Prevent closed context from being refreshed again by an HTTP request

Prior to this commit, EmbeddedWebApplicationContext would perform its
close processing and then stop the embedded container. This could
lead to the closed context's dispatcher servlet handling an HTTP
request and refreshing the context again. This opened up two
possibilities that we need to avoid:

1. Another HTTP request could be received by the dispatcher servlet
   while the context is still being refreshed. This could lead to the
   context being used before its refreshed. I believe this could be
   the cause of the current modification exception described in
   gh-3239 and SPR-13123.
2. It can lead to a race during shutdown as the shutdown hook's
   attempt to close the context races with the refresh initiated by
   the HTTP request. This is possible as the shutdown hook bypasses
   the sychronization on startupShutdownMonitor that would normally
   prevent refresh and close from occurring in parallel. This race
   can lead to a deadlock as described in gh-4130

Closes gh-4130

spring-boot/src/main/java/org/springframework/boot/context/embedded/EmbeddedWebApplicationContext.java

@@ -146,8 +146,8 @@ public class EmbeddedWebApplicationContext extends GenericWebApplicationContext
 
 	@Override
 	protected void doClose() {
-		super.doClose();
 		stopAndReleaseEmbeddedServletContainer();
+		super.doClose();
 	}
 
 	private synchronized void createEmbeddedServletContainer() {

spring-boot/src/test/java/org/springframework/boot/context/embedded/EmbeddedWebApplicationContextTests.java

@@ -36,11 +36,14 @@ import org.junit.Test;
 import org.junit.rules.ExpectedException;
 import org.mockito.InOrder;
 import org.springframework.beans.MutablePropertyValues;
+import org.springframework.beans.factory.DisposableBean;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.beans.factory.config.ConstructorArgumentValues;
 import org.springframework.beans.factory.config.Scope;
+import org.springframework.beans.factory.support.BeanDefinitionBuilder;
 import org.springframework.beans.factory.support.RootBeanDefinition;
+import org.springframework.boot.context.embedded.MockEmbeddedServletContainerFactory.MockEmbeddedServletContainer;
 import org.springframework.context.ApplicationContextException;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.support.AbstractApplicationContext;
@@ -54,6 +57,7 @@ import org.springframework.web.filter.GenericFilterBean;
 
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.instanceOf;
+import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.nullValue;
 import static org.hamcrest.Matchers.sameInstance;
 import static org.junit.Assert.assertEquals;
@@ -429,6 +433,22 @@ public class EmbeddedWebApplicationContextTests {
 				sameInstance(scope));
 	}
 
+	@Test
+	public void containerIsStoppedBeforeContextIsClosed() {
+		addEmbeddedServletContainerFactoryBean();
+		this.context.registerBeanDefinition("shutdownOrderingValidator",
+				BeanDefinitionBuilder.rootBeanDefinition(ShutdownOrderingValidator.class)
+						.addConstructorArgReference("embeddedServletContainerFactory")
+						.getBeanDefinition());
+		this.context.refresh();
+		ShutdownOrderingValidator validator = this.context
+				.getBean(ShutdownOrderingValidator.class);
+		this.context.close();
+		assertThat(validator.destroyed, is(true));
+		assertThat(validator.containerStoppedFirst, is(true));
+
+	}
+
 	private void addEmbeddedServletContainerFactoryBean() {
 		this.context.registerBeanDefinition("embeddedServletContainerFactory",
 				new RootBeanDefinition(MockEmbeddedServletContainerFactory.class));
@@ -478,4 +498,25 @@ public class EmbeddedWebApplicationContextTests {
 
 	}
 
+	protected static class ShutdownOrderingValidator implements DisposableBean {
+
+		private final MockEmbeddedServletContainer servletContainer;
+
+		private boolean destroyed = false;
+
+		private boolean containerStoppedFirst = false;
+
+		ShutdownOrderingValidator(
+				MockEmbeddedServletContainerFactory servletContainerFactory) {
+			this.servletContainer = servletContainerFactory.getContainer();
+		}
+
+		@Override
+		public void destroy() {
+			this.destroyed = true;
+			this.containerStoppedFirst = this.servletContainer.isStopped();
+		}
+
+	}
+
 }

spring-boot/src/test/java/org/springframework/boot/context/embedded/MockEmbeddedServletContainerFactory.java

@@ -90,6 +90,8 @@ public class MockEmbeddedServletContainerFactory
 
 		private final int port;
 
+		private boolean stopped = false;
+
 		public MockEmbeddedServletContainer(ServletContextInitializer[] initializers,
 				int port) {
 			this.initializers = initializers;
@@ -188,6 +190,11 @@ public class MockEmbeddedServletContainerFactory
 		public void stop() {
 			this.servletContext = null;
 			this.registeredServlets.clear();
+			this.stopped = true;
+		}
+
+		public boolean isStopped() {
+			return this.stopped;
 		}
 
 		public Servlet[] getServlets() {