Defensively expect concurrent registration of BeanPostProcessors

Declaring beanPostProcessors (and also embeddedValueResolvers) as CopyOnWriteArrayList prevents ConcurrentModificationExceptions in case of concurrent registration/access attempts.

Issue: SPR-17286

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

@@ -29,11 +29,11 @@ import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
-import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.CopyOnWriteArrayList;
 
 import org.springframework.beans.BeanUtils;
 import org.springframework.beans.BeanWrapper;
@@ -145,16 +145,16 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 	private TypeConverter typeConverter;
 
 	/** String resolvers to apply e.g. to annotation attribute values. */
-	private final List<StringValueResolver> embeddedValueResolvers = new LinkedList<>();
+	private final List<StringValueResolver> embeddedValueResolvers = new CopyOnWriteArrayList<>();
 
 	/** BeanPostProcessors to apply in createBean. */
-	private final List<BeanPostProcessor> beanPostProcessors = new ArrayList<>();
+	private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();
 
 	/** Indicates whether any InstantiationAwareBeanPostProcessors have been registered. */
-	private boolean hasInstantiationAwareBeanPostProcessors;
+	private volatile boolean hasInstantiationAwareBeanPostProcessors;
 
 	/** Indicates whether any DestructionAwareBeanPostProcessors have been registered. */
-	private boolean hasDestructionAwareBeanPostProcessors;
+	private volatile boolean hasDestructionAwareBeanPostProcessors;
 
 	/** Map from scope identifier String to corresponding Scope. */
 	private final Map<String, Scope> scopes = new LinkedHashMap<>(8);
@@ -850,14 +850,17 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 	@Override
 	public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
 		Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
+		// Remove from old position, if any
 		this.beanPostProcessors.remove(beanPostProcessor);
-		this.beanPostProcessors.add(beanPostProcessor);
+		// Track whether it is instantiation/destruction aware
 		if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
 			this.hasInstantiationAwareBeanPostProcessors = true;
 		}
 		if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
 			this.hasDestructionAwareBeanPostProcessors = true;
 		}
+		// Add to end of list
+		this.beanPostProcessors.add(beanPostProcessor);
 	}
 
 	@Override
@@ -988,7 +991,6 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 	@Override
 	public BeanDefinition getMergedBeanDefinition(String name) throws BeansException {
 		String beanName = transformedBeanName(name);
-
 		// Efficiently check whether bean definition exists in this factory.
 		if (!containsBeanDefinition(beanName) && getParentBeanFactory() instanceof ConfigurableBeanFactory) {
 			return ((ConfigurableBeanFactory) getParentBeanFactory()).getMergedBeanDefinition(beanName);
@@ -1000,18 +1002,15 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 	@Override
 	public boolean isFactoryBean(String name) throws NoSuchBeanDefinitionException {
 		String beanName = transformedBeanName(name);
-
 		Object beanInstance = getSingleton(beanName, false);
 		if (beanInstance != null) {
 			return (beanInstance instanceof FactoryBean);
 		}
-
 		// No singleton instance found -> check bean definition.
 		if (!containsBeanDefinition(beanName) && getParentBeanFactory() instanceof ConfigurableBeanFactory) {
 			// No bean definition found in this factory -> delegate to parent.
 			return ((ConfigurableBeanFactory) getParentBeanFactory()).isFactoryBean(name);
 		}
-
 		return isFactoryBean(beanName, getMergedLocalBeanDefinition(beanName));
 	}