cms/util/Queue.java

/* 
 * i-scream central monitoring system
 * 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.server.util;

//---IMPORTS---
import java.util.LinkedList;
import java.util.NoSuchElementException;
import java.util.Random;
import uk.org.iscream.cms.server.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 1.23 2001/12/10 22:20:23 tdb Exp $
 */
public class Queue {

//---FINAL ATTRIBUTES---

    /**
     * The current CVS revision of this class
     */
    public static final String REVISION = "$Revision: 1.23 $";
    
    /**
     * 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:	1.24
Committed:	Sat May 18 18:16:03 2002 UTC (21 years, 11 months ago) by tdb
Branch:	MAIN
Changes since 1.23:	+22 -3 lines
Log Message:	i-scream is now licensed under the GPL. I've added the GPL headers to every source file, and put a full copy of the license in the appropriate places. I think I've covered everything. This is going to be a mad commit ;)
#	User	Rev	Content
1	tdb	1.24	/*
2			* i-scream central monitoring system
3			* Copyright (C) 2000-2002 i-scream
4			*
5			* This program is free software; you can redistribute it and/or
6			* modify it under the terms of the GNU General Public License
7			* as published by the Free Software Foundation; either version 2
8			* of the License, or (at your option) any later version.
9			*
10			* This program is distributed in the hope that it will be useful,
11			* but WITHOUT ANY WARRANTY; without even the implied warranty of
12			* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13			* GNU General Public License for more details.
14			*
15			* You should have received a copy of the GNU General Public License
16			* along with this program; if not, write to the Free Software
17			* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18			*/
19
20	tdb	1.1	//---PACKAGE DECLARATION---
21	tdb	1.22	package uk.org.iscream.cms.server.util;
22	tdb	1.1
23			//---IMPORTS---
24			import java.util.LinkedList;
25			import java.util.NoSuchElementException;
26	tdb	1.14	import java.util.Random;
27	tdb	1.22	import uk.org.iscream.cms.server.util.*;
28	tdb	1.1
29			/**
30			* A Queue class designed to operate in a multi-threaded environment, with
31			* added support for multiple "consumer" threads. Also offers blocking on
32			* the get() methods, which ensures the consumer waits until the queue
33			* actually contains some elements.
34			*
35	tdb	1.24	* @author $Author: tdb $
36			* @version $Id: Queue.java,v 1.23 2001/12/10 22:20:23 tdb Exp $
37	tdb	1.1	*/
38	tdb	1.2	public class Queue {
39	tdb	1.1
40			//---FINAL ATTRIBUTES---
41
42			/**
43			* The current CVS revision of this class
44			*/
45	tdb	1.24	public static final String REVISION = "$Revision: 1.23 $";
46	tdb	1.14
47			/**
48			* Pass to constructor to remove a RANDOM item from
49			* the Queue upon reaching the maximum limit.
50			*/
51			public static final int RANDOM = 0;
52
53			/**
54			* Pass to constructor to remove the FIRST item from
55			* the Queue upon reaching the maximum limit.
56			*/
57			public static final int FIRST = 1;
58
59			/**
60			* Pass to constructor to remove the LAST item from
61			* the Queue upon reaching the maximum limit.
62			*/
63			public static final int LAST = 2;
64
65			/**
66			* Pass to constructor to drop the new item upon reaching
67			* the maximum Queue limit.
68			*/
69			public static final int DROP = 3;
70	tdb	1.17
71			/**
72			* To allow opposite lookups.
73			*/
74			public static final String[] algorithms = {"RANDOM", "FIRST", "LAST", "DROP"};
75	tdb	1.1
76			//---STATIC METHODS---
77
78			//---CONSTRUCTORS---
79	tdb	1.14
80			/**
81			* Constructs a new Queue with a maximum size limit on
82			* any individual queue. This should be used to stop
83			* conditions where the Queue cannot be guaranteed to
84			* be emptied as quick as it's filled.
85			*
86			* An algorithm will be used to remove data when new data
87			* arrives. There may be choices of algorithms later on.
