[GitHub] aljoscha commented on a change in pull request #7470: [FLINK-11283] Accessing the key when processing connected keyed stream

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aljoscha commented on a change in pull request #7470: [FLINK-11283] Accessing the key when processing connected keyed stream
URL: https://github.com/apache/flink/pull/7470#discussion_r247888995
 
 

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 File path: flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/co/KeyedCoProcessFunction.java
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+/*
+ * 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
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.functions.co;
+
+import org.apache.flink.api.common.functions.AbstractRichFunction;
+import org.apache.flink.streaming.api.TimeDomain;
+import org.apache.flink.streaming.api.TimerService;
+import org.apache.flink.util.Collector;
+import org.apache.flink.util.OutputTag;
+
+/**
+ * A function that processes elements of two keyed streams and produces a single output one.
+ *
+ * <p>The function will be called for every element in the input streams and can produce
+ * zero or more output elements. Contrary to the {@link CoFlatMapFunction}, this function can also
+ * query the time (both event and processing) and set timers, through the provided {@link Context}.
+ * When reacting to the firing of set timers the function can emit yet more elements.
+ *
+ * <p>An example use-case for connected streams would be the application of a set of rules that change
+ * over time ({@code stream A}) to the elements contained in another stream (stream {@code B}). The rules
+ * contained in {@code stream A} can be stored in the state and wait for new elements to arrive on
+ * {@code stream B}. Upon reception of a new element on {@code stream B}, the function can now apply the
+ * previously stored rules to the element and directly emit a result, and/or register a timer that
+ * will trigger an action in the future.
+ *
+ * @param <K> Type of the key.
+ * @param <IN1> Type of the first input.
+ * @param <IN2> Type of the second input.
+ * @param <OUT> Output type.
+ */
+public abstract class KeyedCoProcessFunction<K, IN1, IN2, OUT> extends AbstractRichFunction {
+
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * This method is called for each element in the first of the connected streams.
+	 *
+	 * <p>This function can output zero or more elements using the {@link Collector} parameter
+	 * and also update internal state or set timers using the {@link CoProcessFunction.Context} parameter.
 
 Review comment:
   This should not refer to `CoProcessFunction.Context`. Same for the other references to that in this file.

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