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https://issues.apache.org/jira/browse/KAFKA-4205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15715331#comment-15715331
]
ASF GitHub Bot commented on KAFKA-4205:
---------------------------------------
GitHub user ataraxer opened a pull request:
https://github.com/apache/kafka/pull/2204
KAFKA-4205; KafkaApis: fix NPE caused by conversion to array
NPE was caused by `log.logSegments.toArray` resulting in array containing
`null` values. The exact reason still remains somewhat a mystery to me, but it
seems that the culprit is `JavaConverters` in combination with concurrent data
structure access.
Here's a simple code example to prove that:
```scala
import java.util.concurrent.ConcurrentSkipListMap
// Same as `JavaConversions`, but allows explicit conversions via
`asScala`/`asJava` methods.
import scala.collection.JavaConverters._
case object Value
val m = new ConcurrentSkipListMap[Int, Value.type]
new Thread { override def run() = { while (true) m.put(9000, Value) }
}.start()
new Thread { override def run() = { while (true) m.remove(9000) } }.start()
new Thread { override def run() = { while (true) {
println(m.values.asScala.toArray.headOption) } } }.start()
```
Running the example will occasionally print `Some(null)` indicating that
there's something shady going on during `toArray` conversion.
`null`s magically disappear by making the following change:
```diff
- println(m.values.asScala.toArray.headOption)
+ println(m.values.asScala.toSeq.headOption)
```
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/ataraxer/kafka KAFKA-4205
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/kafka/pull/2204.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #2204
----
commit bcd32760015e9dfd564813076a07dbe1612eab00
Author: Anton Karamanov <[email protected]>
Date: 2016-12-02T14:37:42Z
KAFKA-4205; KafkaApis: fix NPE caused by conversion to array
----
> NullPointerException in fetchOffsetsBefore
> ------------------------------------------
>
> Key: KAFKA-4205
> URL: https://issues.apache.org/jira/browse/KAFKA-4205
> Project: Kafka
> Issue Type: Bug
> Components: core
> Affects Versions: 0.9.0.1
> Reporter: Andrew Grasso
> Labels: reliability
> Fix For: 0.10.1.1
>
>
> We recently observed the following error in brokers running 0.9.0.1:
> A client saw an Unkown error code in response to an offset request for
> TOPICX, partition 0
> The server logs look like:
> {code}
> [2016-09-21 21:26:07,143] INFO Scheduling log segment 527235760 for log
> TOPICX-0 for deletion. (kafka.log.Log)
> [2016-09-21 21:26:07,144] ERROR [KafkaApi-13] Error while responding to
> offset request (kafka.server.KafkaApis)
> java.lang.NullPointerException
> at kafka.server.KafkaApis.fetchOffsetsBefore(KafkaApis.scala:513)
> at kafka.server.KafkaApis.fetchOffsets(KafkaApis.scala:501)
> at kafka.server.KafkaApis$$anonfun$18.apply(KafkaApis.scala:461)
> at kafka.server.KafkaApis$$anonfun$18.apply(KafkaApis.scala:452)
> at
> scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
> at
> scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
> at scala.collection.immutable.Map$Map1.foreach(Map.scala:109)
> at
> scala.collection.TraversableLike$class.map(TraversableLike.scala:244)
> at scala.collection.AbstractTraversable.map(Traversable.scala:105)
> at kafka.server.KafkaApis.handleOffsetRequest(KafkaApis.scala:452)
> at kafka.server.KafkaApis.handle(KafkaApis.scala:70)
> at kafka.server.KafkaRequestHandler.run(KafkaRequestHandler.scala:60)
> at java.lang.Thread.run(Thread.java:745)
> [2016-09-21 21:27:07,143] INFO Deleting segment 527235760 from log TOPICX-0.
> (kafka.log.Log)
> [2016-09-21 21:27:07,263] INFO Deleting index
> /path/to/kafka/data/TOPICX-0/00000000000527235760.index.deleted
> (kafka.log.OffsetIndex)
> {code}
> I suspect a race condition between {{Log.deleteSegment}} (which takes a lock
> on the log) and {{KafkaApis.fetchOffsetsBefore}}, which does not take any
> lock. In particular, line 513 in KafkaApis looks like:
> {code:title=KafkaApis.scala|borderStyle=solid}
> 510 private def fetchOffsetsBefore(log: Log, timestamp: Long, maxNumOffsets:
> Int): Seq[Long] = {
> 511 val segsArray = log.logSegments.toArray
> 512 var offsetTimeArray: Array[(Long, Long)] = null
> 513 val lastSegmentHasSize = segsArray.last.size > 0;
> {code}
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