From 3b11235d3c65c7416e8e092d0a8d4aeb45c0c85c Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Fri, 21 Jan 2022 20:45:10 +0900
Subject: [PATCH] Fix potentially cyclic subscription registration if a
 subscription's delegate accesses `Context`

---
 osu.Game/Database/RealmContextFactory.cs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/osu.Game/Database/RealmContextFactory.cs b/osu.Game/Database/RealmContextFactory.cs
index c11ff61039..d9c66ccc69 100644
--- a/osu.Game/Database/RealmContextFactory.cs
+++ b/osu.Game/Database/RealmContextFactory.cs
@@ -88,6 +88,8 @@ namespace osu.Game.Database
                             registerSubscription(action);
                     }
 
+                    Debug.Assert(context != null);
+
                     // creating a context will ensure our schema is up-to-date and migrated.
                     return context;
                 }
@@ -261,10 +263,13 @@ namespace osu.Game.Database
         {
             Debug.Assert(ThreadSafety.IsUpdateThread);
 
+            // Get context outside of flag update to ensure beyond doubt this can't be cyclic.
+            var realm = Context;
+
             lock (contextLock)
             {
                 current_thread_subscriptions_allowed.Value = true;
-                subscriptionActions[action] = action(Context);
+                subscriptionActions[action] = action(realm);
                 current_thread_subscriptions_allowed.Value = false;
             }
         }