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https://issues.apache.org/jira/browse/FLINK-4391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15581097#comment-15581097
 ] 

ASF GitHub Bot commented on FLINK-4391:
---------------------------------------

Github user bjlovegithub commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2629#discussion_r83573944
  
    --- Diff: 
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/async/AsyncCollector.java
 ---
    @@ -0,0 +1,85 @@
    +/*
    + * 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.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 AsyncCollectorBuffer<IN, OUT> buffer;
    +
    +   public AsyncCollector(AsyncCollectorBuffer<IN, OUT> buffer) {
    +           this.buffer = buffer;
    +   }
    +
    +   public AsyncCollector(AsyncCollectorBuffer<IN, OUT> buffer, boolean 
isDone) {
    +           this(buffer);
    +           this.isDone = isDone;
    +   }
    +
    +   /**
    +    * Set result
    +    * @param result A list of results.
    +    */
    +   public void collect(List<OUT> result) {
    +           this.result = result;
    +           isDone = true;
    +           buffer.mark(this);
    +   }
    +
    +   /**
    +    * Set error
    +    * @param error A Throwable object.
    +    */
    +   public void collect(Throwable error) {
    +           this.error = error;
    +           isDone = true;
    +           buffer.mark(this);
    +   }
    +
    +   /**
    +    * Get result. Throw RuntimeException while encountering an error.
    +    *
    +    * @return A List of result.
    +    * @throws RuntimeException RuntimeException wrapping errors from user 
codes.
    +    */
    +   public List<OUT> getResult() throws RuntimeException {
    --- End diff --
    
    That makes me clarify about how to use RuntimeException ;D
    I prefer using IOException, since the error is from I/O process. I will 
change RuntimeException into IOException in the codes.


> 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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