Merge branch '5.2.x'

# Conflicts:
#	build.gradle

build.gradle

@@ -1,11 +1,11 @@
 plugins {
 	id 'io.spring.dependency-management' version '1.0.9.RELEASE' apply false
+	id 'io.spring.nohttp' version '0.0.5.RELEASE'
 	id 'org.jetbrains.kotlin.jvm' version '1.4.0' apply false
 	id 'org.jetbrains.dokka' version '0.10.1' apply false
 	id 'org.asciidoctor.jvm.convert' version '2.4.0'
-	id 'io.spring.nohttp' version '0.0.5.RELEASE'
-	id 'de.undercouch.download' version '4.0.4'
-	id "io.freefair.aspectj" version '5.0.0' apply false
+	id 'de.undercouch.download' version '4.1.1'
+	id "io.freefair.aspectj" version '5.1.1' apply false
 	id "com.github.ben-manes.versions" version '0.28.0'
 	id "me.champeau.gradle.jmh" version "0.5.0" apply false
 }

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

@@ -81,7 +81,7 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);
 
 	/** Cache of early singleton objects: bean name to bean instance. */
-	private final Map<String, Object> earlySingletonObjects = new HashMap<>(16);
+	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);
@@ -178,16 +178,24 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	 */
 	@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)) {
-			synchronized (this.singletonObjects) {
-				singletonObject = this.earlySingletonObjects.get(beanName);
-				if (singletonObject == null && allowEarlyReference) {
-					ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
-					if (singletonFactory != null) {
-						singletonObject = singletonFactory.getObject();
-						this.earlySingletonObjects.put(beanName, singletonObject);
-						this.singletonFactories.remove(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);
+							}
+						}
 					}
 				}
 			}