Change "synchronized" to reentrant lock for virtual-threads

Fix checkstyles before merge

Code cleanup

Double-Checked Locking Optimization was used to avoid unnecessary locking overhead.

binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/main/java/org/springframework/cloud/stream/binder/kafka/streams/KafkaStreamsBinderMetrics.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2019-2019 the original author or authors.
+ * Copyright 2019-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,6 +24,7 @@ import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.function.ToDoubleFunction;
 
 import io.micrometer.core.instrument.FunctionCounter;
@@ -52,6 +53,7 @@ import org.springframework.kafka.config.StreamsBuilderFactoryBean;
  * We will keep this class, as long as we support Boot 2.2.x.
  *
  * @author Soby Chacko
+ * @author Omer Celik
  * @since 3.0.0
  */
 public class KafkaStreamsBinderMetrics {
@@ -84,6 +86,8 @@ public class KafkaStreamsBinderMetrics {
 
 	private volatile Set<MetricName> currentMeters = new HashSet<>();
 
+	private static final ReentrantLock metricsLock = new ReentrantLock();
+
 	public KafkaStreamsBinderMetrics(MeterRegistry meterRegistry) {
 		this.meterRegistry = meterRegistry;
 	}
@@ -108,9 +112,13 @@ public class KafkaStreamsBinderMetrics {
 	}
 
 	public void addMetrics(Set<StreamsBuilderFactoryBean> streamsBuilderFactoryBeans) {
-		synchronized (KafkaStreamsBinderMetrics.this) {
+		try {
+			metricsLock.lock();
 			this.bindTo(streamsBuilderFactoryBeans);
 		}
+		finally {
+			metricsLock.unlock();
+		}
 	}
 
 	void prepareToBindMetrics(MeterRegistry registry, Map<MetricName, ? extends Metric> metrics) {

binders/kafka-binder/spring-cloud-stream-binder-kafka/src/main/java/org/springframework/cloud/stream/binder/kafka/KafkaBinderMetrics.java

@@ -30,6 +30,7 @@ import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.function.ToDoubleFunction;
 
 import io.micrometer.core.instrument.Gauge;
@@ -68,6 +69,7 @@ import org.springframework.util.ObjectUtils;
  * @author Tomek Szmytka
  * @author Nico Heller
  * @author Kurt Hong
+ * @author Omer Celik
  */
 public class KafkaBinderMetrics
 		implements MeterBinder, ApplicationListener<BindingCreatedEvent>, AutoCloseable {
@@ -97,6 +99,8 @@ public class KafkaBinderMetrics
 
 	ScheduledExecutorService scheduler;
 
+	private final ReentrantLock consumerFactoryLock = new ReentrantLock();
+
 	public KafkaBinderMetrics(KafkaMessageChannelBinder binder,
 							KafkaBinderConfigurationProperties binderConfigurationProperties,
 							ConsumerFactory<?, ?> defaultConsumerFactory,
@@ -231,25 +235,36 @@ public class KafkaBinderMetrics
 		return lag;
 	}
 
