1 files changed, 111 insertions, 0 deletions
diff --git a/qpid/java/broker-core/src/main/java/org/apache/qpid/server/message/AbstractServerMessageImpl.java b/qpid/java/broker-core/src/main/java/org/apache/qpid/server/message/AbstractServerMessageImpl.java
new file mode 100644
index 0000000000..8311dbd5ff
--- /dev/null
+++ b/qpid/java/broker-core/src/main/java/org/apache/qpid/server/message/AbstractServerMessageImpl.java
@@ -0,0 +1,111 @@
+/*
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ *
+ */
+package org.apache.qpid.server.message;
+
+import org.apache.qpid.server.store.StorableMessageMetaData;
+import org.apache.qpid.server.store.StoredMessage;
+
+import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
+
+public abstract class AbstractServerMessageImpl<T extends StorableMessageMetaData> implements ServerMessage<T>
+{
+
+    private static final AtomicIntegerFieldUpdater<AbstractServerMessageImpl> _refCountUpdater =
+            AtomicIntegerFieldUpdater.newUpdater(AbstractServerMessageImpl.class, "_referenceCount");
+
+    private volatile int _referenceCount = 0;
+    private final StoredMessage<T> _handle;
+
+    public AbstractServerMessageImpl(StoredMessage<T> handle)
+    {
+        _handle = handle;
+    }
+
+    public StoredMessage<T> getStoredMessage()
+    {
+        return _handle;
+    }
+
+    public boolean incrementReference()
+    {
+        return incrementReference(1);
+    }
+
+    public boolean incrementReference(int count)
+    {
+        if(_refCountUpdater.addAndGet(this, count) <= 0)
+        {
+            _refCountUpdater.addAndGet(this, -count);
+            return false;
+        }
+        else
+        {
+            return true;
+        }
+    }
+
+    /**
+     * Threadsafe. This will decrement the reference count and when it reaches zero will remove the message from the
+     * message store.
+     *
+     */
+    public void decrementReference()
+    {
+        int count = _refCountUpdater.decrementAndGet(this);
+
+        // note that the operation of decrementing the reference count and then removing the message does not
+        // have to be atomic since the ref count starts at 1 and the exchange itself decrements that after
+        // the message has been passed to all queues. i.e. we are
+        // not relying on the all the increments having taken place before the delivery manager decrements.
+        if (count == 0)
+        {
+            // set the reference count way below 0 so that we can detect that the message has been deleted
+            // this is to guard against the message being spontaneously recreated (from the mgmt console)
+            // by copying from other queues at the same time as it is being removed.
+            _refCountUpdater.set(this,Integer.MIN_VALUE/2);
+
+            // must check if the handle is null since there may be cases where we decide to throw away a message
+            // and the handle has not yet been constructed
+            if (_handle != null)
+            {
+                _handle.remove();
+            }
+        }
+        else
+        {
+            if (count < 0)
+            {
+                throw new RuntimeException("Reference count for message id " + debugIdentity()
+                                                  + " has gone below 0.");
+            }
+        }
+    }
+
+    public String debugIdentity()
+    {
+        return "(HC:" + System.identityHashCode(this) + " ID:" + getMessageNumber() + " Ref:" + getReferenceCount() + ")";
+    }
+
+    protected int getReferenceCount()
+    {
+        return _referenceCount;
+    }
+}