code: func Run(workers int, gen func(chan<- func() error)) <-chan error {
  	r := Runner{
  		Maximum:   workers,
  		Sustained: workers,
  	}
  	return r.runThen(gen, r.Close)
  }
docs: // Run executes a generator function, dispatching each generated task to the
  // Runner. Run returns immediately with an error channel that can be used to
  // reap the results of those tasks.
  //
  // The returned error channel must be consumed, or it can block additional
  // functions from being run from gen. A common consumption function is
  // errors.MultiErrorFromErrors, which will buffer all non-nil errors into an
  // errors.MultiError. Other functions to consider are Must and Ignore (in this
  // package).
  //
  // Note that there is no association between error channel's error order and
  // the generated task order. However, the channel will return exactly one error
  // result for each generated task.
  //
  // If workers is <= 0, it will be unbounded; otherwise, a pool of at most
  // workers sustained goroutines will be used to execute the task.