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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.queue;
import org.apache.qpid.server.message.ServerMessage;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
public class SimpleQueueEntryList implements QueueEntryList<SimpleQueueEntryImpl>
{
private final SimpleQueueEntryImpl _head;
private volatile SimpleQueueEntryImpl _tail;
static final AtomicReferenceFieldUpdater<SimpleQueueEntryList, SimpleQueueEntryImpl>
_tailUpdater =
AtomicReferenceFieldUpdater.newUpdater
(SimpleQueueEntryList.class, SimpleQueueEntryImpl.class, "_tail");
private final AMQQueue _queue;
static final AtomicReferenceFieldUpdater<SimpleQueueEntryImpl, SimpleQueueEntryImpl>
_nextUpdater = SimpleQueueEntryImpl._nextUpdater;
private AtomicLong _scavenges = new AtomicLong(0L);
private final long _scavengeCount = Integer.getInteger("qpid.queue.scavenge_count", 50);
private final AtomicReference<SimpleQueueEntryImpl> _unscavengedHWM = new AtomicReference<SimpleQueueEntryImpl>();
public SimpleQueueEntryList(AMQQueue queue)
{
_queue = queue;
_head = new SimpleQueueEntryImpl(this);
_tail = _head;
}
void scavenge()
{
SimpleQueueEntryImpl hwm = _unscavengedHWM.getAndSet(null);
SimpleQueueEntryImpl next = _head.getNextValidEntry();
if(hwm != null)
{
while (next != null && hwm.compareTo(next)>0)
{
next = next.getNextValidEntry();
}
}
}
public AMQQueue getQueue()
{
return _queue;
}
public SimpleQueueEntryImpl add(ServerMessage message)
{
SimpleQueueEntryImpl node = createQueueEntry(message);
for (;;)
{
SimpleQueueEntryImpl tail = _tail;
SimpleQueueEntryImpl next = tail.getNextNode();
if (tail == _tail)
{
if (next == null)
{
node.setEntryId(tail.getEntryId()+1);
if (_nextUpdater.compareAndSet(tail, null, node))
{
_tailUpdater.compareAndSet(this, tail, node);
return node;
}
}
else
{
_tailUpdater.compareAndSet(this,tail, next);
}
}
}
}
protected SimpleQueueEntryImpl createQueueEntry(ServerMessage message)
{
return new SimpleQueueEntryImpl(this, message);
}
public SimpleQueueEntryImpl next(SimpleQueueEntryImpl node)
{
return node.getNextValidEntry();
}
public static class QueueEntryIteratorImpl implements QueueEntryIterator<SimpleQueueEntryImpl>
{
private SimpleQueueEntryImpl _lastNode;
QueueEntryIteratorImpl(SimpleQueueEntryImpl startNode)
{
_lastNode = startNode;
}
public boolean atTail()
{
return _lastNode.getNextValidEntry() == null;
}
public SimpleQueueEntryImpl getNode()
{
return _lastNode;
}
public boolean advance()
{
SimpleQueueEntryImpl nextValidNode = _lastNode.getNextValidEntry();
if(nextValidNode != null)
{
_lastNode = nextValidNode;
}
return nextValidNode != null;
}
}
public QueueEntryIteratorImpl iterator()
{
return new QueueEntryIteratorImpl(_head);
}
public SimpleQueueEntryImpl getHead()
{
return _head;
}
public void entryDeleted(SimpleQueueEntryImpl queueEntry)
{
SimpleQueueEntryImpl next = _head.getNextNode();
SimpleQueueEntryImpl newNext = _head.getNextValidEntry();
// the head of the queue has not been deleted, hence the deletion must have been mid queue.
if (next == newNext)
{
SimpleQueueEntryImpl unscavengedHWM = _unscavengedHWM.get();
while(unscavengedHWM == null || unscavengedHWM.compareTo(queueEntry)<0)
{
_unscavengedHWM.compareAndSet(unscavengedHWM, queueEntry);
unscavengedHWM = _unscavengedHWM.get();
}
if (_scavenges.incrementAndGet() > _scavengeCount)
{
_scavenges.set(0L);
scavenge();
}
}
else
{
SimpleQueueEntryImpl unscavengedHWM = _unscavengedHWM.get();
if(unscavengedHWM != null && (next == null || unscavengedHWM.compareTo(next) < 0))
{
_unscavengedHWM.compareAndSet(unscavengedHWM, null);
}
}
}
public int getPriorities()
{
return 0;
}
static class Factory implements QueueEntryListFactory
{
public SimpleQueueEntryList createQueueEntryList(AMQQueue queue)
{
return new SimpleQueueEntryList(queue);
}
}
}
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