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https://issues.apache.org/jira/browse/LUCENE-8754?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Simon Willnauer resolved LUCENE-8754.
-------------------------------------
Resolution: Fixed
Fix Version/s: master (9.0)
8.1
> SegmentInfo#toString can cause ConcurrentModificationException
> --------------------------------------------------------------
>
> Key: LUCENE-8754
> URL: https://issues.apache.org/jira/browse/LUCENE-8754
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Simon Willnauer
> Priority: Major
> Fix For: 8.1, master (9.0)
>
> Time Spent: 3h
> Remaining Estimate: 0h
>
> A recent change increased the likelihood for this issue to show up but it can
> already happen before since we are using the attributes map in the
> StoredFieldsFormat for quite some time. I found this issue due to a test
> failure on our CI:
> {noformat}
> 13:11:56 [junit4] Suite: org.apache.lucene.index.TestIndexSorting
> 13:11:56 [junit4] 2> apr 05, 2019 8:11:53 AM
> com.carrotsearch.randomizedtesting.RandomizedRunner$QueueUncaughtExceptionsHandler
> uncaughtException
> 13:11:56 [junit4] 2> WARNING: Uncaught exception in thread:
> Thread[Thread-507,5,TGRP-TestIndexSorting]
> 13:11:56 [junit4] 2> java.util.ConcurrentModificationException
> 13:11:56 [junit4] 2> at
> __randomizedtesting.SeedInfo.seed([7C25B308F180203B]:0)
> 13:11:56 [junit4] 2> at
> java.util.HashMap$HashIterator.nextNode(HashMap.java:1442)
> 13:11:56 [junit4] 2> at
> java.util.HashMap$EntryIterator.next(HashMap.java:1476)
> 13:11:56 [junit4] 2> at
> java.util.HashMap$EntryIterator.next(HashMap.java:1474)
> 13:11:56 [junit4] 2> at
> java.util.AbstractMap.toString(AbstractMap.java:554)
> 13:11:56 [junit4] 2> at
> org.apache.lucene.index.SegmentInfo.toString(SegmentInfo.java:222)
> 13:11:56 [junit4] 2> at
> org.apache.lucene.index.SegmentCommitInfo.toString(SegmentCommitInfo.java:345)
> 13:11:56 [junit4] 2> at
> org.apache.lucene.index.SegmentCommitInfo.toString(SegmentCommitInfo.java:364)
> 13:11:56 [junit4] 2> at java.lang.String.valueOf(String.java:2994)
> 13:11:56 [junit4] 2> at
> java.lang.StringBuilder.append(StringBuilder.java:131)
> 13:11:56 [junit4] 2> at
> java.util.AbstractMap.toString(AbstractMap.java:557)
> 13:11:56 [junit4] 2> at
> java.util.Collections$UnmodifiableMap.toString(Collections.java:1493)
> 13:11:56 [junit4] 2> at java.lang.String.valueOf(String.java:2994)
> 13:11:56 [junit4] 2> at
> java.lang.StringBuilder.append(StringBuilder.java:131)
> 13:11:56 [junit4] 2> at
> org.apache.lucene.index.TieredMergePolicy.findForcedMerges(TieredMergePolicy.java:628)
> 13:11:56 [junit4] 2> at
> org.apache.lucene.index.IndexWriter.updatePendingMerges(IndexWriter.java:2181)
> 13:11:56 [junit4] 2> at
> org.apache.lucene.index.IndexWriter.maybeMerge(IndexWriter.java:2154)
> 13:11:56 [junit4] 2> at
> org.apache.lucene.index.IndexWriter.forceMerge(IndexWriter.java:1988)
> 13:11:56 [junit4] 2> at
> org.apache.lucene.index.IndexWriter.forceMerge(IndexWriter.java:1939)
> 13:11:56 [junit4] 2> at
> org.apache.lucene.index.TestIndexSorting$UpdateRunnable.run(TestIndexSorting.java:1851)
> 13:11:56 [junit4] 2> at java.lang.Thread.run(Thread.java:748)
> 13:11:56 [junit4] 2>
> 13:11:56 [junit4] 2> NOTE: reproduce with: ant test
> -Dtestcase=TestIndexSorting -Dtests.method=testConcurrentUpdates
> -Dtests.seed=7C25B308F180203B -Dtests.slow=true -Dtest
> {noformat}
> The issue is that we update the attributes map (also we similarly do the same
> for diagnostics but it's not necessarily causing the issue since the
> diagnostics map is never modified) during the merge process but access it in
> the merge policy when looking at running merges and there we call toString on
> SegmentCommitInfo which happens without any synchronization. This is
> technically unsafe publication but IW is a mess along those lines and real
> fixes would require significant changes.
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