server/Queue/Queue.java

//---PACKAGE DECLARATION---
//package uk.ac.ukc.iscream.util;

//---IMPORTS---
import java.util.LinkedList;
import java.util.NoSuchElementException;
import java.util.Random;
//import uk.ac.ukc.iscream.util.*;

/**
 * A Queue class designed to operate in a multi-threaded environment, with
 * added support for multiple "consumer" threads. Also offers blocking on
 * the get() methods, which ensures the consumer waits until the queue
 * actually contains some elements.
 *
 * @author  $Author: tdb1 $
 * @version $Id: Queue.java,v 1.15 2001/03/01 01:18:09 tdb1 Exp $
 */
public class Queue {

//---FINAL ATTRIBUTES---

    /**
     * The current CVS revision of this class
     */
    public static final String REVISION = "$Revision: 1.15 $";
    
    /**
     * Pass to constructor to remove a RANDOM item from
     * the Queue upon reaching the maximum limit.
     */
    public static final int RANDOM = 0;
    
    /**
     * Pass to constructor to remove the FIRST item from
     * the Queue upon reaching the maximum limit.
     */
    public static final int FIRST = 1;
    
    /**
     * Pass to constructor to remove the LAST item from
     * the Queue upon reaching the maximum limit.
     */
    public static final int LAST = 2;
    
    /**
     * Pass to constructor to drop the new item upon reaching
     * the maximum Queue limit.
     */
    public static final int DROP = 3;
    
//---STATIC METHODS---

//---CONSTRUCTORS---  
    
    /**
     * Constructs a new Queue with a maximum size limit on
     * any individual queue. This should be used to stop
     * conditions where the Queue cannot be guaranteed to
     * be emptied as quick as it's filled.
     *
     * An algorithm will be used to remove data when new data
     * arrives. There may be choices of algorithms later on.
     *
     * @param maxSize the upper limit for a queue
     * @param removeAlgorithm the remove algorithm to use upon reaching the maxSize
     */
    public Queue(int maxSize, int removeAlgorithm) {
        _maxSize = maxSize;
        _removeAlgorithm = removeAlgorithm;
    }
    
    /**
     * Constructs a Queue with no maximum size.
     */
    public Queue() {
        _maxSize = -1;
    }

//---PUBLIC METHODS---
    
    /**
     * This method adds a given object to every queue. It will notify
     * any waiting consumers (on an empty queue) during this process.
     *
     * @param o An Object to be added to the queues.
     */
    public void add(Object o) {
        for(int i=0; i < _lists.size(); i++) {
            // skip over any gaps left in the list
            if(_lists.get(i) != null) {
                // get size before adding to the Queue
                int s = ((LinkedList) _lists.get(i)).size();
                // check whether we need to remove an item from the current Queue
                if(_maxSize!=-1 && s==_maxSize && _removeAlgorithm!=DROP) {
                    // we need to remove an item
                    removeQueueItem((LinkedList) _lists.get(i));
                }
                // check if we should add (not if Queue full, and using DROP algorithm)
                if(!(s==_maxSize && _removeAlgorithm==DROP)) {
                    // add the next item, ensuring we lock
                    synchronized(this) {
                        // LinkedList.add() does the same thing, but this ensures behaviour
                        ((LinkedList) _lists.get(i)).addLast(o);
                    }
                }
                // if the queue was empty before the add it is possible
                // that a consumer is waiting... so we notify them
                if (s == 0) {
                    synchronized(((LinkedList) _lists.get(i))) {
                        ((LinkedList) _lists.get(i)).notifyAll();
                    }
                }
            }
        }
        // we keep track of the total additions for the status() method
        _count++;
    }
    
    /**
     * This method returns an object from the front of a given queue.
     * It will block until data exists in the queue if required.
     *
     * @param The queue to retrieve data from.
     * @return The object from the front of the queue.
     * @throws InvalidQueueException if the queue does not exist.
     */
    public Object get(int queue) throws InvalidQueueException {
        // make sure queue exists
        if (queue >= _lists.size() || _lists.get(queue) == null) {
            throw new InvalidQueueException("Requested queue "+queue+" does not exist");
        }
        // block if the queue is empty
        if (((LinkedList) _lists.get(queue)).size() == 0) {
            synchronized(((LinkedList) _lists.get(queue))) {
                try { ((LinkedList) _lists.get(queue)).wait(); } catch(Exception e) {}
            }
        }
        // get an item, it should never be null due to the blocking above
        Object o = null;
        synchronized(this) {
            try {
                o = ((LinkedList) _lists.get(queue)).removeFirst();
            }
            catch (NoSuchElementException e) {
                // This should never happen !
            }
        }
        return o;
    }
    
