org.springframework/spring-beans/5.3.3 : org/springframework/beans/factory/support/DefaultSingletonBeanRegistry.java

DefaultSingletonBeanRegistry
https://github.com/spring-projects/spring-framework: Spring Beans (Spring IO)
Apache License, Version 2.0
Juergen Hoeller
/*
 * Copyright 2002-2020 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.support;

import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

import org.springframework.beans.factory.BeanCreationException;
import org.springframework.beans.factory.BeanCreationNotAllowedException;
import org.springframework.beans.factory.BeanCurrentlyInCreationException;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.config.SingletonBeanRegistry;
import org.springframework.core.SimpleAliasRegistry;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

Generic registry for shared bean instances, implementing the SingletonBeanRegistry. Allows for registering singleton instances that should be shared for all callers of the registry, to be obtained via bean name. Also supports registration of DisposableBean instances, (which might or might not correspond to registered singletons), to be destroyed on shutdown of the registry. Dependencies between beans can be registered to enforce an appropriate shutdown order. 
This class mainly serves as base class for BeanFactory implementations, factoring out the common management of singleton bean instances. Note that the ConfigurableBeanFactory interface extends the SingletonBeanRegistry interface. 
Note that this class assumes neither a bean definition concept nor a specific creation process for bean instances, in contrast to AbstractBeanFactory and DefaultListableBeanFactory (which inherit from it). Can alternatively also be used as a nested helper to delegate to. 
Author: Juergen Hoeller
See Also: registerSingleton
registerDisposableBean
DisposableBean
ConfigurableBeanFactory
Since: 2.0/**
 * Generic registry for shared bean instances, implementing the
 * {@link org.springframework.beans.factory.config.SingletonBeanRegistry}.
 * Allows for registering singleton instances that should be shared
 * for all callers of the registry, to be obtained via bean name.
 *
 * <p>Also supports registration of
 * {@link org.springframework.beans.factory.DisposableBean} instances,
 * (which might or might not correspond to registered singletons),
 * to be destroyed on shutdown of the registry. Dependencies between
 * beans can be registered to enforce an appropriate shutdown order.
 *
 * <p>This class mainly serves as base class for
 * {@link org.springframework.beans.factory.BeanFactory} implementations,
 * factoring out the common management of singleton bean instances. Note that
 * the {@link org.springframework.beans.factory.config.ConfigurableBeanFactory}
 * interface extends the {@link SingletonBeanRegistry} interface.
 *
 * <p>Note that this class assumes neither a bean definition concept
 * nor a specific creation process for bean instances, in contrast to
 * {@link AbstractBeanFactory} and {@link DefaultListableBeanFactory}
 * (which inherit from it). Can alternatively also be used as a nested
 * helper to delegate to.
 *
 * @author Juergen Hoeller
 * @since 2.0
 * @see #registerSingleton
 * @see #registerDisposableBean
 * @see org.springframework.beans.factory.DisposableBean
 * @see org.springframework.beans.factory.config.ConfigurableBeanFactory
 */
public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements SingletonBeanRegistry {

	Maximum number of suppressed exceptions to preserve. /** Maximum number of suppressed exceptions to preserve. */
	private static final int SUPPRESSED_EXCEPTIONS_LIMIT = 100;


	Cache of singleton objects: bean name to bean instance. /** Cache of singleton objects: bean name to bean instance. */
	private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);

	Cache of singleton factories: bean name to ObjectFactory. /** Cache of singleton factories: bean name to ObjectFactory. */
	private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);

	Cache of early singleton objects: bean name to bean instance. /** Cache of early singleton objects: bean name to bean instance. */
	private final Map<String, Object> earlySingletonObjects = new ConcurrentHashMap<>(16);

	Set of registered singletons, containing the bean names in registration order. /** Set of registered singletons, containing the bean names in registration order. */
	private final Set<String> registeredSingletons = new LinkedHashSet<>(256);

	Names of beans that are currently in creation. /** Names of beans that are currently in creation. */
	private final Set<String> singletonsCurrentlyInCreation =
			Collections.newSetFromMap(new ConcurrentHashMap<>(16));

