Use reverse order for shutdown hooks

Refine `SpringApplicationShutdownHook` so that shutdown happens in
reverse order to registration.

See gh-43430

Author: philwebb

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplicationShutdownHook.java

@@ -16,8 +16,10 @@
 
 package org.springframework.boot;
 
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.LinkedHashSet;
+import java.util.List;
 import java.util.Set;
 import java.util.WeakHashMap;
 import java.util.concurrent.TimeUnit;
@@ -103,12 +105,13 @@ void deregisterFailedApplicationContext(ConfigurableApplicationContext applicati
 	public void run() {
 		Set<ConfigurableApplicationContext> contexts;
 		Set<ConfigurableApplicationContext> closedContexts;
-		Set<Handler> handlers;
+		List<Handler> handlers;
 		synchronized (SpringApplicationShutdownHook.class) {
 			this.inProgress = true;
 			contexts = new LinkedHashSet<>(this.contexts);
 			closedContexts = new LinkedHashSet<>(this.closedContexts);
-			handlers = new LinkedHashSet<>(this.handlers.getActions());
+			handlers = new ArrayList<>(this.handlers.getActions());
+			Collections.reverse(handlers);
 		}
 		contexts.forEach(this::closeAndWait);
 		closedContexts.forEach(this::closeAndWait);

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationShutdownHookTests.java

@@ -207,7 +207,7 @@ void deregistersFailedContext() {
 	}
 
 	@Test
-	void handlersRunInDeterministicOrder() {
+	void handlersRunInDeterministicOrderFromLastRegisteredToFirst() {
 		TestSpringApplicationShutdownHook shutdownHook = new TestSpringApplicationShutdownHook();
 		Runnable r1 = mock(Runnable.class);
 		Runnable r2 = mock(Runnable.class);
@@ -217,9 +217,9 @@ void handlersRunInDeterministicOrder() {
 		shutdownHook.getHandlers().add(r3);
 		shutdownHook.run();
 		InOrder ordered = inOrder(r1, r2, r3);
-		ordered.verify(r2).run();
-		ordered.verify(r1).run();
 		ordered.verify(r3).run();
+		ordered.verify(r1).run();
+		ordered.verify(r2).run();
 		ordered.verifyNoMoreInteractions();
 	}