Merge branch 'master' into saravea

1 files changed, 12 insertions, 1 deletions

diff --git a/upgrade.php b/upgrade.php
index 60764ba93..c5f158c61 100644
--- a/upgrade.php
+++ b/upgrade.php
@@ -9,6 +9,8 @@
  * new version of the script. Deleting the script is not a requirement and
  * leaving it behind does not affect the security of the site.
  *
+ * Upgrades use a table {db_prefix}upgrade_lock as a mutex to prevent concurrent upgrades.
+ *
  * @package Elgg.Core
  * @subpackage Upgrade
  */
@@ -20,6 +22,12 @@ 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 (!_elgg_upgrade_lock()) {
+		register_error(elgg_echo('upgrade:locked'));
+		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 +41,9 @@ if (get_input('upgrade') == 'upgrade') {
 	elgg_trigger_event('upgrade', 'system', null);
 	elgg_invalidate_simplecache();
 	elgg_reset_system_cache();
+	
+	_elgg_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 +64,4 @@ if (get_input('upgrade') == 'upgrade') {
 	exit;
 }
 
-forward();
\ No newline at end of file
+forward();