	Names of beans currently excluded from in creation checks. /** Names of beans currently excluded from in creation checks. */
	private final Set<String> inCreationCheckExclusions =
			Collections.newSetFromMap(new ConcurrentHashMap<>(16));

	Collection of suppressed Exceptions, available for associating related causes. /** Collection of suppressed Exceptions, available for associating related causes. */
	@Nullable
	private Set<Exception> suppressedExceptions;

	Flag that indicates whether we're currently within destroySingletons. /** Flag that indicates whether we're currently within destroySingletons. */
	private boolean singletonsCurrentlyInDestruction = false;

	Disposable bean instances: bean name to disposable instance. /** Disposable bean instances: bean name to disposable instance. */
	private final Map<String, Object> disposableBeans = new LinkedHashMap<>();

	Map between containing bean names: bean name to Set of bean names that the bean contains. /** Map between containing bean names: bean name to Set of bean names that the bean contains. */
	private final Map<String, Set<String>> containedBeanMap = new ConcurrentHashMap<>(16);

	Map between dependent bean names: bean name to Set of dependent bean names. /** Map between dependent bean names: bean name to Set of dependent bean names. */
	private final Map<String, Set<String>> dependentBeanMap = new ConcurrentHashMap<>(64);

	Map between depending bean names: bean name to Set of bean names for the bean's dependencies. /** Map between depending bean names: bean name to Set of bean names for the bean's dependencies. */
	private final Map<String, Set<String>> dependenciesForBeanMap = new ConcurrentHashMap<>(64);


	@Override
	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) {
			Object oldObject = this.singletonObjects.get(beanName);
			if (oldObject != null) {
				throw new IllegalStateException("Could not register object [" + singletonObject +
						"] under bean name '" + beanName + "': there is already object [" + oldObject + "] bound");
			}
			addSingleton(beanName, singletonObject);
		}
	}

	Add the given singleton object to the singleton cache of this factory.
To be called for eager registration of singletons.
Params: beanName – the name of the bean
singletonObject – the singleton object/**
	 * Add the given singleton object to the singleton cache of this factory.
	 * <p>To be called for eager registration of singletons.
	 * @param beanName the name of the bean
	 * @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
if necessary.
To be called for eager registration of singletons, e.g. to be able to
resolve circular references.
Params: beanName – the name of the bean
singletonFactory – the factory for the singleton object/**
	 * Add the given singleton factory for building the specified singleton
	 * if necessary.
	 * <p>To be called for eager registration of singletons, e.g. to be able to
	 * resolve circular references.
	 * @param beanName the name of the bean
	 * @param singletonFactory the factory for the singleton object
	 */
	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
	public Object getSingleton(String beanName) {
		return getSingleton(beanName, true);
	}

	Return the (raw) singleton object registered under the given name.
Checks already instantiated singletons and also allows for an early
reference to a currently created singleton (resolving a circular reference).
Params: beanName – the name of the bean to look for
allowEarlyReference – whether early references should be created or not
Returns: the registered singleton object, or null if none found/**
	 * Return the (raw) singleton object registered under the given name.
	 * <p>Checks already instantiated singletons and also allows for an early
	 * reference to a currently created singleton (resolving a circular reference).
	 * @param beanName the name of the bean to look for
	 * @param allowEarlyReference whether early references should be created or not
	 * @return the registered singleton object, or {@code null} if none found
	 */
	@Nullable
	protected Object getSingleton(String beanName, boolean allowEarlyReference) {
		// Quick check for existing instance without full singleton lock
		Object singletonObject = this.singletonObjects.get(beanName);
		if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
			singletonObject = this.earlySingletonObjects.get(beanName);
			if (singletonObject == null && allowEarlyReference) {
				synchronized (this.singletonObjects) {
					// Consistent creation of early reference within full singleton lock
					singletonObject = this.singletonObjects.get(beanName);
					if (singletonObject == null) {
						singletonObject = this.earlySingletonObjects.get(beanName);
						if (singletonObject == null) {
							ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
							if (singletonFactory != null) {
								singletonObject = singletonFactory.getObject();
								this.earlySingletonObjects.put(beanName, singletonObject);
								this.singletonFactories.remove(beanName);
							}
						}
					}
				}
			}
		}
		return singletonObject;
	}

