forwarder

type GoWhere func([]string, []string) ([]VertexBuffer, error)

type StarterStopper interface {
	Start() <-chan struct{}
	Stop()
	ForceStop()
}

type ToWhichStepDecider interface {
	// WhereTo decides where to forward the result to based on the name of the step it returns.
	// It supports 2 addition keywords which need not be a step name. They are "ALL" and "DROP"
	// where former means, forward to all the neighbouring steps and latter means do not forward anywhere.
	WhereTo([]string, []string) ([]VertexBuffer, error)
}

type VertexBuffer struct {
	ToVertexName         string
	ToVertexPartitionIdx int32
}