Revise singleton registry for lenient locking (fallback instead of deadlock)

Closes gh-23501

spring-aop/src/main/java/org/springframework/aop/aspectj/annotation/BeanFactoryAspectInstanceFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -109,13 +109,8 @@ public class BeanFactoryAspectInstanceFactory implements MetadataAwareAspectInst
 			// Rely on singleton semantics provided by the factory -> no local lock.
 			return null;
 		}
-		else if (this.beanFactory instanceof ConfigurableBeanFactory cbf) {
-			// No singleton guarantees from the factory -> let's lock locally but
-			// reuse the factory's singleton lock, just in case a lazy dependency
-			// of our advice bean happens to trigger the singleton lock implicitly...
-			return cbf.getSingletonMutex();
-		}
 		else {
+			// No singleton guarantees from the factory -> let's lock locally.
 			return this;
 		}
 	}

spring-aop/src/main/java/org/springframework/aop/support/AbstractBeanFactoryPointcutAdvisor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -23,7 +23,6 @@ import org.aopalliance.aop.Advice;
 
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
-import org.springframework.beans.factory.config.ConfigurableBeanFactory;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
@@ -52,7 +51,7 @@ public abstract class AbstractBeanFactoryPointcutAdvisor extends AbstractPointcu
 	@Nullable
 	private transient volatile Advice advice;
 
-	private transient volatile Object adviceMonitor = new Object();
+	private transient Object adviceMonitor = new Object();
 
 
 	/**
@@ -78,16 +77,6 @@ public abstract class AbstractBeanFactoryPointcutAdvisor extends AbstractPointcu
 	@Override
 	public void setBeanFactory(BeanFactory beanFactory) {
 		this.beanFactory = beanFactory;
-		resetAdviceMonitor();
-	}
-
-	private void resetAdviceMonitor() {
-		if (this.beanFactory instanceof ConfigurableBeanFactory cbf) {
-			this.adviceMonitor = cbf.getSingletonMutex();
-		}
-		else {
-			this.adviceMonitor = new Object();
-		}
 	}
 
 	/**
@@ -118,9 +107,7 @@ public abstract class AbstractBeanFactoryPointcutAdvisor extends AbstractPointcu
 			return advice;
 		}
 		else {
-			// No singleton guarantees from the factory -> let's lock locally but
+			// No singleton guarantees from the factory -> let's lock locally.
-			// reuse the factory's singleton lock, just in case a lazy dependency
-			// of our advice bean happens to trigger the singleton lock implicitly...
 			synchronized (this.adviceMonitor) {
 				advice = this.advice;
 				if (advice == null) {
@@ -155,7 +142,7 @@ public abstract class AbstractBeanFactoryPointcutAdvisor extends AbstractPointcu
 		ois.defaultReadObject();
 
 		// Initialize transient fields.
-		resetAdviceMonitor();
+		this.adviceMonitor = new Object();
 	}
 
 }

spring-beans/src/main/java/org/springframework/beans/factory/config/SingletonBeanRegistry.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -129,7 +129,10 @@ public interface SingletonBeanRegistry {
 	 * Return the singleton mutex used by this registry (for external collaborators).
 	 * @return the mutex object (never {@code null})
 	 * @since 4.2
+	 * @deprecated as of 6.2, in favor of lenient singleton locking
+	 * (with this method returning an arbitrary object to lock on)
 	 */
+	@Deprecated(since = "6.2")
 	Object getSingletonMutex();
 
 }

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

@@ -972,7 +972,6 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 	 */
 	@Nullable
 	private FactoryBean<?> getSingletonFactoryBeanForTypeCheck(String beanName, RootBeanDefinition mbd) {
-		synchronized (getSingletonMutex()) {
 		BeanWrapper bw = this.factoryBeanInstanceCache.get(beanName);
 		if (bw != null) {
 			return (FactoryBean<?>) bw.getWrappedInstance();
@@ -995,6 +994,7 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 			if (instance == null) {
 				bw = createBeanInstance(beanName, mbd, null);
 				instance = bw.getWrappedInstance();
+				this.factoryBeanInstanceCache.put(beanName, bw);
 			}
 		}
 		catch (UnsatisfiedDependencyException ex) {
@@ -1019,12 +1019,7 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 			afterSingletonCreation(beanName);
 		}
 
