addIndexes(CodecReader...) throws AlreadyClosedException 'this IndexWriter is closed' on an open writer when it overlaps a deleteAll() that is waiting for a running merge to abort, although deleteAll's javadoc says such callers may receive MergeAbortedException

Finding LFV-632Area: index / IndexWriter addIndexes(CodecReader...) entry check vs deleteAll (abortMerges)Priority: lowImpact: wrong errorNovelty: new

Finding page for LFV-632

AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

One thread calls deleteAll() on an IndexWriter while a merge is running, and another thread calls addIndexes(CodecReader...) on the same writer. You expect the overlapping call either to succeed or to fail with MergePolicy.MergeAbortedException, as deleteAll's javadoc says for concurrent addIndexes(CodecReader[]) callers and as most such overlaps do. Instead, when the call reaches its entry check while deleteAll is waiting for the running merge to abort, it throws AlreadyClosedException 'this IndexWriter is closed. Cannot execute addIndexes(CodecReaders...) API' although the writer is open: isOpen() is true, deleteAll returns normally and the next addIndexes call on the same writer succeeds.

The test shows that an addIndexes(CodecReader...) call that has passed its flush reaches its merges-enabled check while deleteAll() waits for a running merge to abort, and it throws AlreadyClosedException although the writer is open.

Expected vs actual

Expected, per the deleteAll() javadoc: success or MergePolicy.MergeAbortedException. Actual: AlreadyClosedException: this IndexWriter is closed. Cannot execute addIndexes(CodecReaders...) API with isOpen()=true.

Files

• src/org/apache/lucene/index/TestAddIndexesDuringDeleteAll.java (JUnit test)

Run it

• Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
• Tested on Lucene main 645d4fe14a20 (2026-10-28): reproduced.
• Recorded outcome of run 1 on Lucene main 645d4fe14a20: 1 test(s) run, 1 failed.
• How to read the outcome: a failing test is the finding reproducing (the failure message states expected against actual).
• Seeds: a rerun with the same seed replays the same random choices. Assertions off (-da -dsa -Dtests.asserts=false) is the production-like setting.

# Lucene checkout at the tested commit, built with: ./gradlew --no-daemon assemble   (JDK 25)
LUCENE=/path/to/lucene; V=12.0.0-SNAPSHOT
CP=$LUCENE/lucene/core/build/libs/lucene-core-$V.jar
CP=$CP:$LUCENE/lucene/codecs/build/libs/lucene-codecs-$V.jar
CP=$CP:$LUCENE/lucene/test-framework/build/libs/lucene-test-framework-$V.jar
CP=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar   # test-framework dependencies (Maven Central)
CP=$CP:junit-platform-console-standalone-6.1.3.jar   # JUnit Platform console launcher (Maven Central)

javac -d classes -cp "$CP" $(find src -name '*.java')

# run 1: assertions on, seed DEADBEEF
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
     -cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.index.TestAddIndexesDuringDeleteAll

Gradle alternative: copy the test into the matching module's src/test/ tree of the checkout and run ./gradlew -p lucene/<module> test --tests <class> -Ptests.seed=<seed> (add -Ptests.asserts=false for a run without assertions).

Formal models and scripts this finding's part of the hunt used: iw-addindexes-merge-source-tla

Feedback

Open an issue in lucene-ai-bug-hunt. Please do not open issues or pull requests in apache/lucene about this finding unless a Lucene committer agrees it should be filed.

Snapshot of 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.