Connect nodes in parallel

[Stebalien]

See: #61 (comment)

[davinci26]

What do you about either expanding or writing a function similar to mapWithOutput to do the connect calls in parallel. Its basically a combination of connectNodes with mapWithOutput

func mapConnectWithOutput(from, to []int, nodes []testbedi.Core, timeout time.Duration) ([]Result, error) {
	var wg sync.WaitGroup
	var lk sync.Mutex

	var results []Result

       	if err := validRange(to, len(nodes)); err != nil {
		return results, err
	}

	if err := validRange(from, len(nodes)); err != nil {
		return results, err
	}

	for _, f := range from {
		for _, t := range to {
			wg.Add(1)
			go func(from, to int, nodeFrom, nodeTo testbedi.Core) {
				defer wg.Done()
				ctx, cancel := context.WithTimeout(context.Background(), timeout)
				defer cancel()

				err := nodeFrom.Connect(ctx, nodeTo)

				lk.Lock()
				defer lk.Unlock()
				results = append(results, Result{
					Node:   from,
					Output: nil,
					Error:  errors.Wrapf(err, "node[%d] => node[%d]", from, to),
				})

			}(f, t, nodes[f], nodes[t])
		}
	}

	wg.Wait()
	return results, nil
}

It definitely needs testing and polishing but I think it conveys the idea.

Another idea is to use the mapListWithOutput that is under development in PR #75

What do you think?

[travisperson]

We can probably throw that code into connectNodes. Returning the results is fine as well, I just wouldn't call it mapConnectWithOutput as it's not really a map like function (apply a function over an input).