    /**
     * This method releases a get() method that's currently
     * waiting on an empty queue. This was designed for
     * shutdown() type methods that may have problems closing
     * if the thread of control is waiting on a queue.
     *
     * @param queue the queue to release.
     */
    public void releaseQueue(int queue) {
        synchronized(((LinkedList) _lists.get(queue))) {
                ((LinkedList) _lists.get(queue)).notifyAll();
        }
    }

    /**
     * This method erases the contents of a given queue. This
     * method should be used with care. It can only empty one
     * internal queue, not all of them. This must be called
     * multiple times to empty all queues.
     *
     * @param queue the queue to empty.
     */
    public void clearQueue(int queue) {
        synchronized(this) {
            ((LinkedList) _lists.get(queue)).clear();
        }
    }
    
    /**
     * This method returns an XML textual status of the queues.
     * It is merely for observation, and would most likely be
     * used by a larger "monitoring" component. Information
     * returned includes the current size of each queue, and
     * the total items passed through.
     *
     * @return A String message containing status information in XML format
     */
    public String xmlStatus() {
        String status = "<queue ";
        for(int i=0; i < _lists.size(); i++) {
            // check for null entries
            if(_lists.get(i) != null) {
                status += "queue"+i+"=\""+((LinkedList) _lists.get(i)).size()+"\" ";
            }
            else {
                status += "queue"+i+"=\"[deleted]\" ";
            }
        }
        status += "total=\""+_count+"\"";
        if(_maxSize != -1) {
            status += " maxSize=\""+_maxSize+"\"";
        }
        status += "></queue>";
        return status;
    }
    
    /**
     * Returns the size of a given queue. A consumer can use
     * this to see how big their queue is at any given time.
     * they should use their queue number as the parameter.
     *
     * @param queue The queue number to query.
     * @return the current size of the queue.
     * @throws InvalidQueueException if the queue does not exist.
     */
    public int queueSize(int queue) throws InvalidQueueException {
        if (queue >= _lists.size() || _lists.get(queue) == null) {
            throw new InvalidQueueException("Requested queue "+queue+" does not exist");
        }
        return ((LinkedList) _lists.get(queue)).size();
    }
    
    /**
     * Returns the total numer of elements to have passed
     * through this queue (ie. a counter on the add method).
     *
     * @return the element-ometer.
     */
    public int elementCount() {
        return _count;
    }
    
    /**
     * This method assigns a queue to a consumer. The idea behind
     * this is to ensure that only 1 consumer can be associated with
     * a given queue, otherwise the whole "blocking" thing fails
     * miserably. Queues are created upon requested.
     *
     * It is IMPORTANT that removeQueue() is used when the queue is
     * no longer required.
     *
     * @return An integer to be passed to the get() method.
     */
    public int getQueue() {
        int pos = -1;
        for(int i=0; i < _lists.size(); i++) {
            if(_lists.get(i) == null) {
                // found a gap, re-use it
                pos = i;
                _lists.set(i, new LinkedList());
            }
        }
        if(pos == -1) {
            //we didn't find a gap, add at end
            pos = _lists.size();
            _lists.add(pos, new LinkedList());
        }
        return pos;
    }
    
    /**
     * This method sets a entry to null in the list. This ensures
     * that it will no longer be added to after it is no longer
     * required be a consumer.
     *
     * @param queue The integer identifier for the queue, given by getQueue().
     */
    public void removeQueue(int queue) {
        _lists.set(queue, null);
    }
    
    /**
     * Start a monitor on our own Queue. This will log XML
     * statistics about our Queue to a given Queue (could be
     * the one being monitored).
     *
     * @param interval The long interval, in milliseconds, at which to take samples
     * @param destQueue The queue to monitor to
     * @param name A name to identify this Queue with
     * @return whether we succeeded
     */
    public boolean startMonitor(long interval, Queue destQueue, String name) {
        if(_queueMon == null) {
            // start a monitor
            _queueMon = new QueueMonitor(this, destQueue, interval, name);
            _queueMon.start();
            return true;
        }
        else {
            // already have a monitor running
            return false;
        }
    }
    
    /**
     * Start a monitor on our own Queue. This will log XML
     * statistics about our Queue to this Queue.
     *
     * @param interval The long interval, in milliseconds, at which to take samples
     * @param name A name to identify this Queue with
     * @return whether we succeeded
     */
    public boolean startMonitor(long interval, String name) {
        return startMonitor(interval, this, name);
    }
    
