In this lesson, you will learn how to manually trigger Unreal Engine’s Garbage Collector during loading screens to reclaim memory without causing distracting gameplay stutters.
The Problem with Automatic Cleanup
Under normal circumstances, Unreal Engine automatically runs the Garbage Collector (GC) at specific intervals. However, when your game performs memory-intensive tasks—like loading a massive new level or swapping out heavy texture sets—the engine’s memory footprint can spike. If you wait for the automatic cycle, your game might hit a memory ceiling, leading to crashes or performance hits right when you need smoothness the most.
Taking Control with ForceGarbageCollection
Because you already understand the UObject lifecycle and the importance of UPROPERTY references, you know that the GC identifies "unreachable" objects and wipes them from memory. When you are transitioning between levels, the player is usually staring at a loading screen. This is the "safe zone" where we can force the engine to work immediately.
To manually trigger this process, you use the ForceGarbageCollection function. This forces a full sweep of all objects that are no longer referenced.
// Inside your loading manager class during a level transition:
#include "Engine/Engine.h"
void AMyLoadingManager::PerformCleanup()
{
// Force a full GC cycle to free up memory before the next level starts
GEngine->ForceGarbageCollection(true);
}
Why during a Loading Screen?
Triggering a collection cycle is a heavy operation. It pauses the game logic to traverse the object graph and verify references. If you trigger this during active gameplay, the player will perceive it as a sudden "hitch" or frame drop. By calling it during a loading screen, you hide the performance cost behind an existing transition, ensuring the new level begins with a clean, lean memory state.
Always ensure you have properly cleared your UPROPERTY references before calling this, otherwise, the GC will see those references and keep those objects alive, defeating the purpose of your manual clear.
Key Takeaway: Use GEngine->ForceGarbageCollection(true) only during non-interactive loading states to aggressively reclaim memory and prevent performance hitches during active gameplay.