pkuwm commented on a change in pull request #1066:
URL: https://github.com/apache/helix/pull/1066#discussion_r460222051
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File path: helix-core/src/main/java/org/apache/helix/HelixManager.java
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@@ -419,6 +420,17 @@ void
addExternalViewChangeListener(org.apache.helix.ExternalViewChangeListener l
*/
Long getSessionStartTime();
+ /**
+ * Checks whether the cluster manager is leader and returns the session ID
associated to the
+ * connection of cluster data store, if and only if it is leader.
+ *
+ * @return {@code Optional<String>} session ID is present inside the {@code
Optional} object
+ * if the cluster manager is leader. Otherwise, returns an empty {@code
Optional} object.
+ */
+ default Optional<String> getSessionIdIfLead() {
Review comment:
manager.getSessionIdIfLead checks whether the cluster manager is leader
and returns the session ID associated to the connection of cluster data store,
if and only if it is leader. It combines isLeader() and getSessionId() in one
method to ensure the session id returning is what we check leadership in
isLeader().
Without it, we may do this:
if (isLeader()) {
sessionId = manager.getSessionId();
}
The problem is race condition. sessionId may change after isLeader().
So we need manager.getSessionIdIfLead to check leadership and get sessionId
at the same time.
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