Merge branch '6.2.x'

# Conflicts:
#	spring-beans/src/main/java/org/springframework/beans/factory/support/DefaultListableBeanFactory.java
#	spring-jdbc/src/main/java/org/springframework/jdbc/core/StatementCreatorUtils.java

Author: jhoeller

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

@@ -133,6 +133,11 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 	 * System property that instructs Spring to enforce strict locking during bean creation,
 	 * rather than the mix of strict and lenient locking that 6.2 applies by default. Setting
 	 * this flag to "true" restores 6.1.x style locking in the entire pre-instantiation phase.
+	 * <p>By default, the factory infers strict locking from the encountered thread names:
+	 * If additional threads have names that match the thread prefix of the main bootstrap thread,
+	 * they are considered external (multiple external bootstrap threads calling into the factory)
+	 * and therefore have strict locking applied to them. This inference can be turned off through
+	 * explicitly setting this flag to "false" rather than leaving it unspecified.
 	 * @since 6.2.6
 	 * @see #preInstantiateSingletons()
 	 */
@@ -156,8 +161,8 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 	private static final Map<String, Reference<DefaultListableBeanFactory>> serializableFactories =
 			new ConcurrentHashMap<>(8);
 
-	/** Whether lenient locking is allowed in this factory. */
-	private final boolean lenientLockingAllowed = !SpringProperties.getFlag(STRICT_LOCKING_PROPERTY_NAME);
+	/** Whether strict locking is enforced or relaxed in this factory. */
+	private @Nullable final Boolean strictLocking = SpringProperties.checkFlag(STRICT_LOCKING_PROPERTY_NAME);
 
 	/** Optional id for this factory, for serialization purposes. */
 	private @Nullable String serializationId;
@@ -208,6 +213,8 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 
 	private volatile boolean preInstantiationPhase;
 
+	private @Nullable volatile String mainThreadPrefix;
+
 	private final NamedThreadLocal<PreInstantiation> preInstantiationThread =
 			new NamedThreadLocal<>("Pre-instantiation thread marker");
 
@@ -1030,7 +1037,7 @@ protected void checkMergedBeanDefinition(RootBeanDefinition mbd, String beanName
 			}
 		}
 		else {
-			// Bean intended to be initialized in main bootstrap thread
+			// Bean intended to be initialized in main bootstrap thread.
 			if (this.preInstantiationThread.get() == PreInstantiation.BACKGROUND) {
 				throw new BeanCurrentlyInCreationException(beanName, "Bean marked for mainline initialization " +
 						"but requested in background thread - enforce early instantiation in mainline thread " +
@@ -1041,8 +1048,28 @@ protected void checkMergedBeanDefinition(RootBeanDefinition mbd, String beanName
 
 	@Override
 	protected @Nullable Boolean isCurrentThreadAllowedToHoldSingletonLock() {
-		return (this.lenientLockingAllowed && this.preInstantiationPhase ?
-				this.preInstantiationThread.get() != PreInstantiation.BACKGROUND : null);
+		if (this.preInstantiationPhase) {
+			// We only differentiate in the preInstantiateSingletons phase.
+			PreInstantiation preInstantiation = this.preInstantiationThread.get();
+			if (preInstantiation != null) {
+				// A Spring-managed thread:
+				// MAIN is allowed to lock (true) or even forced to lock (null),
+				// BACKGROUND is never allowed to lock (false).
+				return switch (preInstantiation) {
+					case MAIN -> (Boolean.TRUE.equals(this.strictLocking) ? null : true);
+					case BACKGROUND -> false;
+				};
+			}
+			if (Boolean.FALSE.equals(this.strictLocking) ||
+					(this.strictLocking == null && !getThreadNamePrefix().equals(this.mainThreadPrefix))) {
+				// An unmanaged thread (assumed to be application-internal) with lenient locking,
+				// and not part of the same thread pool that provided the main bootstrap thread
+				// (excluding scenarios where we are hit by multiple external bootstrap threads).
+				return true;
+			}
+		}
+		// Traditional behavior: forced to always hold a full lock.
+		return null;
 	}
 
 	@Override
@@ -1060,6 +1087,7 @@ public void preInstantiateSingletons() throws BeansException {
 
 		this.preInstantiationPhase = true;
 		this.preInstantiationThread.set(PreInstantiation.MAIN);
+		this.mainThreadPrefix = getThreadNamePrefix();
 		try {
 			for (String beanName : beanNames) {
 				RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
@@ -1072,6 +1100,7 @@ public void preInstantiateSingletons() throws BeansException {
 			}
 		}
 		finally {
+			this.mainThreadPrefix = null;
 			this.preInstantiationThread.remove();
 			this.preInstantiationPhase = false;
 		}
@@ -1166,6 +1195,12 @@ private void instantiateSingleton(String beanName) {
 		}
 	}
 
