mgao0 opened a new issue #1296:
URL: https://github.com/apache/helix/issues/1296
### Describe the bug
When handle child changes in CallbackHandler, under certain condition we
will remove the listener.
@Override
public void handleChildChange(String parentPath, List<String>
currentChilds) {
if (logger.isDebugEnabled()) {
logger.debug("Data change callback: child changed, path: {} , current
child count: {}",
parentPath, currentChilds == null ? 0 : currentChilds.size());
}
try {
updateNotificationTime(System.nanoTime());
if (parentPath != null && parentPath.startsWith(_path)) {
if (currentChilds == null && parentPath.equals(_path)) {
// _path has been removed, remove this listener
// removeListener will call handler.reset(), which in turn call
invoke() on FINALIZE type
_manager.removeListener(_propertyKey, _listener);
} else {
if (!isReady()) {
// avoid leaking CallbackHandler
logger.info("Callbackhandler {} with path {} is in reset state.
Stop subscription to ZK client to avoid leaking",
this, parentPath);
return;
}
NotificationContext changeContext = new
NotificationContext(_manager);
changeContext.setType(NotificationContext.Type.CALLBACK);
changeContext.setPathChanged(parentPath);
changeContext.setChangeType(_changeType);
subscribeForChanges(changeContext.getType(), _path, _watchChild);
enqueueTask(changeContext);
}
}
} catch (Exception e) {
String msg = "exception in handling child-change. instance: " +
_manager.getInstanceName()
+ ", parentPath: " + parentPath + ", listener: " + _listener;
ZKExceptionHandler.getInstance().handle(msg, e);
}
}
This will send a FINALIZE event to the routing table provider which is
listening on this path.
When routing table provider handles this event, it calls reset() and the
entire routing table will be reset.
`if (changeContext.getType() == NotificationContext.Type.FINALIZE) {
reset();
}
`
It caused problems in customized view feature, that when an aggregation
enabled customized state type is dropped from customized view, a FINALIZE event
is sent to the routing table provider, and triggers the reset of routing table.
If there is on more events incoming, we will see an empty routing table.
### To Reproduce
Initialize a routing table provider listening to customized state type A and
B, set aggregation enabled customized state types in controller to be A andB,
update some customized states for both types. Then set aggregation enabled
customized state types in controller to be only A, and get routing table
snapshot from routing table provider, and the routing table is empty.
### Expected behavior
We can fix this in two ways:
1. Fix callback handler, so it doesn't enqueue FINALIZE event for the
change. For example, in the above piece of code, for CurrentState, when
dropping a resource, the callback handler enqueue a CALLBACK typed event, so
the routing table provider won't be reset unexpectedly.
2. Add granularity into routing table provider, so we don't shut down the
entire routing table provider when getting FINALIZE event on one path.
### Additional context
Add any other context about the problem here.
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