Fix: Unreal UObject Async Load Hang on Shutdown

A game with heavy asset streaming hangs on exit. Editor freezes for ~30 seconds before closing. Crash dumps show pending async load on the call stack. The game shut down with loads in flight.

The Pattern

void UMySubsystem::PreloadAssets() {
    auto& Manager = UAssetManager::Get().GetStreamableManager();
    LoadHandle = Manager.RequestAsyncLoad(SoftPaths, [this]() {
        OnLoaded();
    });
}

If shutdown happens before completion, the load continues; the captured this may dangle.

Fix: Cancel in Deinitialize

void UMySubsystem::Deinitialize() {
    if (LoadHandle.IsValid()) {
        LoadHandle->CancelHandle();
        LoadHandle.Reset();
    }
    Super::Deinitialize();
}

Cancel runs synchronously: outstanding load is aborted, callbacks won’t fire. No dangling lambdas.

Use Weak This in Callbacks

TWeakObjectPtr<UMySubsystem> WeakThis(this);
LoadHandle = Manager.RequestAsyncLoad(SoftPaths, [WeakThis]() {
    if (UMySubsystem* Self = WeakThis.Get()) {
        Self->OnLoaded();
    }
});

Defense in depth: even if cancel is missed, the callback won’t crash. WeakObjectPtr nulls out when the object is destroyed.

Don't Start Loads in EndPlay

EndPlay runs during shutdown sequencing. Starting new async loads there guarantees they hang. If you need cleanup-time loads (rare), use sync loads.

Verifying

Stress test: trigger preloads, then exit immediately. Editor closes within 1–2 seconds. Logs show “Cancelled async load: ...” messages. No crash dumps.

“Cancel before shutdown, capture weak. Async loads in flight are guaranteed to outlive the systems that started them.”

For shipping builds especially, the hang appears as the spinning beachball — user experience destroyed by something easy to fix.