# \[UE 5.8.2\] Render thread crash (null UWorld deref) in FComputeViewExtension::GetFlags() during map travel with HW ray tracing 

**URL:** <https://forums.unrealengine.com/t/ue-5-8-2-render-thread-crash-null-uworld-deref-in-fcomputeviewextension-getflags-during-map-travel-with-hw-ray-tracing/2853527>\
**Category:** Issues and Bug Reporting (Unreal Engine)\
**Tags:** unreal-engine\
**Created:** [November 10, 2026, 6:20pm UTC](https://forums.unrealengine.com/t/ue-5-8-2-render-thread-crash-null-uworld-deref-in-fcomputeviewextension-getflags-during-map-travel-with-hw-ray-tracing/2853527 "2026-11-10T18:20:37Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![AlexandreStAmant](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@AlexandreStAmant](https://forums.unrealengine.com/u/AlexandreStAmant)\
**Post date:** [November 10, 2026, 6:20pm UTC](https://forums.unrealengine.com/t/ue-5-8-2-render-thread-crash-null-uworld-deref-in-fcomputeviewextension-getflags-during-map-travel-with-hw-ray-tracing/2853527/1 "2026-11-10T18:20:37Z")

</div>

### Summary

**Engine:** 5.8.2 (source build). The code is unchanged on `ue5-main` as of Nov 2026.  
**Platform / RHI:** Windows 64-bit, D3D12, Development (packaged game)  
**Crash GUID:** `UECC-Windows-2D88016E44A335279D969F99C9934A4D_0000`

`FComputeViewExtension::GetFlags()` (ComputeFramework plugin) runs on the **render thread** and dereferences the extension’s `TWeakObjectPtr<UWorld>`. The game thread can destroy that world during `LoadMap` at the same time. The weak pointer is validated with `IsValid()` and then dereferenced again through `operator->`, which calls `Get()` a second time. If the world is invalidated between those two calls, `Get()` returns `nullptr` and the render thread crashes.

```auto
Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x0000000000000258

```

The low address points to a null-pointer member access, consistent with `WorldPtr->Scene` on a null `UWorld*`.

**Faulty code:** `Engine/Plugins/Runtime/ComputeFramework/Source/ComputeFramework/Private/ComputeViewExtension.cpp`

```cpp
ESceneViewExtensionFlags FComputeViewExtension::GetFlags() const
{
    const TWeakObjectPtr<UWorld> WorldPtr = GetWorld();

    // Race: IsValid() and operator-> each resolve the weak pointer separately.
    if (const FSceneInterface* Scene = WorldPtr.IsValid() ? WorldPtr->Scene : nullptr)
    {
        ComputeWorkers.Empty(ComputeWorkers.Num()); // mutable member used as scratch buffer
        Scene->GetComputeTaskWorkers(ComputeWorkers);
        ...

```

`PostTLASBuild_RenderThread()` uses the same pattern.

There are two problems:

1. A `UWorld` is accessed from the render thread while the game thread may be destroying it.
2. `mutable TArray ComputeWorkers` is used as a scratch buffer. It is not thread-safe if several view families for the same world call `GetFlags()` concurrently.

This code path seems to have been introduced in commit `344f81b` (“[PCG] Add engine infrastructure for PCG GPU inline ray tracing”, March 26, 2026).

### What Type of Bug are you experiencing?

Rendering (Graphics / Niagara)

### Steps to Reproduce

1. Create a project with `r.RayTracing=True` and the ComputeFramework plugin enabled.
2. Package a Development build.
3. Run a loop that calls `OpenLevel` between three small maps continuously (we use Attract → Round → Outro, one transition every ~3–4 s).
4. Leave it running. In our case the crash happened after ~9 h (~700 `LoadMap` calls); the race window is very narrow.

### Expected Result

No crash during map travel.

### Observed Result

Access violation (reading 0x258) on the render thread in `FComputeViewExtension::GetFlags()` while the previous world is being torn down in `LoadMap`.