	Return the (raw) singleton object registered under the given name,
creating and registering a new one if none registered yet.
Params: beanName – the name of the bean
singletonFactory – the ObjectFactory to lazily create the singleton
with, if necessary
Returns: the registered singleton object/**
	 * Return the (raw) singleton object registered under the given name,
	 * creating and registering a new one if none registered yet.
	 * @param beanName the name of the bean
	 * @param singletonFactory the ObjectFactory to lazily create the singleton
	 * with, if necessary
	 * @return the registered singleton object
	 */
	public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
		Assert.notNull(beanName, "Bean name must not be null");
		synchronized (this.singletonObjects) {
			Object singletonObject = this.singletonObjects.get(beanName);
			if (singletonObject == null) {
				if (this.singletonsCurrentlyInDestruction) {
					throw new BeanCreationNotAllowedException(beanName,
							"Singleton bean creation not allowed while singletons of this factory are in destruction " +
							"(Do not request a bean from a BeanFactory in a destroy method implementation!)");
				}
				if (logger.isDebugEnabled()) {
					logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
				}
				beforeSingletonCreation(beanName);
				boolean newSingleton = false;
				boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
				if (recordSuppressedExceptions) {
					this.suppressedExceptions = new LinkedHashSet<>();
				}
				try {
					singletonObject = singletonFactory.getObject();
					newSingleton = true;
				}
				catch (IllegalStateException ex) {
					// Has the singleton object implicitly appeared in the meantime ->
					// if yes, proceed with it since the exception indicates that state.
					singletonObject = this.singletonObjects.get(beanName);
					if (singletonObject == null) {
						throw ex;
					}
				}
				catch (BeanCreationException ex) {
					if (recordSuppressedExceptions) {
						for (Exception suppressedException : this.suppressedExceptions) {
							ex.addRelatedCause(suppressedException);
						}
					}
					throw ex;
				}
				finally {
					if (recordSuppressedExceptions) {
						this.suppressedExceptions = null;
					}
					afterSingletonCreation(beanName);
				}
				if (newSingleton) {
					addSingleton(beanName, singletonObject);
				}
			}
			return singletonObject;
		}
	}

	Register an exception that happened to get suppressed during the creation of a
singleton bean instance, e.g. a temporary circular reference resolution problem.
The default implementation preserves any given exception in this registry's collection of suppressed exceptions, up to a limit of 100 exceptions, adding them as related causes to an eventual top-level BeanCreationException. 
Params: ex – the Exception to register
See Also: BeanCreationException.getRelatedCauses()/**
	 * Register an exception that happened to get suppressed during the creation of a
	 * singleton bean instance, e.g. a temporary circular reference resolution problem.
	 * <p>The default implementation preserves any given exception in this registry's
	 * collection of suppressed exceptions, up to a limit of 100 exceptions, adding
	 * them as related causes to an eventual top-level {@link BeanCreationException}.
	 * @param ex the Exception to register
	 * @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.
Params: beanName – the name of the bean
See Also: getSingletonMutex()/**
	 * 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) {
		return this.singletonObjects.containsKey(beanName);
	}

	@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) {
		Assert.notNull(beanName, "Bean name must not be null");
		if (!inCreation) {
			this.inCreationCheckExclusions.add(beanName);
		}
		else {
			this.inCreationCheckExclusions.remove(beanName);
		}
	}

	public boolean isCurrentlyInCreation(String beanName) {
		Assert.notNull(beanName, "Bean name must not be null");
		return (!this.inCreationCheckExclusions.contains(beanName) && isActuallyInCreation(beanName));
	}

	protected boolean isActuallyInCreation(String beanName) {
		return isSingletonCurrentlyInCreation(beanName);
	}

	Return whether the specified singleton bean is currently in creation
(within the entire factory).
Params: beanName – the name of the bean/**
	 * Return whether the specified singleton bean is currently in creation
	 * (within the entire factory).
	 * @param beanName the name of the bean
	 */
	public boolean isSingletonCurrentlyInCreation(String beanName) {
		return this.singletonsCurrentlyInCreation.contains(beanName);
	}

