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https://issues.apache.org/jira/browse/KAFKA-7421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16912290#comment-16912290
]
Ivan Yurchenko commented on KAFKA-7421:
---------------------------------------
I wonder if {{PluginClassLoader}}'s {{loadClass}} method needs to be
{{synchronized}} in
[here|https://github.com/apache/kafka/blob/3cdc78e6bb1f83973a14ce1550fe3874f7348b05/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/isolation/PluginClassLoader.java#L89]:
it has fine-grain synchronization immediately inside (due to being registered
as parallel capable). This method's outher synchronization on {{this}} is what
seems to cause occasional deadlocks on concurrent class loading.
> Deadlock in Kafka Connect
> -------------------------
>
> Key: KAFKA-7421
> URL: https://issues.apache.org/jira/browse/KAFKA-7421
> Project: Kafka
> Issue Type: Bug
> Components: KafkaConnect
> Affects Versions: 2.0.0
> Reporter: Maciej Bryński
> Assignee: Konstantine Karantasis
> Priority: Major
>
> I'm getting this deadlock on half of Kafka Connect runs when having two
> different types connectors (in this configuration it's debezium and hdfs).
> Thread 1:
> {code}
> "pool-22-thread-2@4748" prio=5 tid=0x4d nid=NA waiting for monitor entry
> java.lang.Thread.State: BLOCKED
> waiting for pool-22-thread-1@4747 to release lock on <0x1423> (a
> org.apache.kafka.connect.runtime.isolation.PluginClassLoader)
> at
> org.apache.kafka.connect.runtime.isolation.PluginClassLoader.loadClass(PluginClassLoader.java:91)
> at
> org.apache.kafka.connect.runtime.isolation.DelegatingClassLoader.loadClass(DelegatingClassLoader.java:367)
> at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
> at java.lang.Class.forName0(Class.java:-1)
> at java.lang.Class.forName(Class.java:348)
> at
> org.apache.kafka.common.config.ConfigDef.parseType(ConfigDef.java:715)
> at
> org.apache.kafka.connect.runtime.ConnectorConfig.enrich(ConnectorConfig.java:295)
> at
> org.apache.kafka.connect.runtime.ConnectorConfig.<init>(ConnectorConfig.java:200)
> at
> org.apache.kafka.connect.runtime.ConnectorConfig.<init>(ConnectorConfig.java:194)
> at
> org.apache.kafka.connect.runtime.Worker.startConnector(Worker.java:233)
> at
> org.apache.kafka.connect.runtime.distributed.DistributedHerder.startConnector(DistributedHerder.java:916)
> at
> org.apache.kafka.connect.runtime.distributed.DistributedHerder.access$1300(DistributedHerder.java:111)
> at
> org.apache.kafka.connect.runtime.distributed.DistributedHerder$15.call(DistributedHerder.java:932)
> at
> org.apache.kafka.connect.runtime.distributed.DistributedHerder$15.call(DistributedHerder.java:928)
> at java.util.concurrent.FutureTask.run(FutureTask.java:266)
> at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
> at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
> at java.lang.Thread.run(Thread.java:748)
> {code}
> Thread 2:
> {code}
> "pool-22-thread-1@4747" prio=5 tid=0x4c nid=NA waiting for monitor entry
> java.lang.Thread.State: BLOCKED
> blocks pool-22-thread-2@4748
> waiting for pool-22-thread-2@4748 to release lock on <0x1421> (a
> org.apache.kafka.connect.runtime.isolation.DelegatingClassLoader)
> at java.lang.ClassLoader.loadClass(ClassLoader.java:406)
> at
> org.apache.kafka.connect.runtime.isolation.DelegatingClassLoader.loadClass(DelegatingClassLoader.java:358)
> at java.lang.ClassLoader.loadClass(ClassLoader.java:411)
> - locked <0x1424> (a java.lang.Object)
> at
> org.apache.kafka.connect.runtime.isolation.PluginClassLoader.loadClass(PluginClassLoader.java:104)
> - locked <0x1423> (a
> org.apache.kafka.connect.runtime.isolation.PluginClassLoader)
> at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
> at
> io.debezium.transforms.ByLogicalTableRouter.<clinit>(ByLogicalTableRouter.java:57)
> at java.lang.Class.forName0(Class.java:-1)
> at java.lang.Class.forName(Class.java:348)
> at
> org.apache.kafka.common.config.ConfigDef.parseType(ConfigDef.java:715)
> at
> org.apache.kafka.connect.runtime.ConnectorConfig.enrich(ConnectorConfig.java:295)
> at
> org.apache.kafka.connect.runtime.ConnectorConfig.<init>(ConnectorConfig.java:200)
> at
> org.apache.kafka.connect.runtime.ConnectorConfig.<init>(ConnectorConfig.java:194)
> at
> org.apache.kafka.connect.runtime.Worker.startConnector(Worker.java:233)
> at
> org.apache.kafka.connect.runtime.distributed.DistributedHerder.startConnector(DistributedHerder.java:916)
> at
> org.apache.kafka.connect.runtime.distributed.DistributedHerder.access$1300(DistributedHerder.java:111)
> at
> org.apache.kafka.connect.runtime.distributed.DistributedHerder$15.call(DistributedHerder.java:932)
> at
> org.apache.kafka.connect.runtime.distributed.DistributedHerder$15.call(DistributedHerder.java:928)
> at java.util.concurrent.FutureTask.run(FutureTask.java:266)
> at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
> at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
> at java.lang.Thread.run(Thread.java:748)
> {code}
> I'm using official Confluent Docker images.
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