cms/util/Queue.java

/* 
 * i-scream central monitoring system
 * http://www.i-scream.org
 * Copyright (C) 2000-2002 i-scream
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

//---PACKAGE DECLARATION---
package uk.org.iscream.cms.util;

//---IMPORTS---
import java.util.LinkedList;
import java.util.NoSuchElementException;
import java.util.Random;
//import uk.org.iscream.cms.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: tdb $
 * @version $Id: Queue.java,v 1.26 2003/02/05 14:27:59 tdb Exp $
 */
public class Queue {

//---FINAL ATTRIBUTES---

    /**
     * The current CVS revision of this class
     */
    public static final String REVISION = "$Revision: 1.26 $";
    
    /**
     * 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;
    
    /**
     * To allow opposite lookups.
     */
    public static final String[] algorithms = {"RANDOM", "FIRST", "LAST", "DROP"};
    
//---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) {
                synchronized(((LinkedList) _lists.get(i))) {
                    // 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
                        //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
        synchronized(((LinkedList) _lists.get(queue))) {
            if (((LinkedList) _lists.get(queue)).size() == 0) {
                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. This is essentially 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 synchronized 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 synchronized 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.org.iscream.cms.server.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:	1.27
Committed:	Sun Aug 1 10:41:08 2004 UTC (19 years, 8 months ago) by tdb
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.26:	+3 -3 lines
Log Message:	Catch a lot of old URL's and update them. Also remove a couple of old files that aren't used.
#	Content
1	/*
2	* i-scream central monitoring system
3	* http://www.i-scream.org
4	* Copyright (C) 2000-2002 i-scream
5	*
6	* This program is free software; you can redistribute it and/or
7	* modify it under the terms of the GNU General Public License
8	* as published by the Free Software Foundation; either version 2
9	* of the License, or (at your option) any later version.
10	*
11	* This program is distributed in the hope that it will be useful,
12	* but WITHOUT ANY WARRANTY; without even the implied warranty of
13	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14	* GNU General Public License for more details.
15	*
16	* You should have received a copy of the GNU General Public License
17	* along with this program; if not, write to the Free Software
18	* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
19	*/
20
21	//---PACKAGE DECLARATION---
22	package uk.org.iscream.cms.util;
23
24	//---IMPORTS---
25	import java.util.LinkedList;
26	import java.util.NoSuchElementException;
27	import java.util.Random;
28	//import uk.org.iscream.cms.util.*;
29
30	/**
31	* A Queue class designed to operate in a multi-threaded environment, with
32	* added support for multiple "consumer" threads. Also offers blocking on
33	* the get() methods, which ensures the consumer waits until the queue
34	* actually contains some elements.
35	*
36	* @author $Author: tdb $
37	* @version $Id: Queue.java,v 1.26 2003/02/05 14:27:59 tdb Exp $
38	*/
39	public class Queue {
40
41	//---FINAL ATTRIBUTES---
42
43	/**
44	* The current CVS revision of this class
45	*/
46	public static final String REVISION = "$Revision: 1.26 $";
47
48	/**
49	* Pass to constructor to remove a RANDOM item from
50	* the Queue upon reaching the maximum limit.
51	*/
52	public static final int RANDOM = 0;
53
54	/**
55	* Pass to constructor to remove the FIRST item from
56	* the Queue upon reaching the maximum limit.
57	*/
58	public static final int FIRST = 1;
59
60	/**
61	* Pass to constructor to remove the LAST item from
62	* the Queue upon reaching the maximum limit.
63	*/
64	public static final int LAST = 2;
65
66	/**
67	* Pass to constructor to drop the new item upon reaching
68	* the maximum Queue limit.
69	*/
70	public static final int DROP = 3;
71
72	/**
73	* To allow opposite lookups.
74	*/
75	public static final String[] algorithms = {"RANDOM", "FIRST", "LAST", "DROP"};
76
77	//---STATIC METHODS---
78
79	//---CONSTRUCTORS---
80
81	/**
82	* Constructs a new Queue with a maximum size limit on
83	* any individual queue. This should be used to stop
84	* conditions where the Queue cannot be guaranteed to
85	* be emptied as quick as it's filled.
86	*
87	* An algorithm will be used to remove data when new data
88	* arrives. There may be choices of algorithms later on.
89	*
90	* @param maxSize the upper limit for a queue
91	* @param removeAlgorithm the remove algorithm to use upon reaching the maxSize
92	*/
93	public Queue(int maxSize, int removeAlgorithm) {
94	_maxSize = maxSize;
95	_removeAlgorithm = removeAlgorithm;
96	}
97
98	/**
99	* Constructs a Queue with no maximum size.
100	*/
101	public Queue() {
102	_maxSize = -1;
103	}
104