+	private static String getThreadNamePrefix() {
+		String name = Thread.currentThread().getName();
+		int numberSeparator = name.lastIndexOf('-');
+		return (numberSeparator >= 0 ? name.substring(0, numberSeparator) : name);
+	}
+
 
 	//---------------------------------------------------------------------
 	// Implementation of BeanDefinitionRegistry interface

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

@@ -270,7 +270,7 @@ public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
 						// Thread-safe exposure is still guaranteed, there is just a risk of collisions
 						// when triggering creation of other beans as dependencies of the current bean.
 						if (logger.isInfoEnabled()) {
-							logger.info("Creating singleton bean '" + beanName + "' in thread \"" +
+							logger.info("Obtaining singleton bean '" + beanName + "' in thread \"" +
 									Thread.currentThread().getName() + "\" while other thread holds " +
 									"singleton lock for other beans " + this.singletonsCurrentlyInCreation);
 						}
@@ -441,12 +441,16 @@ private boolean checkDependentWaitingThreads(Thread waitingThread, Thread candid
 
 	/**
 	 * Determine whether the current thread is allowed to hold the singleton lock.
-	 * <p>By default, any thread may acquire and hold the singleton lock, except
-	 * background threads from {@link DefaultListableBeanFactory#setBootstrapExecutor}.
-	 * @return {@code false} if the current thread is explicitly not allowed to hold
-	 * the lock, {@code true} if it is explicitly allowed to hold the lock but also
-	 * accepts lenient fallback behavior, or {@code null} if there is no specific
-	 * indication (traditional behavior: always holding a full lock)
+	 * <p>By default, all threads are forced to hold a full lock through {@code null}.
+	 * {@link DefaultListableBeanFactory} overrides this to specifically handle its
+	 * threads during the pre-instantiation phase: {@code true} for the main thread,
+	 * {@code false} for managed background threads, and configuration-dependent
+	 * behavior for unmanaged threads.
+	 * @return {@code true} if the current thread is explicitly allowed to hold the
+	 * lock but also accepts lenient fallback behavior, {@code false} if it is
+	 * explicitly not allowed to hold the lock and therefore forced to use lenient
+	 * fallback behavior, or {@code null} if there is no specific indication
+	 * (traditional behavior: forced to always hold a full lock)
 	 * @since 6.2
 	 */
 	protected @Nullable Boolean isCurrentThreadAllowedToHoldSingletonLock() {

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

@@ -77,7 +77,6 @@
 import org.springframework.beans.testfixture.beans.SideEffectBean;
 import org.springframework.beans.testfixture.beans.TestBean;
 import org.springframework.beans.testfixture.beans.factory.DummyFactory;
-import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.MethodParameter;
 import org.springframework.core.Ordered;
 import org.springframework.core.ResolvableType;
@@ -1419,7 +1418,6 @@ void autowireWithTwoMatchesForConstructorDependency() {
 		lbf.registerBeanDefinition("rod", bd);
 		RootBeanDefinition bd2 = new RootBeanDefinition(TestBean.class);
 		lbf.registerBeanDefinition("rod2", bd2);
-		lbf.setParameterNameDiscoverer(new DefaultParameterNameDiscoverer());
 
 		assertThatExceptionOfType(UnsatisfiedDependencyException.class)
 				.isThrownBy(() -> lbf.autowire(ConstructorDependency.class, AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR, false))
@@ -1490,7 +1488,6 @@ void autowirePreferredConstructors() {
 		RootBeanDefinition bd = new RootBeanDefinition(ConstructorDependenciesBean.class);
 		bd.setAutowireMode(RootBeanDefinition.AUTOWIRE_CONSTRUCTOR);
 		lbf.registerBeanDefinition("bean", bd);
-		lbf.setParameterNameDiscoverer(new DefaultParameterNameDiscoverer());
 
 		ConstructorDependenciesBean bean = lbf.getBean(ConstructorDependenciesBean.class);
 		Object spouse1 = lbf.getBean("spouse1");
@@ -1508,7 +1505,6 @@ void autowirePreferredConstructorsFromAttribute() {
 		bd.setAttribute(GenericBeanDefinition.PREFERRED_CONSTRUCTORS_ATTRIBUTE,
 				ConstructorDependenciesBean.class.getConstructors());
 		lbf.registerBeanDefinition("bean", bd);
-		lbf.setParameterNameDiscoverer(new DefaultParameterNameDiscoverer());
 
