From fd4e13634b2212d9821ef39025bdcaa5dc48241b Mon Sep 17 00:00:00 2001
From: Bosanac Dejan <dejanb@apache.org>
Date: Mon, 22 Nov 2010 11:34:39 +0000
Subject: [PATCH] https://issues.apache.org/activemq/browse/AMQ-2950 - prevent
 ConcurrentModificationException when removing the connection

git-svn-id: https://svn.apache.org/repos/asf/activemq/trunk@1037675 13f79535-47bb-0310-9956-ffa450edef68
---
 .../activemq/broker/TransactionBroker.java    | 33 +++++++++++--------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/activemq-core/src/main/java/org/apache/activemq/broker/TransactionBroker.java b/activemq-core/src/main/java/org/apache/activemq/broker/TransactionBroker.java
index 26b7f54408..d2c1bf5da1 100755
--- a/activemq-core/src/main/java/org/apache/activemq/broker/TransactionBroker.java
+++ b/activemq-core/src/main/java/org/apache/activemq/broker/TransactionBroker.java
@@ -16,11 +16,8 @@
  */
 package org.apache.activemq.broker;
 
-import java.util.ArrayList;
-import java.util.Iterator;
-import java.util.LinkedHashMap;
-import java.util.List;
-import java.util.Map;
+
+import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
 
 import javax.jms.JMSException;
@@ -252,15 +249,25 @@ public class TransactionBroker extends BrokerFilter {
             iter.remove();
         }
 
+        synchronized (xaTransactions) {
+            // first find all txs that belongs to the connection
+            ArrayList<XATransaction> txs = new ArrayList<XATransaction>();
+            for (XATransaction tx : xaTransactions.values()) {
+                if (tx.getConnectionId().equals(info.getConnectionId()) && !tx.isPrepared()) {
+                    txs.add(tx);
+                }
+            }
+
+            // then remove them
+            // two steps needed to avoid ConcurrentModificationException, from removeTransaction()
+            for (XATransaction tx : txs) {
+                try {
+                    tx.rollback();
+                } catch (Exception e) {
+                    LOG.warn("ERROR Rolling back disconnected client's xa transactions: ", e);
+                }
+            }
 
-        for (XATransaction tx : xaTransactions.values()) {
-           try {
-             if (tx.getConnectionId().equals(info.getConnectionId()) && !tx.isPrepared()) {
-                tx.rollback();
-             }
-           } catch (Exception e) {
-               LOG.warn("ERROR Rolling back disconnected client's xa transactions: ", e);
-           }
         }
         next.removeConnection(context, info, error);
     }