Go CPU usage more than 100% without goroutine

Hi everyone,

I am new to go. I am wondering why my go program use more than 100% cpu. I got confused because I did not use any goroutine. In the test example below, it used 130% and 200% of CPU in a short period of time during the execution on my machine (I have the other program that processes a file into a map[string]*Person that runs constantly at 200%). Does go automatically implement the program concurrently? I cannot find any material about it due to my poor google skills. Thank you very much for the helps!

package main

import (

type Person struct {
	Name string
	ID   int

func main() {
	n := int(10e6)
	people := make(map[int]*Person)
	for i := 1; i < n; i++ {
		person := RandPerson()
		people[person.ID] = person
	println(len(people), "#####", n)

func RandPerson() *Person {
	name := make([]byte, 50)
	for i := 0; i < 50; i++ {
		name[i] = byte(65 + rand.Intn(25))
	id := rand.Intn(10e6)
	return &Person{
		Name: string(name),
		ID:   id,

time ./randperson
real 0m11.924s
user 0m17.379s
sys 0m0.544s

Garbage collection. You’re allocating a lot of memory, so there will be certain amount of garbage collection in order to free up memory, even though you’re not generating much garbage in this example.

1 Like

Thank you. Do you know what usually will cause the program run more than 1 thread besides garbage collection? All those “unintentionally” cpu usage should be safe?

I good trick to avoid CPU overhead in this cases is to insert a small delay in the main loop, eg:


Of course you can use a smaller convenient value…

1 Like

If you don’t do any concurrent processing yourself, or use packages that do, I wouldn’t expect any concurrent processing, no. But garbage collection is always concurrent with the rest of the program. This is normal, expected and indeed safe.

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