Synchronized access to method overrides (in particular for @Lookup)

Issue: SPR-14333

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -731,7 +731,7 @@ public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccess
 	/**
 	 * Return information about methods to be overridden by the IoC
 	 * container. This will be empty if there are no method overrides.
-	 * Never returns null.
+	 * Never returns {@code null}.
 	 */
 	public MethodOverrides getMethodOverrides() {
 		return this.methodOverrides;
@@ -934,8 +934,11 @@ public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccess
 		// Check that lookup methods exists.
 		MethodOverrides methodOverrides = getMethodOverrides();
 		if (!methodOverrides.isEmpty()) {
-			for (MethodOverride mo : methodOverrides.getOverrides()) {
-				prepareMethodOverride(mo);
+			Set<MethodOverride> overrides = methodOverrides.getOverrides();
+			synchronized (overrides) {
+				for (MethodOverride mo : overrides) {
+					prepareMethodOverride(mo);
+				}
 			}
 		}
 	}

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -17,6 +17,7 @@
 package org.springframework.beans.factory.support;
 
 import java.lang.reflect.Method;
+import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
@@ -34,7 +35,10 @@ import java.util.Set;
  */
 public class MethodOverrides {
 
-	private final Set<MethodOverride> overrides = new LinkedHashSet<MethodOverride>(0);
+	private final Set<MethodOverride> overrides =
+			Collections.synchronizedSet(new LinkedHashSet<MethodOverride>(0));
+
+	private volatile boolean modified = false;
 
 
 	/**
@@ -56,7 +60,8 @@ public class MethodOverrides {
 	 */
 	public void addOverrides(MethodOverrides other) {
 		if (other != null) {
-			this.overrides.addAll(other.getOverrides());
+			this.modified = true;
+			this.overrides.addAll(other.overrides);
 		}
 	}
 
@@ -64,6 +69,7 @@ public class MethodOverrides {
 	 * Add the given method override.
 	 */
 	public void addOverride(MethodOverride override) {
+		this.modified = true;
 		this.overrides.add(override);
 	}
 
@@ -73,6 +79,7 @@ public class MethodOverrides {
 	 * @see MethodOverride
 	 */
 	public Set<MethodOverride> getOverrides() {
+		this.modified = true;
 		return this.overrides;
 	}
 
@@ -80,7 +87,7 @@ public class MethodOverrides {
 	 * Return whether the set of method overrides is empty.
 	 */
 	public boolean isEmpty() {
-		return this.overrides.isEmpty();
+		return (!this.modified || this.overrides.isEmpty());
 	}
 
 	/**
@@ -89,13 +96,18 @@ public class MethodOverrides {
 	 * @return the method override, or {@code null} if none
 	 */
 	public MethodOverride getOverride(Method method) {
-		MethodOverride match = null;
-		for (MethodOverride candidate : this.overrides) {
-			if (candidate.matches(method)) {
-				match = candidate;
-			}
+		if (!this.modified) {
+			return null;
+		}
+		synchronized (this.overrides) {
+			MethodOverride match = null;
+			for (MethodOverride candidate : this.overrides) {
+				if (candidate.matches(method)) {
+					match = candidate;
+				}
+			}
+			return match;
 		}
-		return match;
 	}