    /**
     * Stop a monitor on our Queue if we have on running.
     *
     * @return whether we succeeded
     */
    public boolean stopMonitor() {
        if(_queueMon != null) {
            // stop a monitor
            _queueMon.shutdown();
            _queueMon = null;
            return true;
        }
        else {
            // no monitor running
            return false;
        }
    }
    
    /**
     * Overrides the {@link java.lang.Object#toString() Object.toString()}
     * method to provide clean logging (every class should have this).
     *
     * This uses the uk.ac.ukc.iscream.util.FormatName class
     * to format the toString()
     *
     * @return the name of this class and its CVS revision.
     */
    public String toString() {
        return FormatName.getName(
            _name,
            getClass().getName(),
            REVISION);
    }

//---PRIVATE METHODS---
    
    /**
     * This method removes an item from a Queue, using a method
     * requested at construction.
     *
     * @param list The LinkedList from which to remove an item.
     */
    private void removeQueueItem(LinkedList list) {
        // look at our algorithm
        // remove a random item from the list
        if(_removeAlgorithm==RANDOM) {
            // new Random, with a good seed
            Random rand = new Random(System.currentTimeMillis());
            int i = rand.nextInt(_maxSize);
            synchronized(this) {
                list.remove(i);
            }
        }
        // remove the first item from the list
        else if(_removeAlgorithm==FIRST) {
            synchronized(this) {
                list.removeFirst();
            }
        }
        // remove the last item from the list
        else if(_removeAlgorithm==LAST) {
            synchronized(this) {
                list.removeLast();
            }
        }
    }
    
//---ACCESSOR/MUTATOR METHODS---

//---ATTRIBUTES---
    
    /**
     * The LinkedLists of queues.
     */
    private LinkedList _lists = new LinkedList();
    
    /**
     * A counter so we know how many data items have been
     * passed through, for statistical purposes.
     */
    private int _count = 0;
    
    /**
     * A reference to our QueueMonitor, if we have one.
     */
    private QueueMonitor _queueMon = null;
    
    /**
     * The maximum size of any Queue.
     */
    private int _maxSize = -1;
    
    /**
     * The remove algorithm to use upon a Queue reaching
     * it's maximum size.
     */
    private int _removeAlgorithm = -1;
    
    /**
     * This is the friendly identifier of the
     * component this class is running in.
     * eg, a Filter may be called "filter1",
     * If this class does not have an owning
     * component,  a name from the configuration
     * can be placed here.  This name could also
     * be changed to null for utility classes.
     */
    private String _name = null;

