DefaultSubscriptionRegistry returns safe to iterate Map

Prior to this change when adding subscriptions
DefaultSubscriptionRegistry (incorrectly) made a copy of the given map
for its "access" cache rather than for its "update" cache.

Issue: SPR-12665

spring-messaging/src/test/java/org/springframework/messaging/simp/broker/DefaultSubscriptionRegistryTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -18,6 +18,7 @@ package org.springframework.messaging.simp.broker;
 
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.Iterator;
 import java.util.List;
 
 import org.junit.Before;
@@ -31,6 +32,7 @@ import org.springframework.util.MultiValueMap;
 
 import static org.junit.Assert.*;
 
+
 /**
  * Test fixture for {@link org.springframework.messaging.simp.broker.DefaultSubscriptionRegistry}.
  *
@@ -326,6 +328,23 @@ public class DefaultSubscriptionRegistryTests {
 		assertEquals("Expected no elements " + actual, 0, actual.size());
 	}
 
+	// SPR-12665
+
+	@Test
+	public void findSubscriptionsReturnsMapSafeToIterate() throws Exception {
+		this.registry.registerSubscription(subscribeMessage("sess1", "1", "/foo"));
+		this.registry.registerSubscription(subscribeMessage("sess2", "1", "/foo"));
+		MultiValueMap<String, String> subscriptions = this.registry.findSubscriptions(message("/foo"));
+		assertEquals(2, subscriptions.size());
+
+		Iterator iterator = subscriptions.entrySet().iterator();
+		iterator.next();
+
+		this.registry.registerSubscription(subscribeMessage("sess3", "1", "/foo"));
+
+		iterator.next();
+		// no ConcurrentModificationException
+	}
 
 	private Message<?> subscribeMessage(String sessionId, String subscriptionId, String destination) {
 		SimpMessageHeaderAccessor headers = SimpMessageHeaderAccessor.create(SimpMessageType.SUBSCRIBE);