DefaultQueue not really threadsafe?

[Peter Royal]

I've been using the DefaultQueue from Excalibur 4.1 in a small pipeline-based 
project here. Although the javadocs state that its thread safe, I think 
there's a bug somewhere. Check out these numbers:

Default queue:

Statistics:
        Source: [read: 21196]
        Connector: [read: 4868, write: 4868]
        Destination: [write: 3871]

Statistics:
        Source: [read: 21196]
        Connector: [read: 4868, write: 4867]
        Destination: [write: 3870]

Statistics:
        Source: [read: 21196]
        Connector: [read: 4868, write: 4868]
        Destination: [write: 2846]

Statistics:
        Source: [read: 21196]
        Connector: [read: 5062, write: 5062]
        Destination: [write: 3040]

Statistics:
        Source: [read: 21196]
        Connector: [read: 9159, write: 9159]
        Destination: [write: 5088]

Statistics:
        Source: [read: 21196]
        Connector: [read: 13061, write: 13061]
        Destination: [write: 8990]

LinkedListQueue (attached):

Statistics:
        Source: [read: 21196]
        Connector: [read: 21196, write: 21195]
        Destination: [write: 21195]

The off-by-one between the read/write in the connector is due to an element 
that doesn't pass it. That element doesn't make it to the connector each time!

My setup is that I have 3 threads going, with a queue between each (2 
queues). There is a sizeable number of elements being dropped in each stage. 

The LinkedListQueue is definitly much slower, ~6min versus ~1m for the 
DefaultQueue.

I'm curious as to other's experiences with the DefaultQueue in a threaded 
environment.
-pete

-- 
peter royal -> [EMAIL PROTECTED]

package com.pace2020.edi.util;

import java.util.Stack;
import java.util.LinkedList;
import java.util.Collections;
import java.util.List;
import java.util.NoSuchElementException;

import org.apache.avalon.excalibur.event.Queue;
import org.apache.avalon.excalibur.event.QueueElement;
import org.apache.avalon.excalibur.event.SourceException;
import org.apache.avalon.excalibur.event.PreparedEnqueue;
import org.apache.avalon.excalibur.event.AbstractQueue;

/**
 * @author Peter Royal
 * @version VSS $Revision: $ $Date: $
 */
public class LinkedListQueue extends AbstractQueue
{
    private LinkedList list = new LinkedList();

    public void enqueue(QueueElement element)
      throws SourceException
    {
        synchronized (this) {
            this.list.add(element);
        }
    }

    public QueueElement dequeue()
    {
        synchronized (this) {
            try {
                return (QueueElement) this.list.removeFirst();
            } catch (NoSuchElementException e) {
                return null;
            }
        }
    }

    public void enqueue(QueueElement[] elements)
      throws SourceException
    {
        throw new UnsupportedOperationException();
    }

    public QueueElement[] dequeueAll()
    {
        throw new UnsupportedOperationException();
    }

    public boolean tryEnqueue(QueueElement element)
    {
        throw new UnsupportedOperationException();
    }

    public QueueElement[] dequeue(int num)
    {
        throw new UnsupportedOperationException();
    }

    public PreparedEnqueue prepareEnqueue(QueueElement[] elements)
      throws SourceException
    {
        throw new UnsupportedOperationException();
    }

    public int size()
    {
        synchronized(this) {
            return this.list.size();
        }
    }
}

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