Remove the use of synchronized in the getBinder method of DefaultBinderFactory class for virtual-threads

The getBinder method in DefaultBinderFactory was made thread-safe using ReentrantLock. This commit ensures that the method is friendly for virtual threads to avoid blocking and pinning. The lock is acquired at the beginning of the method and released in a finally block to ensure it is always released, even if an exception occurs. Fixes gh-3004

Author: Fernando Blanch

core/spring-cloud-stream/src/main/java/org/springframework/cloud/stream/binder/DefaultBinderFactory.java

@@ -30,6 +30,7 @@
 import java.util.Map.Entry;
 import java.util.Properties;
 import java.util.Set;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.stream.Stream;
 
 import org.apache.commons.logging.Log;
@@ -98,6 +99,8 @@ public class DefaultBinderFactory implements BinderFactory, DisposableBean, Appl
 
 	private volatile String defaultBinder;
 
+	private static final ReentrantLock lock = new ReentrantLock();
+
 	public DefaultBinderFactory(Map<String, BinderConfiguration> binderConfigurations,
 								BinderTypeRegistry binderTypeRegistry, BinderCustomizer binderCustomizer) {
 		this.binderConfigurations = new HashMap<>(binderConfigurations);
@@ -142,34 +145,39 @@ public void destroy() {
 
 	@SuppressWarnings({ "unchecked", "rawtypes" })
 	@Override
+	public <T> Binder<T, ?, ?> getBinder(String name, Class<? extends T> bindingTargetType) {
+		lock.lock();
+		try {
+			String binderName = StringUtils.hasText(name) ? name : this.defaultBinder;
 
-	public synchronized <T> Binder<T, ?, ?> getBinder(String name, Class<? extends T> bindingTargetType) {
-		String binderName = StringUtils.hasText(name) ? name : this.defaultBinder;
-
-		Map<String, Binder> binders = this.context == null ? Collections.emptyMap() : this.context.getBeansOfType(Binder.class);
-		Binder<T, ConsumerProperties, ProducerProperties> binder;
-		if (StringUtils.hasText(binderName) && binders.containsKey(binderName)) {
-			binder = (Binder<T, ConsumerProperties, ProducerProperties>) this.context.getBean(binderName);
-		}
-		else if (binders.size() == 1) {
-			binder = binders.values().iterator().next();
-		}
-		else if (binders.size() > 1) {
-			throw new IllegalStateException(
+			Map<String, Binder> binders = this.context == null ? Collections.emptyMap() : this.context.getBeansOfType(Binder.class);
+			Binder<T, ConsumerProperties, ProducerProperties> binder;
+			if (StringUtils.hasText(binderName) && binders.containsKey(binderName)) {
+				binder = (Binder<T, ConsumerProperties, ProducerProperties>) this.context.getBean(binderName);
+			}
+			else if (binders.size() == 1) {
+				binder = binders.values().iterator().next();
+			}
+			else if (binders.size() > 1) {
+				throw new IllegalStateException(
 					"Multiple binders are available, however neither default nor "
-							+ "per-destination binder name is provided. Available binders are "
-							+ binders.keySet());
-		}
-		else {
-			/*
-			 * This is the fallback to the old bootstrap that relies on spring.binders.
-			 */
-			binder = this.doGetBinder(binderName, bindingTargetType);
+						+ "per-destination binder name is provided. Available binders are "
+						+ binders.keySet());
+			}
+			else {
+				/*
+				 * This is the fallback to the old bootstrap that relies on spring.binders.
+				 */
+				binder = this.doGetBinder(binderName, bindingTargetType);
+			}
+			if (this.binderCustomizer != null) {
+				this.binderCustomizer.customize(binder, binderName);
+			}
+			return binder;
 		}
-		if (this.binderCustomizer != null) {
-			this.binderCustomizer.customize(binder, binderName);
+		finally {
+			lock.unlock();
 		}
-		return binder;
 	}
 
 	private <T> Binder<T, ConsumerProperties, ProducerProperties> doGetBinder(String name, Class<? extends T> bindingTargetType) {