What is GC?

Learn the main goal of the garbage collector.

What is GC?

The garbage collector (GC) automatically reclaims heap memory the program can no longer reach. Go has no free call; if no root (globals, goroutine stacks, registers) can reach an object, the GC collects it.

func yeni() *Dugum {
    d := &Dugum{}  // escapes to the heap
    return d
}

p := yeni()
p = nil  // no longer reachable → collected at the next GC

Go's GC is concurrent and low-latency: pauses are usually under a millisecond.

Stack or heap?

Only heap memory loads the GC. Values that stay inside a function and don't escape live on the stack and are freed for free when the function returns. The compiler decides where each goes with escape analysis. Fewer heap allocations = less GC work.

Exercise GC count

Read NumGC with runtime.ReadMemStats, call runtime.GC() and read it again. Print whether the count increased (after > before).

Show example solution

package main

import (
    "fmt"
    "runtime"
)

func main() {
    var a, b runtime.MemStats
    runtime.ReadMemStats(&a)
    runtime.GC()
    runtime.ReadMemStats(&b)
    fmt.Println(b.NumGC > a.NumGC)
}

Test yourself

What is required for an object to be collected?
- The function must have returned
- It must be unreachable from every root
- It must be marked with free
- It must have been assigned nil
Show answer

It must be unreachable from every root — The GC looks at reachability; assigning nil only makes the object unreachable if it was the last reference.

Trigger GC manually

runtime.____()  // genellikle gerekmez

Show answer

runtime.GC()  // genellikle gerekmez

Memory concepts

Root

Global and stack references
Heap

Memory the GC manages
Stack

Freed with the function
Unreachable object

Gets collected

Next lesson: Tri-color marking

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