XComp commented on code in PR #22380:
URL: https://github.com/apache/flink/pull/22380#discussion_r1169834833
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flink-runtime/src/main/java/org/apache/flink/runtime/leaderelection/DefaultLeaderElectionService.java:
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@@ -37,35 +37,58 @@
* Default implementation for leader election service. Composed with different
{@link
* LeaderElectionDriver}, we could perform a leader election for the
contender, and then persist the
* leader information to various storage.
+ *
+ * <p>{@code DefaultLeaderElectionService} handles a single {@link
LeaderContender}.
*/
public class DefaultLeaderElectionService
- implements LeaderElectionService, LeaderElectionEventHandler {
+ implements LeaderElectionService, LeaderElectionEventHandler,
AutoCloseable {
private static final Logger LOG =
LoggerFactory.getLogger(DefaultLeaderElectionService.class);
private final Object lock = new Object();
private final LeaderElectionDriverFactory leaderElectionDriverFactory;
- /** The leader contender which applies for leadership. */
+ /**
+ * {@code leaderContender} being {@code null} indicates that no {@link
LeaderContender} is
+ * registered that participates in the leader election, yet. See {@link
#start(LeaderContender)}
+ * and {@link #stop()} for lifecycle management.
+ *
+ * <p>{@code @Nullable} isn't used here to avoid having multiple warnings
spread over this class
+ * in a supporting IDE.
+ */
@GuardedBy("lock")
- // @Nullable is commented-out to avoid having multiple warnings spread
over this class
- // this.running=true ensures that leaderContender != null
- private volatile LeaderContender leaderContender;
+ private LeaderContender leaderContender;
+ /**
+ * Saves the session ID which was issued by the {@link
LeaderElectionDriver} iff the leadership
+ * is acquired by this service. {@code issuedLeaderSessionID} being {@code
null} indicates that
+ * this service isn't the leader right now (i.e. {@code
+ * leaderElectionDriver.hasLeadership(UUID)} would return {@code false}
for any session ID.
+ */
@GuardedBy("lock")
@Nullable
- private volatile UUID issuedLeaderSessionID;
+ private UUID issuedLeaderSessionID;
+ /**
+ * Saves the leader information for a registered {@link LeaderContender}
after this contender
+ * confirmed the leadership.
+ */
@GuardedBy("lock")
- private volatile LeaderInformation confirmedLeaderInformation;
+ private LeaderInformation confirmedLeaderInformation;
+ /**
+ * {@code leaderElectionDriver} being {@code null} indicates that the
connection to the
+ * LeaderElection backend isn't established, yet. See {@link
#startLeaderElectionBackend()} and
+ * {@link #close()} for lifecycle management. The lifecycle of the driver
should have been
+ * established before registering a {@link LeaderContender} and stopped
after the contender has
+ * been removed.
+ *
+ * <p>{@code @Nullable} isn't used here to avoid having multiple warnings
spread over this class
+ * in a supporting IDE.
+ */
@GuardedBy("lock")
- private volatile boolean running;
-
- // @Nullable is commented-out to avoid having multiple warnings spread
over this class
- // this.running=true ensures that leaderContender != null
- private LeaderElectionDriver leaderElectionDriver;
+ private volatile LeaderElectionDriver leaderElectionDriver;
Review Comment:
Yes, my mistake. Thanks for pointing it out.
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