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https://issues.apache.org/jira/browse/SOLR-17413?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17889281#comment-17889281
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Jason Gerlowski commented on SOLR-17413:
----------------------------------------
bq. This should be somewhat straightforward to fix by creating a copy of the
request in the ThreadLocal.withInitial lambda.
I like this approach for its simplicity. IMO it also tracks in terms of the
"Principle of Least Surprise" - creating copies is a pretty standard way to
work around threadsafety limitations. Gonna try to reproduce this in tests
today, and will create a PR if I can validate the fix.
> UpdateLog Replay can throw ConcurrentModificationException from sharing the
> request
> -----------------------------------------------------------------------------------
>
> Key: SOLR-17413
> URL: https://issues.apache.org/jira/browse/SOLR-17413
> Project: Solr
> Issue Type: Bug
> Reporter: David Smiley
> Priority: Major
> Labels: newdev
>
> I saw org.apache.solr.cloud.BasicDistributedZkTest fail with a stack trace
> revealing we have a real issue with UpdateLog replay. Essentially, a
> SolrQueryRequest is not threadsafe but we replay logs in parallel sharing the
> same request instance. Creating DistributedUpdateProcessor ends up adding to
> a shared HashMap in req.getContext() that should not be shared.
> {noformat}
> 2> WARNING: Uncaught exception in thread:
> Thread[replayUpdatesExecutor-590-thread-2,5,TGRP-BasicDistributedZkTest]
> 2> java.util.ConcurrentModificationException
> 2> at __randomizedtesting.SeedInfo.seed([F2227B12A8FC234]:0)
> 2> at java.base/java.util.HashMap.computeIfAbsent(HashMap.java:1135)
> 2> at
> org.apache.solr.update.processor.DistributedUpdateProcessorFactory.addParamToDistributedRequestWhitelist(DistributedUpdateProcessorFactory.java:46)
> 2> at
> org.apache.solr.update.processor.DistributedUpdateProcessor.<init>(DistributedUpdateProcessor.java:190)
> 2> at
> org.apache.solr.update.processor.DistributedUpdateProcessor.<init>(DistributedUpdateProcessor.java:160)
> 2> at
> org.apache.solr.update.processor.DistributedZkUpdateProcessor.<init>(DistributedZkUpdateProcessor.java:114)
> 2> at
> org.apache.solr.update.processor.DistributedUpdateProcessorFactory.getInstance(DistributedUpdateProcessorFactory.java:59)
> 2> at
> org.apache.solr.update.processor.UpdateRequestProcessorChain.createProcessor(UpdateRequestProcessorChain.java:242)
> 2> at
> org.apache.solr.update.processor.UpdateRequestProcessorChain.createProcessor(UpdateRequestProcessorChain.java:214)
> 2> at
> org.apache.solr.update.UpdateLog$LogReplayer.lambda$doReplay$0(UpdateLog.java:2103)
> 2> at
> java.base/java.lang.ThreadLocal$SuppliedThreadLocal.initialValue(ThreadLocal.java:305)
> 2> at java.base/java.lang.ThreadLocal.setInitialValue(ThreadLocal.java:195)
> 2> at java.base/java.lang.ThreadLocal.get(ThreadLocal.java:172)
> 2> at
> org.apache.solr.update.UpdateLog$LogReplayer.lambda$execute$2(UpdateLog.java:2342)
> 2> at
> org.apache.solr.util.OrderedExecutor.lambda$execute$0(OrderedExecutor.java:68)
> 2> at
> org.apache.solr.common.util.ExecutorUtil$MDCAwareThreadPoolExecutor.lambda$execute$1(ExecutorUtil.java:449)
> 2> at
> java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
> 2> at
> java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
> 2> at java.base/java.lang.Thread.run(Thread.java:829)
> {noformat}
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