Avoid potential deadlocks between event multicaster and singleton registry through shared lock

Issue: SPR-12739
(cherry picked from commit 772552b)

Author: jhoeller

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -317,7 +317,7 @@ public boolean isSingletonCurrentlyInCreation(String beanName) {
 
 	/**
 	 * Callback before singleton creation.
-	 * <p>Default implementation register the singleton as currently in creation.
+	 * <p>The default implementation register the singleton as currently in creation.
 	 * @param beanName the name of the singleton about to be created
 	 * @see #isSingletonCurrentlyInCreation
 	 */
@@ -539,13 +539,13 @@ protected void destroyBean(String beanName, DisposableBean bean) {
 	}
 
 	/**
-	 * Expose the singleton mutex to subclasses.
+	 * Exposes the singleton mutex to subclasses and external collaborators.
 	 * <p>Subclasses should synchronize on the given Object if they perform
 	 * any sort of extended singleton creation phase. In particular, subclasses
 	 * should <i>not</i> have their own mutexes involved in singleton creation,
 	 * to avoid the potential for deadlocks in lazy-init situations.
 	 */
-	protected final Object getSingletonMutex() {
+	public final Object getSingletonMutex() {
 		return this.singletonObjects;
 	}
 

spring-context/src/main/java/org/springframework/context/event/AbstractApplicationEventMulticaster.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
+import org.springframework.beans.factory.support.AbstractBeanFactory;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationListener;
 import org.springframework.core.OrderComparator;
@@ -64,70 +65,76 @@ public abstract class AbstractApplicationEventMulticaster
 
 	private BeanFactory beanFactory;
 
+	private Object retrievalMutex = this.defaultRetriever;
+
+
+	public void setBeanClassLoader(ClassLoader classLoader) {
+		this.beanClassLoader = classLoader;
+	}
+
+	public void setBeanFactory(BeanFactory beanFactory) {
+		this.beanFactory = beanFactory;
+		if (this.beanClassLoader == null && beanFactory instanceof ConfigurableBeanFactory) {
+			this.beanClassLoader = ((ConfigurableBeanFactory) beanFactory).getBeanClassLoader();
+		}
+		if (beanFactory instanceof AbstractBeanFactory) {
+			this.retrievalMutex = ((AbstractBeanFactory) beanFactory).getSingletonMutex();
+		}
+	}
+
+	private BeanFactory getBeanFactory() {
+		if (this.beanFactory == null) {
+			throw new IllegalStateException("ApplicationEventMulticaster cannot retrieve listener beans " +
+					"because it is not associated with a BeanFactory");
+		}
+		return this.beanFactory;
+	}
+
 
 	public void addApplicationListener(ApplicationListener listener) {
-		synchronized (this.defaultRetriever) {
+		synchronized (this.retrievalMutex) {
 			this.defaultRetriever.applicationListeners.add(listener);
 			this.retrieverCache.clear();
 		}
 	}
 
 	public void addApplicationListenerBean(String listenerBeanName) {
-		synchronized (this.defaultRetriever) {
+		synchronized (this.retrievalMutex) {
 			this.defaultRetriever.applicationListenerBeans.add(listenerBeanName);
 			this.retrieverCache.clear();
 		}
 	}
 
 	public void removeApplicationListener(ApplicationListener listener) {
-		synchronized (this.defaultRetriever) {
+		synchronized (this.retrievalMutex) {
 			this.defaultRetriever.applicationListeners.remove(listener);
 			this.retrieverCache.clear();
 		}
 	}
 
 	public void removeApplicationListenerBean(String listenerBeanName) {
-		synchronized (this.defaultRetriever) {
+		synchronized (this.retrievalMutex) {
 			this.defaultRetriever.applicationListenerBeans.remove(listenerBeanName);
 			this.retrieverCache.clear();
 		}
 	}
 
 	public void removeAllListeners() {
-		synchronized (this.defaultRetriever) {
+		synchronized (this.retrievalMutex) {
 			this.defaultRetriever.applicationListeners.clear();
 			this.defaultRetriever.applicationListenerBeans.clear();
 			this.retrieverCache.clear();
 		}
 	}
 
-	public void setBeanClassLoader(ClassLoader classLoader) {
-		this.beanClassLoader = classLoader;
-	}
-
-	public void setBeanFactory(BeanFactory beanFactory) {
-		this.beanFactory = beanFactory;
-		if (this.beanClassLoader == null && beanFactory instanceof ConfigurableBeanFactory) {
-			this.beanClassLoader = ((ConfigurableBeanFactory) beanFactory).getBeanClassLoader();
-		}
-	}
-
-	private BeanFactory getBeanFactory() {
-		if (this.beanFactory == null) {
-			throw new IllegalStateException("ApplicationEventMulticaster cannot retrieve listener beans " +
-					"because it is not associated with a BeanFactory");
-		}
-		return this.beanFactory;
-	}
-
 
 	/**
 	 * Return a Collection containing all ApplicationListeners.
 	 * @return a Collection of ApplicationListeners
 	 * @see org.springframework.context.ApplicationListener
 	 */
 	protected Collection<ApplicationListener> getApplicationListeners() {
-		synchronized (this.defaultRetriever) {
+		synchronized (this.retrievalMutex) {
 			return this.defaultRetriever.getApplicationListeners();
 		}
 	}
@@ -156,13 +163,14 @@ protected Collection<ApplicationListener> getApplicationListeners(ApplicationEve
 				(ClassUtils.isCacheSafe(eventType, this.beanClassLoader) &&
 						(sourceType == null || ClassUtils.isCacheSafe(sourceType, this.beanClassLoader)))) {
 			// Fully synchronized building and caching of a ListenerRetriever
-			synchronized (this.defaultRetriever) {
+			synchronized (this.retrievalMutex) {
 				retriever = this.retrieverCache.get(cacheKey);
 				if (retriever != null) {
 					return retriever.getApplicationListeners();
 				}
 				retriever = new ListenerRetriever(true);
-				Collection<ApplicationListener> listeners = retrieveApplicationListeners(eventType, sourceType, retriever);
+				Collection<ApplicationListener> listeners =
+						retrieveApplicationListeners(eventType, sourceType, retriever);
 				this.retrieverCache.put(cacheKey, retriever);
 				return listeners;
 			}
@@ -186,7 +194,7 @@ private Collection<ApplicationListener> retrieveApplicationListeners(
 		LinkedList<ApplicationListener> allListeners = new LinkedList<ApplicationListener>();
 		Set<ApplicationListener> listeners;
 		Set<String> listenerBeans;
-		synchronized (this.defaultRetriever) {
+		synchronized (this.retrievalMutex) {
 			listeners = new LinkedHashSet<ApplicationListener>(this.defaultRetriever.applicationListeners);
 			listenerBeans = new LinkedHashSet<String>(this.defaultRetriever.applicationListenerBeans);
 		}