Enforce cacheLimit in DefaultSubscriptionRegistry

When the cacheLimit is reached and there is an eviction from the
updateCache, the accessCache is now also updated.

This change also ensures that adding a destination to the cache is
protected with synchronization on the updateCache.

Issue: SPR-13555

spring-messaging/src/main/java/org/springframework/messaging/simp/broker/DefaultSubscriptionRegistry.java

@@ -177,31 +177,13 @@ public class DefaultSubscriptionRegistry extends AbstractSubscriptionRegistry {
 	}
 
 	@Override
-	protected MultiValueMap<String, String> findSubscriptionsInternal(String destination,
-			Message<?> message) {
-
-		LinkedMultiValueMap<String, String> result = this.destinationCache.getSubscriptions(destination);
-		if (result != null) {
-			return filterSubscriptions(result, message);
-		}
-		result = new LinkedMultiValueMap<String, String>();
-		for (SessionSubscriptionInfo info : this.subscriptionRegistry.getAllSubscriptions()) {
-			for (String destinationPattern : info.getDestinations()) {
-				if (this.pathMatcher.match(destinationPattern, destination)) {
-					for (Subscription subscription : info.getSubscriptions(destinationPattern)) {
-						result.add(info.sessionId, subscription.getId());
-					}
-				}
-			}
-		}
-		if (!result.isEmpty()) {
-			this.destinationCache.addSubscriptions(destination, result);
-		}
+	protected MultiValueMap<String, String> findSubscriptionsInternal(String destination, Message<?> message) {
+		MultiValueMap<String, String> result = this.destinationCache.getSubscriptions(destination, message);
 		return filterSubscriptions(result, message);
 	}
 
-	private MultiValueMap<String, String> filterSubscriptions(MultiValueMap<String, String> allMatches,
-			Message<?> message) {
+	private MultiValueMap<String, String> filterSubscriptions(
+			MultiValueMap<String, String> allMatches, Message<?> message) {
 
 		EvaluationContext context = null;
 		MultiValueMap<String, String> result = new LinkedMultiValueMap<String, String>(allMatches.size());
@@ -264,20 +246,38 @@ public class DefaultSubscriptionRegistry extends AbstractSubscriptionRegistry {
 				new LinkedHashMap<String, LinkedMultiValueMap<String, String>>(DEFAULT_CACHE_LIMIT, 0.75f, true) {
 					@Override
 					protected boolean removeEldestEntry(Map.Entry<String, LinkedMultiValueMap<String, String>> eldest) {
-						return size() > getCacheLimit();
+						if (size() > getCacheLimit()) {
+							accessCache.remove(eldest.getKey());
+							return true;
+						}
+						else {
+							return false;
+						}
 					}
 				};
 
 
-		public LinkedMultiValueMap<String, String> getSubscriptions(String destination) {
-			return this.accessCache.get(destination);
-		}
-
-		public void addSubscriptions(String destination, LinkedMultiValueMap<String, String> subscriptions) {
-			synchronized (this.updateCache) {
-				this.updateCache.put(destination, subscriptions.deepCopy());
-				this.accessCache.put(destination, subscriptions);
+		public LinkedMultiValueMap<String, String> getSubscriptions(String destination, Message<?> message) {
+			LinkedMultiValueMap<String, String> result = this.accessCache.get(destination);
+			if (result == null) {
+				synchronized (this.updateCache) {
+					result = new LinkedMultiValueMap<String, String>();
+					for (SessionSubscriptionInfo info : subscriptionRegistry.getAllSubscriptions()) {
+						for (String destinationPattern : info.getDestinations()) {
+							if (getPathMatcher().match(destinationPattern, destination)) {
+								for (Subscription subscription : info.getSubscriptions(destinationPattern)) {
+									result.add(info.sessionId, subscription.getId());
+								}
+							}
+						}
+					}
+					if (!result.isEmpty()) {
+						this.updateCache.put(destination, result.deepCopy());
+						this.accessCache.put(destination, result);
+					}
+				}
 			}
+			return result;
 		}
 
 		public void updateAfterNewSubscription(String destination, String sessionId, String subsId) {

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

@@ -21,9 +21,6 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
-import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicReference;
 
 import org.junit.Test;
 
