Structure locks (#3148)

CHANGELOG-v3.md

@@ -1,5 +1,10 @@
 # Release Notes for Craft CMS 3.x
 
+## Unreleased
+
+### Changed
+- Structure operations now ensure that no other operations are being performed on the same structure, reducing the risk of corrupting the structure. ([#3148](https://github.com/craftcms/cms/issues/3148))
+
 ## 3.0.17.1 - 2018-07-24
 
 ### Fixed

src/services/Structures.php

@@ -345,6 +345,13 @@ private function _getRootElementRecord(int $structureId): StructureElement
      */
     private function _doIt($structureId, ElementInterface $element, StructureElement $targetElementRecord, $action, $mode): bool
     {
+        // Get a lock or bust
+        $lockName = 'structure:' . $structureId;
+        $mutex = Craft::$app->getMutex();
+        if (!$mutex->acquire($lockName)) {
+            throw new Exception('Unable to acquire a lock for the structure ' . $structureId);
+        }
+
         $elementRecord = null;
 
         /** @var Element $element */
@@ -376,14 +383,15 @@ private function _doIt($structureId, ElementInterface $element, StructureElement
 
         // Tell the element about it
         if (!$element->beforeMoveInStructure($structureId)) {
+            $mutex->release($lockName);
             return false;
         }
 
         $transaction = Craft::$app->getDb()->beginTransaction();
         try {
             if (!$elementRecord->$action($targetElementRecord)) {
                 $transaction->rollBack();
-
+                $mutex->release($lockName);
                 return false;
             }
 
@@ -409,10 +417,12 @@ private function _doIt($structureId, ElementInterface $element, StructureElement
             $transaction->commit();
         } catch (\Throwable $e) {
             $transaction->rollBack();
-
+            $mutex->release($lockName);
             throw $e;
         }
 
+        $mutex->release($lockName);
+
         if ($mode === 'update' && $this->hasEventHandlers(self::EVENT_AFTER_MOVE_ELEMENT)) {
             // Fire an 'afterMoveElement' event
             $this->trigger(self::EVENT_AFTER_MOVE_ELEMENT, new MoveElementEvent([