### Affects Versions

5.8

### Platform(s)

Windows

### For crash reports, include your callstack

Unhandled Exception: EXCEPTION\_ACCESS\_VIOLATION reading address 0x0000000000000258

RenderThread:  
FComputeViewExtension::GetFlags() Line 53  
FDeferredShadingSceneRenderer::SetupRayTracingRenderingData(FRDGBuilder & GraphBuilder, RayTracing::FGatherInstancesTaskData & RayTracingGatherInstancesTaskData) Line 1160  
FDeferredShadingSceneRenderer::Render(FRDGBuilder & GraphBuilder, const FSceneRenderUpdateInputs \* SceneUpdateInputs) Line 3035  
RenderViewFamily\_RenderThread(FRDGBuilder & GraphBuilder, FSceneRenderer \* Renderer, const FSceneRenderUpdateInputs \* SceneUpdateInputs) Line 5232  
[Inline Frame] FRendererModule::BeginRenderingViewFamilies::\_\_l130::(FRDGBuilder &) Line 5527  
FRendererModule::BeginRenderingViewFamilies::\<lambda\_invoker\_cdecl\> Line 5529  
FSceneRenderProcessor::Execute::\_\_l32::(FRHICommandListImmediate & RHICmdList) Line 895  
ExecuteCommand(…) Line 1534  
UE::RenderCommandPipe::FCommandList::ConsumeCommands\<…\> Line 336  
FRenderThreadCommandPipe::EnqueueAndLaunch::\_\_l5::\<lambda\_1\>::operator()() Line 1928  
TGraphTask\<TFunctionGraphTaskImpl\<void \_\_cdecl(void),1\>\>::ExecuteTask() Line 704  
UE::Tasks::Private::FTaskBase::TryExecuteTask() Line 525  
FNamedTaskThread::ProcessTasksNamedThread(int QueueIndex, bool bAllowStall) Line 807  
FNamedTaskThread::ProcessTasksUntilQuit(int QueueIndex) Line 696  
RenderingThreadMain(FEvent \* TaskGraphBoundSyncEvent) Line 262  
FRenderingThread::Run() Line 390  
FRunnableThreadWin::Run() Line 167  
FRunnableThreadWin::GuardedRun() Line 87

Log context at time of crash:  
LogLoad: LoadMap: /Game/…/MAP\_Round01  
LogWorld: BeginTearingDown for /Game/…/MAP\_Attract  
LogWorld: UWorld::CleanupWorld for MAP\_Attract, bSessionEnded=true, bCleanupResources=true

### Additional Notes

**Suggested fix**  
Do not touch the `UWorld` from the render thread. `FComputeFrameworkSystem::CreateWorkers()` already receives the `FSceneInterface*`, so it can be passed to the extension and cached. The `FScene` is released through a render command (`Scene->Release()`), so it stays valid for the duration of any frame already in flight. Replace the mutable member with a local array:

```cpp
// ComputeSystem.cpp
ViewExtensions.Add(InScene, FSceneViewExtensions::NewExtension<FComputeViewExtension>(World, InScene));

// ComputeViewExtension.cpp
ESceneViewExtensionFlags FComputeViewExtension::GetFlags() const
{
    if (Scene)
    {
        TArray<IComputeTaskWorker*, TInlineAllocator<8>> Workers;
        Scene->GetComputeTaskWorkers(Workers);
        for (IComputeTaskWorker* Worker : Workers)
        {
            if (Worker->HasWork(ComputeTaskExecutionGroup::PostTLASBuild))
            {
                return ESceneViewExtensionFlags::SubscribesToPostTLASBuild
                     | ESceneViewExtensionFlags::RequiresHardwareInlineRayTracing;
            }
        }
    }
    return ESceneViewExtensionFlags::None;
}
// Same change in PostTLASBuild_RenderThread().

```

**Workaround:** set `r.RayTracing=False`. Both call sites of `GetFlags()` in `FDeferredShadingSceneRenderer` (lines 1160 and 3314) are behind `IsRayTracingEnabled()`.

Minidump, CrashContext.runtime-xml and the full log are available on request.