kaisun2000 commented on a change in pull request #1035:
URL: https://github.com/apache/helix/pull/1035#discussion_r435010689
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File path:
helix-core/src/main/java/org/apache/helix/manager/zk/CallbackHandler.java
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@@ -539,7 +539,15 @@ private void subscribeChildChange(String path,
NotificationContext.Type callback
logger.debug(_manager.getInstanceName() + " subscribes child-change.
path: " + path
+ ", listener: " + _listener);
}
- _zkClient.subscribeChildChanges(path, this);
+ // In the lifecycle of CallbackHandler, INIT is the first stage of
registration of watch.
+ // For some usage case such as current state, the path can be created
later. Thus we would
+ // install watch anyway event the path is not yet created.
+ // Later, CALLBACK type, the CallbackHandler already registered the
watch and knows the
+ // path was created. Here, to avoid leaking path in ZooKeeper server, we
would not let
+ // CallbackHandler to install exists watch, namely watch for path not
existing.
+ // Note when path is removed, the CallbackHanler would remove itself
from ZkHelixManager too
+ // to avoid leaking a CallbackHandler.
+ _zkClient.subscribeChildChanges(path, this, callbackType != Type.INIT);
Review comment:
If CallbackType is CALLBACK, ignore it is just want we want. That is
exactly the case of async removal of a parent current state. This would result
in hanldeChildren() first code path, removing the callbackhandler from the
zkhelixmanager.
If CallbackType is INIT, it would not fail.
So let us add a debug log for general case. Only failure case, info log. As
general case would be too much.
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