Leniently tolerate late bean retrieval during destroySingletons()

Closes gh-22526
Closes gh-29730

spring-beans/src/main/java/org/springframework/beans/factory/support/DefaultSingletonBeanRegistry.java

@@ -99,13 +99,13 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	@Nullable
 	private volatile Thread singletonCreationThread;
 
+	/** Flag that indicates whether we're currently within destroySingletons. */
+	private volatile boolean singletonsCurrentlyInDestruction = false;
+
 	/** Collection of suppressed Exceptions, available for associating related causes. */
 	@Nullable
 	private Set<Exception> suppressedExceptions;
 
-	/** Flag that indicates whether we're currently within destroySingletons. */
-	private boolean singletonsCurrentlyInDestruction = false;
-
 	/** Disposable bean instances: bean name to disposable instance. */
 	private final Map<String, DisposableBean> disposableBeans = new LinkedHashMap<>();
 
@@ -562,13 +562,7 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 		if (logger.isTraceEnabled()) {
 			logger.trace("Destroying singletons in " + this);
 		}
-		this.singletonLock.lock();
-		try {
-			this.singletonsCurrentlyInDestruction = true;
-		}
-		finally {
-			this.singletonLock.unlock();
-		}
+		this.singletonsCurrentlyInDestruction = true;
 
 		String[] disposableBeanNames;
 		synchronized (this.disposableBeans) {
@@ -610,21 +604,28 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	 * @see #destroyBean
 	 */
 	public void destroySingleton(String beanName) {
-		// Remove a registered singleton of the given name, if any.
-		this.singletonLock.lock();
-		try {
-			removeSingleton(beanName);
-		}
-		finally {
-			this.singletonLock.unlock();
-		}
-
 		// Destroy the corresponding DisposableBean instance.
+		// This also triggers the destruction of dependent beans.
 		DisposableBean disposableBean;
 		synchronized (this.disposableBeans) {
 			disposableBean = this.disposableBeans.remove(beanName);
 		}
 		destroyBean(beanName, disposableBean);
+
+		// destroySingletons() removes all singleton instances at the end,
+		// leniently tolerating late retrieval during the shutdown phase.
+		if (!this.singletonsCurrentlyInDestruction) {
+			// For an individual destruction, remove the registered instance now.
+			// As of 6.2, this happens after the current bean's destruction step,
+			// allowing for late bean retrieval by on-demand suppliers etc.
+			this.singletonLock.lock();
+			try {
+				removeSingleton(beanName);
+			}
+			finally {
+				this.singletonLock.unlock();
+			}
+		}
 	}
 
 	/**

spring-context/src/test/java/org/springframework/context/support/Service.java

@@ -85,12 +85,11 @@ public class Service implements ApplicationContextAware, MessageSourceAware, Dis
 			Assert.state(applicationContext.getBean("messageSource") instanceof StaticMessageSource,
 					"Invalid MessageSource bean");
 			try {
+				// Should not throw BeanCreationNotAllowedException on 6.2 anymore
 				applicationContext.getBean("service2");
-				// Should have thrown BeanCreationNotAllowedException
-				properlyDestroyed = false;
 			}
 			catch (BeanCreationNotAllowedException ex) {
-				// expected
+				properlyDestroyed = false;
 			}
 		});
 		thread.start();