Add distibuted action

- New module spring-statemachine-cluster which is
  based on spring-cloud-cluster to provide leader
  election.
- Ensemble now has a concept of a leader if implementation
  supports it.
- New DistributedLeaderAction can use leader info to execute
  action only on a leader.
- Tweak web sample with these new concepts.
- Fixes #176

spring-statemachine-core/src/main/java/org/springframework/statemachine/action/DistributedLeaderAction.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.statemachine.action;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.springframework.statemachine.StateContext;
+import org.springframework.statemachine.StateMachine;
+import org.springframework.statemachine.ensemble.StateMachineEnsemble;
+import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
+
+/**
+ * {@link Action} which is used to wrap execution of an {@link Action}
+ * so that only a {@link StateMachine} considered to be a leader in an
+ * {@link StateMachineEnsemble} will do the execution.
+ *
+ * Executing action via {@code DistributedLeaderAction} is bound to if
+ * current machine is a leader or not. Effectively this means that if
+ * leader doesn't exist, execution is discarded.
+ *
+ * @author Janne Valkealahti
+ *
+ * @param <S> the type of state
+ * @param <E> the type of event
+ */
+public class DistributedLeaderAction<S, E> implements Action<S, E> {
+
+	private final static Log log = LogFactory.getLog(DistributedLeaderAction.class);
+	private final Action<S, E> action;
+	private final StateMachineEnsemble<S, E> ensemble;
+
+	/**
+	 * Instantiates a new distributed leader action.
+	 *
+	 * @param action the action
+	 * @param ensemble the ensemble
+	 */
+	public DistributedLeaderAction(Action<S, E> action, StateMachineEnsemble<S, E> ensemble) {
+		Assert.notNull(action, "Action must be set");
+		Assert.notNull(ensemble, "Ensemble must be set");
+		this.action = action;
+		this.ensemble = ensemble;
+	}
+
+	@Override
+	public void execute(StateContext<S, E> context) {
+		StateMachine<S, E> left = context.getStateMachine();
+		StateMachine<S, E> right = ensemble.getLeader();
+		boolean leader = (left != null & right != null) && ObjectUtils.nullSafeEquals(left.getUuid(), right.getUuid());
+		if (log.isDebugEnabled()) {
+			log.debug("Distibuted action leader status is " + leader);
+		}
+		if (leader) {
+			action.execute(context);
+		}
+	}
+}

spring-statemachine-core/src/main/java/org/springframework/statemachine/ensemble/CompositeEnsembleListener.java

@@ -64,4 +64,19 @@ public class CompositeEnsembleListener<S, E> extends AbstractCompositeListener<E
 		}
 	}
 
+	@Override
+	public void ensembleLeaderGranted(StateMachine<S, E> stateMachine) {
+		for (Iterator<EnsembleListener<S, E>> iterator = getListeners().reverse(); iterator.hasNext();) {
+			EnsembleListener<S, E> listener = iterator.next();
+			listener.ensembleLeaderGranted(stateMachine);
+		}
+	}
+
+	@Override
+	public void ensembleLeaderRevoked(StateMachine<S, E> stateMachine) {
+		for (Iterator<EnsembleListener<S, E>> iterator = getListeners().reverse(); iterator.hasNext();) {
+			EnsembleListener<S, E> listener = iterator.next();
+			listener.ensembleLeaderRevoked(stateMachine);
+		}
+	}
 }

spring-statemachine-core/src/main/java/org/springframework/statemachine/ensemble/DistributedStateMachine.java

@@ -312,6 +312,13 @@ public class DistributedStateMachine<S, E> extends LifecycleObjectSupport implem
 			throw exception;
 		}
 
+		@Override
+		public void ensembleLeaderGranted(StateMachine<S, E> stateMachine) {
+		}
+
+		@Override
+		public void ensembleLeaderRevoked(StateMachine<S, E> stateMachine) {
+		}
 	}
 
 }

spring-statemachine-core/src/main/java/org/springframework/statemachine/ensemble/EnsembleListener.java

@@ -69,4 +69,19 @@ public interface EnsembleListener<S, E> {
 	 */
 	void ensembleError(StateMachineEnsembleException exception);
 
