mpb render delay bug example

main.go

package main

import (
	"context"
	"fmt"
	"math/rand"
	"sync"
	"time"

	"github.com/vbauerster/mpb/v8"
	"github.com/vbauerster/mpb/v8/decor"
)

func main() {
	const delay = time.Second * 10
	var wg sync.WaitGroup
	// passed wg will be accounted at p.Wait() call
	p := mpb.New(mpb.WithWaitGroup(&wg), mpb.WithRenderDelay(renderDelay(context.Background(), delay)))
	total, numBars := 100, 3
	wg.Add(numBars)

	for i := 0; i < numBars; i++ {
		name := fmt.Sprintf("Bar#%d:", i)
		bar := p.AddBar(int64(total),
			mpb.PrependDecorators(
				decor.Name(name),
				decor.Percentage(decor.WCSyncSpace),
			),
		)
		// simulating some work
		go func() {
			defer wg.Done()
			rng := rand.New(rand.NewSource(time.Now().UnixNano()))
			max := 100 * time.Millisecond
			for i := 0; i < total; i++ {
				time.Sleep(time.Duration(rng.Intn(10)+1) * max / 10)
				bar.IncrBy(i)
			}
			bar.Abort(true) // BAD: Causes a render even if render delay hasn't expired.
		}()
	}
	// wait for passed wg and for all bars to complete and flush
	p.Wait()
}

// renderDelay returns a channel that will be closed after d,
// or if ctx is done.
func renderDelay(ctx context.Context, d time.Duration) <-chan struct{} {
	ch := make(chan struct{})
	t := time.NewTimer(d)
	go func() {
		defer close(ch)
		defer t.Stop()
		select {
		case <-ctx.Done():
		case <-t.C:
		}
	}()
	return ch
}