 		ConstructorDependenciesBean bean = lbf.getBean(ConstructorDependenciesBean.class);
 		Object spouse1 = lbf.getBean("spouse1");
@@ -1526,7 +1522,6 @@ void autowirePreferredConstructorFromAttribute() throws Exception {
 		bd.setAttribute(GenericBeanDefinition.PREFERRED_CONSTRUCTORS_ATTRIBUTE,
 				ConstructorDependenciesBean.class.getConstructor(TestBean.class));
 		lbf.registerBeanDefinition("bean", bd);
-		lbf.setParameterNameDiscoverer(new DefaultParameterNameDiscoverer());
 
 		ConstructorDependenciesBean bean = lbf.getBean(ConstructorDependenciesBean.class);
 		Object spouse = lbf.getBean("spouse1");

spring-context/src/test/java/org/springframework/context/annotation/BackgroundBootstrapTests.java

@@ -16,6 +16,9 @@
 
 package org.springframework.context.annotation;
 
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.Timeout;
 
@@ -67,7 +70,7 @@ void bootstrapWithUnmanagedThreads() {
 	@Test
 	@Timeout(10)
 	@EnabledForTestGroups(LONG_RUNNING)
-	void bootstrapWithStrictLockingThread() {
+	void bootstrapWithStrictLockingFlag() {
 		SpringProperties.setFlag(DefaultListableBeanFactory.STRICT_LOCKING_PROPERTY_NAME);
 		try {
 			ConfigurableApplicationContext ctx = new AnnotationConfigApplicationContext(StrictLockingBeanConfig.class);
@@ -79,6 +82,42 @@ void bootstrapWithStrictLockingThread() {
 		}
 	}
 
+	@Test
+	@Timeout(10)
+	@EnabledForTestGroups(LONG_RUNNING)
+	void bootstrapWithStrictLockingInferred() throws InterruptedException {
+		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
+		ctx.register(InferredLockingBeanConfig.class);
+		ExecutorService threadPool = Executors.newFixedThreadPool(2);
+		threadPool.submit(() -> ctx.refresh());
+		Thread.sleep(500);
+		threadPool.submit(() -> ctx.getBean("testBean2"));
+		Thread.sleep(1000);
+		assertThat(ctx.getBean("testBean2", TestBean.class).getSpouse()).isSameAs(ctx.getBean("testBean1"));
+		ctx.close();
+	}
+
+	@Test
+	@Timeout(10)
+	@EnabledForTestGroups(LONG_RUNNING)
+	void bootstrapWithStrictLockingTurnedOff() throws InterruptedException {
+		SpringProperties.setFlag(DefaultListableBeanFactory.STRICT_LOCKING_PROPERTY_NAME, false);
+		try {
+			AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
+			ctx.register(InferredLockingBeanConfig.class);
+			ExecutorService threadPool = Executors.newFixedThreadPool(2);
+			threadPool.submit(() -> ctx.refresh());
+			Thread.sleep(500);
+			threadPool.submit(() -> ctx.getBean("testBean2"));
+			Thread.sleep(1000);
+			assertThat(ctx.getBean("testBean2", TestBean.class).getSpouse()).isNull();
+			ctx.close();
+		}
+		finally {
+			SpringProperties.setProperty(DefaultListableBeanFactory.STRICT_LOCKING_PROPERTY_NAME, null);
+		}
+	}
+
 	@Test
 	@Timeout(10)
 	@EnabledForTestGroups(LONG_RUNNING)
@@ -128,6 +167,24 @@ void bootstrapWithCustomExecutor() {
 		ctx.close();
 	}
 
+	@Test
+	@Timeout(10)
+	@EnabledForTestGroups(LONG_RUNNING)
+	void bootstrapWithCustomExecutorAndStrictLocking() {
+		SpringProperties.setFlag(DefaultListableBeanFactory.STRICT_LOCKING_PROPERTY_NAME);
+		try {
+			ConfigurableApplicationContext ctx = new AnnotationConfigApplicationContext(CustomExecutorBeanConfig.class);
+			ctx.getBean("testBean1", TestBean.class);
+			ctx.getBean("testBean2", TestBean.class);
+			ctx.getBean("testBean3", TestBean.class);
+			ctx.getBean("testBean4", TestBean.class);
+			ctx.close();
+		}
+		finally {
+			SpringProperties.setProperty(DefaultListableBeanFactory.STRICT_LOCKING_PROPERTY_NAME, null);
+		}
+	}
+
 
