mikemccand commented on a change in pull request #1274: LUCENE-9164: Prevent IW
from closing gracefully if threads are still modifying
URL: https://github.com/apache/lucene-solr/pull/1274#discussion_r386975715
##########
File path: lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
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@@ -326,6 +327,9 @@ static int getActualMaxDocs() {
private long mergeGen;
private boolean stopMerges;
private boolean didMessageState;
+ // This allows to ensure that all modifying threads have left IW before we
are closing / rolling back
+ // see {@link IndexWriter#rollbackInternal}
+ private final Semaphore modificationLease = new Semaphore(Integer.MAX_VALUE,
true);
Review comment:
Why are we passing `true` for `fair`? I guess it's to prevent starvation of
one thread trying to close, while other threads continue indexing? Maybe leave
a comment?
Also, maybe add comment explaining lock acquisition order? At least, it
seems if we are `synchronized` we do not need the `modificationLease`?
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