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https://issues.apache.org/jira/browse/KAFKA-12308?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17290793#comment-17290793
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Tom Bentley commented on KAFKA-12308:
-------------------------------------
[~kkonstantine] I'm not an expert in classloaders but I'm still not sure that
DCL shouldn't be considered parallel. The referred class loader guide
explicitly says that an acyclic CL should delegate to {{super}} _first_. I
understand that delegating to PCL first is intentional, but it doesn't fit with
the definition given AFAICS. The fact that the CLs it delegates to are both
parallel doesn't seem to be relevant. Also, the parent of the PCL is the DCL,
which looks like a cycle to me (but, as I said, I'm no expert, so happy to be
corrected).
Assuming the {{synchronized}} was removed from PCL {{loadClass}}, then
{noformat}
"StartAndStopExecutor-connect-1-6":
at
org.apache.kafka.connect.runtime.isolation.PluginClassLoader.loadClass(PluginClassLoader.java:91)
// lock PCLX (synchronized)
{noformat}
wouldn't get blocked, but there would still be two threads contenting two locks
when racing to load the same class, those locks would be the
{{getClassLoadingLock()}} on the PCL and the monitor of the DCL instance
itself, so I think perhaps a deadlock would still be possible, just on
different monitors.
> ConfigDef.parseType deadlock
> ----------------------------
>
> Key: KAFKA-12308
> URL: https://issues.apache.org/jira/browse/KAFKA-12308
> Project: Kafka
> Issue Type: Bug
> Components: config, KafkaConnect
> Affects Versions: 2.5.0
> Environment: kafka 2.5.0
> centos7
> java version "1.8.0_231"
> Reporter: cosmozhu
> Priority: Major
> Attachments: deadlock.log
>
>
> hi,
> the problem was found, when I restarted *ConnectDistributed*
> I restart ConnectDistributed in the single node for the test, with not delete
> connectors.
> sometimes the process stopped when creating connectors.
> I add some logger and found it had a deadlock in `ConfigDef.parseType`.My
> connectors always have the same transforms. I guess when connector startup
> (in startAndStopExecutor which default 8 threads) and load the same class
> file it has something wrong.
> I attached the jstack log file.
> thanks for any help.
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