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/*
*
* 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 java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import org.apache.qpid.server.store.StorableMessageMetaData;
import org.apache.qpid.server.store.StoredMessage;
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.
*
*
* @throws org.apache.qpid.server.queue.MessageCleanupException when an attempt was made to remove the message from the message store and that
* failed
*/
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;
}
}
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