golang parallel async tasks, sending results to channel, completion tracked by WaitGroup

main.go

package main

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

type QueryResult struct {
	key    string
	result string
}

func main() {
	// runs tasks in parallel, tracking completion with a WaitGroup.
	// tasks publish their result to a channel.
	// channel is closed when WaitGroup finishes.
	start := time.Now()
	queries := map[string]int{
		"a": 1,
		"b": 3,
		"c": 3,
		"d": 3,
		"e": 5,
	}
	numQueries := len(queries)

	var wg sync.WaitGroup
	wg.Add(numQueries)

	resultChan := make(chan QueryResult)

	for key, waitTime := range queries {
		go func(k string, num int) {
			defer wg.Done()
			fmt.Printf("Going to query for key %s...\n", k)
			// sleep to mock a long running task
			time.Sleep(time.Duration(num) * time.Second)

			res := QueryResult{key: k, result: "done"}
			resultChan <- res
		}(key, waitTime)
	}

  // async wait and close channel
	go func() {
		wg.Wait()
		close(resultChan)
	}()

	results := map[string]string{}

	for res := range resultChan {
		fmt.Println("received result", res)
		results[res.key] = res.result
	}

	fmt.Println("collected results:", results)
	fmt.Println("took", time.Since(start))
}