//---STATIC ATTRIBUTES---

}
Revision:	1.9
Committed:	Thu Mar 1 03:04:28 2001 UTC (23 years, 8 months ago) by tdb
Branch:	MAIN
CVS Tags:	PROJECT_COMPLETION, HEAD
Changes since 1.8:	+112 -7 lines
Log Message:	Brought inline with main source tree.
#	User	Rev	Content
1	tdb	1.2	//---PACKAGE DECLARATION---
2	tdb	1.7	//package uk.ac.ukc.iscream.util;
3	tdb	1.2
4			//---IMPORTS---
5	tdb	1.1	import java.util.LinkedList;
6			import java.util.NoSuchElementException;
7	tdb	1.9	import java.util.Random;
8	tdb	1.7	//import uk.ac.ukc.iscream.util.*;
9	tdb	1.1
10	tdb	1.2	/**
11			* A Queue class designed to operate in a multi-threaded environment, with
12			* added support for multiple "consumer" threads. Also offers blocking on
13			* the get() methods, which ensures the consumer waits until the queue
14			* actually contains some elements.
15			*
16	tdb	1.3	* @author $Author: tdb1 $
17	tdb	1.9	* @version $Id: Queue.java,v 1.15 2001/03/01 01:18:09 tdb1 Exp $
18	tdb	1.2	*/
19	tdb	1.4	public class Queue {
20	tdb	1.2
21			//---FINAL ATTRIBUTES---
22
23			/**
24			* The current CVS revision of this class
25			*/
26	tdb	1.9	public static final String REVISION = "$Revision: 1.15 $";
27
28			/**
29			* Pass to constructor to remove a RANDOM item from
30			* the Queue upon reaching the maximum limit.
31			*/
32			public static final int RANDOM = 0;
33
34			/**
35			* Pass to constructor to remove the FIRST item from
36			* the Queue upon reaching the maximum limit.
37			*/
38			public static final int FIRST = 1;
39
40			/**
41			* Pass to constructor to remove the LAST item from
42			* the Queue upon reaching the maximum limit.
43			*/
44			public static final int LAST = 2;
45
46			/**
47			* Pass to constructor to drop the new item upon reaching
48			* the maximum Queue limit.
49			*/
50			public static final int DROP = 3;
51	tdb	1.2
52			//---STATIC METHODS---
53
54	tdb	1.3	//---CONSTRUCTORS---
55	tdb	1.9
56			/**
57			* Constructs a new Queue with a maximum size limit on
58			* any individual queue. This should be used to stop
59			* conditions where the Queue cannot be guaranteed to
60			* be emptied as quick as it's filled.
61			*
62			* An algorithm will be used to remove data when new data
63			* arrives. There may be choices of algorithms later on.
64			*
65			* @param maxSize the upper limit for a queue
66			* @param removeAlgorithm the remove algorithm to use upon reaching the maxSize
67			*/
68			public Queue(int maxSize, int removeAlgorithm) {
69			_maxSize = maxSize;
70			_removeAlgorithm = removeAlgorithm;
71			}
72
73			/**
74			* Constructs a Queue with no maximum size.
75			*/
76			public Queue() {
77			_maxSize = -1;
78			}
79	tdb	1.3
80	tdb	1.2	//---PUBLIC METHODS---
81
82			/**
83			* This method adds a given object to every queue. It will notify
84			* any waiting consumers (on an empty queue) during this process.
85			*
86			* @param o An Object to be added to the queues.
87			*/
88			public void add(Object o) {
89	tdb	1.3	for(int i=0; i < _lists.size(); i++) {
90			// skip over any gaps left in the list
91			if(_lists.get(i) != null) {
92	tdb	1.9	// get size before adding to the Queue
93	tdb	1.3	int s = ((LinkedList) _lists.get(i)).size();
94	tdb	1.9	// check whether we need to remove an item from the current Queue
95			if(_maxSize!=-1 && s==_maxSize && _removeAlgorithm!=DROP) {
96			// we need to remove an item
97			removeQueueItem((LinkedList) _lists.get(i));
98			}
99			// check if we should add (not if Queue full, and using DROP algorithm)
100			if(!(s==_maxSize && _removeAlgorithm==DROP)) {
101			// add the next item, ensuring we lock
102			synchronized(this) {
103			// LinkedList.add() does the same thing, but this ensures behaviour
104			((LinkedList) _lists.get(i)).addLast(o);
105			}
106	tdb	1.3	}
107			// if the queue was empty before the add it is possible
108			// that a consumer is waiting... so we notify them
109			if (s == 0) {
110			synchronized(((LinkedList) _lists.get(i))) {
111			((LinkedList) _lists.get(i)).notifyAll();
112			}
113	tdb	1.2	}
114			}
115	tdb	1.1	}
116	tdb	1.2	// we keep track of the total additions for the status() method
117	tdb	1.1	_count++;
118			}
119
120	tdb	1.2	/**
121			* This method returns an object from the front of a given queue.
122			* It will block until data exists in the queue if required.
123			*
124	tdb	1.6	* @param The queue to retrieve data from.
125	tdb	1.2	* @return The object from the front of the queue.
126	tdb	1.3	* @throws InvalidQueueException if the queue does not exist.
127	tdb	1.2	*/
128	tdb	1.3	public Object get(int queue) throws InvalidQueueException {