+	/**
+	 * Called when a state machine is granted a leader role
+	 * in an ensemble.
+	 *
+	 * @param stateMachine the state machine
+	 */
+	void ensembleLeaderGranted(StateMachine<S, E> stateMachine);
+
+	/**
+	 * Called when a state machine is revoked from a leader role
+	 * in an ensemble.
+	 *
+	 * @param stateMachine the state machine
+	 */
+	void ensembleLeaderRevoked(StateMachine<S, E> stateMachine);
 }

spring-statemachine-core/src/main/java/org/springframework/statemachine/ensemble/EnsembleListenerAdapter.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.statemachine.ensemble;
+
+import org.springframework.statemachine.StateMachine;
+import org.springframework.statemachine.StateMachineContext;
+
+/**
+ * Adapter implementation of {@link EnsembleListener} implementing all
+ * methods which extended implementation can override.
+ *
+ * @author Janne Valkealahti
+ *
+ * @param <S> the type of state
+ * @param <E> the type of event
+ */
+public class EnsembleListenerAdapter<S, E> implements EnsembleListener<S, E> {
+
+	@Override
+	public void stateMachineJoined(StateMachine<S, E> stateMachine, StateMachineContext<S, E> context) {
+	}
+
+	@Override
+	public void stateMachineLeft(StateMachine<S, E> stateMachine, StateMachineContext<S, E> context) {
+	}
+
+	@Override
+	public void stateChanged(StateMachineContext<S, E> context) {
+	}
+
+	@Override
+	public void ensembleError(StateMachineEnsembleException exception) {
+	}
+
+	@Override
+	public void ensembleLeaderGranted(StateMachine<S, E> stateMachine) {
+	}
+
+	@Override
+	public void ensembleLeaderRevoked(StateMachine<S, E> stateMachine) {
+	}
+}

spring-statemachine-core/src/main/java/org/springframework/statemachine/ensemble/StateMachineEnsemble.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015 the original author or authors.
+ * Copyright 2015-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -80,4 +80,12 @@ public interface StateMachineEnsemble<S, E> {
 	 */
 	StateMachineContext<S, E> getState();
 
+	/**
+	 * Gets the ensemble leader. If returned machine
+	 * is {@code NULL} it indicates that this ensemble
+	 * doesn't know any leader.
+	 *
+	 * @return the ensemble leader
+	 */
+	StateMachine<S, E> getLeader();
 }

spring-statemachine-core/src/main/java/org/springframework/statemachine/ensemble/StateMachineEnsembleObjectSupport.java

@@ -63,11 +63,18 @@ public abstract class StateMachineEnsembleObjectSupport<S, E> extends LifecycleO
 		ensembleListener.ensembleError(exception);
 	}
 
+	protected void notifyGranted(StateMachine<S, E> stateMachine) {
+		ensembleListener.ensembleLeaderGranted(stateMachine);
+	}
+
+	protected void notifyRevoked(StateMachine<S, E> stateMachine) {
+		ensembleListener.ensembleLeaderRevoked(stateMachine);
+	}
+
 	protected void notifyStateChanged(StateMachineContext<S, E> context) {
 		if (log.isTraceEnabled()) {
 			log.trace("Notify notifyStateChanged " + context);
 		}
 		ensembleListener.stateChanged(context);
 	}
-
 }

spring-statemachine-core/src/test/java/org/springframework/statemachine/action/DistributedLeaderActionTests.java

