Fix event defer issues

- Event may get not accepted in some cases
  while it should be deferred. Check defer
  again before accept would return false.
- Relates to #131

spring-statemachine-core/src/main/java/org/springframework/statemachine/support/AbstractStateMachine.java

@@ -592,6 +592,13 @@ public abstract class AbstractStateMachine<S, E> extends StateMachineObjectSuppo
 				}
 			}
 		}
+		// if we're about to not accept event, check defer again in case
+		// state was changed between original check and now
+		if ((currentState != null && currentState.shouldDefer(message))) {
+			log.info("Current state " + currentState + " deferred event " + message);
+			stateMachineExecutor.queueDeferredEvent(message);
+			return true;
+		}
 		return false;
 	}
 

spring-statemachine-core/src/main/java/org/springframework/statemachine/support/DefaultStateMachineExecutor.java

@@ -272,6 +272,7 @@ public class DefaultStateMachineExecutor<S, E> extends LifecycleObjectSupport im
 		State<S,E> currentState = stateMachine.getState();
 		if (queuedEvent != null) {
 			if ((currentState != null && currentState.shouldDefer(queuedEvent))) {
+				log.info("Current state " + currentState + " deferred event " + queuedEvent);
 				queueDeferredEvent(queuedEvent);
 				return true;
 			}

spring-statemachine-core/src/test/java/org/springframework/statemachine/EventDeferTests.java

@@ -153,6 +153,39 @@ public class EventDeferTests extends AbstractStateMachineTests {
 		assertThat(machine.getState().getIds(), contains("READY"));
 	}
 
+	@Test
+	public void testDeferWithSubs2ThreadExecutor() throws Exception {
+		context.register(Config1.class, ExecutorConfig.class);
+		context.refresh();
+		@SuppressWarnings("unchecked")
+		StateMachine<String, String> machine = context.getBean(StateMachineSystemConstants.DEFAULT_ID_STATEMACHINE, StateMachine.class);
+		TestListener listener = new TestListener();
+		machine.addStateListener(listener);
+		machine.start();
+
+		assertThat(listener.stateMachineStartedLatch.await(3, TimeUnit.SECONDS), is(true));
+		assertThat(listener.stateChangedLatch.await(3, TimeUnit.SECONDS), is(true));
+
+		listener.reset(0, 0, 2, 0);
+		machine.sendEvent("E2");
+		machine.sendEvent("E2");
+
+		assertThat(listener.readyStateEnteredLatch.await(3, TimeUnit.SECONDS), is(true));
+		assertThat(listener.readyStateEnteredCount, is(2));
+
+		assertThat(machine.getState().getIds(), contains("READY"));
+	}
+
+	@Test
+	public void testDeferWithSubs2ThreadExecutorSmoke() throws Exception {
+		// smoke above test to see threading issues
+		for (int i = 0; i < 500; i++) {
+			setup();
+			testDeferWithSubs2ThreadExecutor();
+			clean();
+		}
+	}
+
 	@Test
 	public void testSubNotDeferOverrideSuperTransition() throws Exception {
 		context.register(Config3.class);