cms/util/Queue.java

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

//---IMPORTS---
import java.util.LinkedList;
import java.util.NoSuchElementException;
import java.util.Random;
import uk.org.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 1.17 2001/03/16 15:17:06 tdb1 Exp $
 */
public class Queue {

//---FINAL ATTRIBUTES---

    /**
     * The current CVS revision of this class
     */
    public static final String REVISION = "$Revision: 1.17 $";
    
    /**
     * 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) {
                // 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
        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 (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.org.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:	1.18
Committed:	Sat Mar 17 18:48:22 2001 UTC (23 years, 1 month ago) by tdb
Branch:	MAIN
Changes since 1.17:	+4 -4 lines
Log Message:	This changes alieviates a problem whereby the queue state could change between the two lines changed, and result in waiting forever.
#	User	Rev	Content
1	tdb	1.1	//---PACKAGE DECLARATION---
2	tdb	1.16	package uk.org.iscream.util;
3	tdb	1.1
4			//---IMPORTS---
5			import java.util.LinkedList;
6			import java.util.NoSuchElementException;
7	tdb	1.14	import java.util.Random;
8	tdb	1.16	import uk.org.iscream.util.*;
9	tdb	1.1
10			/**
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			* @author $Author: tdb1 $
17	tdb	1.18	* @version $Id: Queue.java,v 1.17 2001/03/16 15:17:06 tdb1 Exp $
18	tdb	1.1	*/
19	tdb	1.2	public class Queue {
20	tdb	1.1
21			//---FINAL ATTRIBUTES---
22
23			/**
24			* The current CVS revision of this class
25			*/
26	tdb	1.18	public static final String REVISION = "$Revision: 1.17 $";
27	tdb	1.14
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	1.17
52			/**
53			* To allow opposite lookups.
54			*/
55			public static final String[] algorithms = {"RANDOM", "FIRST", "LAST", "DROP"};
56	tdb	1.1
57			//---STATIC METHODS---
58
59			//---CONSTRUCTORS---
60	tdb	1.14
61			/**
62			* Constructs a new Queue with a maximum size limit on
63			* any individual queue. This should be used to stop
64			* conditions where the Queue cannot be guaranteed to
65			* be emptied as quick as it's filled.
66			*
67			* An algorithm will be used to remove data when new data
68			* arrives. There may be choices of algorithms later on.
69			*
70			* @param maxSize the upper limit for a queue
71			* @param removeAlgorithm the remove algorithm to use upon reaching the maxSize
72			*/
73			public Queue(int maxSize, int removeAlgorithm) {
74			_maxSize = maxSize;
75			_removeAlgorithm = removeAlgorithm;
76			}
77
78			/**
79			* Constructs a Queue with no maximum size.
80			*/
81			public Queue() {
82			_maxSize = -1;
83			}
84	tdb	1.1
85			//---PUBLIC METHODS---
86
87			/**
88			* This method adds a given object to every queue. It will notify
89			* any waiting consumers (on an empty queue) during this process.
90			*
91			* @param o An Object to be added to the queues.
92			*/
93			public void add(Object o) {
94			for(int i=0; i < _lists.size(); i++) {
95			// skip over any gaps left in the list
96			if(_lists.get(i) != null) {
97	tdb	1.14	// get size before adding to the Queue
98	tdb	1.1	int s = ((LinkedList) _lists.get(i)).size();
99	tdb	1.14	// check whether we need to remove an item from the current Queue
100			if(_maxSize!=-1 && s==_maxSize && _removeAlgorithm!=DROP) {
101			// we need to remove an item
102			removeQueueItem((LinkedList) _lists.get(i));
103			}
104			// check if we should add (not if Queue full, and using DROP algorithm)
105			if(!(s==_maxSize && _removeAlgorithm==DROP)) {
106			// add the next item, ensuring we lock
107			synchronized(this) {
108			// LinkedList.add() does the same thing, but this ensures behaviour
109			((LinkedList) _lists.get(i)).addLast(o);
110			}
111	tdb	1.1	}
112			// if the queue was empty before the add it is possible
113			// that a consumer is waiting... so we notify them
114			if (s == 0) {
115			synchronized(((LinkedList) _lists.get(i))) {
116			((LinkedList) _lists.get(i)).notifyAll();
117			}
118			}
119			}
120			}
121			// we keep track of the total additions for the status() method
122			_count++;
123			}
124
125			/**
126			* This method returns an object from the front of a given queue.
127			* It will block until data exists in the queue if required.
128			*
129	tdb	1.8	* @param The queue to retrieve data from.
130	tdb	1.1	* @return The object from the front of the queue.
131			* @throws InvalidQueueException if the queue does not exist.
132			*/
