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 <atara...@yandex-team.ru>
Date: 2016-12-02T14:37:42Z
KAFKA-4205; KafkaApis: fix NPE caused by conversion to array
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