-			FactoryBean<?> fb = getFactoryBean(beanName, instance);
+		return getFactoryBean(beanName, instance);
-			if (bw != null) {
-				this.factoryBeanInstanceCache.put(beanName, bw);
-			}
-			return fb;
-		}
 	}
 
 	/**
@@ -1912,22 +1907,18 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 	 */
 	@Override
 	protected void removeSingleton(String beanName) {
-		synchronized (getSingletonMutex()) {
 		super.removeSingleton(beanName);
 		this.factoryBeanInstanceCache.remove(beanName);
 	}
-	}
 
 	/**
 	 * Overridden to clear FactoryBean instance cache as well.
 	 */
 	@Override
 	protected void clearSingletonCache() {
-		synchronized (getSingletonMutex()) {
 		super.clearSingletonCache();
 		this.factoryBeanInstanceCache.clear();
 	}
-	}
 
 	/**
 	 * Expose the logger to collaborating delegates.

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -25,6 +25,8 @@ import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
 import org.springframework.beans.factory.BeanCreationException;
 import org.springframework.beans.factory.BeanCreationNotAllowedException;
@@ -84,7 +86,9 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	private final Map<String, Object> earlySingletonObjects = new ConcurrentHashMap<>(16);
 
 	/** Set of registered singletons, containing the bean names in registration order. */
-	private final Set<String> registeredSingletons = new LinkedHashSet<>(256);
+	private final Set<String> registeredSingletons = Collections.synchronizedSet(new LinkedHashSet<>(256));
+
+	private final Lock singletonLock = new ReentrantLock();
 
 	/** Names of beans that are currently in creation. */
 	private final Set<String> singletonsCurrentlyInCreation =
@@ -94,6 +98,9 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	private final Set<String> inCreationCheckExclusions =
 			Collections.newSetFromMap(new ConcurrentHashMap<>(16));
 
+	@Nullable
+	private volatile Thread singletonCreationThread;
+
 	/** Collection of suppressed Exceptions, available for associating related causes. */
 	@Nullable
 	private Set<Exception> suppressedExceptions;
@@ -118,7 +125,8 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	public void registerSingleton(String beanName, Object singletonObject) throws IllegalStateException {
 		Assert.notNull(beanName, "Bean name must not be null");
 		Assert.notNull(singletonObject, "Singleton object must not be null");
-		synchronized (this.singletonObjects) {
+		this.singletonLock.lock();
+		try {
 			Object oldObject = this.singletonObjects.get(beanName);
 			if (oldObject != null) {
 				throw new IllegalStateException("Could not register object [" + singletonObject +
@@ -126,6 +134,9 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 			}
 			addSingleton(beanName, singletonObject);
 		}
+		finally {
+			this.singletonLock.unlock();
+		}
 	}
 
 	/**
@@ -135,13 +146,11 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	 * @param singletonObject the singleton object
 	 */
 	protected void addSingleton(String beanName, Object singletonObject) {
-		synchronized (this.singletonObjects) {
 		this.singletonObjects.put(beanName, singletonObject);
 		this.singletonFactories.remove(beanName);
 		this.earlySingletonObjects.remove(beanName);
 		this.registeredSingletons.add(beanName);
 	}
-	}
 
 	/**
 	 * Add the given singleton factory for building the specified singleton
@@ -153,14 +162,10 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	 */
 	protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
 		Assert.notNull(singletonFactory, "Singleton factory must not be null");
-		synchronized (this.singletonObjects) {
-			if (!this.singletonObjects.containsKey(beanName)) {
 		this.singletonFactories.put(beanName, singletonFactory);
 		this.earlySingletonObjects.remove(beanName);
 		this.registeredSingletons.add(beanName);
 	}
-		}
-	}
 
