[jira] [Created] (KAFKA-10723) LogManager shutdown error handler doesn't shutdown all internal thread pools

["Kowshik Prakasam (Jira)" <ji...@apache.org>]

Kowshik Prakasam created KAFKA-10723:
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             Summary: LogManager shutdown error handler doesn't shutdown all internal thread pools
                 Key: KAFKA-10723
                 URL: https://issues.apache.org/jira/browse/KAFKA-10723
             Project: Kafka
          Issue Type: Bug
            Reporter: Kowshik Prakasam


*TL;DR:*

The asynchronous shutdown in LogManager has the shortcoming that if during shutdown any of the internal futures fail, then we do not always ensure that all futures are completed before LogManager.shutdown returns. As a result, despite the shut down completed message from KafkaServer is seen in the error logs, some futures continue to run from inside LogManager attempting to close the logs.



*Description:*

When LogManager is shutting down, exceptions in log closure are handled [here|https://github.com/apache/kafka/blob/trunk/core/src/main/scala/kafka/log/LogManager.scala#L497-L501]. However, this [line|https://github.com/apache/kafka/blob/trunk/core/src/main/scala/kafka/log/LogManager.scala#L502] in the finally clause may still throw an exception once again (for ex: if any of the tasks fail during thread pool shutdown):

threadPools.foreach(_.shutdown())

Note that ExecutorService.shutdown() initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted (see javadoc link [here|https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ExecutorService.html#shutdown()]). It is possible that any of the other running threads that asynchronously close logs may throw an exception. When this happens, ExecutoreService.shutdown() can throw an exception. This situation is not handled inside the finally clause which means that some of the thread pools which are closing logs could be leaked and continue to run in the background, after the control returns to the caller (i.e. KafkaServer).

As a result, even after the `shut down completed` message is seen in the error logs, log closures continue to happen in the background. 
 

*Proposed fix:*

It seems useful that we maintain the contract with KafkaServer that after LogManager.shutdown is called once, all thread pools that close the logs are guaranteed to be attempted shutdown once before the control returns to the caller (either via an exception case or a success case). Supposing when multiple exceptions are raised when closing the logs (from different thread pools), probably we can just raise the first exception among these to the caller of LogManager.shutdown (i.e. KafkaServer ) while optionally logging the rest of the exceptions to stderr.



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