From 6f4c337a5696ef2e51c10511ceeed873cd0834b3 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Mon, 24 Jan 2022 20:52:27 +0900
Subject: [PATCH 1/3] Fix a failed `BlockAllOperations` leaving update realm in
 unretrieved state

If the operation timed out on..

```csharp
   throw new TimeoutException(@"Took too long to acquire lock");
```

..from an update thread, it would not restore the update context.

The next call would then fail on the assert that ensures a non-null
context in such cases.

Can add test coverage if required.
---
 osu.Game/Database/RealmAccess.cs | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/osu.Game/Database/RealmAccess.cs b/osu.Game/Database/RealmAccess.cs
index 66b4edbe84..64063664eb 100644
--- a/osu.Game/Database/RealmAccess.cs
+++ b/osu.Game/Database/RealmAccess.cs
@@ -595,8 +595,8 @@ namespace osu.Game.Database
                 {
                     if (updateRealm == null)
                     {
-                        // null realm means the update thread has not yet retrieved its instance.
-                        // we don't need to worry about reviving the update instance in this case, so don't bother with the SynchronizationContext.
+                        // null context means the update thread has not yet retrieved its context.
+                        // we don't need to worry about reviving the update context in this case, so don't bother with the SynchronizationContext.
                         Debug.Assert(!ThreadSafety.IsUpdateThread);
                     }
                     else
@@ -639,18 +639,19 @@ namespace osu.Game.Database
             }
             catch
             {
-                realmCreationLock.Release();
+                restoreOperation();
                 throw;
             }
 
-            return new InvokeOnDisposal<RealmAccess>(this, factory =>
-            {
-                factory.realmCreationLock.Release();
-                Logger.Log(@"Restoring realm operations.", LoggingTarget.Database);
+            return new InvokeOnDisposal(restoreOperation);
 
+            void restoreOperation()
+            {
+                Logger.Log(@"Restoring realm operations.", LoggingTarget.Database);
+                realmCreationLock.Release();
                 // Post back to the update thread to revive any subscriptions.
                 syncContext?.Post(_ => ensureUpdateRealm(), null);
-            });
+            }
         }
 
         // https://github.com/realm/realm-dotnet/blob/32f4ebcc88b3e80a3b254412665340cd9f3bd6b5/Realm/Realm/Extensions/ReflectionExtensions.cs#L46

From 8116806db3fa6b06e96d1f38eac77964a96435a2 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Tue, 25 Jan 2022 14:00:58 +0900
Subject: [PATCH 2/3] Add test coverage of calling `BlockAllOperations` a
 second time after timeout

---
 osu.Game.Tests/Database/GeneralUsageTests.cs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/osu.Game.Tests/Database/GeneralUsageTests.cs b/osu.Game.Tests/Database/GeneralUsageTests.cs
index 2533c832e6..8262ef18d4 100644
--- a/osu.Game.Tests/Database/GeneralUsageTests.cs
+++ b/osu.Game.Tests/Database/GeneralUsageTests.cs
@@ -95,6 +95,11 @@ namespace osu.Game.Tests.Database
                 });
 
                 stopThreadedUsage.Set();
+
+                // Ensure we can block a second time after the usage has ended.
+                using (realm.BlockAllOperations())
+                {
+                }
             });
         }
     }

From 56d7d814658d1d202e405f237cf74d8a386d078b Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Tue, 25 Jan 2022 14:47:21 +0900
Subject: [PATCH 3/3] Fix broken test due to `SynchronizationContext` never
 running expected work

---
 osu.Game.Tests/Database/GeneralUsageTests.cs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/osu.Game.Tests/Database/GeneralUsageTests.cs b/osu.Game.Tests/Database/GeneralUsageTests.cs
index 8262ef18d4..dc0d42595b 100644
--- a/osu.Game.Tests/Database/GeneralUsageTests.cs
+++ b/osu.Game.Tests/Database/GeneralUsageTests.cs
@@ -87,6 +87,11 @@ namespace osu.Game.Tests.Database
 
                 hasThreadedUsage.Wait();
 
+                // Usually the host would run the synchronization context work per frame.
+                // For the sake of keeping this test simple (there's only one update invocation),
+                // let's replace it so we can ensure work is run immediately.
+                SynchronizationContext.SetSynchronizationContext(new ImmediateExecuteSynchronizationContext());
+
                 Assert.Throws<TimeoutException>(() =>
                 {
                     using (realm.BlockAllOperations())
@@ -102,5 +107,10 @@ namespace osu.Game.Tests.Database
                 }
             });
         }
+
+        private class ImmediateExecuteSynchronizationContext : SynchronizationContext
+        {
+            public override void Post(SendOrPostCallback d, object? state) => d(state);
+        }
     }
 }