105	//---PUBLIC METHODS---
106
107	/**
108	* This method adds a given object to every queue. It will notify
109	* any waiting consumers (on an empty queue) during this process.
110	*
111	* @param o An Object to be added to the queues.
112	*/
113	public void add(Object o) {
114	for(int i=0; i < _lists.size(); i++) {
115	// skip over any gaps left in the list
116	if(_lists.get(i) != null) {
117	synchronized(((LinkedList) _lists.get(i))) {
118	// get size before adding to the Queue
119	int s = ((LinkedList) _lists.get(i)).size();
120	// check whether we need to remove an item from the current Queue
121	if(_maxSize!=-1 && s>=_maxSize && _removeAlgorithm!=DROP) {
122	// we need to remove an item
123	removeQueueItem((LinkedList) _lists.get(i));
124	}
125	// check if we should add (not if Queue full, and using DROP algorithm)
126	if(!(s>=_maxSize && _removeAlgorithm==DROP)) {
127	// add the next item, ensuring we lock
128	synchronized(this) {
129	// LinkedList.add() does the same thing, but this ensures behaviour
130	((LinkedList) _lists.get(i)).addLast(o);
131	}
132	// if the queue was empty before the add it is possible
133	// that a consumer is waiting... so we notify them
134	//synchronized(((LinkedList) _lists.get(i))) {
135	((LinkedList) _lists.get(i)).notifyAll();
136	//}
137	}
138	}
139	}
140	}
141	// we keep track of the total additions for the status() method
142	_count++;
143	}
144
145	/**
146	* This method returns an object from the front of a given queue.
147	* It will block until data exists in the queue if required.
148	*
149	* @param The queue to retrieve data from.
150	* @return The object from the front of the queue.
151	* @throws InvalidQueueException if the queue does not exist.
152	*/
153	public Object get(int queue) throws InvalidQueueException {
154	// make sure queue exists
155	if (queue >= _lists.size() \|\| _lists.get(queue) == null) {
156	throw new InvalidQueueException("Requested queue "+queue+" does not exist");
157	}
158	// block if the queue is empty
159	synchronized(((LinkedList) _lists.get(queue))) {
160	if (((LinkedList) _lists.get(queue)).size() == 0) {
161	try { ((LinkedList) _lists.get(queue)).wait(); } catch(Exception e) {}
162	}
163	}
164	// get an item, it should never be null due to the blocking above
165	Object o = null;
166	synchronized(this) {
167	try {
168	o = ((LinkedList) _lists.get(queue)).removeFirst();
169	}
170	catch (NoSuchElementException e) {
171	// This should never happen !
172	}
173	}
174	return o;
175	}
176
177	/**
178	* This method releases a get() method that's currently
179	* waiting on an empty queue. This was designed for
180	* shutdown() type methods that may have problems closing
181	* if the thread of control is waiting on a queue.
182	*
183	* @param queue the queue to release.
184	*/
185	public void releaseQueue(int queue) {
186	synchronized(((LinkedList) _lists.get(queue))) {
187	((LinkedList) _lists.get(queue)).notifyAll();
188	}
189	}
190
191	/**
192	* This method erases the contents of a given queue. This
193	* method should be used with care. It can only empty one
194	* internal queue, not all of them. This must be called
195	* multiple times to empty all queues.
196	*
197	* @param queue the queue to empty.
198	*/
199	public void clearQueue(int queue) {
200	synchronized(this) {
201	((LinkedList) _lists.get(queue)).clear();
202	}
203	}
204
205	/**
206	* This method returns an XML textual status of the queues.
207	* It is merely for observation, and would most likely be
208	* used by a larger "monitoring" component. Information
209	* returned includes the current size of each queue, and
210	* the total items passed through.
211	*
212	* @return A String message containing status information in XML format
213	*/
214	public String xmlStatus() {
215	String status = "<queue ";
216	for(int i=0; i < _lists.size(); i++) {
217	// check for null entries
218	if(_lists.get(i) != null) {
219	status += "queue"+i+"=\""+((LinkedList) _lists.get(i)).size()+"\" ";
220	}
221	else {
222	status += "queue"+i+"=\"[deleted]\" ";
223	}
224	}
225	status += "total=\""+_count+"\"";
226	if(_maxSize != -1) {
227	status += " maxSize=\""+_maxSize+"\"";
228	}
229	status += "></queue>";
230	return status;
231	}
232
233	/**
234	* Returns the size of a given queue. A consumer can use
235	* this to see how big their queue is at any given time.
236	* they should use their queue number as the parameter.
237	*
238	* @param queue The queue number to query.
239	* @return the current size of the queue.
240	* @throws InvalidQueueException if the queue does not exist.
241	*/
242	public int queueSize(int queue) throws InvalidQueueException {
243	if (queue >= _lists.size() \|\| _lists.get(queue) == null) {
244	throw new InvalidQueueException("Requested queue "+queue+" does not exist");
245	}
246	return ((LinkedList) _lists.get(queue)).size();
247	}
248
249	/**
250	* Returns the total numer of elements to have passed
251	* through this queue. This is essentially a counter
252	* on the add method.
253	*
254	* @return the element-ometer.
255	*/