133			public Object get(int queue) throws InvalidQueueException {
134			// make sure queue exists
135			if (queue >= _lists.size() \|\| _lists.get(queue) == null) {
136			throw new InvalidQueueException("Requested queue "+queue+" does not exist");
137			}
138			// block if the queue is empty
139	tdb	1.18	synchronized(((LinkedList) _lists.get(queue))) {
140			if (((LinkedList) _lists.get(queue)).size() == 0) {
141	tdb	1.1	try { ((LinkedList) _lists.get(queue)).wait(); } catch(Exception e) {}
142			}
143			}
144			// get an item, it should never be null due to the blocking above
145			Object o = null;
146			synchronized(this) {
147			try {
148			o = ((LinkedList) _lists.get(queue)).removeFirst();
149			}
150			catch (NoSuchElementException e) {
151			// This should never happen !
152			}
153			}
154			return o;
155			}
156	tdb	1.6
157			/**
158			* This method releases a get() method that's currently
159			* waiting on an empty queue. This was designed for
160			* shutdown() type methods that may have problems closing
161			* if the thread of control is waiting on a queue.
162			*
163	tdb	1.8	* @param queue the queue to release.
164	tdb	1.6	*/
165			public void releaseQueue(int queue) {
166			synchronized(((LinkedList) _lists.get(queue))) {
167			((LinkedList) _lists.get(queue)).notifyAll();
168	tdb	1.7	}
169			}
170
171			/**
172			* This method erases the contents of a given queue. This
173			* method should be used with care. It can only empty one
174			* internal queue, not all of them. This must be called
175			* multiple times to empty all queues.
176			*
177			* @param queue the queue to empty.
178			*/
179			public void clearQueue(int queue) {
180			synchronized(this) {
181			((LinkedList) _lists.get(queue)).clear();
182	tdb	1.6	}
183			}
184
185	tdb	1.1	/**
186	tdb	1.9	* This method returns an XML textual status of the queues.
187			* It is merely for observation, and would most likely be
188			* used by a larger "monitoring" component. Information
189			* returned includes the current size of each queue, and
190			* the total items passed through.
191	tdb	1.1	*
192	tdb	1.9	* @return A String message containing status information in XML format
193	tdb	1.1	*/
194	tdb	1.9	public String xmlStatus() {
195			String status = "<queue ";
196	tdb	1.1	for(int i=0; i < _lists.size(); i++) {
197			// check for null entries
198			if(_lists.get(i) != null) {
199	tdb	1.9	status += "queue"+i+"=\""+((LinkedList) _lists.get(i)).size()+"\" ";
200	tdb	1.1	}
201			else {
202	tdb	1.13	status += "queue"+i+"=\"[deleted]\" ";
203	tdb	1.1	}
204			}
205	tdb	1.14	status += "total=\""+_count+"\"";
206			if(_maxSize != -1) {
207			status += " maxSize=\""+_maxSize+"\"";
208			}
209	tdb	1.15	status += "></queue>";
210	tdb	1.1	return status;
211	tdb	1.4	}
212
213			/**
214			* Returns the size of a given queue. A consumer can use
215			* this to see how big their queue is at any given time.
216			* they should use their queue number as the parameter.
217			*
218			* @param queue The queue number to query.
219			* @return the current size of the queue.
220	tdb	1.8	* @throws InvalidQueueException if the queue does not exist.
221	tdb	1.4	*/
222			public int queueSize(int queue) throws InvalidQueueException {
223	tdb	1.5	if (queue >= _lists.size() \|\| _lists.get(queue) == null) {
224	tdb	1.4	throw new InvalidQueueException("Requested queue "+queue+" does not exist");
225			}
226	tdb	1.5	return ((LinkedList) _lists.get(queue)).size();
227	tdb	1.4	}
228
229			/**
230			* Returns the total numer of elements to have passed
231			* through this queue (ie. a counter on the add method).
232			*
233	tdb	1.8	* @return the element-ometer.
234	tdb	1.4	*/
235			public int elementCount() {
236	tdb	1.5	return _count;
237	tdb	1.1	}
238
239			/**
240			* This method assigns a queue to a consumer. The idea behind
241			* this is to ensure that only 1 consumer can be associated with
242			* a given queue, otherwise the whole "blocking" thing fails
243			* miserably. Queues are created upon requested.
244			*
245			* It is IMPORTANT that removeQueue() is used when the queue is
246			* no longer required.
247			*
248			* @return An integer to be passed to the get() method.
249			*/
250			public int getQueue() {
251			int pos = -1;
252			for(int i=0; i < _lists.size(); i++) {
253			if(_lists.get(i) == null) {
254			// found a gap, re-use it
255			pos = i;
256			_lists.set(i, new LinkedList());
257			}
258			}
259			if(pos == -1) {
260			//we didn't find a gap, add at end
261			pos = _lists.size();
262			_lists.add(pos, new LinkedList());
263			}
