AbstractBeanFactory.markBeanAsCreated() reliably clears merged bean definition only once

Issue: SPR-14269
(cherry picked from commit 9064d38)

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -1498,11 +1498,14 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 	 */
 	protected void markBeanAsCreated(String beanName) {
 		if (!this.alreadyCreated.contains(beanName)) {
-			this.alreadyCreated.add(beanName);
-
-			// Let the bean definition get re-merged now that we're actually creating
-			// the bean... just in case some of its metadata changed in the meantime.
-			clearMergedBeanDefinition(beanName);
+			synchronized (this.mergedBeanDefinitions) {
+				if (!this.alreadyCreated.contains(beanName)) {
+					// Let the bean definition get re-merged now that we're actually creating
+					// the bean... just in case some of its metadata changed in the meantime.
+					clearMergedBeanDefinition(beanName);
+					this.alreadyCreated.add(beanName);
+				}
+			}
 		}
 	}
 
@@ -1511,7 +1514,9 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 	 * @param beanName the name of the bean
 	 */
 	protected void cleanupAfterBeanCreationFailure(String beanName) {
-		this.alreadyCreated.remove(beanName);
+		synchronized (this.mergedBeanDefinitions) {
+			this.alreadyCreated.remove(beanName);
+		}
 	}
 
 	/**