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https://issues.apache.org/jira/browse/LUCENE-8754?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16814159#comment-16814159
]
ASF subversion and git services commented on LUCENE-8754:
---------------------------------------------------------
Commit addb3977fd735bd852aad2c737c27d8888f70dca in lucene-solr's branch
refs/heads/branch_8x from Simon Willnauer
[ https://gitbox.apache.org/repos/asf?p=lucene-solr.git;h=addb397 ]
LUCENE-8754: Prevent ConcurrentModificationException in SegmentInfo (#637)
In order to prevent ConcurrentModificationException this change makes
an unmodifiable copy on write for all maps in SegmentInfo. MergePolicies
can access these maps without synchronization and cause exceptions if
it's modified in the merge thread.
> 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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