Garbage collector

Learn how the C# GC works and the cost of allocation.

What is the garbage collector?

In a C# program the memory of objects that are no longer used is reclaimed automatically. The structure that does this is called the garbage collector (GC). When an object has no references left, the GC can clean it up.

Nesne kasa = new Nesne(); // allocation
kasa = null;              // no reference left
// the GC can clean this object

Thanks to the GC there is no need to free memory by hand.

The cost of allocation

Creating a new object means reserving memory, that is, an allocation. Every allocation raises the chance of the GC running, and small hiccups can happen at collection time. This is why producing new objects every frame is avoided.

void Update()
{
    // an allocation every frame raises GC pressure
    int[] dizi = new int[8];
}

A game with fewer allocations runs smoother.

Exercise Keep an allocation counter

In a class named BellekTakibi, define a string field named islem with the value "Tahsis" and an integer field named nesneSayisi with the value 3. In the Start method increase nesneSayisi by two and print the text "Toplam nesne: " joined with nesneSayisi using Debug.Log.

Show example solution

using UnityEngine;

public class BellekTakibi : MonoBehaviour
{
    string islem = "Tahsis";
    int nesneSayisi = 3;

    void Start()
    {
        nesneSayisi = nesneSayisi + 2;
        Debug.Log("Toplam nesne: " + nesneSayisi);
    }
}

Test yourself

When can an object be cleaned by the GC?
- Automatically in every frame
- When the script is compiled
- When the GameObject is added to the scene
- When it has no references left
Show answer

When it has no references left — The GC only cleans objects that no longer have any references; it does not touch reachable objects.

Trigger a GC collection manually

    System.____.Collect();

Show answer

    System.GC.Collect();

GC terms

GC (Garbage Collector)

The structure that reclaims memory
Tahsis

Reserving memory for a new object
Summing

The cleanup pass of the GC
Referans

The link that points to an object

Next lesson: Heap allocation

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