 	@Configuration(proxyBeanMethods = false)
 	static class UnmanagedThreadBeanConfig {
@@ -220,6 +277,27 @@ public TestBean testBean2(ConfigurableListableBeanFactory beanFactory) {
 	}
 
 
+	@Configuration(proxyBeanMethods = false)
+	static class InferredLockingBeanConfig {
+
+		@Bean
+		public TestBean testBean1() {
+			try {
+				Thread.sleep(1000);
+			}
+			catch (InterruptedException ex) {
+				Thread.currentThread().interrupt();
+			}
+			return new TestBean("testBean1");
+		}
+
+		@Bean
+		public TestBean testBean2(ConfigurableListableBeanFactory beanFactory) {
+			return new TestBean((TestBean) beanFactory.getSingleton("testBean1"));
+		}
+	}
+
+
 	@Configuration(proxyBeanMethods = false)
 	static class CircularReferenceAgainstMainThreadBeanConfig {
 
@@ -377,13 +455,13 @@ public ThreadPoolTaskExecutor bootstrapExecutor() {
 
 		@Bean(bootstrap = BACKGROUND) @DependsOn("testBean3")
 		public TestBean testBean1(TestBean testBean3) throws InterruptedException {
-			Thread.sleep(3000);
+			Thread.sleep(6000);
 			return new TestBean();
 		}
 
 		@Bean(bootstrap = BACKGROUND) @Lazy
 		public TestBean testBean2() throws InterruptedException {
-			Thread.sleep(3000);
+			Thread.sleep(6000);
 			return new TestBean();
 		}
 

spring-core/src/main/java/org/springframework/cglib/core/ReflectUtils.java

@@ -527,15 +527,26 @@ public static Class defineClass(String className, byte[] b, ClassLoader loader,
 				c = lookup.defineClass(b);
 			}
 			catch (LinkageError | IllegalAccessException ex) {
-				throw new CodeGenerationException(ex) {
-					@Override
-					public String getMessage() {
-						return "ClassLoader mismatch for [" + contextClass.getName() +
-								"]: JVM should be started with --add-opens=java.base/java.lang=ALL-UNNAMED " +
-								"for ClassLoader.defineClass to be accessible on " + loader.getClass().getName() +
-								"; consider co-locating the affected class in that target ClassLoader instead.";
+				if (ex instanceof LinkageError) {
+					// Could be a ClassLoader mismatch with the class pre-existing in a
+					// parent ClassLoader -> try loadClass before giving up completely.
+					try {
+						c = contextClass.getClassLoader().loadClass(className);
 					}
-				};
+					catch (ClassNotFoundException cnfe) {
+					}
+				}
+				if (c == null) {
+					throw new CodeGenerationException(ex) {
+						@Override
+						public String getMessage() {
+							return "ClassLoader mismatch for [" + contextClass.getName() +
+									"]: JVM should be started with --add-opens=java.base/java.lang=ALL-UNNAMED " +
+									"for ClassLoader.defineClass to be accessible on " + loader.getClass().getName() +
+									"; consider co-locating the affected class in that target ClassLoader instead.";
+						}
+					};
+				}
 			}
 			catch (Throwable ex) {
 				throw new CodeGenerationException(ex);

spring-core/src/main/java/org/springframework/core/SpringProperties.java

@@ -117,7 +117,18 @@ public static void setProperty(String key, @Nullable String value) {
 	 * @param key the property key
 	 */
 	public static void setFlag(String key) {
-		localProperties.put(key, Boolean.TRUE.toString());
+		localProperties.setProperty(key, Boolean.TRUE.toString());
+	}
+
+	/**
+	 * Programmatically set a local flag to the given value, overriding
+	 * an entry in the {@code spring.properties} file (if any).
+	 * @param key the property key
+	 * @param value the associated boolean value
+	 * @since 6.2.6
+	 */
+	public static void setFlag(String key, boolean value) {
+		localProperties.setProperty(key, Boolean.toString(value));
 	}
 
 	/**
@@ -130,4 +141,19 @@ public static boolean getFlag(String key) {
 		return Boolean.parseBoolean(getProperty(key));
 	}
 
+	/**
+	 * Retrieve the flag for the given property key, returning {@code null}
+	 * instead of {@code false} in case of no actual flag set.
+	 * @param key the property key
+	 * @return {@code true} if the property is set to the string "true"
+	 * (ignoring case), {@code} false if it is set to any other value,
+	 * {@code null} if it is not set at all
+	 * @since 6.2.6
+	 */
+	@Nullable
+	public static Boolean checkFlag(String key) {
+		String flag = getProperty(key);
+		return (flag != null ? Boolean.valueOf(flag) : null);
+	}
+
 }