If multiple concurrent threads were creating vm://localhost connection, it was possible multiple "localhost" broker would be started.

git-svn-id: https://svn.apache.org/repos/asf/incubator/activemq/trunk@388082 13f79535-47bb-0310-9956-ffa450edef68

activemq-core/src/main/java/org/apache/activemq/broker/BrokerRegistry.java

@@ -16,7 +16,7 @@
  */
 package org.apache.activemq.broker;
 
-import edu.emory.mathcs.backport.java.util.concurrent.ConcurrentHashMap;
+import java.util.HashMap;
 
 /**
  * 
@@ -30,21 +30,29 @@ public class BrokerRegistry {
         return instance;
     }
 
-    ConcurrentHashMap brokers = new ConcurrentHashMap();
+    private final Object mutex = new Object();
-    
+    private final HashMap brokers = new HashMap();
-    private BrokerRegistry() {        
-    }
     
     public BrokerService lookup(String brokerName) {
+        synchronized(mutex) {
             return (BrokerService)brokers.get(brokerName);
         }
+    }
     
     public void bind(String brokerName, BrokerService broker) {
+        synchronized(mutex) {
             brokers.put(brokerName, broker);
         }
+    }
     
     public void unbind(String brokerName) {
+        synchronized(mutex) {
             brokers.remove(brokerName);
         }
+    }
+
+    public Object getRegistryMutext() {
+        return mutex;
+    }
 
 }

activemq-core/src/main/java/org/apache/activemq/transport/vm/VMTransportFactory.java

@@ -86,7 +86,12 @@ public class VMTransportFactory extends TransportFactory{
         VMTransportServer server=(VMTransportServer) servers.get(host);
         // validate the broker is still active
         if(!validateBroker(host)||server==null){
-            BrokerService broker=BrokerRegistry.getInstance().lookup(host);
+            BrokerService broker=null;
+            // Synchronize on the registry so that multiple concurrent threads 
+            // doing this do not think that the broker has not been created and cause multiple
+            // brokers to be started.
+            synchronized( BrokerRegistry.getInstance().getRegistryMutext() ) {
+                broker=BrokerRegistry.getInstance().lookup(host);
                 if(broker==null){
                     try{
                         if(brokerFactoryHandler!=null){
@@ -100,6 +105,7 @@ public class VMTransportFactory extends TransportFactory{
                     }
                     brokers.put(host,broker);
                 }
+                
                 server=(VMTransportServer) servers.get(host);
                 if(server==null){
                     server=(VMTransportServer) bind(location,true);
@@ -108,7 +114,10 @@ public class VMTransportFactory extends TransportFactory{
                     connector.start();
                     connectors.put(host,connector);
                 }
-        }else{}
+                
+            }
+        }
+        
         VMTransport vmtransport=server.connect();
         IntrospectionSupport.setProperties(vmtransport,options);
         Transport transport=vmtransport;