Allow for initialising a pool without starting it

[wjessop]

Maybe fixes #123

It's not perfect however: https://youtu.be/Oo_L_MHvEmo. In the video pb.go is:

package main

import (
	"math/rand"
	"os"
	"sync"
	"time"

	"github.com/wjessop/pb"
)

func main() {
	// create bars
	first := pb.New64(1000).Prefix("one ").SetUnits(pb.U_BYTES)
	second := pb.New64(1000).Prefix("two ").SetUnits(pb.U_BYTES)

	first.Output = os.Stderr
	second.Output = os.Stderr

	// start pool
	// pool, err := pb.StartPool(first, second)
	pool := pb.NewPool()
	pool.Output = os.Stderr
	err := pool.Start()
	if err != nil {
		panic(err)
	}

	// update bars
	wg := new(sync.WaitGroup)
	for _, bar := range []*pb.ProgressBar{first, second} {
		wg.Add(1)
		go func(cb *pb.ProgressBar) {
			for n := 0; n < 200; n++ {
				// cb.Increment()
				time.Sleep(time.Millisecond * time.Duration(rand.Intn(100)))
				cb.Add(5)
			}
			cb.Finish()
			wg.Done()
		}(bar)
	}
	wg.Wait()
	// close pool
	pool.Stop()
}

[cheggaaa]

Thank you! Merged

first.Output = os.Stderr
second.Output = os.Stderr

But these lines in example don't make sense. Only pool.Output has an effect in multiple bars case

[wjessop]

Any idea why the second run (see video) prints out three lines instead of two? It happens to me when running the example about 50% of the time.

[cheggaaa]

@wjessop how are you stopping the program?
pool waits to Interrupt signal for correct stop (or call pool.Stop() )

[wjessop]

I'm running the program with:

go run pb.go 

Go version go version go1.10 darwin/amd64

I'm just letting the program exit normally, so pool.Stop() should be getting called on the second to last line of the code above.

[cheggaaa]

Oh, I'm running your code whole and see the same result.
It's the small mistake in your code, you forgot to add bars objects to pb.NewPool
Just replace to pb.NewPool(first, second).

And I think I found new bug... in go 1.10 pool does not sense stop with ctrl+c (in go 1.9 all ok)

[wjessop]

When I add the progress bars to the pool the output it works as expected:

pool := pb.NewPool()
pool.Output = os.Stderr
pool.Add(first)
pool.Add(second)

I also noticed that if I ctrl-c the process nothing happens. If I ctrl-c the process twice it does interrupt.