From 61fef743e8be3e0e4df21a233bf2d738a080c2af Mon Sep 17 00:00:00 2001
From: "Hiram R. Chirino" <chirino@apache.org>
Date: Thu, 23 Mar 2006 07:24:28 +0000
Subject: [PATCH] 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/broker/BrokerRegistry.java       | 26 ++++++----
 .../transport/vm/VMTransportFactory.java      | 49 +++++++++++--------
 2 files changed, 46 insertions(+), 29 deletions(-)

diff --git a/activemq-core/src/main/java/org/apache/activemq/broker/BrokerRegistry.java b/activemq-core/src/main/java/org/apache/activemq/broker/BrokerRegistry.java
index 9a671449a3..65d1df117f 100755
--- a/activemq-core/src/main/java/org/apache/activemq/broker/BrokerRegistry.java
+++ b/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;
 
 /**
  * 
@@ -29,22 +29,30 @@ public class BrokerRegistry {
     public static BrokerRegistry getInstance() {
         return instance;
     }
-    
-    ConcurrentHashMap brokers = new ConcurrentHashMap();
-    
-    private BrokerRegistry() {        
-    }
 
+    private final Object mutex = new Object();
+    private final HashMap brokers = new HashMap();
+    
     public BrokerService lookup(String brokerName) {
-        return (BrokerService)brokers.get(brokerName);
+        synchronized(mutex) {
+            return (BrokerService)brokers.get(brokerName);
+        }
     }
     
     public void bind(String brokerName, BrokerService broker) {
-        brokers.put(brokerName, broker);
+        synchronized(mutex) {
+            brokers.put(brokerName, broker);
+        }
     }
     
     public void unbind(String brokerName) {
-        brokers.remove(brokerName);
+        synchronized(mutex) {
+            brokers.remove(brokerName);
+        }
+    }
+
+    public Object getRegistryMutext() {
+        return mutex;
     }
 
 }
diff --git a/activemq-core/src/main/java/org/apache/activemq/transport/vm/VMTransportFactory.java b/activemq-core/src/main/java/org/apache/activemq/transport/vm/VMTransportFactory.java
index ced1fcf82c..f267ffa4c3 100755
--- a/activemq-core/src/main/java/org/apache/activemq/transport/vm/VMTransportFactory.java
+++ b/activemq-core/src/main/java/org/apache/activemq/transport/vm/VMTransportFactory.java
@@ -86,29 +86,38 @@ 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);
-            if(broker==null){
-                try{
-                    if(brokerFactoryHandler!=null){
-                        broker=brokerFactoryHandler.createBroker(brokerURI);
-                    }else{
-                        broker=BrokerFactory.createBroker(brokerURI);
+            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){
+                            broker=brokerFactoryHandler.createBroker(brokerURI);
+                        }else{
+                            broker=BrokerFactory.createBroker(brokerURI);
+                        }
+                        broker.start();
+                    }catch(URISyntaxException e){
+                        throw IOExceptionSupport.create(e);
                     }
-                    broker.start();
-                }catch(URISyntaxException e){
-                    throw IOExceptionSupport.create(e);
+                    brokers.put(host,broker);
                 }
-                brokers.put(host,broker);
+                
+                server=(VMTransportServer) servers.get(host);
+                if(server==null){
+                    server=(VMTransportServer) bind(location,true);
+                    TransportConnector connector=new TransportConnector(broker.getBroker(),server);
+                    connector.setTaskRunnerFactory( broker.getTaskRunnerFactory() );
+                    connector.start();
+                    connectors.put(host,connector);
+                }
+                
             }
-            server=(VMTransportServer) servers.get(host);
-            if(server==null){
-                server=(VMTransportServer) bind(location,true);
-                TransportConnector connector=new TransportConnector(broker.getBroker(),server);
-                connector.setTaskRunnerFactory( broker.getTaskRunnerFactory() );
-                connector.start();
-                connectors.put(host,connector);
-            }
-        }else{}
+        }
+        
         VMTransport vmtransport=server.connect();
         IntrospectionSupport.setProperties(vmtransport,options);
         Transport transport=vmtransport;