REPNOTIFY_Always的指针类型, 一次同步会触发两次OnRep

发表于 2024-05-15 更新于 2024-04-30 分类于 UE ， UE网络， Replication 阅读次数：本文字数： 978 阅读时长 ≈ 4 分钟

前言

当指针类型进行OnRep时候, 可能会触发两次. 触发条件为

该指针成员指向的对象还没有创建, 但是其GUID已经随Bunch发送而来.
该成员被设置成REPNOTIFY_Always类型.

触发流程

构造复现环境

创建两个Actor, 然后指针互相指向对方.

FVector Loc = FVector::ZeroVector;
FRotator Rot = FRotator::ZeroRotator;
FActorSpawnParameters Par;
Par.SpawnCollisionHandlingOverride = ESpawnActorCollisionHandlingMethod::AlwaysSpawn;
UClass* pClass = LoadObject<UClass>(this, TEXT("Blueprint'/Game/Test/TestRepFlow/BPTestRepFlowSpawnedActor.BPTestRepFlowSpawnedActor_C'"));
TestRepFlowSpawnedActor = GetWorld()->SpawnActor<AActor>(pClass, Loc, Rot, Par);
TestRepFlowSpawnedActor->SetAutonomousProxy(true);
TestRepFlowSpawnedActor->SetOwner(this);

TestRepFlowSpawnedActor12 = GetWorld()->SpawnActor<AActor>(pClass, Loc, Rot, Par);
TestRepFlowSpawnedActor12->SetAutonomousProxy(true);
TestRepFlowSpawnedActor12->SetOwner(this);

if (ATestRepFlowSpawnedActor *pTestRepFlowSpawnedActor = Cast<ATestRepFlowSpawnedActor>(TestRepFlowSpawnedActor))
{
    pTestRepFlowSpawnedActor->TestRepFlowSpawnedActor = TestRepFlowSpawnedActor12;
    ATestRepFlowSpawnedActor* pTestRepFlowSpawnedActor12 = Cast<ATestRepFlowSpawnedActor>(TestRepFlowSpawnedActor12);
    pTestRepFlowSpawnedActor12->TestRepFlowSpawnedActor = pTestRepFlowSpawnedActor;
}

// 成员设置成REPNOTIFY_Always
void ATestRepFlowSpawnedActor::GetLifetimeReplicatedProps(TArray<FLifetimeProperty>& OutLifetimeProps) const
{
    Super::GetLifetimeReplicatedProps(OutLifetimeProps);
    DOREPLIFETIME_CONDITION_NOTIFY(ATestRepFlowSpawnedActor, TestRepFlowSpawnedActor, COND_None, REPNOTIFY_Always);
}

序列化Actor

在收到SerializeNewActor Bunch时候, 创建Actor.

// Always Replicate的指针类型, 一次同步会触发两次OnRep---创建Actor
--UIpNetDriver.TickDispatch.for.else.if 
|--UNetConnection.ReceivedRawPacket.if.if.if 
| |--UNetConnection.ReceivedRawPacket.if.if.if 
| | |--UChannel.ReceivedRawBunch.else 
| | | |--UChannel.ReceivedNextBunch.if 
| | | | |--UChannel.ReceivedSequencedBunch 
| | | | | |--UActorChannel.ReceivedBunch 
| | | | | | |--UActorChannel.ProcessBunch.if 
| | | | | | | |--UPackageMapClient.SerializeNewActor.if.if.if.if.if 
| | | | | | | | |--UWorld.SpawnActorAbsolute 
| | | | | | | | | |--UWorld.SpawnActor 
| | | | | | | | | | |--NewObject 
| | | | | | | | | | | |--StaticConstructObject_Internal.if 
| | | | | | | | | | | | |--ATestRepFlowSpawnedActor.ATestRepFlowSpawnedActor

将Property放入RepNotifies中

在解析Bunch时候, 由于GUID指向的对象还没有创建, 所以序列化属性失败, 但是Property的RepNotifyCondition类型为REPNOTIFY_Always, 所以无论无论序列化成功与否, 都会将其塞入RepNotifies中, 等待OnRep.

