to change it at any time as usually.
+                rename($tempfile, $candidatesheet);
+                error_reporting($reporting);
+                ignore_user_abort($prevabort);
             }
 
             $baseurl = $CFG->httpswwwroot.'/theme/styles_debug.php';