[jira] [Commented] (KAFKA-6277) Make loadClass thread-safe for class loaders of Connect plugins

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-6277?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16327763#comment-16327763 ] 

ASF GitHub Bot commented on KAFKA-6277:
---------------------------------------

kkonstantine opened a new pull request #4428: KAFKA-6277: Ensure loadClass for plugin class loaders is thread-safe.
URL: https://github.com/apache/kafka/pull/4428
 
 
   `loadClass` needs to be synchronized to protect subsequent calls to `defineClass`. 
   
   Details in the javadoc of this PR as well as here too: https://docs.oracle.com/javase/7/docs/technotes/guides/lang/cl-mt.html
   
   /cc @ewencp @rhauch 
   
   ### Committer Checklist (excluded from commit message)
   - [ ] Verify design and implementation 
   - [ ] Verify test coverage and CI build status
   - [ ] Verify documentation (including upgrade notes)
   

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> Make loadClass thread-safe for class loaders of Connect plugins
> ---------------------------------------------------------------
>
>                 Key: KAFKA-6277
>                 URL: https://issues.apache.org/jira/browse/KAFKA-6277
>             Project: Kafka
>          Issue Type: Bug
>          Components: KafkaConnect
>    Affects Versions: 1.0.0, 0.11.0.2
>            Reporter: Konstantine Karantasis
>            Assignee: Konstantine Karantasis
>            Priority: Major
>             Fix For: 1.0.1, 0.11.0.3
>
>
> In Connect's classloading isolation framework, {{PluginClassLoader}} class encounters a race condition when several threads corresponding to tasks using a specific plugin (e.g. a Connector) try to load the same class at the same time on a single JVM. 
> The race condition is related to calls to method {{defineClass}} which, contract to {{findClass}}, is not thread safe for classloaders that override {{loadClass}}. More details here: 
> https://docs.oracle.com/javase/7/docs/technotes/guides/lang/cl-mt.html



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