From 3d18d5990422d8e92eb1e71cd3348f6131b8456c Mon Sep 17 00:00:00 2001
From: "Hiram R. Chirino" <chirino@apache.org>
Date: Mon, 3 Mar 2008 18:03:21 +0000
Subject: [PATCH] Protect the messagesWaitingForSpace variable against
 concurrent modification.

git-svn-id: https://svn.apache.org/repos/asf/activemq/trunk@633210 13f79535-47bb-0310-9956-ffa450edef68
---
 .../java/org/apache/activemq/broker/region/Queue.java    | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/activemq-core/src/main/java/org/apache/activemq/broker/region/Queue.java b/activemq-core/src/main/java/org/apache/activemq/broker/region/Queue.java
index 5b7df0d0c3..b3c6659587 100755
--- a/activemq-core/src/main/java/org/apache/activemq/broker/region/Queue.java
+++ b/activemq-core/src/main/java/org/apache/activemq/broker/region/Queue.java
@@ -885,9 +885,12 @@ public class Queue extends BaseDestination implements Task {
                 log.error("Failed to page in more queue messages ", e);
             }
         }
-        while (!messagesWaitingForSpace.isEmpty() && !memoryUsage.isFull()) {
-            Runnable op = messagesWaitingForSpace.removeFirst();
-            op.run();
+        
+        synchronized(messagesWaitingForSpace) {
+               while (!messagesWaitingForSpace.isEmpty() && !memoryUsage.isFull()) {
+                   Runnable op = messagesWaitingForSpace.removeFirst();
+                   op.run();
+               }
         }
         return false;
     }