Fixes #4643. Locks the upgrade process while it is running.

diff --git a/upgrade.php b/upgrade.php
index 60764ba936c35cb6b5d75b00df9ffb071865a29b..38be476a4d9ceb8bb975a349cc3b2db7e2ec7827 100644 (file)
--- a/upgrade.php
+++ b/upgrade.php
@@ -13,6 +13,35 @@
  * @subpackage Upgrade
  */
 
+function upgrade_lock() {
+       global $CONFIG, $DB_QUERY_CACHE;
+       
+       $is_locked = count(get_data("show tables like '{$CONFIG->dbprefix}locked'"));
+       
+       // Invalidate query cache
+       if ($DB_QUERY_CACHE) {
+               $DB_QUERY_CACHE->clear();
+               elgg_log("Query cache invalidated", 'NOTICE');
+       }
+       
+       if (!$is_locked) {
+               // lock it
+               insert_data("create table {$CONFIG->dbprefix}locked (id INT)");
+               error_log('Upgrade continue running');
+               return true;
+       }
+       
+       error_log('Upgrade is locked');
+       return false;
+}
+
+function upgrade_unlock() {
+       global $CONFIG;
+       delete_data("drop table {$CONFIG->dbprefix}locked");
+       error_log('Upgrade unlocks itself');
+}
+
+
 // we want to know if an error occurs
 ini_set('display_errors', 1);
 
@@ -20,6 +49,12 @@ define('UPGRADING', 'upgrading');
 require_once(dirname(__FILE__) . "/engine/start.php");
 
 if (get_input('upgrade') == 'upgrade') {
+       
+       // prevent someone from running the upgrade script in parallel (see #4643)
+       if (!upgrade_lock()) {
+               forward();
+       }
+       
        // disable the system log for upgrades to avoid exceptions when the schema changes.
        elgg_unregister_event_handler('log', 'systemlog', 'system_log_default_logger');
        elgg_unregister_event_handler('all', 'all', 'system_log_listener');
@@ -33,6 +68,10 @@ if (get_input('upgrade') == 'upgrade') {
        elgg_trigger_event('upgrade', 'system', null);
        elgg_invalidate_simplecache();
        elgg_reset_system_cache();
+       
+       // critical region has past
+       upgrade_unlock();
+       
 } else {
        // if upgrading from < 1.8.0, check for the core view 'welcome' and bail if it's found.
        // see http://trac.elgg.org/ticket/3064
@@ -53,4 +92,4 @@ if (get_input('upgrade') == 'upgrade') {
        exit;
 }
 
-forward();
\ No newline at end of file
+forward();