Fix regressions in SimpleThreadScope and SimpleTransactionScope

PR gh-25038 introduced regressions in SimpleThreadScope and
SimpleTransactionScope in Spring Framework 5.2.7. Specifically, if a
thread-scoped or transaction-scoped bean has a dependency on another
thread-scoped or transaction-scoped bean, respectively, a
ConcurrentModificationException will be thrown on Java 11 or higher.

The reason is that Java 11 introduced a check for concurrent
modification in java.util.HashMap's computeIfAbsent() implementation,
and such a modification can occur when a thread-scoped bean is being
created in order to satisfy a dependency of another thread-scoped bean
that is currently being created.

This commit fixes these regressions by switching from HashMap to
ConcurrentHashMap for the instance maps in SimpleThreadScope and
SimpleTransactionScope.

Closes gh-25618

spring-context/src/main/java/org/springframework/context/support/SimpleThreadScope.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -16,8 +16,8 @@
 
 package org.springframework.context.support;
 
-import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -59,7 +59,7 @@ public class SimpleThreadScope implements Scope {
 			new NamedThreadLocal<Map<String, Object>>("SimpleThreadScope") {
 				@Override
 				protected Map<String, Object> initialValue() {
-					return new HashMap<>();
+					return new ConcurrentHashMap<>();
 				}
 			};
 

spring-context/src/test/java/org/springframework/context/support/SimpleThreadScopeTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -30,14 +30,14 @@
  * @author Arjen Poutsma
  * @author Sam Brannen
  */
-public class SimpleThreadScopeTests {
+class SimpleThreadScopeTests {
 
 	private final ApplicationContext applicationContext =
 			new ClassPathXmlApplicationContext("simpleThreadScopeTests.xml", getClass());
 
 
 	@Test
-	public void getFromScope() throws Exception {
+	void getFromScope() throws Exception {
 		String name = "threadScopedObject";
 		TestBean bean = this.applicationContext.getBean(name, TestBean.class);
 		assertThat(bean).isNotNull();
@@ -47,7 +47,7 @@ public void getFromScope() throws Exception {
 	}
 
 	@Test
-	public void getMultipleInstances() throws Exception {
+	void getMultipleInstances() throws Exception {
 		// Arrange
 		TestBean[] beans = new TestBean[2];
 		Thread thread1 = new Thread(() -> beans[0] = applicationContext.getBean("threadScopedObject", TestBean.class));

spring-context/src/test/resources/org/springframework/context/support/simpleThreadScopeTests.xml

@@ -1,51 +1,21 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<beans xmlns="http://www.springframework.org/schema/beans"
-	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	   xsi:schemaLocation="http://www.springframework.org/schema/beans
-                https://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
+<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd">
 
 	<bean class="org.springframework.beans.factory.config.CustomScopeConfigurer">
 		<property name="scopes">
 			<map>
 				<entry key="thread">
-					<bean class="org.springframework.context.support.SimpleThreadScope"/>
+					<bean class="org.springframework.context.support.SimpleThreadScope" />
 				</entry>
 			</map>
 		</property>
 	</bean>
 
-	<bean id="threadScopedObject" class="org.springframework.beans.testfixture.beans.TestBean" scope="thread"/>
-
-	<!--
-	<bean id="requestScopedDisposableObject" class="org.springframework.beans.testfixture.beans.DerivedTestBean" scope="request"/>
-
-	<bean id="requestScopedFactoryBean" class="org.springframework.beans.testfixture.beans.factory.DummyFactory" scope="request"/>
-
-	<bean id="requestScopedObjectCircle1" class="org.springframework.beans.testfixture.beans.TestBean" scope="request">
-		<property name="spouse" ref="requestScopedObjectCircle2"/>
+	<bean id="threadScopedObject" class="org.springframework.beans.testfixture.beans.TestBean" scope="thread">
+		<property name="spouse" ref="threadScopedObject2" />
 	</bean>
 
-	<bean id="requestScopedObjectCircle2" class="org.springframework.beans.testfixture.beans.TestBean" scope="request">
-		<property name="spouse" ref="requestScopedObjectCircle1"/>
-	</bean>
-
-  <bean id="requestScopedOuterBean" class="org.springframework.beans.testfixture.beans.DerivedTestBean" scope="request">
-    <property name="name" value="outer"/>
-    <property name="spouse">
-      <bean class="org.springframework.beans.testfixture.beans.DerivedTestBean">
-        <property name="name" value="inner"/>
-      </bean>
-    </property>
-  </bean>
-
-  <bean id="singletonOuterBean" class="org.springframework.beans.testfixture.beans.DerivedTestBean" lazy-init="true">
-    <property name="name" value="outer"/>
-    <property name="spouse">
-      <bean class="org.springframework.beans.testfixture.beans.DerivedTestBean" scope="request">
-        <property name="name" value="inner"/>
-      </bean>
-    </property>
-  </bean>
+	<bean id="threadScopedObject2" class="org.springframework.beans.testfixture.beans.TestBean" scope="thread" />
 
--->
 </beans>

spring-tx/src/main/java/org/springframework/transaction/support/SimpleTransactionScope.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -16,9 +16,9 @@
 
 package org.springframework.transaction.support;
 
-import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.springframework.beans.factory.ObjectFactory;
 import org.springframework.beans.factory.config.Scope;
@@ -92,7 +92,7 @@ public String getConversationId() {
 	 */
 	static class ScopedObjectsHolder {
 
-		final Map<String, Object> scopedInstances = new HashMap<>();
+		final Map<String, Object> scopedInstances = new ConcurrentHashMap<>();
 
 		final Map<String, Runnable> destructionCallbacks = new LinkedHashMap<>();
 	}