	Callback before singleton creation.
The default implementation register the singleton as currently in creation.
Params: beanName – the name of the singleton about to be created
See Also: isSingletonCurrentlyInCreation/**
	 * Callback before singleton 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
	 */
	protected void beforeSingletonCreation(String beanName) {
		if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.add(beanName)) {
			throw new BeanCurrentlyInCreationException(beanName);
		}
	}

	Callback after singleton creation.
The default implementation marks the singleton as not in creation anymore.
Params: beanName – the name of the singleton that has been created
See Also: isSingletonCurrentlyInCreation/**
	 * Callback after singleton creation.
	 * <p>The default implementation marks the singleton as not in creation anymore.
	 * @param beanName the name of the singleton that has been created
	 * @see #isSingletonCurrentlyInCreation
	 */
	protected void afterSingletonCreation(String beanName) {
		if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.remove(beanName)) {
			throw new IllegalStateException("Singleton '" + beanName + "' isn't currently in creation");
		}
	}


	Add the given bean to the list of disposable beans in this registry.
Disposable beans usually correspond to registered singletons,
matching the bean name but potentially being a different instance
(for example, a DisposableBean adapter for a singleton that does not
naturally implement Spring's DisposableBean interface).
Params: beanName – the name of the bean
bean – the bean instance/**
	 * Add the given bean to the list of disposable beans in this registry.
	 * <p>Disposable beans usually correspond to registered singletons,
	 * matching the bean name but potentially being a different instance
	 * (for example, a DisposableBean adapter for a singleton that does not
	 * naturally implement Spring's DisposableBean interface).
	 * @param beanName the name of the bean
	 * @param bean the bean instance
	 */
	public void registerDisposableBean(String beanName, DisposableBean bean) {
		synchronized (this.disposableBeans) {
			this.disposableBeans.put(beanName, bean);
		}
	}

	Register a containment relationship between two beans,
e.g. between an inner bean and its containing outer bean.
Also registers the containing bean as dependent on the contained bean
in terms of destruction order.
Params: containedBeanName – the name of the contained (inner) bean
containingBeanName – the name of the containing (outer) bean
See Also: registerDependentBean/**
	 * Register a containment relationship between two beans,
	 * e.g. between an inner bean and its containing outer bean.
	 * <p>Also registers the containing bean as dependent on the contained bean
	 * in terms of destruction order.
	 * @param containedBeanName the name of the contained (inner) bean
	 * @param containingBeanName the name of the containing (outer) bean
	 * @see #registerDependentBean
	 */
	public void registerContainedBean(String containedBeanName, String containingBeanName) {
		synchronized (this.containedBeanMap) {
			Set<String> containedBeans =
					this.containedBeanMap.computeIfAbsent(containingBeanName, k -> new LinkedHashSet<>(8));
			if (!containedBeans.add(containedBeanName)) {
				return;
			}
		}
		registerDependentBean(containedBeanName, containingBeanName);
	}

	Register a dependent bean for the given bean,
to be destroyed before the given bean is destroyed.
Params: beanName – the name of the bean
dependentBeanName – the name of the dependent bean/**
	 * Register a dependent bean for the given bean,
	 * to be destroyed before the given bean is destroyed.
	 * @param beanName the name of the bean
	 * @param dependentBeanName the name of the dependent bean
	 */
	public void registerDependentBean(String beanName, String dependentBeanName) {
		String canonicalName = canonicalName(beanName);

		synchronized (this.dependentBeanMap) {
			Set<String> dependentBeans =
					this.dependentBeanMap.computeIfAbsent(canonicalName, k -> new LinkedHashSet<>(8));
			if (!dependentBeans.add(dependentBeanName)) {
				return;
			}
		}

		synchronized (this.dependenciesForBeanMap) {
			Set<String> dependenciesForBean =
					this.dependenciesForBeanMap.computeIfAbsent(dependentBeanName, k -> new LinkedHashSet<>(8));
			dependenciesForBean.add(canonicalName);
		}
	}