256	public int elementCount() {
257	return _count;
258	}
259
260	/**
261	* This method assigns a queue to a consumer. The idea behind
262	* this is to ensure that only 1 consumer can be associated with
263	* a given queue, otherwise the whole "blocking" thing fails
264	* miserably. Queues are created upon requested.
265	*
266	* It is IMPORTANT that removeQueue() is used when the queue is
267	* no longer required.
268	*
269	* @return An integer to be passed to the get() method.
270	*/
271	public synchronized int getQueue() {
272	int pos = -1;
273	for(int i=0; i < _lists.size(); i++) {
274	if(_lists.get(i) == null) {
275	// found a gap, re-use it
276	pos = i;
277	_lists.set(i, new LinkedList());
278	}
279	}
280	if(pos == -1) {
281	//we didn't find a gap, add at end
282	pos = _lists.size();
283	_lists.add(pos, new LinkedList());
284	}
285	return pos;
286	}
287
288	/**
289	* This method sets a entry to null in the list. This ensures
290	* that it will no longer be added to after it is no longer
291	* required be a consumer.
292	*
293	* @param queue The integer identifier for the queue, given by getQueue().
294	*/
295	public synchronized void removeQueue(int queue) {
296	_lists.set(queue, null);
297	}
298
299	/**
300	* Start a monitor on our own Queue. This will log XML
301	* statistics about our Queue to a given Queue (could be
302	* the one being monitored).
303	*
304	* @param interval The long interval, in milliseconds, at which to take samples
305	* @param destQueue The queue to monitor to
306	* @param name A name to identify this Queue with
307	* @return whether we succeeded
308	*/
309	public boolean startMonitor(long interval, Queue destQueue, String name) {
310	if(_queueMon == null) {
311	// start a monitor
312	_queueMon = new QueueMonitor(this, destQueue, interval, name);
313	_queueMon.start();
314	return true;
315	}
316	else {
317	// already have a monitor running
318	return false;
319	}
320	}
321
322	/**
323	* Start a monitor on our own Queue. This will log XML
324	* statistics about our Queue to this Queue.
325	*
326	* @param interval The long interval, in milliseconds, at which to take samples
327	* @param name A name to identify this Queue with
328	* @return whether we succeeded
329	*/
330	public boolean startMonitor(long interval, String name) {
331	return startMonitor(interval, this, name);
332	}
333
334	/**
335	* Stop a monitor on our Queue if we have on running.
336	*
337	* @return whether we succeeded
338	*/
339	public boolean stopMonitor() {
340	if(_queueMon != null) {
341	// stop a monitor
342	_queueMon.shutdown();
343	_queueMon = null;
344	return true;
345	}
346	else {
347	// no monitor running
348	return false;
349	}
350	}
351
352	/**
353	* Overrides the {@link java.lang.Object#toString() Object.toString()}
354	* method to provide clean logging (every class should have this).
355	*
356	* This uses the uk.org.iscream.cms.server.util.FormatName class
357	* to format the toString()
358	*
359	* @return the name of this class and its CVS revision.
360	*/
361	public String toString() {
362	return FormatName.getName(
363	_name,
364	getClass().getName(),
365	REVISION);
366	}
367
368	//---PRIVATE METHODS---
369
370	/**
371	* This method removes an item from a Queue, using a method
372	* requested at construction.
373	*
374	* @param list The LinkedList from which to remove an item.
375	*/
376	private void removeQueueItem(LinkedList list) {
377	// look at our algorithm
378	// remove a random item from the list
379	if(_removeAlgorithm==RANDOM) {
380	// new Random, with a good seed
381	Random rand = new Random(System.currentTimeMillis());
382	int i = rand.nextInt(_maxSize);
383	synchronized(this) {
384	list.remove(i);
385	}
386	}
387	// remove the first item from the list
388	else if(_removeAlgorithm==FIRST) {
389	synchronized(this) {
390	list.removeFirst();
391	}
392	}
393	// remove the last item from the list
394	else if(_removeAlgorithm==LAST) {
395	synchronized(this) {
396	list.removeLast();
397	}
398	}
399	}
400
401	//---ACCESSOR/MUTATOR METHODS---
402
403	//---ATTRIBUTES---
404
405	/**
406	* The LinkedLists of queues.
407	*/
408	private LinkedList _lists = new LinkedList();
409
410	/**
411	* A counter so we know how many data items have been
412	* passed through, for statistical purposes.
413	*/
414	private int _count = 0;
415
416	/**
417	* A reference to our QueueMonitor, if we have one.
418	*/
419	private QueueMonitor _queueMon = null;
420
421	/**
422	* The maximum size of any Queue.
423	*/
424	private int _maxSize = -1;
425
426	/**
427	* The remove algorithm to use upon a Queue reaching
428	* it's maximum size.
429	*/
430	private int _removeAlgorithm = -1;
431
432	/**
433	* This is the friendly identifier of the
434	* component this class is running in.
435	* eg, a Filter may be called "filter1",
436	* If this class does not have an owning
437	* component, a name from the configuration
438	* can be placed here. This name could also
439	* be changed to null for utility classes.
440	*/
441	private String _name = null;
442
443	//---STATIC ATTRIBUTES---
444
445	}