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https://issues.apache.org/jira/browse/FLINK-4391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15633108#comment-15633108
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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_r86308340
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/async/AsyncCollector.java
---
@@ -0,0 +1,86 @@
+/*
+ * 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 java.io.IOException;
+import java.util.List;
+
+/**
+ * {@link AsyncCollector} collects data / error in user codes while
processing async i/o.
+ *
+ * @param <IN> Input type
+ * @param <OUT> Output type
+ */
+@Internal
+public class AsyncCollector<IN, OUT> {
+ private List<OUT> result;
+ private Throwable error;
+
+ private boolean isDone = false;
+
+ private final AsyncCollectorBuffer<IN, OUT> buffer;
+
+ public AsyncCollector(AsyncCollectorBuffer<IN, OUT> buffer) {
+ this.buffer = buffer;
--- End diff --
Maybe we could check for not null via `Preconditions.checkNotNull()`. This
allows to fail early when preconditions are not fulfilled.
> 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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