264			return pos;
265			}
266
267			/**
268			* This method sets a entry to null in the list. This ensures
269			* that it will no longer be added to after it is no longer
270			* required be a consumer.
271			*
272			* @param queue The integer identifier for the queue, given by getQueue().
273			*/
274			public void removeQueue(int queue) {
275			_lists.set(queue, null);
276			}
277
278			/**
279	tdb	1.9	* Start a monitor on our own Queue. This will log XML
280			* statistics about our Queue to a given Queue (could be
281			* the one being monitored).
282			*
283			* @param interval The long interval, in milliseconds, at which to take samples
284			* @param destQueue The queue to monitor to
285			* @param name A name to identify this Queue with
286			* @return whether we succeeded
287			*/
288			public boolean startMonitor(long interval, Queue destQueue, String name) {
289			if(_queueMon == null) {
290			// start a monitor
291			_queueMon = new QueueMonitor(this, destQueue, interval, name);
292			_queueMon.start();
293			return true;
294			}
295			else {
296			// already have a monitor running
297			return false;
298			}
299			}
300
301			/**
302			* Start a monitor on our own Queue. This will log XML
303			* statistics about our Queue to this Queue.
304			*
305			* @param interval The long interval, in milliseconds, at which to take samples
306			* @param name A name to identify this Queue with
307			* @return whether we succeeded
308			*/
309			public boolean startMonitor(long interval, String name) {
310			return startMonitor(interval, this, name);
311			}
312
313			/**
314			* Stop a monitor on our Queue if we have on running.
315			*
316			* @return whether we succeeded
317			*/
318			public boolean stopMonitor() {
319			if(_queueMon != null) {
320			// stop a monitor
321			_queueMon.shutdown();
322			_queueMon = null;
323			return true;
324			}
325			else {
326			// no monitor running
327			return false;
328			}
329			}
330
331			/**
332	tdb	1.1	* Overrides the {@link java.lang.Object#toString() Object.toString()}
333			* method to provide clean logging (every class should have this).
334			*
335	tdb	1.16	* This uses the uk.org.iscream.util.FormatName class
336	tdb	1.1	* to format the toString()
337			*
338	tdb	1.8	* @return the name of this class and its CVS revision.
339	tdb	1.1	*/
340	tdb	1.3	public String toString() {
341	tdb	1.1	return FormatName.getName(
342			_name,
343			getClass().getName(),
344			REVISION);
345	tdb	1.3	}
346	tdb	1.1
347			//---PRIVATE METHODS---
348	tdb	1.14
349			/**
350			* This method removes an item from a Queue, using a method
351			* requested at construction.
352			*
353			* @param list The LinkedList from which to remove an item.
354			*/
355			private void removeQueueItem(LinkedList list) {
356			// look at our algorithm
357			// remove a random item from the list
358			if(_removeAlgorithm==RANDOM) {
359			// new Random, with a good seed
360			Random rand = new Random(System.currentTimeMillis());
361			int i = rand.nextInt(_maxSize);
362			synchronized(this) {
363			list.remove(i);
364			}
365			}
366			// remove the first item from the list
367			else if(_removeAlgorithm==FIRST) {
368			synchronized(this) {
369			list.removeFirst();
370			}
371			}
372			// remove the last item from the list
373			else if(_removeAlgorithm==LAST) {
374			synchronized(this) {
375			list.removeLast();
376			}
377			}
378			}
379
380	tdb	1.1	//---ACCESSOR/MUTATOR METHODS---
381
382			//---ATTRIBUTES---
383
384			/**
385			* The LinkedLists of queues.
386			*/
387			private LinkedList _lists = new LinkedList();
388
389			/**
390			* A counter so we know how many data items have been
391			* passed through, for statistical purposes.
392			*/
393			private int _count = 0;
394	tdb	1.9
395			/**
396			* A reference to our QueueMonitor, if we have one.
397			*/
398			private QueueMonitor _queueMon = null;
399	tdb	1.14
400			/**
401			* The maximum size of any Queue.
402			*/
403			private int _maxSize = -1;
404
405			/**
406			* The remove algorithm to use upon a Queue reaching
407			* it's maximum size.
408			*/
409			private int _removeAlgorithm = -1;
410	tdb	1.1
411			/**
412			* This is the friendly identifier of the
413			* component this class is running in.
414			* eg, a Filter may be called "filter1",
415			* If this class does not have an owning
416			* component, a name from the configuration
417			* can be placed here. This name could also
418			* be changed to null for utility classes.
419			*/
420	tdb	1.3	private String _name = null;
421	tdb	1.1
422			//---STATIC ATTRIBUTES---
423
424			}