@@ -0,0 +1,142 @@
+/*
+ * Copyright 2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.statemachine.action;
+
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.assertThat;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+import org.junit.Test;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.statemachine.AbstractStateMachineTests;
+import org.springframework.statemachine.StateContext;
+import org.springframework.statemachine.StateMachine;
+import org.springframework.statemachine.config.EnableStateMachineFactory;
+import org.springframework.statemachine.config.StateMachineConfigurerAdapter;
+import org.springframework.statemachine.config.StateMachineFactory;
+import org.springframework.statemachine.config.builders.StateMachineConfigurationConfigurer;
+import org.springframework.statemachine.config.builders.StateMachineStateConfigurer;
+import org.springframework.statemachine.config.builders.StateMachineTransitionConfigurer;
+import org.springframework.statemachine.ensemble.InMemoryStateMachineEnsemble;
+import org.springframework.statemachine.ensemble.StateMachineEnsemble;
+
+public class DistributedLeaderActionTests extends AbstractStateMachineTests {
+
+	@Override
+	protected AnnotationConfigApplicationContext buildContext() {
+		return new AnnotationConfigApplicationContext();
+	}
+
+	@Test
+	public void testAction() throws Exception {
+		context.register(Config1.class);
+		context.refresh();
+
+		TestLeaderAction action = context.getBean("testLeaderAction", TestLeaderAction.class);
+
+		@SuppressWarnings("unchecked")
+		StateMachineFactory<String, String> factory = context.getBean(StateMachineFactory.class);
+
+		StateMachine<String, String> machine1 = factory.getStateMachine();
+		StateMachine<String, String> machine2 = factory.getStateMachine();
+		machine1.sendEvent("E1");
+		assertThat(action.latch.await(1, TimeUnit.SECONDS), is(false));
+		assertThat(action.count, is(1));
+		action.reset(2);
+
+		machine2.sendEvent("E2");
+		assertThat(action.latch.await(1, TimeUnit.SECONDS), is(false));
+		assertThat(action.count, is(1));
+	}
+
+	@Configuration
+	@EnableStateMachineFactory
+	static class Config1 extends StateMachineConfigurerAdapter<String, String> {
+
+		@Override
+		public void configure(StateMachineConfigurationConfigurer<String, String> config) throws Exception {
+			config
+				.withConfiguration()
+					.autoStartup(true)
+					.and()
+				.withDistributed()
+					.ensemble(ensemble());
+		}
+
+		@Override
+		public void configure(StateMachineStateConfigurer<String, String> states) throws Exception {
+			states
+				.withStates()
+					.initial("S1")
+					.state("S2", testDistributedLeaderAction(), null)
+					.state("S3", testDistributedLeaderAction(), null);
+		}
+
+		@Override
+		public void configure(StateMachineTransitionConfigurer<String, String> transitions) throws Exception {
+			transitions
+				.withExternal()
+					.source("S1").target("S2")
+					.event("E1")
+					.and()
+				.withExternal()
+					.source("S2").target("S3")
+					.event("E2")
+					.and()
+				.withExternal()
+					.source("S3").target("S1")
+					.event("E3");
+		}
+
+		@Bean
+		public StateMachineEnsemble<String, String> ensemble() {
+			return new InMemoryStateMachineEnsemble<String, String>();
+		}
+
+		@Bean
+		public Action<String, String> testLeaderAction() {
+			return new TestLeaderAction();
+		}
+
+		@Bean
+		public Action<String, String> testDistributedLeaderAction() {
+			return new DistributedLeaderAction<>(testLeaderAction(), ensemble());
+		}
+
+	}
+
+	static class TestLeaderAction implements Action<String, String> {
+
+		CountDownLatch latch = new CountDownLatch(2);
+		int count = 0;
+
+		@Override
+		public void execute(StateContext<String, String> context) {
+			count++;
+			latch.countDown();
+		}
+
+		public void reset(int a1) {
+			count = 0;
+			latch = new CountDownLatch(a1);
+		}
+	}
+
+}

spring-statemachine-core/src/test/java/org/springframework/statemachine/ensemble/InMemoryStateMachineEnsemble.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015 the original author or authors.
+ * Copyright 2015-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,13 +24,16 @@ import org.springframework.statemachine.StateMachineContext;
 public class InMemoryStateMachineEnsemble<S, E> extends StateMachineEnsembleObjectSupport<S, E> {
 
 	private final Set<StateMachine<S, E>> joined = new HashSet<StateMachine<S,E>>();
-
+	private StateMachine<S, E> leader;
 	private StateMachineContext<S, E> current;
 
 	@Override
 	public void join(StateMachine<S, E> stateMachine) {
 		if (!joined.contains(stateMachine)) {
 			joined.add(stateMachine);
+			if (leader == null) {
+				leader = stateMachine;
+			}
 			notifyJoined(stateMachine, current);
 		}
 	}
@@ -38,6 +41,14 @@ public class InMemoryStateMachineEnsemble<S, E> extends StateMachineEnsembleObje
 	@Override
 	public void leave(StateMachine<S, E> stateMachine) {
 		if (joined.remove(stateMachine)) {
+			if (leader == stateMachine) {
+				StateMachine<S, E> newLeader = null;
+				try {
+					newLeader = joined.iterator().next();
+				} catch (Exception e) {
+				}
+				leader = newLeader;
+			}
 			notifyLeft(stateMachine, current);
 		}
 	}
@@ -53,4 +64,8 @@ public class InMemoryStateMachineEnsemble<S, E> extends StateMachineEnsembleObje
 		return current;
 	}
 
+	@Override
+	public StateMachine<S, E> getLeader() {
+		return leader;
+	}
 }