 	@Override
 	@Nullable
@@ -183,7 +188,8 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 		if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
 			singletonObject = this.earlySingletonObjects.get(beanName);
 			if (singletonObject == null && allowEarlyReference) {
-				synchronized (this.singletonObjects) {
+				this.singletonLock.lock();
+				try {
 					// Consistent creation of early reference within full singleton lock
 					singletonObject = this.singletonObjects.get(beanName);
 					if (singletonObject == null) {
@@ -198,6 +204,9 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 						}
 					}
 				}
+				finally {
+					this.singletonLock.unlock();
+				}
 			}
 		}
 		return singletonObject;
@@ -213,9 +222,33 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	 */
 	public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
 		Assert.notNull(beanName, "Bean name must not be null");
-		synchronized (this.singletonObjects) {
+
+		boolean locked = this.singletonLock.tryLock();
+		try {
 			Object singletonObject = this.singletonObjects.get(beanName);
 			if (singletonObject == null) {
+				if (locked) {
+					this.singletonCreationThread = Thread.currentThread();
+				}
+				else {
+					Thread otherThread = this.singletonCreationThread;
+					if (otherThread != null) {
+						// Another thread is busy in a singleton factory callback, potentially blocked.
+						// Fallback as of 6.2: process given singleton bean outside of singleton lock.
+						// Thread-safe exposure is still guaranteed, there is just a risk of collisions
+						// when triggering creation of other beans as dependencies of the current bean.
+						if (logger.isInfoEnabled()) {
+							logger.info("Creating singleton bean '" + beanName + "' in thread \"" +
+									Thread.currentThread().getName() + "\" while thread \"" + otherThread.getName() +
+									"\" holds singleton lock for other beans " + this.singletonsCurrentlyInCreation);
+						}
+					}
+					else {
+						// Singleton lock currently held by some other registration method -> wait.
+						this.singletonLock.lock();
+						locked = true;
+					}
+				}
 				if (this.singletonsCurrentlyInDestruction) {
 					throw new BeanCreationNotAllowedException(beanName,
 							"Singleton bean creation not allowed while singletons of this factory are in destruction " +
@@ -226,10 +259,11 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 				}
 				beforeSingletonCreation(beanName);
 				boolean newSingleton = false;
-				boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
+				boolean recordSuppressedExceptions = (locked && this.suppressedExceptions == null);
 				if (recordSuppressedExceptions) {
 					this.suppressedExceptions = new LinkedHashSet<>();
 				}
+				this.singletonCreationThread = Thread.currentThread();
 				try {
 					singletonObject = singletonFactory.getObject();
 					newSingleton = true;
@@ -251,6 +285,7 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 					throw ex;
 				}
 				finally {
+					this.singletonCreationThread = null;
 					if (recordSuppressedExceptions) {
 						this.suppressedExceptions = null;
 					}
@@ -262,6 +297,11 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 			}
 			return singletonObject;
 		}
+		finally {
+			if (locked) {
+				this.singletonLock.unlock();
+			}
+		}
 	}
 
 	/**
@@ -274,27 +314,22 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	 * @see BeanCreationException#getRelatedCauses()
 	 */
 	protected void onSuppressedException(Exception ex) {
-		synchronized (this.singletonObjects) {
 		if (this.suppressedExceptions != null && this.suppressedExceptions.size() < SUPPRESSED_EXCEPTIONS_LIMIT) {
 			this.suppressedExceptions.add(ex);
 		}
 	}
-	}
 
 	/**
 	 * Remove the bean with the given name from the singleton cache of this factory,
 	 * to be able to clean up eager registration of a singleton if creation failed.
 	 * @param beanName the name of the bean
-	 * @see #getSingletonMutex()
 	 */
 	protected void removeSingleton(String beanName) {
-		synchronized (this.singletonObjects) {
 		this.singletonObjects.remove(beanName);
 		this.singletonFactories.remove(beanName);
 		this.earlySingletonObjects.remove(beanName);
 		this.registeredSingletons.remove(beanName);
 	}
-	}
 
