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https://issues.apache.org/jira/browse/FLINK-4391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15633117#comment-15633117
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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_r86308486
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/async/AsyncCollectorBuffer.java
---
@@ -0,0 +1,494 @@
+/*
+ * 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.streaming.api.datastream.AsyncDataStream;
+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.util.Preconditions;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * AsyncCollectorBuffer will hold all {@link AsyncCollector} in its
internal buffer,
+ * and emit results from {@link AsyncCollector} to the next operators
following it by
+ * calling {@link Output#collect(Object)}
+ */
+@Internal
+public class AsyncCollectorBuffer<IN, OUT> {
+ private static final Logger LOG =
LoggerFactory.getLogger(AsyncCollectorBuffer.class);
+
+ /**
+ * Max number of {@link AsyncCollector} in the buffer.
+ */
+ private final int bufferSize;
+
+ private final AsyncDataStream.OutputMode mode;
+
+ private final AsyncWaitOperator<IN, OUT> operator;
+
+ /**
+ * {@link AsyncCollector} queue.
+ */
+ private final SimpleLinkedList<AsyncCollector<IN, OUT>> queue = new
SimpleLinkedList<>();
+ /**
+ * A hash map keeping {@link AsyncCollector} and their corresponding
{@link StreamElement}
+ */
+ private final Map<AsyncCollector<IN, OUT>, StreamElement>
collectorToStreamElement = new HashMap<>();
+ /**
+ * A hash map keeping {@link AsyncCollector} and their node references
in the #queue.
+ */
+ private final Map<AsyncCollector<IN, OUT>, SimpleLinkedList.Node>
collectorToQueue = new HashMap<>();
+
+ private final LinkedList<AsyncCollector> finishedCollectors = new
LinkedList<>();
+
+ /**
+ * {@link TimestampedCollector} and {@link Output} to collect results
and watermarks.
+ */
+ private TimestampedCollector<OUT> timestampedCollector;
+ private Output<StreamRecord<OUT>> output;
+
+ /**
+ * Locks and conditions to synchronize with main thread and emitter
thread.
+ */
+ private final Lock lock;
+ private final Condition notFull;
+ private final Condition taskDone;
+ private final Condition isEmpty;
+
+ /**
+ * Error from user codes.
+ */
+ private volatile Exception error;
+
+ private final Emitter emitter;
+ private final Thread emitThread;
+
+ private boolean isCheckpointing;
+
+ public AsyncCollectorBuffer(int maxSize, AsyncDataStream.OutputMode
mode, AsyncWaitOperator operator) {
+ Preconditions.checkArgument(maxSize > 0, "Future buffer size
should be greater than 0.");
+
+ this.bufferSize = maxSize;
--- End diff --
maybe we could rename `maxSize` into `bufferSize`. This makes it clearer
what the parameter is used for.
> 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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