[FLINK-20764] In BatchGroupedReduceOperator, fix timer logic

This closes apache#14489

flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/BatchGroupedReduceOperator.java

@@ -69,9 +69,13 @@ public void processElement(StreamRecord<IN> element) throws Exception {
  IN value = element.getValue();
  IN currentValue = values.value();
 
- if (currentValue != null) {
- value = userFunction.reduce(currentValue, value);
+ if (currentValue == null) {
+ // register a timer for emitting the result at the end when this is the
+ // first input for this key
  timerService.registerEventTimeTimer(VoidNamespace.INSTANCE, Long.MAX_VALUE);
+ } else {
+ // otherwise, reduce things
+ value = userFunction.reduce(currentValue, value);
  }
  values.update(value);
  }

flink-streaming-java/src/test/java/org/apache/flink/streaming/api/operators/BatchGroupedReduceOperatorTest.java

@@ -0,0 +1,124 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ * <p>
+ * http:https://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.streaming.api.operators;
+
+import org.apache.flink.api.common.functions.ReduceFunction;
+import org.apache.flink.api.common.typeinfo.BasicTypeInfo;
+import org.apache.flink.api.common.typeutils.base.StringSerializer;
+import org.apache.flink.streaming.api.watermark.Watermark;
+import org.apache.flink.streaming.runtime.streamrecord.StreamRecord;
+import org.apache.flink.streaming.util.KeyedOneInputStreamOperatorTestHarness;
+import org.apache.flink.util.TestLogger;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import java.util.ArrayDeque;
+
+import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.empty;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Tests {@link BatchGroupedReduceOperator}.
+ */
+public class BatchGroupedReduceOperatorTest extends TestLogger {
+
+ @Rule
+ public ExpectedException expectedException = ExpectedException.none();
+
+ @Test
+ public void noIncrementalResults() throws Exception {
+ KeyedOneInputStreamOperatorTestHarness<String, String, String> testHarness = createTestHarness();
+
+ testHarness.processElement(new StreamRecord<>("hello"));
+ testHarness.processElement(new StreamRecord<>("hello"));
+ testHarness.processElement(new StreamRecord<>("ciao"));
+ testHarness.processElement(new StreamRecord<>("ciao"));
+
+ assertThat(
+ testHarness.getOutput(),
+ empty());
+ }
+
+ @Test
+ public void resultsOnMaxWatermark() throws Exception {
+ KeyedOneInputStreamOperatorTestHarness<String, String, String> testHarness = createTestHarness();
+
+ testHarness.processElement(new StreamRecord<>("hello"));
+ testHarness.processElement(new StreamRecord<>("hello"));
+ testHarness.processElement(new StreamRecord<>("ciao"));
+ testHarness.processElement(new StreamRecord<>("ciao"));
+ testHarness.processElement(new StreamRecord<>("ciao"));
+
+ testHarness.processWatermark(Long.MAX_VALUE);
+
+ ArrayDeque<Object> expectedOutput = new ArrayDeque<>();
+ expectedOutput.add(new StreamRecord<>("hellohello", Long.MAX_VALUE));
+ expectedOutput.add(new StreamRecord<>("ciaociaociao", Long.MAX_VALUE));
+ expectedOutput.add(new Watermark(Long.MAX_VALUE));
+
+ assertThat(
+ testHarness.getOutput(),
+ contains(expectedOutput.toArray()));
+ }
+
+ @Test
+ public void resultForSingleInput() throws Exception {
+ KeyedOneInputStreamOperatorTestHarness<String, String, String> testHarness = createTestHarness();
+
+ testHarness.processElement(new StreamRecord<>("hello"));
+ testHarness.processElement(new StreamRecord<>("ciao"));
+
+ testHarness.processWatermark(Long.MAX_VALUE);
+
+ ArrayDeque<Object> expectedOutput = new ArrayDeque<>();
+ expectedOutput.add(new StreamRecord<>("hello", Long.MAX_VALUE));
+ expectedOutput.add(new StreamRecord<>("ciao", Long.MAX_VALUE));
+ expectedOutput.add(new Watermark(Long.MAX_VALUE));
+
+ assertThat(
+ testHarness.getOutput(),
+ contains(expectedOutput.toArray()));
+ }
+
+ private KeyedOneInputStreamOperatorTestHarness<String, String, String> createTestHarness() throws Exception {
+ BatchGroupedReduceOperator<String, Object> operator =
+ new BatchGroupedReduceOperator<>(new Concatenator(), StringSerializer.INSTANCE);
+
+ KeyedOneInputStreamOperatorTestHarness<String, String, String> testHarness =
+ new KeyedOneInputStreamOperatorTestHarness<>(
+ operator,
+ in -> in,
+ BasicTypeInfo.STRING_TYPE_INFO);
+
+ testHarness.setup();
+ testHarness.open();
+
+ return testHarness;
+ }
+
+ static class Concatenator implements ReduceFunction<String> {
+ @Override
+ public String reduce(String value1, String value2) throws Exception {
+ return value1 + value2;
+ }
+ }
+}