ZOOKEEPER-4475: Fix NodeChildrenChanged delivered to recursive watcher

The semantics of persistent recursive watch promise no child events on descendant nodes. When there are standard child watches on descendants of node being watches in persistent recursive mode, server will deliver child events to client inevitably. So we have to filter out child events for persistent recursive watches on client side.
apache · Oct 10, 2022 · e33fddf · e33fddf
1 parent 3daefac
commit e33fddf
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Showing 2 changed files with 32 additions and 4 deletions.
diff --git a/zookeeper-server/src/main/java/org/apache/zookeeper/ZKWatchManager.java b/zookeeper-server/src/main/java/org/apache/zookeeper/ZKWatchManager.java
@@ -404,13 +404,13 @@ public Set<Watcher> materialize(
             synchronized (existWatches) {
                 addTo(existWatches.remove(clientPath), result);
             }
-            addPersistentWatches(clientPath, result);
+            addPersistentWatches(clientPath, type, result);
             break;
         case NodeChildrenChanged:
             synchronized (childWatches) {
                 addTo(childWatches.remove(clientPath), result);
             }
-            addPersistentWatches(clientPath, result);
+            addPersistentWatches(clientPath, type, result);
             break;
         case NodeDeleted:
             synchronized (dataWatches) {
@@ -427,7 +427,7 @@ public Set<Watcher> materialize(
             synchronized (childWatches) {
                 addTo(childWatches.remove(clientPath), result);
             }
-            addPersistentWatches(clientPath, result);
+            addPersistentWatches(clientPath, type, result);
             break;
         default:
             String errorMsg = String.format(
@@ -442,10 +442,17 @@ public Set<Watcher> materialize(
         return result;
     }
 
-    private void addPersistentWatches(String clientPath, Set<Watcher> result) {
+    private void addPersistentWatches(String clientPath, Watcher.Event.EventType type, Set<Watcher> result) {
         synchronized (persistentWatches) {
             addTo(persistentWatches.get(clientPath), result);
         }
+        // The semantics of persistent recursive watch promise no child events on descendant nodes. When there
+        // are standard child watches on descendants of node being watched in persistent recursive mode, server
+        // will deliver child events to client inevitably. So we have to filter out child events for persistent
+        // recursive watches on client side.
+        if (type == Watcher.Event.EventType.NodeChildrenChanged) {
+            return;
+        }
         synchronized (persistentRecursiveWatches) {
             for (String path : PathParentIterator.forAll(clientPath).asIterable()) {
                 addTo(persistentRecursiveWatches.get(path), result);

diff --git a/zookeeper-server/src/test/java/org/apache/zookeeper/test/PersistentRecursiveWatcherTest.java b/zookeeper-server/src/test/java/org/apache/zookeeper/test/PersistentRecursiveWatcherTest.java
@@ -114,6 +114,27 @@ public void testRemoval()
         }
     }
 
+    @Test
+    public void testNoChildEvents() throws Exception {
+        try (ZooKeeper zk = createClient()) {
+            zk.create("/a", new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
+
+            zk.addWatch("/", persistentWatcher, PERSISTENT_RECURSIVE);
+
+            BlockingQueue<WatchedEvent> childEvents = new LinkedBlockingQueue<>();
+            zk.getChildren("/a", childEvents::add);
+
+            zk.create("/a/b", new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
+            zk.create("/a/b/c", new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
+
+            assertEvent(childEvents, Watcher.Event.EventType.NodeChildrenChanged, "/a");
+
+            assertEvent(events, Watcher.Event.EventType.NodeCreated, "/a/b");
+            assertEvent(events, Watcher.Event.EventType.NodeCreated, "/a/b/c");
+            assertTrue(events.isEmpty());
+        }
+    }
+
     @Test
     public void testDisconnect() throws Exception {
         try (ZooKeeper zk = createClient(new CountdownWatcher(), hostPort)) {