When does instances get garbage collected ?

Development Programming & Scripting
,
1

I have a simple code snippet that runs on tick

On the first tick i create a scene component that i have derived into my own class UCSWSceneComponent

I have a UPROPERTY() declaration in a parent scene component

UPROPERTY(Transient, VisibleAnywhere, Category = "CSW");
TObjectPtr<UCSWSceneComponent> trans;

I have a counter so the first tick i call

trans = NewObject<UCSWSceneComponent>(this,TEXT("Test"));

trans->RegisterComponent();

trans->AttachToComponent(this, FAttachmentTransformRules::KeepRelativeTransform);

and when tick has run for 1000 times i call

trans->DestroyComponent();		

trans = nullptr;

But the code never gets deallocated. Either in play mode or in editor mode ?
When will it be GCed ?

2

Assuming you meant the object, it will. How are you testing this? Logging in destructor?

Typically, sometime within 1 minute.

3

I can see that my test code wasnt exact. I added a sub component (USceneComponent) to trans instance component before i called DestroyComponent. If i dont add this component it will be GCed but when i add the sub component, the sub component is transfered to the parent of the trans component but trans will never be GCed even if it is marked for GC

4

You could invoke garbage collection manually via

GEngine->ForceGarbageCollection(true);
5

Interesting.

I threw together a quick test to try to reproduce, but everything worked as expected (in 5.4.4):

[2024.12.03-16.19.43:083][589]LogTemp: Creating TestSceneComponent
[2024.12.03-16.19.43:083][589]LogTemp: TestSceneComponent Constructed
[2024.12.03-16.19.43:083][589]LogTemp: TestChildSceneComponent parent is now TestSceneComponent (was null)
[2024.12.03-16.19.45:691][738]LogTemp: Destroying TestSceneComponent
[2024.12.03-16.19.45:692][738]LogTemp: TestChildSceneComponent parent is now RootComponent (was TestSceneComponent)
[2024.12.03-16.20.32:091][296]LogTemp: TestSceneComponent Destructed

What version are you using?
Not sure how different out setups are, this is the actor code I was using:

ATestActor::ATestActor() : TestComponent(nullptr), TickCounter(0)
{
 	PrimaryActorTick.bCanEverTick = true;
	USceneComponent *RootComponent = CreateDefaultSubobject<USceneComponent>(TEXT("RootComponent"));
	SetRootComponent(RootComponent);
}

void ATestActor::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);
	++TickCounter;
	if (TickCounter == 1) {
		UE_LOG(LogTemp, Log, TEXT("Creating TestSceneComponent"));
		TestComponent = NewObject<UTestSceneComponent>(this, TEXT("TestSceneComponent"));
		TestComponent->RegisterComponent();
		TestComponent->AttachToComponent(GetRootComponent(), FAttachmentTransformRules::KeepRelativeTransform);
		UTestChildSceneComponent *TestChildComponent = NewObject<UTestChildSceneComponent>(this, TEXT("TestChildSceneComponent"));
		TestChildComponent->RegisterComponent();
		TestChildComponent->AttachToComponent(TestComponent, FAttachmentTransformRules::KeepRelativeTransform);
	} else if (TickCounter == 150) {
		UE_LOG(LogTemp, Log, TEXT("Destroying TestSceneComponent"));
		TestComponent->DestroyComponent();
		TestComponent = nullptr;
	}
}

TestSceneComponent just logs in ctor/dtor.
TestChildSceneComponent just constantly checks it parent and logs changes.

6

I do the same in principal but i do tick an actor from the editor as well

Version 5.5.0

7

You can find my project at

wich is a project in work. You can see the problem when unloading/loading maps by changing the map urls between a valid map and an empty string. Map is provided in project under /maps