 	@Override
 	public boolean containsSingleton(String beanName) {
@@ -303,17 +338,13 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 
 	@Override
 	public String[] getSingletonNames() {
-		synchronized (this.singletonObjects) {
 		return StringUtils.toStringArray(this.registeredSingletons);
 	}
-	}
 
 	@Override
 	public int getSingletonCount() {
-		synchronized (this.singletonObjects) {
 		return this.registeredSingletons.size();
 	}
-	}
 
 
 	public void setCurrentlyInCreation(String beanName, boolean inCreation) {
@@ -508,9 +539,13 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 		if (logger.isTraceEnabled()) {
 			logger.trace("Destroying singletons in " + this);
 		}
-		synchronized (this.singletonObjects) {
+		this.singletonLock.lock();
+		try {
 			this.singletonsCurrentlyInDestruction = true;
 		}
+		finally {
+			this.singletonLock.unlock();
+		}
 
 		String[] disposableBeanNames;
 		synchronized (this.disposableBeans) {
@@ -524,22 +559,26 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 		this.dependentBeanMap.clear();
 		this.dependenciesForBeanMap.clear();
 
+		this.singletonLock.lock();
+		try {
 			clearSingletonCache();
 		}
+		finally {
+			this.singletonLock.unlock();
+		}
+	}
 
 	/**
 	 * Clear all cached singleton instances in this registry.
 	 * @since 4.3.15
 	 */
 	protected void clearSingletonCache() {
-		synchronized (this.singletonObjects) {
 		this.singletonObjects.clear();
 		this.singletonFactories.clear();
 		this.earlySingletonObjects.clear();
 		this.registeredSingletons.clear();
 		this.singletonsCurrentlyInDestruction = false;
 	}
-	}
 
 	/**
 	 * Destroy the given bean. Delegates to {@code destroyBean}
@@ -549,7 +588,13 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	 */
 	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.
 		DisposableBean disposableBean;
@@ -621,16 +666,10 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 		this.dependenciesForBeanMap.remove(beanName);
 	}
 
-	/**
+	@Deprecated(since = "6.2")
-	 * 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.
-	 */
 	@Override
 	public final Object getSingletonMutex() {
-		return this.singletonObjects;
+		return new Object();
 	}
 
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -118,7 +118,6 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 	 */
 	protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
 		if (factory.isSingleton() && containsSingleton(beanName)) {
-			synchronized (getSingletonMutex()) {
 			Object object = this.factoryBeanObjectCache.get(beanName);
 			if (object == null) {
 				object = doGetObjectFromFactoryBean(factory, beanName);
@@ -131,7 +130,7 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 				else {
 					if (shouldPostProcess) {
 						if (isSingletonCurrentlyInCreation(beanName)) {
-								// Temporarily return non-post-processed object, not storing it yet..
+							// Temporarily return non-post-processed object, not storing it yet
 							return object;
 						}
 						beforeSingletonCreation(beanName);
@@ -153,7 +152,6 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 			}
 			return object;
 		}
-		}
 		else {
 			Object object = doGetObjectFromFactoryBean(factory, beanName);
 			if (shouldPostProcess) {
@@ -234,21 +232,17 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 	 */
 	@Override
 	protected void removeSingleton(String beanName) {
-		synchronized (getSingletonMutex()) {
 		super.removeSingleton(beanName);
 		this.factoryBeanObjectCache.remove(beanName);
 	}
-	}
 
 	/**
 	 * Overridden to clear the FactoryBean object cache as well.
 	 */
 	@Override
 	protected void clearSingletonCache() {
-		synchronized (getSingletonMutex()) {
 		super.clearSingletonCache();
 		this.factoryBeanObjectCache.clear();
 	}
-	}
 
