narendly 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_r353570633
##########
File path:
helix-core/src/main/java/org/apache/helix/manager/zk/zookeeper/ZkClient.java
##########
@@ -1147,6 +1236,35 @@ private void acquireEventLock() {
throw new IllegalStateException(
"ZkConnection is in invalid state! Please close this ZkClient
and create new client.");
}
+
+ /*
+ * If the callable is a SessionAwareCallable, we need to validate
the session.
+ * If the session of current ZK connection does not match the
expected session in
+ * SessionAwareCallable, HelixException is thrown and call()
operation will not be run.
+ * Acquiring event lock is needed to make sure no new session is
established,
+ * while the session is being checked.
+ */
+ if (callable instanceof SessionAwareCallable) {
+ SessionAwareCallable<T> sessionAwareCallable =
(SessionAwareCallable<T>) callable;
+ acquireEventLock();
+ try {
+ final ZooKeeper zooKeeper = zkConnection.getZookeeper();
+ final String currentSessionId =
Long.toHexString(zooKeeper.getSessionId());
+ if
(!currentSessionId.equals(sessionAwareCallable.getSessionId())) {
+ throw new HelixException(
+ "Session id is mismatched, expected: 0x" +
sessionAwareCallable.getSessionId()
Review comment:
Nit: "Failed to create ephemeral node! There's a session id mismatch.
Expected: {}, Actual currentSessionId: {}"
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