What is GC?
- Go course
- Expert
- Lesson 7/34
- 4 min
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 GCGo'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.
Practice GC count
Read NumGC with runtime.ReadMemStats, call runtime.GC() and read it again. Print whether the count increased (after > before).
Starter code
package main
import (
"fmt"
"runtime"
)
func main() {
// buraya yaz
}Sample 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)
}Expected output
true
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is required for an object to be collected?
- The function must have returned
- It must be unreachable from every root Correct answer
- It must be marked with free
- It must have been assigned nil
Explanation: The GC looks at reachability; assigning nil only makes the object unreachable if it was the last reference.
2 Trigger GC manually
runtime.____() // genellikle gerekmezruntime.GC() // genellikle gerekmezExplanation: runtime.GC() forces a collection cycle; it is rarely used outside measurements and tests.
3 Memory concepts
| Term | Meaning |
|---|---|
Root |
Global and stack references |
Heap |
Memory the GC manages |
Stack |
Freed with the function |
Unreachable object |
Gets collected |