	Determine whether the specified dependent bean has been registered as
dependent on the given bean or on any of its transitive dependencies.
Params: beanName – the name of the bean to check
dependentBeanName – the name of the dependent bean
Since: 4.0/**
	 * Determine whether the specified dependent bean has been registered as
	 * dependent on the given bean or on any of its transitive dependencies.
	 * @param beanName the name of the bean to check
	 * @param dependentBeanName the name of the dependent bean
	 * @since 4.0
	 */
	protected boolean isDependent(String beanName, String dependentBeanName) {
		synchronized (this.dependentBeanMap) {
			return isDependent(beanName, dependentBeanName, null);
		}
	}

	private boolean isDependent(String beanName, String dependentBeanName, @Nullable Set<String> alreadySeen) {
		if (alreadySeen != null && alreadySeen.contains(beanName)) {
			return false;
		}
		String canonicalName = canonicalName(beanName);
		Set<String> dependentBeans = this.dependentBeanMap.get(canonicalName);
		if (dependentBeans == null) {
			return false;
		}
		if (dependentBeans.contains(dependentBeanName)) {
			return true;
		}
		for (String transitiveDependency : dependentBeans) {
			if (alreadySeen == null) {
				alreadySeen = new HashSet<>();
			}
			alreadySeen.add(beanName);
			if (isDependent(transitiveDependency, dependentBeanName, alreadySeen)) {
				return true;
			}
		}
		return false;
	}

	Determine whether a dependent bean has been registered for the given name.
Params: beanName – the name of the bean to check/**
	 * Determine whether a dependent bean has been registered for the given name.
	 * @param beanName the name of the bean to check
	 */
	protected boolean hasDependentBean(String beanName) {
		return this.dependentBeanMap.containsKey(beanName);
	}

	Return the names of all beans which depend on the specified bean, if any.
Params: beanName – the name of the bean
Returns: the array of dependent bean names, or an empty array if none/**
	 * Return the names of all beans which depend on the specified bean, if any.
	 * @param beanName the name of the bean
	 * @return the array of dependent bean names, or an empty array if none
	 */
	public String[] getDependentBeans(String beanName) {
		Set<String> dependentBeans = this.dependentBeanMap.get(beanName);
		if (dependentBeans == null) {
			return new String[0];
		}
		synchronized (this.dependentBeanMap) {
			return StringUtils.toStringArray(dependentBeans);
		}
	}

	Return the names of all beans that the specified bean depends on, if any.
Params: beanName – the name of the bean
Returns: the array of names of beans which the bean depends on,
or an empty array if none/**
	 * Return the names of all beans that the specified bean depends on, if any.
	 * @param beanName the name of the bean
	 * @return the array of names of beans which the bean depends on,
	 * or an empty array if none
	 */
	public String[] getDependenciesForBean(String beanName) {
		Set<String> dependenciesForBean = this.dependenciesForBeanMap.get(beanName);
		if (dependenciesForBean == null) {
			return new String[0];
		}
		synchronized (this.dependenciesForBeanMap) {
			return StringUtils.toStringArray(dependenciesForBean);
		}
	}

	public void destroySingletons() {
		if (logger.isTraceEnabled()) {
			logger.trace("Destroying singletons in " + this);
		}
		synchronized (this.singletonObjects) {
			this.singletonsCurrentlyInDestruction = true;
		}

		String[] disposableBeanNames;
		synchronized (this.disposableBeans) {
			disposableBeanNames = StringUtils.toStringArray(this.disposableBeans.keySet());
		}
		for (int i = disposableBeanNames.length - 1; i >= 0; i--) {
			destroySingleton(disposableBeanNames[i]);
		}

		this.containedBeanMap.clear();
		this.dependentBeanMap.clear();
		this.dependenciesForBeanMap.clear();

		clearSingletonCache();
	}

	Clear all cached singleton instances in this registry.
Since: 4.3.15/**
	 * 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 destroyBean if a corresponding disposable bean instance is found. 
Params: beanName – the name of the bean
See Also: destroyBean/**
	 * Destroy the given bean. Delegates to {@code destroyBean}
	 * if a corresponding disposable bean instance is found.
	 * @param beanName the name of the bean
	 * @see #destroyBean
	 */
	public void destroySingleton(String beanName) {
		// Remove a registered singleton of the given name, if any.
		removeSingleton(beanName);

