GH-173: Leaders: Warn event errors, not re-throw

Fixes GH-173 (https://github.com/spring-projects/spring-integration-extensions/issues/173)

Currently when an error is thrown from the event publishing the role granting is broken and we just go to the role revoking.

* Since it's just an event publishing it shouldn't effect the original leader election.
* `try...catch` event publishing in the `LeaderInitiator` and `logger.warn` an `Exception`

spring-integration-hazelcast/src/main/java/org/springframework/integration/hazelcast/leader/LeaderInitiator.java

@@ -23,6 +23,9 @@ import java.util.concurrent.Future;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
 import org.springframework.beans.factory.DisposableBean;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.context.ApplicationEventPublisherAware;
@@ -49,6 +52,8 @@ import com.hazelcast.core.ILock;
  */
 public class LeaderInitiator implements SmartLifecycle, DisposableBean, ApplicationEventPublisherAware {
 
+	private static final Log logger = LogFactory.getLog(LeaderInitiator.class);
+
 	private static int threadNameCount = 0;
 
 	private static final Context NULL_CONTEXT = new NullContext();
@@ -236,8 +241,13 @@ public class LeaderInitiator implements SmartLifecycle, DisposableBean, Applicat
 					try {
 						this.locked = LeaderInitiator.this.lock.tryLock(Long.MAX_VALUE, TimeUnit.MILLISECONDS);
 						if (this.locked) {
-							LeaderInitiator.this.leaderEventPublisher.publishOnGranted(LeaderInitiator.this,
-									this.context, this.role);
+							try {
+								LeaderInitiator.this.leaderEventPublisher.publishOnGranted(LeaderInitiator.this,
+										this.context, this.role);
+							}
+							catch (Exception e) {
+								logger.warn("Error publishing OnGranted event.", e);
+							}
 							LeaderInitiator.this.candidate.onGranted(this.context);
 							Thread.sleep(Long.MAX_VALUE);
 						}
@@ -249,9 +259,14 @@ public class LeaderInitiator implements SmartLifecycle, DisposableBean, Applicat
 							// The lock was broken and we are no longer leader
 							LeaderInitiator.this.candidate.onRevoked(this.context);
 							if (LeaderInitiator.this.leaderEventPublisher != null) {
-								LeaderInitiator.this.leaderEventPublisher.publishOnRevoked(
-										LeaderInitiator.this, this.context,
-										LeaderInitiator.this.candidate.getRole());
+								try {
+									LeaderInitiator.this.leaderEventPublisher.publishOnRevoked(
+											LeaderInitiator.this, this.context,
+											LeaderInitiator.this.candidate.getRole());
+								}
+								catch (Exception ex) {
+									logger.warn("Error publishing OnRevoked event.", ex);
+								}
 							}
 							Thread.currentThread().interrupt();
 							return null;
@@ -266,8 +281,13 @@ public class LeaderInitiator implements SmartLifecycle, DisposableBean, Applicat
 					// We are stopping, therefore not leading any more
 					LeaderInitiator.this.candidate.onRevoked(this.context);
 					if (LeaderInitiator.this.leaderEventPublisher != null) {
-						LeaderInitiator.this.leaderEventPublisher.publishOnRevoked(
-								LeaderInitiator.this, this.context, this.role);
+						try {
+							LeaderInitiator.this.leaderEventPublisher.publishOnRevoked(
+									LeaderInitiator.this, this.context, this.role);
+						}
+						catch (Exception e) {
+							logger.warn("Error publishing OnRevoked event.", e);
+						}
 					}
 				}
 			}

spring-integration-hazelcast/src/test/java/org/springframework/integration/hazelcast/leader/LeaderInitiatorTests.java

@@ -20,6 +20,9 @@ package org.springframework.integration.hazelcast.leader;
 import static org.hamcrest.CoreMatchers.is;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertThat;
+import static org.mockito.BDDMockito.willAnswer;
+import static org.mockito.Matchers.any;
+import static org.mockito.Mockito.spy;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -36,6 +39,7 @@ import org.springframework.context.annotation.Configuration;
 import org.springframework.integration.leader.Context;
 import org.springframework.integration.leader.DefaultCandidate;
 import org.springframework.integration.leader.event.AbstractLeaderEvent;
+import org.springframework.integration.leader.event.DefaultLeaderEventPublisher;
 import org.springframework.integration.leader.event.LeaderEventPublisher;
 import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.context.ContextConfiguration;
@@ -168,8 +172,43 @@ public class LeaderInitiatorTests {
 		assertThat(revoked11.await(10, TimeUnit.SECONDS), is(true));
 
 		initiator1.destroy();
+
+
+
+		CountDownLatch onGranted = new CountDownLatch(1);
+
+		DefaultCandidate candidate = spy(new DefaultCandidate());
+		willAnswer(invocation -> {
+			try {
+				return invocation.callRealMethod();
+			}
+			finally {
+				onGranted.countDown();
+			}
+		})
+				.given(candidate).onGranted(any(Context.class));
+
+		LeaderInitiator initiator = new LeaderInitiator(this.hazelcastInstance, candidate);
+
+		initiator.setLeaderEventPublisher(new DefaultLeaderEventPublisher() {
+
+			@Override
+			public void publishOnGranted(Object source, Context context, String role) {
+				throw new RuntimeException("intentional");
+			}
+
+		});
+
+		initiator.start();
+
+		assertThat(onGranted.await(5, TimeUnit.SECONDS), is(true));
+
+		assertThat(initiator.getContext().isLeader(), is(true));
+
+		initiator.destroy();
 	}
 
+
 	@Configuration
 	public static class TestConfig {