package main

import (
	"runtime"
	"sync"
	"testing"
	"time"
)

const arraySize = 10

func BenchmarkOneProcessor(t *testing.B) {
	runtime.GOMAXPROCS(1)

	t.Run("Parallel", func(t *testing.B) {
		t.Helper()

		executionParallel("one")
	})

	t.Run("Sync", func(t *testing.B) {
		t.Helper()

		executionSequential("one")
	})
}

func BenchmarkManyProcessors(t *testing.B) {
	runtime.GOMAXPROCS(4)

	t.Run("Parallel", func(t *testing.B) {
		t.Helper()

		executionParallel("more")
	})

	t.Run("Sync", func(t *testing.B) {
		t.Helper()

		executionSequential("more")
	})
}

func doSomeExternalServiceAction() {
	time.Sleep(10 * time.Millisecond)
}

func executionParallel(s string) {
	var wg sync.WaitGroup
	i := 1

	for i < arraySize {
		wg.Add(1)

		go func(wg *sync.WaitGroup, i int) {
			defer wg.Done()

			doSomeExternalServiceAction()
		}(&wg, i)

		i++
	}

	wg.Wait()
}

func executionSequential(s string) {
	i := 1

	for i < arraySize {
		func() {
			doSomeExternalServiceAction()
		}()

		i++
	}
}

goos: linux
goarch: amd64
pkg: golang-parallel
BenchmarkOneProcessor/Parallel-4         	1000000000	         0.0102 ns/op
BenchmarkOneProcessor/Sync-4             	1000000000	         0.0916 ns/op
BenchmarkManyProcessors/Parallel-4       	1000000000	         0.0102 ns/op
BenchmarkManyProcessors/Sync-4           	1000000000	         0.0916 ns/op
PASS
ok  	golang-parallel	1.990s