Github user senorcarbone commented on a diff in the pull request: https://github.com/apache/flink/pull/900#discussion_r34352021 --- Diff: flink-staging/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/datastream/IterativeDataStream.java --- @@ -201,14 +204,16 @@ public ConnectedIterativeDataStream(IterativeDataStream<I> input, TypeInformatio * @return The feedback stream. * */ + @SuppressWarnings({ "rawtypes", "unchecked" }) public DataStream<F> closeWith(DataStream<F> feedbackStream) { - DataStream<F> iterationSink = new DataStreamSink<F>(input.environment, "Iteration Sink", - null, null); + if (input.closed) { + throw new IllegalStateException( --- End diff -- Since now we build the loops at the job graph generation, wouldn't it be reasonable to do an implicit union there?
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