func (r *PipeReader) CloseWithError(err error) error {
	err = r.PipeReader.CloseWithError(err)
	r.wait()
	return err
}

// WaitPipe implements wait-group backend io.Pipe to provide
// synchronization between read() end with write() end.
func WaitPipe() (*PipeReader, *PipeWriter) {
	r, w := io.Pipe()
	var wg sync.WaitGroup
	wg.Add(1)
	return &PipeReader{
			PipeReader: r,
			wait:       wg.Wait,