From e2c94dda6cf20e400c04e0fb5f8ea826d1d2b9f2 Mon Sep 17 00:00:00 2001
From: "byte[]" <byteslice@airmail.cc>
Date: Mon, 10 Apr 2023 22:16:10 -0400
Subject: [PATCH] Lock the topic while computing topic_position

---
 lib/philomena/posts.ex | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/philomena/posts.ex b/lib/philomena/posts.ex
index 6bef4d1b..cefde12c 100644
--- a/lib/philomena/posts.ex
+++ b/lib/philomena/posts.ex
@@ -57,11 +57,16 @@ defmodule Philomena.Posts do
       Topic
       |> where(id: ^topic.id)
 
+    topic_lock_query =
+      topic_query
+      |> lock("FOR UPDATE")
+
     forum_query =
       Forum
       |> where(id: ^topic.forum_id)
 
     Multi.new()
+    |> Multi.all(:topic_lock, topic_lock_query)
     |> Multi.run(:post, fn repo, _ ->
       last_position =
         Post