Fix: Unreal UObject Garbage Collected Mid Async Task

You schedule an HTTP request that captures this as a raw pointer. The actor is destroyed before the response arrives. The callback dereferences the dead pointer; engine crashes.

The Symptom

Crash after a delay following async work. Sometimes the engine logs “dereferenced GC’d UObject” before the crash. Reproduces by destroying the calling actor before the async completes.

The Fix

Pattern: TWeakObjectPtr in capture.

TWeakObjectPtr<APlayer> WeakSelf = this;

Http->OnProcessRequestComplete().BindLambda([WeakSelf](FHttpRequestPtr Req, FHttpResponsePtr Resp, bool bOk)
{
    APlayer* Self = WeakSelf.Get();
    if (!Self || !Self->IsValidLowLevel())
    {
        UE_LOG(LogTemp, Warning, TEXT("Owner gone, dropping callback"));
        return;
    }

    Self->HandleResponse(Resp, bOk);
});

WeakObjectPtr doesn’t keep the referent alive. Get() returns nullptr if it was GC’d. The early return saves you from the dead-pointer access.

UPROPERTY for Members

UObject member fields tagged UPROPERTY() keep their pointee alive while the owning object is alive:

UCLASS()
class AGameDirector : public AActor
{
    UPROPERTY() AEnemy* CurrentEnemy;   // kept alive
};

If you raw-pointer something, GC may collect it. Tag with UPROPERTY whenever the relationship matters.

AddToRoot Use Cases

Singleton-style UObjects (a content registry, a save manager) created at startup that should never be collected: AddToRoot. Pair with RemoveFromRoot in shutdown to allow clean teardown.

Verifying

Reproduce: spawn an actor, kick off async work, destroy the actor before completion. Should log “Owner gone” instead of crashing. Soak-test with many concurrent async kicks plus rapid spawn/destroy.

“Weak in lambdas. UPROPERTY in fields. Validate before deref. No mid-async crashes.”

Related Issues

For Blueprint async pending, see async task. For Replication Graph, see replication.

Weak captures. Validate. Lambdas survive.