[GitHub] [solr] sonatype-lift[bot] commented on a diff in pull request #909: SOLR-16257: `ZkStateReader` changes to avoid race condition between `collectionWatches` and `watchedCollectionStates`

[GitBox <gi...@apache.org>]

sonatype-lift[bot] commented on code in PR #909:
URL: https://github.com/apache/solr/pull/909#discussion_r915385252


##########
solr/solrj/src/java/org/apache/solr/common/cloud/ZkStateReader.java:
##########
@@ -326,12 +432,11 @@ public void forciblyRefreshAllClusterStateSlow() throws KeeperException, Interru
       // No need to set watchers because we should already have watchers registered for everything.
       refreshCollectionList(null);
       refreshLiveNodes(null);
-      // Need a copy so we don't delete from what we're iterating over.
-      Collection<String> safeCopy = new ArrayList<>(watchedCollectionStates.keySet());
+
       Set<String> updatedCollections = new HashSet<>();
-      for (String coll : safeCopy) {
+      for (String coll : collectionWatches.watchedCollections()) {
         DocCollection newState = fetchCollectionState(coll, null);

Review Comment:
   *THREAD_SAFETY_VIOLATION:*  Read/Write race. Non-private method `ZkStateReader.forciblyRefreshAllClusterStateSlow()` indirectly reads with synchronization from `noggit.JSONParser.devNull.end`. Potentially races with unsynchronized write in method `ZkStateReader.compareStateVersions(...)`.
    Reporting because this access may occur on a background thread.
   
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