pkuwm commented on a change in pull request #642: Fix zk session race condition
before creating a live instance
URL: https://github.com/apache/helix/pull/642#discussion_r353000617
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File path:
helix-core/src/main/java/org/apache/helix/manager/zk/ParticipantManager.java
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@@ -158,7 +162,7 @@ private void joinCluster() {
}
}
- private void createLiveInstance() {
+ private void createLiveInstance(final String sessionId) {
Review comment:
> I realized when reviewing the later code that you don't need to pass the
sessionId. Correct me if I am wrong, I think you can just pass _sessionId into
the createEphemeral().
My answer is no. If we pass _sessionId into createEphemeral(), I think that
is what the current code does and why race condition occurs. Session expiration
can occur any time between reconnectOnExpiring() and zookeeper.create(), which
means _sessionId could change during the period. If _sessionId changes before
we pass _sessionId to createEphemeral(), I think that would be incorrect.
Please correct me if I am wrong.
> Does that mean we don't need the new interface?
If we don't have to pass the session id into
ZkHelixManager.handNewSession(sessionId) and just use _sessionId, I don't
believe we need the new interface. But the fact is, I think we need the
sessionId because we expect to create an ephemeral node in the expected
session, not a later/new session.
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