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https://issues.apache.org/jira/browse/FLINK-4391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15633155#comment-15633155
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ASF GitHub Bot commented on FLINK-4391:
---------------------------------------
Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/2629#discussion_r86333894
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/async/AsyncWaitOperator.java
---
@@ -0,0 +1,256 @@
+/*
+ * 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.operators.async;
+
+import org.apache.flink.annotation.Internal;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.core.fs.FSDataInputStream;
+import org.apache.flink.core.fs.FSDataOutputStream;
+import org.apache.flink.core.memory.DataInputViewStreamWrapper;
+import org.apache.flink.runtime.util.DataOutputSerializer;
+import org.apache.flink.streaming.api.datastream.AsyncDataStream;
+import org.apache.flink.streaming.api.functions.async.AsyncFunction;
+import org.apache.flink.streaming.api.graph.StreamConfig;
+import org.apache.flink.streaming.api.operators.AbstractUdfStreamOperator;
+import org.apache.flink.streaming.api.operators.ChainingStrategy;
+import org.apache.flink.streaming.api.operators.OneInputStreamOperator;
+import org.apache.flink.streaming.api.operators.Output;
+import org.apache.flink.streaming.api.operators.TimestampedCollector;
+import org.apache.flink.streaming.api.watermark.Watermark;
+import org.apache.flink.streaming.runtime.streamrecord.LatencyMarker;
+import org.apache.flink.streaming.runtime.streamrecord.StreamElement;
+import org.apache.flink.streaming.runtime.streamrecord.StreamRecord;
+import org.apache.flink.streaming.runtime.tasks.StreamTask;
+import org.apache.flink.util.Preconditions;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+@Internal
+public class AsyncWaitOperator<IN, OUT>
+ extends AbstractUdfStreamOperator<OUT, AsyncFunction<IN, OUT>>
+ implements OneInputStreamOperator<IN, OUT>
+{
+ private final int DEFAULT_BUFFER_SIZE = 1000;
+
+ private static final long serialVersionUID = 1L;
+
+ /**
+ * {@link TypeSerializer} for inputs while making snapshots.
+ */
+ private transient TypeSerializer<IN> inTypeSerializer;
+ private transient DataOutputSerializer outputSerializer;
+
+ /**
+ * input stream elements from the state
+ */
+ private transient List<StreamElement> inputsFromState;
--- End diff --
I think the `inputsFromState` can be of type `Collection`. Maybe we could
rename this field into `unprocessedStreamElements` or `recoveredStreamElements`.
> Provide support for asynchronous operations over streams
> --------------------------------------------------------
>
> Key: FLINK-4391
> URL: https://issues.apache.org/jira/browse/FLINK-4391
> Project: Flink
> Issue Type: New Feature
> Components: DataStream API
> Reporter: Jamie Grier
> Assignee: david.wang
>
> Many Flink users need to do asynchronous processing driven by data from a
> DataStream. The classic example would be joining against an external
> database in order to enrich a stream with extra information.
> It would be nice to add general support for this type of operation in the
> Flink API. Ideally this could simply take the form of a new operator that
> manages async operations, keeps so many of them in flight, and then emits
> results to downstream operators as the async operations complete.
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