Incorrect delay calculation: The max() function compares (_pollingInterval.inMilliseconds - timeSincePoll.inMilliseconds) with _pollingInterval.inMilliseconds. Since timeSincePoll is always positive (time elapsed during the poll), the first argument will always be less than the second, so max() will always return _pollingInterval.inMilliseconds. This means the delay will always be the full polling interval, completely ignoring the time already spent polling. The correct logic should use max(0, _pollingInterval.inMilliseconds - timeSincePoll.inMilliseconds) to ensure the delay is never negative while properly accounting for elapsed time.

Resource leak: The HTTP client _client is never closed when the polling data source stops. Unlike the streaming data source which properly closes _pollingClient in its stop() method (line 158 in streaming_data_source.dart), the polling data source's stop() method doesn't close the client, leading to a resource leak. The stop() method should call _client.close() to properly clean up resources.