Avoid early singleton inference outside of original creation thread

See gh-23501

Author: jhoeller

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

@@ -188,7 +188,10 @@ protected Object getSingleton(String beanName, boolean allowEarlyReference) {
 		if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
 			singletonObject = this.earlySingletonObjects.get(beanName);
 			if (singletonObject == null && allowEarlyReference) {
-				this.singletonLock.lock();
+				if (!this.singletonLock.tryLock()) {
+					// Avoid early singleton inference outside of original creation thread
+					return null;
+				}
 				try {
 					// Consistent creation of early reference within full singleton lock
 					singletonObject = this.singletonObjects.get(beanName);

spring-beans/src/test/java/org/springframework/beans/factory/BeanFactoryLockingTests.java

@@ -22,6 +22,9 @@
 import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.beans.testfixture.beans.TestBean;
 
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+
 /**
  * @author Juergen Hoeller
  * @since 6.2
@@ -31,8 +34,10 @@ class BeanFactoryLockingTests {
 	@Test
 	void fallbackForThreadDuringInitialization() {
 		DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
-		beanFactory.registerBeanDefinition("bean1", new RootBeanDefinition(ThreadDuringInitialization.class));
-		beanFactory.registerBeanDefinition("bean2", new RootBeanDefinition(TestBean.class));
+		beanFactory.registerBeanDefinition("bean1",
+				new RootBeanDefinition(ThreadDuringInitialization.class));
+		beanFactory.registerBeanDefinition("bean2",
+				new RootBeanDefinition(TestBean.class, () -> new TestBean("tb")));
 		beanFactory.getBean(ThreadDuringInitialization.class);
 	}
 
@@ -51,7 +56,12 @@ public void setBeanFactory(BeanFactory beanFactory) {
 		@Override
 		public void afterPropertiesSet() throws Exception {
 			Thread thread = new Thread(() -> {
-				beanFactory.getBean(TestBean.class);
+				// Fail for circular reference from other thread
+				assertThatExceptionOfType(BeanCurrentlyInCreationException.class).isThrownBy(() ->
+						beanFactory.getBean(ThreadDuringInitialization.class));
+				// Leniently create unrelated other bean outside of singleton lock
+				assertThat(beanFactory.getBean(TestBean.class).getName()).isEqualTo("tb");
+				// Creation attempt in other thread was successful
 				initialized = true;
 			});
 			thread.start();