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/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;
+	}
 }