Github user markap14 commented on a diff in the pull request:
https://github.com/apache/nifi/pull/295#discussion_r57018795
--- Diff:
nifi-nar-bundles/nifi-kafka-bundle/nifi-kafka-processors/src/main/java/org/apache/nifi/processors/kafka/Partitioners.java
---
@@ -0,0 +1,87 @@
+/*
+ * 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.nifi.processors.kafka;
+
+import java.util.Random;
+
+import kafka.producer.Partitioner;
+import kafka.utils.VerifiableProperties;
+
+/**
+ * Collection of implementation of common Kafka {@link Partitioner}s.
+ */
+final public class Partitioners {
+
+ private Partitioners() {
+ }
+ /**
+ * {@link Partitioner} that implements 'round-robin' mechanism which
evenly
+ * distributes load between all available partitions.
+ */
+ public static class RoundRobinPartitioner implements Partitioner {
+ private volatile int index;
--- End diff --
The use of 'volatile' here implies that this is intended to be thread-safe.
However, the next() method is not thread-safe. Specifically, Thread 1 could
check `(index == numberOfPartitions)` and get `false`. Then Thread 2 could do
the same thing. Then Thread 1 evaluates `indexToReturn = index++` resulting in
index == numberOfPartitions; Thread 2 then evaluates `indexToReturn = index++`
which results in indexToReturn == numberOfPartitions, which is larger than it
should be.
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