Slice fill with go's concurency based on the number of CPUs.

sliceFillWithConcurency.go

package main

import (
	"fmt"
	"sync"
)

func makeResult(i int) string {
  return fmt.Sprintf("this is %v", i)
}

func main() {
	var wg sync.WaitGroup

	const sliceLenght = 13
	
	applications := make([]int, sliceLenght, 10000)
	appStore := make([]string, len(applications))

	numberOfCPUs := 2
	incrementer := len(applications) / numberOfCPUs
	odd := len(applications) % numberOfCPUs
	moreCPUsThanListLenght := false
	if numberOfCPUs > len(applications) {
		moreCPUsThanListLenght = true
	}

	if moreCPUsThanListLenght {
		fmt.Println("More CPUs than the slice lenght")
		for i := range applications {
			wg.Add(1)
			go func(i int) {
				defer wg.Done()
				appStore[i] = makeResult(i)
			}(i)
		}
	} else {
		fmt.Println("Less CPUs than the slice lenght")
		for i := 1; i <= numberOfCPUs; i++ {
			wg.Add(1)
			go func(i int) {
				defer wg.Done()

				start := (i-1)*incrementer + odd
				if i == 1 {
					start = 0
				}
				end := i*incrementer + odd
				for j := start; j < end; j++ {
					appStore[j] = makeResult(j)
				}

			}(i)
		}
	}

	wg.Wait()
	
	// Let's test the result slice.
	for i := 0; i < sliceLenght; i++ {
		if appStore[i] != makeResult(i) {
			fmt.Printf("the result is not ok in %d, the result is '%v' but it should be '%v'\n", i, appStore[i], makeResult(i))
		}
	}
}