 }

spring-beans/src/test/java/org/springframework/beans/factory/BeanFactoryLockingTests.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2002-2024 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.beans.factory;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.support.DefaultListableBeanFactory;
+import org.springframework.beans.factory.support.RootBeanDefinition;
+import org.springframework.beans.testfixture.beans.TestBean;
+
+/**
+ * @author Juergen Hoeller
+ * @since 6.2
+ */
+class BeanFactoryLockingTests {
+
+	@Test
+	void fallbackForThreadDuringInitialization() {
+		DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
+		beanFactory.registerBeanDefinition("bean1", new RootBeanDefinition(ThreadDuringInitialization.class));
+		beanFactory.registerBeanDefinition("bean2", new RootBeanDefinition(TestBean.class));
+		beanFactory.getBean(ThreadDuringInitialization.class);
+	}
+
+
+	static class ThreadDuringInitialization implements BeanFactoryAware, InitializingBean {
+
+		private BeanFactory beanFactory;
+
+		private volatile boolean initialized;
+
+		@Override
+		public void setBeanFactory(BeanFactory beanFactory) {
+			this.beanFactory = beanFactory;
+		}
+
+		@Override
+		public void afterPropertiesSet() throws Exception {
+			Thread thread = new Thread(() -> {
+				beanFactory.getBean(TestBean.class);
+				initialized = true;
+			});
+			thread.start();
+			thread.join();
+			if (!initialized) {
+				throw new IllegalStateException("Thread not executed");
+			}
+		}
+	}
+
+}

spring-jms/src/main/java/org/springframework/jms/config/JmsListenerEndpointRegistrar.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -22,7 +22,6 @@ import java.util.List;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
 import org.springframework.beans.factory.InitializingBean;
-import org.springframework.beans.factory.config.ConfigurableBeanFactory;
 import org.springframework.lang.Nullable;
 import org.springframework.messaging.handler.annotation.support.DefaultMessageHandlerMethodFactory;
 import org.springframework.messaging.handler.annotation.support.MessageHandlerMethodFactory;
@@ -57,8 +56,6 @@ public class JmsListenerEndpointRegistrar implements BeanFactoryAware, Initializ
 
 	private boolean startImmediately;
 
-	private Object mutex = this.endpointDescriptors;
-
 
 	/**
 	 * Set the {@link JmsListenerEndpointRegistry} instance to use.
@@ -124,9 +121,6 @@ public class JmsListenerEndpointRegistrar implements BeanFactoryAware, Initializ
 	@Override
 	public void setBeanFactory(BeanFactory beanFactory) {
 		this.beanFactory = beanFactory;
-		if (beanFactory instanceof ConfigurableBeanFactory cbf) {
-			this.mutex = cbf.getSingletonMutex();
-		}
 	}
 
 
@@ -137,14 +131,12 @@ public class JmsListenerEndpointRegistrar implements BeanFactoryAware, Initializ
 
 	protected void registerAllEndpoints() {
 		Assert.state(this.endpointRegistry != null, "No JmsListenerEndpointRegistry set");
-		synchronized (this.mutex) {
 		for (JmsListenerEndpointDescriptor descriptor : this.endpointDescriptors) {
 			this.endpointRegistry.registerListenerContainer(
 					descriptor.endpoint, resolveContainerFactory(descriptor));
 		}
 		this.startImmediately = true;  // trigger immediate startup
 	}
-	}
 
 	private JmsListenerContainerFactory<?> resolveContainerFactory(JmsListenerEndpointDescriptor descriptor) {
 		if (descriptor.containerFactory != null) {
@@ -180,7 +172,6 @@ public class JmsListenerEndpointRegistrar implements BeanFactoryAware, Initializ
 		// Factory may be null, we defer the resolution right before actually creating the container
 		JmsListenerEndpointDescriptor descriptor = new JmsListenerEndpointDescriptor(endpoint, factory);
 
-		synchronized (this.mutex) {
 		if (this.startImmediately) {  // register and start immediately
 			Assert.state(this.endpointRegistry != null, "No JmsListenerEndpointRegistry set");
 			this.endpointRegistry.registerListenerContainer(descriptor.endpoint,
@@ -190,7 +181,6 @@ public class JmsListenerEndpointRegistrar implements BeanFactoryAware, Initializ
 			this.endpointDescriptors.add(descriptor);
 		}
 	}
-	}
 
 	/**
 	 * Register a new {@link JmsListenerEndpoint} using the default