code: func (u *ConcurrentUploader) Upload(name string, src isolatedclient.Source, ps *isolatedclient.PushState, done func()) {
  	u.wg.Add(1)
  	go u.upload(name, src, ps, done)
  }
docs: // Upload uploads an item from an isolated.Source. Upload does not block. If
  // not-nil, the done func will be invoked on upload completion (both success
  // and failure).