A concurrent implementation of Sieve of Eratosthenes

sieve_of_eratosthenes.go

package main

import (
	"fmt"
	"os"
	"strconv"
)

func main() {
	if len(os.Args) != 2 {
		fmt.Printf("Usage: %s max_num", os.Args[0])
		return
	}
	maxNum, err := strconv.Atoi(os.Args[1])
	if err != nil {
		fmt.Print(err)
		return
	} else {
		fmt.Printf("Primes below %d\n", maxNum)
	}

	// for every n < maxnum create a sieve for it and pass to a closure which pushes back multiples of n.
	// These values are deleted from a prepared m
	m := make(map[int]bool, maxNum)
	// ch := make(chan int, maxNum)
	for i := 2; i < maxNum; i++ {
		m[i] = true
	}
	ch := make(chan int, maxNum-2)
	for i := 2; i < maxNum; i++ {
		go func(n int, ch chan int) {
			for i := 2; i*n < maxNum; i++ {
				delete(m, i*n)
			}
			ch <- 0
		}(i, ch)
	}
	for i := 2; i < maxNum; i++ {
		<-ch // safer since the map is only traversed after all go routines have exited
	}
	for k := range m {
		fmt.Println(k)
	}
}

Would love to see one using channels but I felt this is good enough.