Change tasks sample to parallel execution

- Now defining parallel region execution policy as
  TaskExecutor won't work anymore.
- Relates #397

docs/src/reference/asciidoc/sm-examples-tasks.adoc

@@ -86,11 +86,9 @@ include::samples/demo/tasks/Application.java[tags=snippetAD]
 ----
 ====
 
-Currently, the default region execution is synchronous, but you can change
-it to be asynchronous by changing `TaskExecutor`. Task simulates
-work by sleeping two seconds so that you can see how actions in
-regions are executed inparallel.
-The following listing shows the `TaskExecutor` bean definition:
+Default region execution is synchronous meaning a regions would be processed
+sequentially. In this sample we simply want all task regions to get processed
+parallel. This can be accomplished by defining `RegionExecutionPolicy`:
 
 ====
 [source,java,indent=0]
@@ -109,22 +107,24 @@ State machine started
 Entry state READY
 
 sm>tasks run
+Exit state READY
 Entry state TASKS
-run task on T3
 run task on T2
 run task on T1
+run task on T3
 run task on T2 done
 run task on T1 done
 run task on T3 done
 Entry state T2
-Entry state T3
 Entry state T1
+Entry state T3
+Exit state T2
+Exit state T1
+Exit state T3
+Entry state T3E
 Entry state T1E
 Entry state T2E
-Entry state T3E
 Exit state TASKS
-Entry state JOIN
-Exit state JOIN
 Entry state READY
 ----
 ====

spring-statemachine-samples/tasks/src/main/java/demo/tasks/Application.java

@@ -33,9 +33,11 @@ import org.springframework.statemachine.action.Action;
 import org.springframework.statemachine.annotation.OnTransition;
 import org.springframework.statemachine.config.EnableStateMachine;
 import org.springframework.statemachine.config.EnumStateMachineConfigurerAdapter;
+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.guard.Guard;
+import org.springframework.statemachine.region.RegionExecutionPolicy;
 import org.springframework.util.ObjectUtils;
 
 import reactor.core.publisher.Mono;
@@ -48,6 +50,16 @@ public class Application  {
 	static class StateMachineConfig
 			extends EnumStateMachineConfigurerAdapter<States, Events> {
 
+//tag::snippetAE[]
+		@Override
+		public void configure(StateMachineConfigurationConfigurer<States, Events> config)
+				throws Exception {
+			config
+				.withConfiguration()
+					.regionExecutionPolicy(RegionExecutionPolicy.PARALLEL);
+		}
+//end::snippetAE[]
+
 //tag::snippetAA[]
 		@Override
 		public void configure(StateMachineStateConfigurer<States, Events> states)
@@ -195,16 +207,6 @@ public class Application  {
 		public Tasks tasks() {
 			return new Tasks();
 		}
-
-//tag::snippetAE[]
-		@Bean(name = StateMachineSystemConstants.TASK_EXECUTOR_BEAN_NAME)
-		public TaskExecutor taskExecutor() {
-			ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
-			taskExecutor.setCorePoolSize(5);
-			return taskExecutor;
-		}
-//end::snippetAE[]
-
 	}
 
 //tag::snippetB[]