129			// make sure queue exists
130			if (queue >= _lists.size() \|\| _lists.get(queue) == null) {
131			throw new InvalidQueueException("Requested queue "+queue+" does not exist");
132			}
133	tdb	1.2	// block if the queue is empty
134	tdb	1.3	if (((LinkedList) _lists.get(queue)).size() == 0) {
135			synchronized(((LinkedList) _lists.get(queue))) {
136			try { ((LinkedList) _lists.get(queue)).wait(); } catch(Exception e) {}
137	tdb	1.2	}
138	tdb	1.1	}
139	tdb	1.2	// get an item, it should never be null due to the blocking above
140	tdb	1.1	Object o = null;
141	tdb	1.2	synchronized(this) {
142			try {
143	tdb	1.3	o = ((LinkedList) _lists.get(queue)).removeFirst();
144	tdb	1.2	}
145			catch (NoSuchElementException e) {
146			// This should never happen !
147			}
148	tdb	1.1	}
149			return o;
150			}
151	tdb	1.5
152			/**
153			* This method releases a get() method that's currently
154			* waiting on an empty queue. This was designed for
155			* shutdown() type methods that may have problems closing
156			* if the thread of control is waiting on a queue.
157			*
158	tdb	1.6	* @param queue the queue to release.
159	tdb	1.5	*/
160			public void releaseQueue(int queue) {
161			synchronized(((LinkedList) _lists.get(queue))) {
162			((LinkedList) _lists.get(queue)).notifyAll();
163			}
164			}
165	tdb	1.6
166			/**
167			* This method erases the contents of a given queue. This
168			* method should be used with care. It can only empty one
169			* internal queue, not all of them. This must be called
170			* multiple times to empty all queues.
171			*
172			* @param queue the queue to empty.
173			*/
174			public void clearQueue(int queue) {
175			synchronized(this) {
176			((LinkedList) _lists.get(queue)).clear();
177			}
178			}
179	tdb	1.5
180	tdb	1.2	/**
181	tdb	1.7	* This method returns an XML textual status of the queues.
182			* It is merely for observation, and would most likely be
183			* used by a larger "monitoring" component. Information
184			* returned includes the current size of each queue, and
185			* the total items passed through.
186	tdb	1.2	*
187	tdb	1.7	* @return A String message containing status information in XML format
188	tdb	1.2	*/
189	tdb	1.7	public String xmlStatus() {
190			String status = "<queue ";
191	tdb	1.3	for(int i=0; i < _lists.size(); i++) {
192			// check for null entries
193			if(_lists.get(i) != null) {
194	tdb	1.7	status += "queue"+i+"=\""+((LinkedList) _lists.get(i)).size()+"\" ";
195	tdb	1.3	}
196			else {
197	tdb	1.8	status += "queue"+i+"=\"[deleted]\" ";
198	tdb	1.3	}
199	tdb	1.2	}
200	tdb	1.9	status += "total=\""+_count+"\"";
201			if(_maxSize != -1) {
202			status += " maxSize=\""+_maxSize+"\"";
203			}
204			status += "></queue>";
205	tdb	1.1	return status;
206			}
207
208	tdb	1.2	/**
209	tdb	1.4	* Returns the size of a given queue. A consumer can use
210			* this to see how big their queue is at any given time.
211			* they should use their queue number as the parameter.
212			*
213			* @param queue The queue number to query.
214			* @return the current size of the queue.
215	tdb	1.6	* @throws InvalidQueueException if the queue does not exist.
216	tdb	1.4	*/
217			public int queueSize(int queue) throws InvalidQueueException {
218	tdb	1.5	if (queue >= _lists.size() \|\| _lists.get(queue) == null) {
219	tdb	1.4	throw new InvalidQueueException("Requested queue "+queue+" does not exist");
220			}
221	tdb	1.5	return ((LinkedList) _lists.get(queue)).size();
222	tdb	1.4	}
223
224			/**
225			* Returns the total numer of elements to have passed
226			* through this queue (ie. a counter on the add method).
227			*
228	tdb	1.6	* @return the element-ometer.
229	tdb	1.4	*/
230			public int elementCount() {
231	tdb	1.5	return _count;
232	tdb	1.4	}
233
234			/**
235	tdb	1.2	* This method assigns a queue to a consumer. The idea behind
236			* this is to ensure that only 1 consumer can be associated with
237			* a given queue, otherwise the whole "blocking" thing fails
238	tdb	1.3	* miserably. Queues are created upon requested.
239			*
240			* It is IMPORTANT that removeQueue() is used when the queue is
241			* no longer required.
242	tdb	1.2	*
243			* @return An integer to be passed to the get() method.
244			*/
245	tdb	1.3	public int getQueue() {
246			int pos = -1;
247			for(int i=0; i < _lists.size(); i++) {
248			if(_lists.get(i) == null) {
249			// found a gap, re-use it
250			pos = i;
251			_lists.set(i, new LinkedList());
252			}
253	tdb	1.2	}
254	tdb	1.3	if(pos == -1) {
255			//we didn't find a gap, add at end
256			pos = _lists.size();
257			_lists.add(pos, new LinkedList());
258	tdb	1.2	}
259	tdb	1.3	return pos;
