Github user olegz commented on a diff in the pull request:
https://github.com/apache/nifi/pull/900#discussion_r75872798
--- Diff:
nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-core/src/main/java/org/apache/nifi/controller/leader/election/CuratorLeaderElectionManager.java
---
@@ -218,14 +227,92 @@ public String getLeader(final String roleName) {
return participantId;
}
+
+ /**
+ * Determines whether or not leader election has already begun for the
role with the given name
+ *
+ * @param roleName the role of interest
+ * @return <code>true</code> if leader election has already begun,
<code>false</code> if it has not or if unable to determine this.
+ */
+ @Override
+ public boolean isLeaderElected(final String roleName) {
+ final String leaderAddress = determineLeaderExternal(roleName);
+ return !StringUtils.isEmpty(leaderAddress);
+ }
+
+
+ /**
+ * Use a new Curator client to determine which node is the elected
leader for the given role.
+ *
+ * @param roleName the name of the role
+ * @return the id of the elected leader, or <code>null</code> if no
leader has been selected or if unable to determine
+ * the leader from ZooKeeper
+ */
+ private String determineLeaderExternal(final String roleName) {
+ final CuratorFramework client = createClient();
+ try {
+ final LeaderSelectorListener electionListener = new
LeaderSelectorListener() {
+ @Override
+ public void stateChanged(CuratorFramework client,
ConnectionState newState) {
+ }
+
+ @Override
+ public void takeLeadership(CuratorFramework client) throws
Exception {
+ }
+ };
+
+ final String electionPath = getElectionPath(roleName);
+
+ // Note that we intentionally do not auto-requeue here, and we
do not start the selector. We do not
+ // want to join the leader election. We simply want to observe.
+ final LeaderSelector selector = new LeaderSelector(client,
electionPath, electionListener);
+
+ try {
+ final Participant leader = selector.getLeader();
+ return leader == null ? null : leader.getId();
+ } catch (final KeeperException.NoNodeException nne) {
+ // If there is no ZNode, then there is no elected leader.
+ return null;
+ } catch (final Exception e) {
+ logger.warn("Unable to determine the Elected Leader for
role '{}' due to {}; assuming no leader has been elected", roleName,
e.toString());
+ if (logger.isDebugEnabled()) {
+ logger.warn("", e);
+ }
+
+ return null;
+ }
+ } finally {
+ client.close();
+ }
+ }
+
+ private CuratorFramework createClient() {
+ // Create a new client because we don't want to try indefinitely
for this to occur.
+ final RetryPolicy retryPolicy = new RetryNTimes(10, 500);
--- End diff --
got it
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