Fixed number worker pool implementation #1

pool.go

type Pool struct {
	n   int
	run func(context.Context)
	ctx    context.Context
	cancel context.CancelFunc
	wg     sync.WaitGroup
}

func NewPool(n int, run func(context.Context)) *Pool {
	ctx, cancel := context.WithCancel(context.Background())
	return &Pool{
		n:      n,
		run:    run,
		ctx:    ctx,
		cancel: cancel,
	}
}

func (p *Pool) Start() {
	for i := 0; i < p.n; i++ {
		go p.launch()
	}
}

func (p *Pool) launch() {
	p.wg.Add(1)
	defer p.wg.Done()
	defer func() {
		select {
		case <-p.ctx.Done():
		default:
			go p.launch()
		}
	}()
	p.run(p.ctx)
}

func (p *Pool) Stop() {
	p.cancel()
}

func (p *Pool) Wait() {
	<-p.ctx.Done()
	p.wg.Wait()
}