-	private synchronized ConsumerFactory<?, ?> createConsumerFactory() {
+	/**
+	 * Double-Checked Locking Optimization was used to avoid unnecessary locking overhead.
+	 */
+	private ConsumerFactory<?, ?> createConsumerFactory() {
 		if (this.defaultConsumerFactory == null) {
-			Map<String, Object> props = new HashMap<>();
-			props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG,
-					ByteArrayDeserializer.class);
-			props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,
-					ByteArrayDeserializer.class);
-			Map<String, Object> mergedConfig = this.binderConfigurationProperties
-					.mergedConsumerConfiguration();
-			if (!ObjectUtils.isEmpty(mergedConfig)) {
-				props.putAll(mergedConfig);
-			}
-			if (!props.containsKey(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG)) {
-				props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,
-						this.binderConfigurationProperties
+			try {
+				this.consumerFactoryLock.lock();
+				if (this.defaultConsumerFactory == null) {
+					Map<String, Object> props = new HashMap<>();
+					props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG,
+						ByteArrayDeserializer.class);
+					props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,
+						ByteArrayDeserializer.class);
+					Map<String, Object> mergedConfig = this.binderConfigurationProperties
+						.mergedConsumerConfiguration();
+					if (!ObjectUtils.isEmpty(mergedConfig)) {
+						props.putAll(mergedConfig);
+					}
+					if (!props.containsKey(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG)) {
+						props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,
+							this.binderConfigurationProperties
 								.getKafkaConnectionString());
+					}
+					this.defaultConsumerFactory = new DefaultKafkaConsumerFactory<>(
+						props);
+				}
+			}
+			finally {
+				this.consumerFactoryLock.unlock();
 			}
-			this.defaultConsumerFactory = new DefaultKafkaConsumerFactory<>(
-					props);
 		}
 		return this.defaultConsumerFactory;
 	}

binders/rabbit-binder/spring-cloud-stream-binder-rabbit-core/src/main/java/org/springframework/cloud/stream/binder/rabbit/provisioning/RabbitExchangeQueueProvisioner.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2023 the original author or authors.
+ * Copyright 2016-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
@@ -79,6 +80,7 @@ import org.springframework.util.StringUtils;
  * @author Oleg Zhurakousky
  * @author Michael Michailidis
  * @author Byungjun You
+ * @author Omer Celik
  */
 // @checkstyle:off
 public class RabbitExchangeQueueProvisioner
@@ -105,6 +107,8 @@ public class RabbitExchangeQueueProvisioner
 
 	private final AtomicInteger producerExchangeBeanNameQualifier = new AtomicInteger();
 
+	private final ReentrantLock autoDeclareContextLock = new ReentrantLock();
+
 	public RabbitExchangeQueueProvisioner(ConnectionFactory connectionFactory) {
 		this(connectionFactory, Collections.emptyList());
 	}
@@ -320,11 +324,15 @@ public class RabbitExchangeQueueProvisioner
 				(q, i) -> IntStream.range(0, i)
 						.mapToObj(j -> rk + "-" + j)
 						.collect(Collectors.toList()));
-		synchronized (this.autoDeclareContext) {
+		try {
+			this.autoDeclareContextLock.lock();
 			if (!this.autoDeclareContext.containsBean(name + ".superStream")) {
 				this.autoDeclareContext.getBeanFactory().registerSingleton(name + ".superStream", ss);
 			}
 		}
+		finally {
+			this.autoDeclareContextLock.unlock();
+		}
 		try {
 			ss.getDeclarables().forEach(dec -> {
 				if (dec instanceof Exchange exch) {
@@ -716,7 +724,8 @@ public class RabbitExchangeQueueProvisioner
 	}
 
 	private void addToAutoDeclareContext(String name, Declarable bean) {
-		synchronized (this.autoDeclareContext) {
+		try {
+			this.autoDeclareContextLock.lock();
 			if (!this.autoDeclareContext.containsBean(name)) {
 				this.autoDeclareContext.getBeanFactory().registerSingleton(name, new Declarables(bean));
 			}
@@ -724,6 +733,9 @@ public class RabbitExchangeQueueProvisioner
 				this.autoDeclareContext.getBean(name, Declarables.class).getDeclarables().add(bean);
 			}
 		}
+		finally {
+			this.autoDeclareContextLock.unlock();
+		}
 	}
 
 	private void declareBinding(String rootName, org.springframework.amqp.core.Binding bindingArg) {
@@ -756,31 +768,36 @@ public class RabbitExchangeQueueProvisioner
 	public void cleanAutoDeclareContext(ConsumerDestination destination,
 			ExtendedConsumerProperties<RabbitConsumerProperties> consumerProperties) {
 
