Bugfix/singleton resumption quickfix (#967)

* Work around for singleton actors not linking correctly when reconnecting server workers

* Handle singleton linking before GSM checkout

* Change log and warning escalation

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Reliable RPC checking no longer breaks compatibility between development and shipping builds.
 - Fixed an issue with schema name collisions.
 - Running Schema (Full Scan) now clears generated schema files first.
+- Singletons authority and state resumes correct when reconnecting servers to snapshot.
 
 ### External contributors:
 

SpatialGDK/Source/SpatialGDK/Private/Interop/GlobalStateManager.cpp

@@ -363,6 +363,17 @@ USpatialActorChannel* UGlobalStateManager::AddSingleton(AActor* SingletonActor)
 	return Channel;
 }
 
+void UGlobalStateManager::RegisterSingletonChannel(AActor* SingletonActor, USpatialActorChannel* SingletonChannel)
+{
+	TPair<AActor*, USpatialActorChannel*>& ActorChannelPair = NetDriver->SingletonActorChannels.FindOrAdd(SingletonActor->GetClass());
+
+	check(ActorChannelPair.Key == nullptr || ActorChannelPair.Key == SingletonActor);
+	check(ActorChannelPair.Value == nullptr || ActorChannelPair.Value == SingletonChannel);
+
+	ActorChannelPair.Key = SingletonActor;
+	ActorChannelPair.Value = SingletonChannel;
+}
+
 void UGlobalStateManager::ExecuteInitialSingletonActorReplication()
 {
 	for (auto& ClassToActorChannel : NetDriver->SingletonActorChannels)

SpatialGDK/Source/SpatialGDK/Private/Interop/SpatialReceiver.cpp

@@ -5,6 +5,7 @@
 #include "Engine/Engine.h"
 #include "Engine/World.h"
 #include "GameFramework/PlayerController.h"
+#include "Kismet/GameplayStatics.h"
 #include "TimerManager.h"
 
 #include "EngineClasses/SpatialFastArrayNetSerialize.h"
@@ -465,6 +466,11 @@ void USpatialReceiver::ReceiveActor(Worker_EntityId EntityId)
 			EntityActor->DispatchBeginPlay();
 		}
 
+		if (EntityActor->GetClass()->HasAnySpatialClassFlags(SPATIALCLASS_Singleton))
+		{
+			GlobalStateManager->RegisterSingletonChannel(EntityActor, Channel);
+		}
+
 		EntityActor->UpdateOverlaps();
 	}
 }
@@ -676,9 +682,7 @@ AActor* USpatialReceiver::CreateActor(UnrealMetadata* UnrealMetadataComp, SpawnD
 	// Initial Singleton Actor replication is handled with GlobalStateManager::LinkExistingSingletonActors
 	if (NetDriver->IsServer() && ActorClass->HasAnySpatialClassFlags(SPATIALCLASS_Singleton))
 	{
-		// If GSM doesn't know of this entity id, queue up data for that entity id, and resolve it when the actor is created - UNR-734
-		// If the GSM does know of this entity id, we could just create the actor instead - UNR-735
-		return nullptr;
+		return FindSingletonActor(ActorClass);
 	}
 
 	// If we're checking out a player controller, spawn it via "USpatialNetDriver::AcceptNewPlayer"
@@ -1275,6 +1279,25 @@ TWeakObjectPtr<USpatialActorChannel> USpatialReceiver::PopPendingActorRequest(Wo
 	return Channel;
 }
 
+AActor* USpatialReceiver::FindSingletonActor(UClass* SingletonClass)
+{
+	TArray<AActor*> FoundActors;
+	UGameplayStatics::GetAllActorsOfClass(NetDriver->World, SingletonClass, FoundActors);
+
+	// There should be only one singleton actor per class
+	if (FoundActors.Num() == 1)
+	{
+		return FoundActors[0];
+	}
+	else
+	{
+		UE_LOG(LogSpatialReceiver, Error, TEXT("Found incorrect number (%d) of singleton actors (%s)"),
+			FoundActors.Num(), *SingletonClass->GetName());
+	}
+
+	return nullptr;
+}
+
 void USpatialReceiver::ProcessQueuedResolvedObjects()
 {
 	for (TPair<UObject*, FUnrealObjectRef>& It : ResolvedObjectQueue)

SpatialGDK/Source/SpatialGDK/Public/Interop/GlobalStateManager.h

@@ -58,6 +58,7 @@ class SPATIALGDK_API UGlobalStateManager : public UObject
 	bool HasAuthority();
 
 	USpatialActorChannel* AddSingleton(AActor* SingletonActor);
+	void RegisterSingletonChannel(AActor* SingletonActor, USpatialActorChannel* SingletonChannel);
 
 	Worker_EntityId GlobalStateManagerEntityId;
 

SpatialGDK/Source/SpatialGDK/Public/Interop/SpatialReceiver.h

@@ -175,6 +175,8 @@ class USpatialReceiver : public UObject
 	void UpdateShadowData(Worker_EntityId EntityId);
 	TWeakObjectPtr<USpatialActorChannel> PopPendingActorRequest(Worker_RequestId RequestId);
 
+	AActor* FindSingletonActor(UClass* SingletonClass);
+
 public:
 	TMap<FUnrealObjectRef, TSet<FChannelObjectPair>> IncomingRefsMap;