// Always Replicate的指针类型, 一次同步会触发两次OnRep---虽然没为属性赋值, 但是已经将其放入RepNotifies中
--UIpNetDriver.TickDispatch.for.else.if 
|--UNetConnection.ReceivedRawPacket.if.if.if 
| |--UNetConnection.ReceivedPacket.while.{ 
| | |--UChannel.ReceivedRawBunch.else 
| | | |--UChannel.ReceivedNextBunch.if 
| | | | |--UChannel.ReceivedSequencedBunch 
| | | | | |--UActorChannel.ReceivedBunch 
| | | | | | |--UActorChannel.ProcessBunch.while 
| | | | | | | |--FObjectReplicator.ReceivedBunch.if 
| | | | | | | | |--FRepLayout.ReceiveProperties 
| | | | | | | | | |--ReceiveProperties_r
| | | | | | | | | | |--ReceivePropertyHelper 
| | | | | | | | | | | |--// 序列化属性, 由于GUID对应的Object还没到来, 所以此次赋值失败
| | | | | | | | | | | |--Cmd.Property->NetSerializeItem(Bunch, Bunch.PackageMap, Data + SwappedCmd);
| | | | | | | | | | | |--// 由于Rep类型为REPNOTIFY_Always, 所以将其加入了RepNotifies中
| | | | | | | | | | | |--RepNotifies->AddUnique(Parent.Property);

触发第一次OnRep

触发第一次OnRep时, 此时Actor属性还没有赋值, 即为空.

// Always Replicate的指针类型, 一次同步会触发两次OnRep---第一次OnRep
--UIpNetDriver.TickDispatch.for.else.if 
|--UNetConnection.ReceivedRawPacket.if.if.if 
| |--UNetConnection.ReceivedPacket.while.{ 
| | |--UChannel.ReceivedRawBunch.else 
| | | |--UChannel.ReceivedNextBunch.if 
| | | | |--UChannel.ReceivedSequencedBunch 
| | | | | |--UActorChannel.ReceivedBunch 
| | | | | | |--UActorChannel.ProcessBunch 
| | | | | | | |--FObjectReplicator.CallRepNotifies 
| | | | | | | | |--FRepLayout.CallRepNotifies.for.switch.{ 
| | | | | | | | | |--AActor.ProcessEvent.if.if 
| | | | | | | | | | |--UObject.ProcessEvent.{ 
| | | | | | | | | | | |--UFunction.Invoke 
| | | | | | | | | | | | |--ATestRepFlowSpawnedActor.OnRep_SpawnedActor

关键调用位置:

触发原因:RepNotifies中存了对应属性, 所以一定会触发. 而且触发完后, 还会清理RepNotifies

设置值

通过每帧Tick, 来查询GUID对应的对象是否存在, 如果存在, 则进行赋值.

// Always Replicate的指针类型, 一次同步会触发两次OnRep---为指针成员赋值
--UNetDriver.TickFlush.if.if.if.for.if 
|--FObjectReplicator.UpdateUnmappedObjects 
| |--FRepLayout.UpdateUnmappedObjects.if 
| | |--FRepLayout.UpdateUnmappedObjects_r.for.if 
| | | |--// 序列化属性
| | | |--FObjectPropertyBase.NetSerializeItem 
| | | | |--FObjectProperty.SetObjectPropertyValue 
| | | |--// 将其塞入RepNotifies中, 等待OnRep.
| | | |--RepState->RepNotifies.AddUnique(Parent.Property);
| |--// 第二次OnRep
| |--FObjectReplicator.CallRepNotifies 
| | |--FRepLayout.CallRepNotifies.for.switch.{ 
| | | |--AActor.ProcessEvent.if.if 
| | | | |--UObject.ProcessEvent.{ 
| | | | | |--UFunction.Invoke 
| | | | | | |--ATestRepFlowSpawnedActor.OnRep_SpawnedActor

在赋值之后, 还要将其塞入RepNotifies中, 等待OnRep.

第二次OnRep

当属性设置完成之后, 会在同一帧调用OnRep.

// Always Replicate的指针类型, 一次同步会触发两次OnRep---为指针成员赋值
--UNetDriver.TickFlush.if.if.if.for.if 
|--FObjectReplicator.UpdateUnmappedObjects 
| |--FRepLayout.UpdateUnmappedObjects.if 
| | |--FRepLayout.UpdateUnmappedObjects_r.for.if 
| | | |--// 序列化属性
| | | |--FObjectPropertyBase.NetSerializeItem 
| | | | |--FObjectProperty.SetObjectPropertyValue 
| | | |--// 将其塞入RepNotifies中, 等待OnRep.
| | | |--RepState->RepNotifies.AddUnique(Parent.Property);
| |--// 第二次OnRep
| |--FObjectReplicator.CallRepNotifies 
| | |--FRepLayout.CallRepNotifies.for.switch.{ 
| | | |--AActor.ProcessEvent.if.if 
| | | | |--UObject.ProcessEvent.{ 
| | | | | |--UFunction.Invoke 
| | | | | | |--ATestRepFlowSpawnedActor.OnRep_SpawnedActor