-		synchronized (this.autoDeclareContext) {
+		try {
+			this.autoDeclareContextLock.lock();
 			Stream.of(StringUtils.tokenizeToStringArray(destination.getName(), ",", true,
-					true)).forEach(name -> {
-						String group = null;
-						String bindingName = null;
-						if (destination instanceof RabbitConsumerDestination rabbitConsumerDestination) {
-							group = rabbitConsumerDestination.getGroup();
-							bindingName = rabbitConsumerDestination.getBindingName();
-						}
-						RabbitConsumerProperties properties = consumerProperties.getExtension();
-						String toRemove = properties.isQueueNameGroupOnly() ? bindingName + "." + group : name.trim();
-						boolean partitioned = consumerProperties.isPartitioned();
-						if (partitioned) {
-							toRemove = removePartitionPart(toRemove);
-						}
-						removeSingleton(toRemove + ".exchange");
-						removeQueueAndBindingBeans(properties, name.trim(), "", group, partitioned);
-					});
+				true)).forEach(name -> {
+				String group = null;
+				String bindingName = null;
+				if (destination instanceof RabbitConsumerDestination rabbitConsumerDestination) {
+					group = rabbitConsumerDestination.getGroup();
+					bindingName = rabbitConsumerDestination.getBindingName();
+				}
+				RabbitConsumerProperties properties = consumerProperties.getExtension();
+				String toRemove = properties.isQueueNameGroupOnly() ? bindingName + "." + group : name.trim();
+				boolean partitioned = consumerProperties.isPartitioned();
+				if (partitioned) {
+					toRemove = removePartitionPart(toRemove);
+				}
+				removeSingleton(toRemove + ".exchange");
+				removeQueueAndBindingBeans(properties, name.trim(), "", group, partitioned);
+			});
+		}
+		finally {
+			this.autoDeclareContextLock.unlock();
 		}
 	}
 
 	public void cleanAutoDeclareContext(ProducerDestination dest,
 			ExtendedProducerProperties<RabbitProducerProperties> properties) {
 
-		synchronized (this.autoDeclareContext) {
+		try {
+			this.autoDeclareContextLock.lock();
 			if (dest instanceof RabbitProducerDestination rabbitProducerDestination) {
 				String qual = rabbitProducerDestination.getBeanNameQualifier();
 				removeSingleton(dest.getName() + "." + qual + ".exchange");
@@ -790,13 +807,13 @@ public class RabbitExchangeQueueProvisioner
 						if (properties.isPartitioned()) {
 							for (int i = 0; i < properties.getPartitionCount(); i++) {
 								removeQueueAndBindingBeans(properties.getExtension(),
-										properties.getExtension().isQueueNameGroupOnly() ? "" : dest.getName(),
-												group + "-" + i, group, true);
+									properties.getExtension().isQueueNameGroupOnly() ? "" : dest.getName(),
+									group + "-" + i, group, true);
 							}
 						}
 						else {
 							removeQueueAndBindingBeans(properties.getExtension(), dest.getName() + "." + group, "",
-									group, false);
+								group, false);
 						}
 					}
 				}
@@ -811,6 +828,9 @@ public class RabbitExchangeQueueProvisioner
 				}
 			}
 		}
+		finally {
+			this.autoDeclareContextLock.unlock();
+		}
 	}
 
 	private void removeQueueAndBindingBeans(RabbitCommonProperties properties, String name, String suffix,

core/spring-cloud-stream/src/main/java/org/springframework/cloud/stream/binding/BindableProxyFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015-2022 the original author or authors.
+ * Copyright 2015-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@ package org.springframework.cloud.stream.binding;
 import java.lang.reflect.Method;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.locks.ReentrantLock;
 
 import org.aopalliance.intercept.MethodInterceptor;
 import org.aopalliance.intercept.MethodInvocation;
@@ -43,6 +44,7 @@ import org.springframework.util.Assert;
  * @author Ilayaperumal Gopinathan
  * @author Oleg Zhurakousky
  * @author Soby Chacko
+ * @author Omer Celik
  */
 public class BindableProxyFactory extends AbstractBindableProxyFactory
 		implements MethodInterceptor, FactoryBean<Object>, InitializingBean, BeanFactoryAware {
@@ -55,21 +57,25 @@ public class BindableProxyFactory extends AbstractBindableProxyFactory
 
 	protected BeanFactory beanFactory;
 
