[GitHub] [kafka] thomaslee commented on pull request #9111: KAFKA-10337: await async commits in commitSync even if no offsets given

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thomaslee commented on pull request #9111:
URL: https://github.com/apache/kafka/pull/9111#issuecomment-669624137


   It's somewhat easy to do it accidentally. The scenario I was concerned about looks something like this with auto offset commits disabled:
   
   ```java
   KafkaConsumer<...> consumer = ...;
   Map<TopicPartition, OffsetAndMetadata> offsets = new HashMap<>();
   
   //
   // in a message processing loop
   //
   consumer.commitAsync(offsets);
   offsets = new HashMap<>();
   
   //
   // before a rebalance (e.g. onPartitionsRevoked)
   //
   consumer.commitSync(offsets);
   ```
   
   Per the docs the `commitSync` call should ensure that the async commit finishes prior to the rebalance, but it may not if `offsets` is empty here.


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