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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