+	private final ReentrantLock lock = new ReentrantLock();
+
 	public BindableProxyFactory(Class<?> type) {
 		super(type);
 		this.type = type;
 	}
 
 	@Override
-	public synchronized Object invoke(MethodInvocation invocation) {
-		Method method = invocation.getMethod();
+	public Object invoke(MethodInvocation invocation) {
+		try {
+			this.lock.lock();
+			Method method = invocation.getMethod();
 
-		// try to use cached target
-		Object boundTarget = this.targetCache.get(method);
-		if (boundTarget != null) {
-			return boundTarget;
+			// try to use cached target
+			return this.targetCache.get(method);
+		}
+		finally {
+			this.lock.unlock();
 		}
-		return null;
 	}
 
 	public void replaceInputChannel(String originalChannelName, String newChannelName, SubscribableChannel messageChannel) {
@@ -97,11 +103,22 @@ public class BindableProxyFactory extends AbstractBindableProxyFactory
 				"'bindingTargetFactories' cannot be empty");
 	}
 
+	/**
+	 * Double-Checked Locking Optimization was used to avoid unnecessary locking overhead.
+	 */
 	@Override
-	public synchronized Object getObject() {
+	public Object getObject() {
 		if (this.proxy == null && this.type != null) {
-			ProxyFactory factory = new ProxyFactory(this.type, this);
-			this.proxy = factory.getProxy();
+			try {
+				this.lock.lock();
+				if (this.proxy == null && this.type != null) {
+					ProxyFactory factory = new ProxyFactory(this.type, this);
+					this.proxy = factory.getProxy();
+				}
+			}
+			finally {
+				this.lock.unlock();
+			}
 		}
 		return this.proxy;
 	}

core/spring-cloud-stream/src/main/java/org/springframework/cloud/stream/binding/BindingService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015-2023 the original author or authors.
+ * Copyright 2015-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,6 +24,7 @@ import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.stream.Stream;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
@@ -63,6 +64,7 @@ import org.springframework.validation.DataBinder;
  * @author Chris Bono
  * @author Artem Bilan
  * @author Byungjun You
+ * @author Omer Celik
  */
 public class BindingService {
 
@@ -451,35 +453,49 @@ public class BindingService {
 
 		private final String bindingName;
 
-		private final Object consumerOrProducerproperties;
+		private final Object consumerOrProducerProperties;
 
 		private final boolean isInput;
 
 		final ObjectMapper objectMapper;
 
-		LateBinding(String bindingName, String error, Object consumerOrProducerproperties, boolean isInput, ObjectMapper objectMapper) {
+		private final ReentrantLock lock = new ReentrantLock();
+
+		LateBinding(String bindingName, String error, Object consumerOrProducerProperties, boolean isInput, ObjectMapper objectMapper) {
 			super();
 			this.error = error;
 			this.bindingName = bindingName;
-			this.consumerOrProducerproperties = consumerOrProducerproperties;
+			this.consumerOrProducerProperties = consumerOrProducerProperties;
 			this.isInput = isInput;
 			this.objectMapper = objectMapper;
 		}
 
-		public synchronized void setDelegate(Binding<T> delegate) {
-			if (this.unbound) {
-				delegate.unbind();
+		public void setDelegate(Binding<T> delegate) {
+			try {
+				this.lock.lock();
+				if (this.unbound) {
+					delegate.unbind();
+				}
+				else {
+					this.delegate = delegate;
+				}
 			}
-			else {
-				this.delegate = delegate;
+			finally {
+				this.lock.unlock();
 			}
 		}
 