260	tdb	1.2	}
261	tdb	1.3
262			/**
263			* This method sets a entry to null in the list. This ensures
264			* that it will no longer be added to after it is no longer
265			* required be a consumer.
266			*
267			* @param queue The integer identifier for the queue, given by getQueue().
268			*/
269			public void removeQueue(int queue) {
270			_lists.set(queue, null);
271			}
272
273	tdb	1.2	/**
274	tdb	1.7	* Start a monitor on our own Queue. This will log XML
275			* statistics about our Queue to a given Queue (could be
276			* the one being monitored).
277			*
278			* @param interval The long interval, in milliseconds, at which to take samples
279			* @param destQueue The queue to monitor to
280			* @param name A name to identify this Queue with
281			* @return whether we succeeded
282			*/
283			public boolean startMonitor(long interval, Queue destQueue, String name) {
284			if(_queueMon == null) {
285			// start a monitor
286			_queueMon = new QueueMonitor(this, destQueue, interval, name);
287			_queueMon.start();
288			return true;
289			}
290			else {
291			// already have a monitor running
292			return false;
293			}
294			}
295
296			/**
297			* Start a monitor on our own Queue. This will log XML
298			* statistics about our Queue to this Queue.
299			*
300			* @param interval The long interval, in milliseconds, at which to take samples
301			* @param name A name to identify this Queue with
302			* @return whether we succeeded
303			*/
304			public boolean startMonitor(long interval, String name) {
305			return startMonitor(interval, this, name);
306			}
307
308			/**
309			* Stop a monitor on our Queue if we have on running.
310			*
311			* @return whether we succeeded
312			*/
313			public boolean stopMonitor() {
314			if(_queueMon != null) {
315			// stop a monitor
316			_queueMon.shutdown();
317			_queueMon = null;
318			return true;
319			}
320			else {
321			// no monitor running
322			return false;
323			}
324			}
325
326			/**
327	tdb	1.2	* Overrides the {@link java.lang.Object#toString() Object.toString()}
328			* method to provide clean logging (every class should have this).
329			*
330			* This uses the uk.ac.ukc.iscream.util.FormatName class
331			* to format the toString()
332			*
333	tdb	1.6	* @return the name of this class and its CVS revision.
334	tdb	1.2	*/
335	tdb	1.4	public String toString() {
336	tdb	1.2	return FormatName.getName(
337			_name,
338			getClass().getName(),
339			REVISION);
340	tdb	1.4	}
341	tdb	1.2
342			//---PRIVATE METHODS---
343	tdb	1.9
344			/**
345			* This method removes an item from a Queue, using a method
346			* requested at construction.
347			*
348			* @param list The LinkedList from which to remove an item.
349			*/
350			private void removeQueueItem(LinkedList list) {
351			// look at our algorithm
352			// remove a random item from the list
353			if(_removeAlgorithm==RANDOM) {
354			// new Random, with a good seed
355			Random rand = new Random(System.currentTimeMillis());
356			int i = rand.nextInt(_maxSize);
357			synchronized(this) {
358			list.remove(i);
359			}
360			}
361			// remove the first item from the list
362			else if(_removeAlgorithm==FIRST) {
363			synchronized(this) {
364			list.removeFirst();
365			}
366			}
367			// remove the last item from the list
368			else if(_removeAlgorithm==LAST) {
369			synchronized(this) {
370			list.removeLast();
371			}
372			}
373			}
374
375	tdb	1.2	//---ACCESSOR/MUTATOR METHODS---
376
377			//---ATTRIBUTES---
378
379			/**
380	tdb	1.3	* The LinkedLists of queues.
381	tdb	1.2	*/
382	tdb	1.3	private LinkedList _lists = new LinkedList();
383	tdb	1.2
384			/**
385			* A counter so we know how many data items have been
386			* passed through, for statistical purposes.
387			*/
388			private int _count = 0;
389	tdb	1.7
390			/**
391			* A reference to our QueueMonitor, if we have one.
392			*/
393			private QueueMonitor _queueMon = null;
394	tdb	1.9
395			/**
396			* The maximum size of any Queue.
397			*/
398			private int _maxSize = -1;
399
400			/**
401			* The remove algorithm to use upon a Queue reaching
402			* it's maximum size.
403			*/
404			private int _removeAlgorithm = -1;
405	tdb	1.2
406			/**
407			* This is the friendly identifier of the
408			* component this class is running in.
409			* eg, a Filter may be called "filter1",
410			* If this class does not have an owning
411			* component, a name from the configuration
412			* can be placed here. This name could also
413			* be changed to null for utility classes.
414			*/
415	tdb	1.4	private String _name = null;
416	tdb	1.2
417			//---STATIC ATTRIBUTES---
418
419			}