GH-1827: Fix Race

- increase idle event interval to prevent sequencer stopping the container too soon.
- tighten up synchronization in the sequencer

**cherry-pick to 2.7.x**

Author: garyrussell

spring-kafka/src/main/java/org/springframework/kafka/listener/ContainerGroupSequencer.java

@@ -140,20 +140,22 @@ public synchronized void onApplicationEvent(ListenerContainerIdleEvent event) {
 			this.executor.execute(() -> {
 				LOGGER.debug(() -> "Stopping: " + container);
 				container.stop(() -> {
-					if (!parent.isChildRunning()) {
-						this.executor.execute(() -> {
-							stopParentAndCheckGroup(parent);
-						});
+					synchronized (this) {
+						if (!parent.isChildRunning()) {
+							this.executor.execute(() -> {
+								stopParentAndCheckGroup(parent);
+							});
+						}
 					}
 				});
 			});
 		}
 	}
 
-	private void stopParentAndCheckGroup(MessageListenerContainer parent) {
-		LOGGER.debug(() -> "Stopping: " + parent);
-		parent.stop(() -> {
-			synchronized (this) {
+	private synchronized void stopParentAndCheckGroup(MessageListenerContainer parent) {
+		if (parent.isRunning()) {
+			LOGGER.debug(() -> "Stopping: " + parent);
+			parent.stop(() -> {
 				if (this.currentGroup != null) {
 					LOGGER.debug(() -> "Checking group: " + this.currentGroup.toString());
 					if (this.currentGroup.allStopped()) {
@@ -167,8 +169,8 @@ private void stopParentAndCheckGroup(MessageListenerContainer parent) {
 						}
 					}
 				}
-			}
-		});
+			});
+		}
 	}
 
 	@Override

spring-kafka/src/test/java/org/springframework/kafka/listener/ContainerGroupSequencerTests.java

@@ -137,7 +137,7 @@ public void stopped(ContainerStoppedEvent event) {
 
 		@Bean
 		ContainerGroupSequencer sequencer(KafkaListenerEndpointRegistry registry) {
-			ContainerGroupSequencer sequencer = new ContainerGroupSequencer(registry, 1000, "g1", "g2");
+			ContainerGroupSequencer sequencer = new ContainerGroupSequencer(registry, 3000, "g1", "g2");
 			sequencer.setStopLastGroupWhenIdle(true);
 			sequencer.setAutoStartup(false);
 			return sequencer;