 		@Override
-		public synchronized void unbind() {
-			this.unbound = true;
-			if (this.delegate != null) {
-				this.delegate.unbind();
+		public void unbind() {
+			try {
+				this.lock.lock();
+				this.unbound = true;
+				if (this.delegate != null) {
+					this.delegate.unbind();
+				}
+			}
+			finally {
+				this.lock.unlock();
 			}
 		}
 
@@ -507,8 +523,8 @@ public class BindingService {
 		public Map<String, Object> getExtendedInfo() {
 			Map<String, Object> extendedInfo = new LinkedHashMap<>();
 			extendedInfo.put("bindingDestination", this.getBindingName());
-			extendedInfo.put(consumerOrProducerproperties.getClass().getSimpleName(),
-					this.objectMapper.convertValue(consumerOrProducerproperties, Map.class));
+			extendedInfo.put(consumerOrProducerProperties.getClass().getSimpleName(),
+					this.objectMapper.convertValue(consumerOrProducerProperties, Map.class));
 			return extendedInfo;
 		}
 

core/spring-cloud-stream/src/main/java/org/springframework/cloud/stream/binding/DynamicDestinationsBindable.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.locks.ReentrantLock;
 
 import org.springframework.cloud.stream.binder.Binding;
 
@@ -29,6 +30,7 @@ import org.springframework.cloud.stream.binder.Binding;
  *
  * @author Ilayaperumal Gopinathan
  * @author Oleg Zhurakousky
+ * @author Omer Celik
  */
 public final class DynamicDestinationsBindable implements Bindable {
 
@@ -37,21 +39,41 @@ public final class DynamicDestinationsBindable implements Bindable {
 	 */
 	private final Map<String, Binding<?>> outputBindings = new HashMap<>();
 
-	public synchronized void addOutputBinding(String name, Binding<?> binding) {
-		this.outputBindings.put(name, binding);
-	}
+	private static final ReentrantLock outputBindingsLock = new ReentrantLock();
 
-	@Override
-	public synchronized Set<String> getOutputs() {
-		return Collections.unmodifiableSet(this.outputBindings.keySet());
-	}
-
-	@Override
-	public synchronized void unbindOutputs(BindingService adapter) {
-		for (Map.Entry<String, Binding<?>> entry : this.outputBindings.entrySet()) {
-			entry.getValue().unbind();
+	public void addOutputBinding(String name, Binding<?> binding) {
+		try {
+			outputBindingsLock.lock();
+			this.outputBindings.put(name, binding);
+		}
+		finally {
+			outputBindingsLock.unlock();
+		}
+	}
+
+	@Override
+	public Set<String> getOutputs() {
+		try {
+			outputBindingsLock.lock();
+			return Collections.unmodifiableSet(this.outputBindings.keySet());
+		}
+		finally {
+			outputBindingsLock.unlock();
+		}
+	}
+
+	@Override
+	public void unbindOutputs(BindingService adapter) {
+		try {
+			outputBindingsLock.lock();
+			for (Map.Entry<String, Binding<?>> entry : this.outputBindings.entrySet()) {
+				entry.getValue().unbind();
+			}
+			this.outputBindings.clear();
+		}
+		finally {
+			outputBindingsLock.unlock();
 		}
-		this.outputBindings.clear();
 	}
 