@@ -31,11 +28,10 @@ import org.springframework.messaging.Message;
 import org.springframework.messaging.simp.SimpMessageHeaderAccessor;
 import org.springframework.messaging.simp.SimpMessageType;
 import org.springframework.messaging.support.MessageBuilder;
-import org.springframework.util.AntPathMatcher;
 import org.springframework.util.MultiValueMap;
-import org.springframework.util.PathMatcher;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
 
 /**
  * Test fixture for
@@ -402,37 +398,22 @@ public class DefaultSubscriptionRegistryTests {
 		// no ConcurrentModificationException
 	}
 
-	@Test  // SPR-13204
-	public void findSubscriptionsWithConcurrentUnregisterAllSubscriptions() throws Exception {
-		final CountDownLatch iterationPausedLatch = new CountDownLatch(1);
-		final CountDownLatch iterationResumeLatch = new CountDownLatch(1);
-		final CountDownLatch iterationDoneLatch = new CountDownLatch(1);
-
-		PathMatcher pathMatcher = new PausingPathMatcher(iterationPausedLatch, iterationResumeLatch);
-		this.registry.setPathMatcher(pathMatcher);
+	@Test // SPR-13555
+	public void cacheLimitExceeded() throws Exception {
+		this.registry.setCacheLimit(1);
 		this.registry.registerSubscription(subscribeMessage("sess1", "1", "/foo"));
-		this.registry.registerSubscription(subscribeMessage("sess2", "1", "/foo"));
-
-		AtomicReference<MultiValueMap<String, String>> subscriptions = new AtomicReference<>();
-		new Thread(() -> {
-			subscriptions.set(registry.findSubscriptions(createMessage("/foo")));
-			iterationDoneLatch.countDown();
-		}).start();
+		this.registry.registerSubscription(subscribeMessage("sess1", "2", "/bar"));
 
-		assertTrue(iterationPausedLatch.await(10, TimeUnit.SECONDS));
+		assertEquals(1, this.registry.findSubscriptions(createMessage("/foo")).size());
+		assertEquals(1, this.registry.findSubscriptions(createMessage("/bar")).size());
 
-		this.registry.unregisterAllSubscriptions("sess1");
-		this.registry.unregisterAllSubscriptions("sess2");
-
-		iterationResumeLatch.countDown();
-		assertTrue(iterationDoneLatch.await(10, TimeUnit.SECONDS));
+		this.registry.registerSubscription(subscribeMessage("sess2", "1", "/foo"));
+		this.registry.registerSubscription(subscribeMessage("sess2", "2", "/bar"));
 
-		MultiValueMap<String, String> result = subscriptions.get();
-		assertNotNull(result);
-		assertEquals(0, result.size());
+		assertEquals(2, this.registry.findSubscriptions(createMessage("/foo")).size());
+		assertEquals(2, this.registry.findSubscriptions(createMessage("/bar")).size());
 	}
 
-
 	private Message<?> createMessage(String destination) {
 		SimpMessageHeaderAccessor accessor = SimpMessageHeaderAccessor.create();
 		accessor.setDestination(destination);
@@ -468,35 +449,4 @@ public class DefaultSubscriptionRegistryTests {
 		return list;
 	}
 
-
-	/**
-	 * An extension of AntPathMatcher with a pair of CountDownLatches to pause
-	 * while matching, allowing another thread to something, and resume when the
-	 * other thread signals it's okay to do so.
-	 */
-	private static class PausingPathMatcher extends AntPathMatcher {
-
-		private final CountDownLatch iterationPausedLatch;
-
-		private final CountDownLatch iterationResumeLatch;
-
-		public PausingPathMatcher(CountDownLatch iterationPausedLatch, CountDownLatch iterationResumeLatch) {
-			this.iterationPausedLatch = iterationPausedLatch;
-			this.iterationResumeLatch = iterationResumeLatch;
-		}
-
-		@Override
-		public boolean match(String pattern, String path) {
-			try {
-				this.iterationPausedLatch.countDown();
-				assertTrue(this.iterationResumeLatch.await(10, TimeUnit.SECONDS));
-				return super.match(pattern, path);
-			}
-			catch (InterruptedException ex) {
-				ex.printStackTrace();
-				return false;
-			}
-		}
-	}
-
 }