Integrate child management context with parent context's lifecycle

Previously, the child management context was created when the
parent context's web server was initialized and it wasn't stopped
or closed until the parent context was closed. This resulted in
the child context being left running when the parent context was
stopped. This would then cause a failure when the parent context
was started again as another web server initialized event would be
received and a second child management context would be started.

This commit updates the initialization of the child management
context to integrate it with the lifecycle of the parent context.
The management context is now created the first time the parent
context is started. It is stopped when the parent context is
stopped and restarted if the parent context is started again.
This lifecycle management is done using a phase that ensures
that the child context is not started until the parent context's
web server has been started.

Fixes gh-38502

Author: wilkinsona

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/web/server/ChildManagementContextInitializer.java

@@ -33,12 +33,13 @@
 import org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration;
 import org.springframework.boot.context.event.ApplicationFailedEvent;
 import org.springframework.boot.web.context.ConfigurableWebServerApplicationContext;
-import org.springframework.boot.web.context.WebServerInitializedEvent;
+import org.springframework.boot.web.context.WebServerGracefulShutdownLifecycle;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextInitializer;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.context.SmartLifecycle;
 import org.springframework.context.annotation.AnnotationConfigRegistry;
 import org.springframework.context.aot.ApplicationContextAotGenerator;
 import org.springframework.context.event.ContextClosedEvent;
@@ -55,15 +56,16 @@
  * @author Andy Wilkinson
  * @author Phillip Webb
  */
-class ChildManagementContextInitializer
-		implements ApplicationListener<WebServerInitializedEvent>, BeanRegistrationAotProcessor {
+class ChildManagementContextInitializer implements BeanRegistrationAotProcessor, SmartLifecycle {
 
 	private final ManagementContextFactory managementContextFactory;
 
 	private final ApplicationContext parentContext;
 
 	private final ApplicationContextInitializer<ConfigurableApplicationContext> applicationContextInitializer;
 
+	private volatile ConfigurableApplicationContext managementContext;
+
 	ChildManagementContextInitializer(ManagementContextFactory managementContextFactory,
 			ApplicationContext parentContext) {
 		this(managementContextFactory, parentContext, null);
@@ -79,14 +81,35 @@ private ChildManagementContextInitializer(ManagementContextFactory managementCon
 	}
 
 	@Override
-	public void onApplicationEvent(WebServerInitializedEvent event) {
-		if (event.getApplicationContext().equals(this.parentContext)) {
+	public void start() {
+		if (this.managementContext == null) {
 			ConfigurableApplicationContext managementContext = createManagementContext();
 			registerBeans(managementContext);
 			managementContext.refresh();
+			this.managementContext = managementContext;
+		}
+		else {
+			this.managementContext.start();
+		}
+	}
+
+	@Override
+	public void stop() {
+		if (this.managementContext != null) {
+			this.managementContext.stop();
 		}
 	}
 
+	@Override
+	public boolean isRunning() {
+		return this.managementContext != null && this.managementContext.isRunning();
+	}
+
+	@Override
+	public int getPhase() {
+		return WebServerGracefulShutdownLifecycle.SMART_LIFECYCLE_PHASE + 512;
+	}
+
 	@Override
 	public BeanRegistrationAotContribution processAheadOfTime(RegisteredBean registeredBean) {
 		Assert.isInstanceOf(ConfigurableApplicationContext.class, this.parentContext);

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/web/server/ManagementContextAutoConfigurationTests.java

@@ -55,6 +55,21 @@ void childManagementContextShouldStartForEmbeddedServer(CapturedOutput output) {
 			.run((context) -> assertThat(output).satisfies(numberOfOccurrences("Tomcat started on port", 2)));
 	}
 
+	@Test
+	void childManagementContextShouldRestartWhenParentIsStoppedThenStarted(CapturedOutput output) {
+		WebApplicationContextRunner contextRunner = new WebApplicationContextRunner(
+				AnnotationConfigServletWebServerApplicationContext::new)
+			.withConfiguration(AutoConfigurations.of(ManagementContextAutoConfiguration.class,
+					ServletWebServerFactoryAutoConfiguration.class, ServletManagementContextAutoConfiguration.class,
+					WebEndpointAutoConfiguration.class, EndpointAutoConfiguration.class));
+		contextRunner.withPropertyValues("server.port=0", "management.server.port=0").run((context) -> {
+			assertThat(output).satisfies(numberOfOccurrences("Tomcat started on port", 2));
+			context.getSourceApplicationContext().stop();
+			context.getSourceApplicationContext().start();
+			assertThat(output).satisfies(numberOfOccurrences("Tomcat started on port", 4));
+		});
+	}
+
 	@Test
 	void givenSamePortManagementServerWhenManagementServerAddressIsConfiguredThenContextRefreshFails() {
 		WebApplicationContextRunner contextRunner = new WebApplicationContextRunner(