Worker Pool

package main

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

func worker(id int, jobs <-chan int, results chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for job := range jobs {
		fmt.Printf("worker %d started job %d\n", id, job)
		time.Sleep(200 * time.Millisecond) // simulate work
		results <- job * 2
	}
	fmt.Printf("worker %d done\n", id)
}

func main() {
	const numJobs = 10
	const numWorkers = 3

	jobs := make(chan int, numJobs)
	results := make(chan int, numJobs)
	var wg sync.WaitGroup

	for i := 1; i <= numWorkers; i++ {
		wg.Add(1)
		go worker(i, jobs, results, &wg)
	}

	for j := 1; j <= numJobs; j++ {
		jobs <- j
	}
	close(jobs) // graceful shutdown: workers drain remaining jobs

	go func() {
		wg.Wait()
		close(results)
	}()

	for r := range results {
		fmt.Println("result:", r)
	}
}