CA global renaming changes

diff --git a/CentralAuth.i18n.php b/CentralAuth.i18n.php
index 07dec15..1d63842 100644
--- a/CentralAuth.i18n.php
+++ b/CentralAuth.i18n.php
@@ -219,6 +219,7 @@ The passwords for local accounts created before the merge will revert to their p
        'centralauth-globalrename-complete' => 'Global rename queued...',
        'action-centralauth-globalrename' => 'globally rename a user',
        'centralauth-globalrename-nonexistent' => 'Global account "<nowiki>$1</nowiki>" does not exist.',
+       'centralauth-globalrename-in-progress' => 'There is already a global rename in progress for <nowiki>$1</nowiki>.',

        // List of global users
        'globalusers'                    => 'Global user list',
@@ -745,6 +746,7 @@ See also:
        'centralauth-renameuser-globalrenameuser' => '{{Logentry}}
 * $4 - the new username',
        'right-centralauth-globalrename' => '{{doc-right|centralauth-globalrename}}',
+       'centralauth-globalrename-in-progress' => 'Error message shown when a global rename is already in progress on this username.',
 );

 /** Afrikaans (Afrikaans)
diff --git a/specials/SpecialCentralAuth.php b/specials/SpecialCentralAuth.php
index a289f23..91b4354 100644
--- a/specials/SpecialCentralAuth.php
+++ b/specials/SpecialCentralAuth.php
@@ -233,14 +233,19 @@ class SpecialCentralAuth extends SpecialPage {
                                return true;
                        }

+                       $cdb = CentralAuthUser::getCentralDB();
+                       if ( !$cdb->lockIsFree( 'centralauth-globalrename:' . $newName, __METHOD__ ) ) {
+                               $this->showError( 'centralauth-globalrename-in-progress', $currentName );
+                               return true;
+                       }
+                       $cdb->lock( "centralauth-globalrename:" . $newName, __METHOD__ );
+
                        $startedLocked = $globalUser->isLocked();
                        // Lock the user before we start changing anything.
                        if ( !$startedLocked ) {
                                $globalUser->adminLock();
                        }

-                       CentralAuthUser::getCentralDB()->lock( "centralauth-globalrename:" . $newName, __METHOD__ );
-
                        // Update the globaluser and localuser tables. The existing hooks should deal with globalnames/localnames...
                        $tables = array( 'globaluser' => 'gu', 'localuser' => 'lu' );
                        foreach ( $tables as $table => $prefix ) {