 }

schema-registry/spring-cloud-stream-schema-registry-core/src/main/java/org/springframework/cloud/stream/schema/registry/controllers/ServerController.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@ package org.springframework.cloud.stream.schema.registry.controllers;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.concurrent.locks.ReentrantLock;
 
 import org.springframework.cloud.stream.schema.registry.config.SchemaServerProperties;
 import org.springframework.cloud.stream.schema.registry.model.Schema;
@@ -52,6 +53,7 @@ import static org.springframework.http.MediaType.APPLICATION_JSON_VALUE;
  * @author Ilayaperumal Gopinathan
  * @author Jeff Maxwell
  * @author Christian Tzolov
+ * @author Omer Celik
  */
 @RestController
 @RequestMapping(path = "${spring.cloud.stream.schema.server.path:}")
@@ -63,6 +65,8 @@ public class ServerController {
 
 	private final SchemaServerProperties schemaServerProperties;
 
+	private static final ReentrantLock lock = new ReentrantLock();
+
 	public ServerController(SchemaRepository repository, Map<String, SchemaValidator> validators,
 			SchemaServerProperties schemaServerProperties) {
 		Assert.notNull(repository, "cannot be null");
@@ -73,41 +77,45 @@ public class ServerController {
 	}
 
 	@RequestMapping(method = RequestMethod.POST, path = "/", consumes = "application/json", produces = "application/json")
-	public synchronized ResponseEntity<Schema> register(@RequestBody Schema schema, UriComponentsBuilder builder) {
+	public ResponseEntity<Schema> register(@RequestBody Schema schema, UriComponentsBuilder builder) {
+		try {
+			lock.lock();
+			SchemaValidator validator = this.validators.get(schema.getFormat());
 
-		SchemaValidator validator = this.validators.get(schema.getFormat());
-
-		if (validator == null) {
-			throw new UnsupportedFormatException(String.format("Invalid format, supported types are: %s",
+			if (validator == null) {
+				throw new UnsupportedFormatException(String.format("Invalid format, supported types are: %s",
 					StringUtils.collectionToCommaDelimitedString(this.validators.keySet())));
-		}
-
-		validator.validate(schema.getDefinition());
-
-		Schema result;
-		List<Schema> registeredEntities =
-				this.repository.findBySubjectAndFormatOrderByVersion(schema.getSubject(), schema.getFormat());
-		if (registeredEntities.isEmpty()) {
-			schema.setVersion(1);
-			result = this.repository.save(schema);
-		}
-		else {
-			result = validator.match(registeredEntities, schema.getDefinition());
-			if (result == null) {
-				schema.setVersion(registeredEntities.get(registeredEntities.size() - 1).getVersion() + 1);
-				result = this.repository.save(schema);
 			}
 
-		}
+			validator.validate(schema.getDefinition());
 
-		HttpHeaders headers = new HttpHeaders();
-		headers.add(HttpHeaders.LOCATION, builder.path("/{subject}/{format}/v{version}")
+			Schema result;
+			List<Schema> registeredEntities =
+				this.repository.findBySubjectAndFormatOrderByVersion(schema.getSubject(), schema.getFormat());
+			if (registeredEntities.isEmpty()) {
+				schema.setVersion(1);
+				result = this.repository.save(schema);
+			}
+			else {
+				result = validator.match(registeredEntities, schema.getDefinition());
+				if (result == null) {
+					schema.setVersion(registeredEntities.get(registeredEntities.size() - 1).getVersion() + 1);
+					result = this.repository.save(schema);
+				}
+
+			}
+
+			HttpHeaders headers = new HttpHeaders();
+			headers.add(HttpHeaders.LOCATION, builder.path("/{subject}/{format}/v{version}")
 				.buildAndExpand(result.getSubject(), result.getFormat(), result.getVersion())
 				.toString());
-		ResponseEntity<Schema> response = new ResponseEntity<>(result, headers, HttpStatus.CREATED);
-
-		return response;
+			ResponseEntity<Schema> response = new ResponseEntity<>(result, headers, HttpStatus.CREATED);
 
+			return response;
+		}
+		finally {
+			lock.unlock();
+		}
 	}
 
 	@RequestMapping(method = RequestMethod.GET, produces = "application/json", path = "/{subject}/{format}/v{version}")