Fall back to local synchronization in getObjectFromFactoryBean

Closes gh-35545

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

@@ -130,7 +130,17 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 			try {
 				Object object = this.factoryBeanObjectCache.get(beanName);
 				if (object == null) {
-					object = doGetObjectFromFactoryBean(factory, beanName);
+					if (locked) {
+						// The common case: within general singleton lock.
+						object = doGetObjectFromFactoryBean(factory, beanName);
+					}
+					else {
+						// Fall back to local synchronization on the given FactoryBean instance,
+						// as a defensive measure for non-thread-safe FactoryBean implementations.
+						synchronized (factory) {
+							object = doGetObjectFromFactoryBean(factory, beanName);
+						}
+					}
 					// Only post-process and store if not put there already during getObject() call above
 					// (for example, because of circular reference processing triggered by custom getBean calls)
 					Object alreadyThere = this.factoryBeanObjectCache.get(beanName);