QPID-3979: [Java Broker] Conflation queues: guard NPE identified by review feedback.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk/qpid@1336295 13f79535-47bb-0310-9956-ffa450edef68

1 files changed, 12 insertions, 5 deletions

diff --git a/java/broker/src/main/java/org/apache/qpid/server/queue/ConflationQueueList.java b/java/broker/src/main/java/org/apache/qpid/server/queue/ConflationQueueList.java
index d8467d2d8e..0b95b9cc47 100644
--- a/java/broker/src/main/java/org/apache/qpid/server/queue/ConflationQueueList.java
+++ b/java/broker/src/main/java/org/apache/qpid/server/queue/ConflationQueueList.java
@@ -72,22 +72,29 @@ public class ConflationQueueList extends SimpleQueueEntryList
             do
             {
                 latestValueReference = getOrPutIfAbsent(keyValue, referenceToEntry);
-                oldEntry = latestValueReference.get();
+                oldEntry = latestValueReference == null ? null : latestValueReference.get();
             }
-            while(oldEntry.compareTo(entry) < 0
+            while(oldEntry != null
+                    && oldEntry.compareTo(entry) < 0
                     && oldEntry != getHead()
                     && !latestValueReference.compareAndSet(oldEntry, entry));
 
-            if(oldEntry.compareTo(entry) < 0)
+            if (oldEntry == null)
             {
-                // We replaced some other entry to become the newest value
-                discardEntry(oldEntry);
+                // Unlikely: A newer entry came along and was consumed (and entry removed from map)
+                // during our processing of getOrPutIfAbsent().  In this case we know our entry has been superseded.
+                discardEntry(entry);
             }
             else if (oldEntry.compareTo(entry) > 0)
             {
                 // A newer entry came along
                 discardEntry(entry);
             }
+            else if (oldEntry.compareTo(entry) < 0)
+            {
+                // We replaced some other entry to become the newest value
+                discardEntry(oldEntry);
+            }
 
             entry.setLatestValueReference(latestValueReference);
         }