		// Destroy the corresponding DisposableBean instance.
		DisposableBean disposableBean;
		synchronized (this.disposableBeans) {
			disposableBean = (DisposableBean) this.disposableBeans.remove(beanName);
		}
		destroyBean(beanName, disposableBean);
	}

	Destroy the given bean. Must destroy beans that depend on the given
bean before the bean itself. Should not throw any exceptions.
Params: beanName – the name of the bean
bean – the bean instance to destroy/**
	 * Destroy the given bean. Must destroy beans that depend on the given
	 * bean before the bean itself. Should not throw any exceptions.
	 * @param beanName the name of the bean
	 * @param bean the bean instance to destroy
	 */
	protected void destroyBean(String beanName, @Nullable DisposableBean bean) {
		// Trigger destruction of dependent beans first...
		Set<String> dependencies;
		synchronized (this.dependentBeanMap) {
			// Within full synchronization in order to guarantee a disconnected Set
			dependencies = this.dependentBeanMap.remove(beanName);
		}
		if (dependencies != null) {
			if (logger.isTraceEnabled()) {
				logger.trace("Retrieved dependent beans for bean '" + beanName + "': " + dependencies);
			}
			for (String dependentBeanName : dependencies) {
				destroySingleton(dependentBeanName);
			}
		}

		// Actually destroy the bean now...
		if (bean != null) {
			try {
				bean.destroy();
			}
			catch (Throwable ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Destruction of bean with name '" + beanName + "' threw an exception", ex);
				}
			}
		}

		// Trigger destruction of contained beans...
		Set<String> containedBeans;
		synchronized (this.containedBeanMap) {
			// Within full synchronization in order to guarantee a disconnected Set
			containedBeans = this.containedBeanMap.remove(beanName);
		}
		if (containedBeans != null) {
			for (String containedBeanName : containedBeans) {
				destroySingleton(containedBeanName);
			}
		}

		// Remove destroyed bean from other beans' dependencies.
		synchronized (this.dependentBeanMap) {
			for (Iterator<Map.Entry<String, Set<String>>> it = this.dependentBeanMap.entrySet().iterator(); it.hasNext();) {
				Map.Entry<String, Set<String>> entry = it.next();
				Set<String> dependenciesToClean = entry.getValue();
				dependenciesToClean.remove(beanName);
				if (dependenciesToClean.isEmpty()) {
					it.remove();
				}
			}
		}

		// Remove destroyed bean's prepared dependency information.
		this.dependenciesForBeanMap.remove(beanName);
	}

	Exposes the singleton mutex to subclasses and external collaborators.
Subclasses should synchronize on the given Object if they perform
any sort of extended singleton creation phase. In particular, subclasses
should not have their own mutexes involved in singleton creation,
to avoid the potential for deadlocks in lazy-init situations.
/**
	 * 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;
	}

}
Author:	Juergen Hoeller
See Also:	registerSingleton registerDisposableBean DisposableBean ConfigurableBeanFactory
Since:	2.0
Params:	beanName – the name of the bean to look for allowEarlyReference – whether early references should be created or not
Returns:	the registered singleton object, or `null` if none found
Params:	beanName – the name of the bean singletonFactory – the ObjectFactory to lazily create the singleton with, if necessary
Returns:	the registered singleton object
Params:	ex – the Exception to register
See Also:	BeanCreationException.getRelatedCauses()
Params:	beanName – the name of the bean
See Also:	getSingletonMutex()
Params:	beanName – the name of the singleton about to be created
See Also:	isSingletonCurrentlyInCreation
Params:	beanName – the name of the singleton that has been created
See Also:	isSingletonCurrentlyInCreation
Params:	containedBeanName – the name of the contained (inner) bean containingBeanName – the name of the containing (outer) bean
See Also:	registerDependentBean
Params:	beanName – the name of the bean to check dependentBeanName – the name of the dependent bean
Since:	4.0
/

org.springframework/ spring-beans/ 5.3.3/ org/springframework/beans/factory/support/DefaultSingletonBeanRegistry.java
