Slices and maps and concurrency in Go

slices-maps-concurrency.go

// https://play.golang.org/p/L8MVDTGHqhi
package main

import (
	"fmt"
	"sync"
)

func main() {
	feedIP([]string{"255.255.255.0", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "255.255.255.0", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "192.168.1.1", "255.255.255.0"})
	//feedIP([]string{"1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "90", "91", "92", "93", "94", "95", "96", "97", "98", "99"})
}

func feedIP(input []string) {
	var mu sync.Mutex
	var wg sync.WaitGroup

	ips := make(map[string]int)

	size := len(input) / 4 // cosidering 4 cores processor, 1 thread per core

	slInput1 := input[:size]             // from index 0 to position ´size´ (index ´size - 1´), in a slice of 1..100, corresponds to 1 to 25
	slInput2 := input[size : size*2]     // from index ´size´ to position ´size*2´ (index ´size*2-1´), in a slice of 1..100 corresponds to 26 to 50
	slInput3 := input[size*2 : size*3+1] // from index ´size*2´ to position ´size*3´ (index ´size*3-1´), in a slice of 1..100 corresponds to 51 to 76
	slInput4 := input[size*3+1:]         // from index ´size*3 + 1´ to the end, in a slice of 1..100, corresponds to 77 to 100; this approach (instead of using len(input)) is needed to handle properly the offset in slices with odd sizes

	/* debug purposes
	fmt.Println(size)
	fmt.Println(slInput1)
	fmt.Println(slInput2)
	fmt.Println(slInput3)
	fmt.Println(slInput4)
	*/

	// ´values´ is passed by value, ´bucket´ is passed by ref (not passed but map elements are pointers by design), ´wg´ is explicitly passed by ref
	feeder := func(values []string, bucket map[string]int, wg *sync.WaitGroup) {
		defer wg.Done()
		for _, i := range values {
			func() {
				mu.Lock()
				defer mu.Unlock()
				bucket[i]++
			}()
		}
	}

	wg.Add(1)
	go feeder(slInput1, ips, &wg)
	wg.Add(1)
	go feeder(slInput2, ips, &wg)
	wg.Add(1)
	go feeder(slInput3, ips, &wg)
	wg.Add(1)
	go feeder(slInput4, ips, &wg)

	wg.Wait()

	fmt.Println(ips)
}