golang-examples/example-go-channel/sendFunction.go

// https://www.digitalocean.com/community/tutorials/how-to-run-multiple-functions-concurrently-in-go
// who came up with the idea of making community tutorials. that was a good idea! (ya, that was me and Etel)

package main

import (
	"log"
	"sync"
)

type funcWait struct {
	f func()
	wgF sync.WaitGroup
	val int
	err error
	res int
}

var functionChan chan *funcWait
var afunc funcWait
var wg sync.WaitGroup

func generateNumbers(total int, ch chan<- *funcWait, af *funcWait) {
	log.Println("generateNumbers() START total =", total)
	ch <- af
	log.Println("generateNumbers() END total =", total)
}

func andlabsGoroutine(ch <-chan *funcWait, wg *sync.WaitGroup) {
	defer wg.Done()

	log.Println("andlabsGoroutine() START")
	for f := range ch {
		log.Println("andlabsGoroutine() read f() from channel")
		f.f()
		f.wgF.Done()
	}
	log.Printf("andlabsGoroutine() END")
}

func main() {
	functionChan = make(chan *funcWait)

	// syntax to get the return values from a channel
//	r := make(chan func() (int, error))
//	afunc.res, afunc.err = (<-r)()

	wg.Add(1)
	go andlabsGoroutine(functionChan, &wg)

	// afunc.wgF = wg
	afunc.f = func() {
		log.Println("\tGOT INSIDE: running f() from inside the structure & inside the wait group goroutine", afunc.val)
	}

	for idx := 1; idx <= 10; idx++ {
		log.Println("START waitgroup idx =", idx)
		afunc.val = idx * 20
		afunc.wgF.Add(1)
		generateNumbers(idx, functionChan, &afunc)
		afunc.wgF.Wait()
		log.Println("END waitgroup idx =", idx)
	}
	wg.Done()

	close(functionChan)
	// close(wg)

	log.Println("Waiting for goroutines to finish...")
	wg.Wait()
	log.Println("Done!")
}