From d3b2e2b36eebcb6913244df225f4007bd014708b Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Fri, 11 Dec 2020 14:43:17 +0900
Subject: [PATCH] Change locking method to better allow cross-thread locking

---
 .../RealtimeMultiplayer/LockUntilDisposal.cs  | 24 -------------------
 .../RealtimeMultiplayer/MultiplayerRoom.cs    | 20 +++++++++++++++-
 2 files changed, 19 insertions(+), 25 deletions(-)
 delete mode 100644 osu.Game/Online/RealtimeMultiplayer/LockUntilDisposal.cs

diff --git a/osu.Game/Online/RealtimeMultiplayer/LockUntilDisposal.cs b/osu.Game/Online/RealtimeMultiplayer/LockUntilDisposal.cs
deleted file mode 100644
index cd16fce2ee..0000000000
--- a/osu.Game/Online/RealtimeMultiplayer/LockUntilDisposal.cs
+++ /dev/null
@@ -1,24 +0,0 @@
-// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
-// See the LICENCE file in the repository root for full licence text.
-
-using System;
-using System.Threading;
-
-namespace osu.Game.Online.RealtimeMultiplayer
-{
-    public readonly struct LockUntilDisposal : IDisposable
-    {
-        private readonly object lockTarget;
-
-        public LockUntilDisposal(object lockTarget)
-        {
-            this.lockTarget = lockTarget;
-            Monitor.Enter(lockTarget);
-        }
-
-        public void Dispose()
-        {
-            Monitor.Exit(lockTarget);
-        }
-    }
-}
diff --git a/osu.Game/Online/RealtimeMultiplayer/MultiplayerRoom.cs b/osu.Game/Online/RealtimeMultiplayer/MultiplayerRoom.cs
index 5704ddd675..e009a34707 100644
--- a/osu.Game/Online/RealtimeMultiplayer/MultiplayerRoom.cs
+++ b/osu.Game/Online/RealtimeMultiplayer/MultiplayerRoom.cs
@@ -5,7 +5,9 @@
 
 using System;
 using System.Collections.Generic;
+using System.Threading;
 using Newtonsoft.Json;
+using osu.Framework.Allocation;
 
 namespace osu.Game.Online.RealtimeMultiplayer
 {
@@ -48,10 +50,26 @@ namespace osu.Game.Online.RealtimeMultiplayer
             RoomID = roomId;
         }
 
+        private object updateLock = new object();
+
+        private ManualResetEventSlim freeForWrite = new ManualResetEventSlim(true);
+
         /// <summary>
         /// Request a lock on this room to perform a thread-safe update.
         /// </summary>
-        public LockUntilDisposal LockForUpdate() => new LockUntilDisposal(writeLock);
+        public IDisposable LockForUpdate()
+        {
+            // ReSharper disable once InconsistentlySynchronizedField
+            freeForWrite.Wait();
+
+            lock (updateLock)
+            {
+                freeForWrite.Wait();
+                freeForWrite.Reset();
+
+                return new ValueInvokeOnDisposal<MultiplayerRoom>(this, r => freeForWrite.Set());
+            }
+        }
 
         public override string ToString() => $"RoomID:{RoomID} Host:{Host?.UserID} Users:{Users.Count} State:{State} Settings: [{Settings}]";
     }