channels_and_wait_groups.go

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	fmt.Println("Starting program...")

	maxItemCount := 10
	wg := sync.WaitGroup{}
	processed := make(chan int)
	final := []int{}

	for i := 0; i < maxItemCount; i++ {
		wg.Add(1)
		go doSomething(&wg, i, processed)
	}

	go func() {
		for item := range processed {
      // Exaggerate a long processing operation when consuming channel items
			time.Sleep(5 * time.Second)
			fmt.Printf("Processed %d\n", item)
			final = append(final, item)
		}
	}()

	wg.Wait()
	close(processed)

	fmt.Printf("Final: %v\n", final)
	fmt.Println("-------------------")
	fmt.Printf("Initial item count:  %d\n", maxItemCount)
	fmt.Printf("Final item count:    %d\n", len(final))
}

func doSomething(wg *sync.WaitGroup, input int, output chan<- int) {
	defer wg.Done()

	fmt.Printf("[%d] Starting DoSomething\n", input)

	fmt.Printf("[%d] Starting long processing\n", input)
	time.Sleep(2 * time.Second)
	fmt.Printf("[%d] Finished long processing\n", input)

	output <- input * 100
}

/*
Starting program...
[0] Starting DoSomething
[0] Starting long processing
[6] Starting DoSomething
[6] Starting long processing
[7] Starting DoSomething
[7] Starting long processing
[8] Starting DoSomething
[8] Starting long processing
[1] Starting DoSomething
[1] Starting long processing
[3] Starting DoSomething
[3] Starting long processing
[2] Starting DoSomething
[2] Starting long processing
[4] Starting DoSomething
[4] Starting long processing
[5] Starting DoSomething
[5] Starting long processing
[9] Starting DoSomething
[9] Starting long processing
[9] Finished long processing
[2] Finished long processing
[8] Finished long processing
[7] Finished long processing
[0] Finished long processing
[1] Finished long processing
[3] Finished long processing
[4] Finished long processing
[6] Finished long processing
[5] Finished long processing
Processed 900
Processed 200
Processed 700
Processed 800
Processed 0
Processed 100
Processed 300
Processed 400
Processed 600
Final: [900 200 700 800 0 100 300 400 600]
-------------------
Initial item count:  10
Final item count:    9
*/