From a5d56c8ddefe48067f0fb23f0d5938c16c4aeca1 Mon Sep 17 00:00:00 2001
From: andris-sevcenko <asevcenko@gmail.com>
Date: Thu, 7 Mar 2019 13:06:04 +0200
Subject: [PATCH] Fixed #3450

---
 CHANGELOG-v3.md               | 1 +
 src/services/AssetIndexer.php | 9 +++++++++
 2 files changed, 10 insertions(+)

diff --git a/CHANGELOG-v3.md b/CHANGELOG-v3.md
index dca2bf6cf50..85fbfd62a19 100644
--- a/CHANGELOG-v3.md
+++ b/CHANGELOG-v3.md
@@ -13,6 +13,7 @@
 - Fixed a bug where the `positionedBefore` element query param was not including direct ancestors in the results.
 - Fixed a bug where HTML in plugin-supplied field instructions was getting encoded. ([#3928](https://github.com/craftcms/cms/issues/3928))
 - Fixed a bug where Craft would prompt for a user’s current password when registering a new user, even if they weren’t assigning any groups or permissions to that user
+- Fixed a bug where a race condition could make Asset indexing inconsistent. ([#3450](https://github.com/craftcms/cms/issues/3450))
 
 ## 3.1.16 - 2019-03-05
 
diff --git a/src/services/AssetIndexer.php b/src/services/AssetIndexer.php
index 88ea0b9d642..d63be55324f 100644
--- a/src/services/AssetIndexer.php
+++ b/src/services/AssetIndexer.php
@@ -233,6 +233,13 @@ public function storeIndexList(array $indexList, string $sessionId, int $volumeI
      */
     public function processIndexForVolume(string $sessionId, int $volumeId, bool $cacheImages = false)
     {
+        $mutex = Craft::$app->getMutex();
+        $lockName = 'idx--' . $sessionId;
+
+        if (!$mutex->acquire($lockName, 5)) {
+            throw new Exception('Could not acquire a lock for the indexing sessiong "' . $sessionId . '".');
+        }
+
         if (($indexEntryModel = $this->getNextIndexEntry($sessionId, $volumeId)) === null) {
             return false;
         }
@@ -240,6 +247,8 @@ public function processIndexForVolume(string $sessionId, int $volumeId, bool $ca
         // Mark as started.
         $this->updateIndexEntry($indexEntryModel->id, ['inProgress' => true]);
 
+        $mutex->release($lockName);
+
         try {
             $asset = $this->_indexFileByIndexData($indexEntryModel, $cacheImages);
             $this->updateIndexEntry($indexEntryModel->id, ['completed' => true, 'inProgress' => false, 'recordId' => $asset->id]);