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ZOOKEEPER-4475: Fix NodeChildrenChanged delivered to recursive watcher #1820

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merged 1 commit into from
Feb 22, 2023
Merged

ZOOKEEPER-4475: Fix NodeChildrenChanged delivered to recursive watcher #1820

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15 changes: 11 additions & 4 deletions zookeeper-server/src/main/java/org/apache/zookeeper/ZKWatchManager.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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) {
Expand All @@ -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(
Expand All @@ -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) {
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A comment about reason to filter NodeChildrenChanged event helps - it's not quite straightforward.

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Add comments to explain why this is necessary and why this must be done in client side.

return;
}
synchronized (persistentRecursiveWatches) {
for (String path : PathParentIterator.forAll(clientPath).asIterable()) {
addTo(persistentRecursiveWatches.get(path), result);
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21 changes: 21 additions & 0 deletions zookeeper-server/src/test/java/org/apache/zookeeper/test/PersistentRecursiveWatcherTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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");
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You may assert no outstanding event here.

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Add assertTrue(events.isEmpty()) to assert that no more events in queue.

assertTrue(events.isEmpty());
}
}

@Test
public void testDisconnect() throws Exception {
try (ZooKeeper zk = createClient(new CountdownWatcher(), hostPort)) {
Expand Down