88			*
89			* @param maxSize the upper limit for a queue
90			* @param removeAlgorithm the remove algorithm to use upon reaching the maxSize
91			*/
92			public Queue(int maxSize, int removeAlgorithm) {
93			_maxSize = maxSize;
94			_removeAlgorithm = removeAlgorithm;
95			}
96
97			/**
98			* Constructs a Queue with no maximum size.
99			*/
100			public Queue() {
101			_maxSize = -1;
102			}
103	tdb	1.1
104			//---PUBLIC METHODS---
105
106			/**
107			* This method adds a given object to every queue. It will notify
108			* any waiting consumers (on an empty queue) during this process.
109			*
110			* @param o An Object to be added to the queues.
111			*/
112			public void add(Object o) {
113			for(int i=0; i < _lists.size(); i++) {
114			// skip over any gaps left in the list
115			if(_lists.get(i) != null) {
116	tdb	1.21	synchronized(((LinkedList) _lists.get(i))) {
117			// get size before adding to the Queue
118			int s = ((LinkedList) _lists.get(i)).size();
119			// check whether we need to remove an item from the current Queue
120			if(_maxSize!=-1 && s>=_maxSize && _removeAlgorithm!=DROP) {
121			// we need to remove an item
122			removeQueueItem((LinkedList) _lists.get(i));
123			}
124			// check if we should add (not if Queue full, and using DROP algorithm)
125			if(!(s>=_maxSize && _removeAlgorithm==DROP)) {
126			// add the next item, ensuring we lock
127			synchronized(this) {
128			// LinkedList.add() does the same thing, but this ensures behaviour
129			((LinkedList) _lists.get(i)).addLast(o);
130			}
131			// if the queue was empty before the add it is possible
132			// that a consumer is waiting... so we notify them
133			//synchronized(((LinkedList) _lists.get(i))) {
134			((LinkedList) _lists.get(i)).notifyAll();
135			//}
136	tdb	1.14	}
137	tdb	1.1	}
138			}
139			}
140			// we keep track of the total additions for the status() method
141			_count++;
142			}
143
144			/**
145			* This method returns an object from the front of a given queue.
146			* It will block until data exists in the queue if required.
147			*
148	tdb	1.8	* @param The queue to retrieve data from.
149	tdb	1.1	* @return The object from the front of the queue.
150			* @throws InvalidQueueException if the queue does not exist.
151			*/
152			public Object get(int queue) throws InvalidQueueException {
153			// make sure queue exists
154			if (queue >= _lists.size() \|\| _lists.get(queue) == null) {
155			throw new InvalidQueueException("Requested queue "+queue+" does not exist");
156			}
157			// block if the queue is empty
158	tdb	1.18	synchronized(((LinkedList) _lists.get(queue))) {
159			if (((LinkedList) _lists.get(queue)).size() == 0) {
160	tdb	1.1	try { ((LinkedList) _lists.get(queue)).wait(); } catch(Exception e) {}
161			}
162			}
163			// get an item, it should never be null due to the blocking above
164			Object o = null;
165			synchronized(this) {
166			try {
167			o = ((LinkedList) _lists.get(queue)).removeFirst();
168			}
169			catch (NoSuchElementException e) {
170			// This should never happen !
171			}
172			}
173			return o;
174			}
175	tdb	1.6
176			/**
177			* This method releases a get() method that's currently
178			* waiting on an empty queue. This was designed for
179			* shutdown() type methods that may have problems closing
180			* if the thread of control is waiting on a queue.
181			*
182	tdb	1.8	* @param queue the queue to release.
183	tdb	1.6	*/
184			public void releaseQueue(int queue) {
185			synchronized(((LinkedList) _lists.get(queue))) {
186			((LinkedList) _lists.get(queue)).notifyAll();
187	tdb	1.7	}
188			}
189
190			/**
191			* This method erases the contents of a given queue. This
192			* method should be used with care. It can only empty one
193			* internal queue, not all of them. This must be called
194			* multiple times to empty all queues.
195			*
196			* @param queue the queue to empty.
197			*/
198			public void clearQueue(int queue) {
199			synchronized(this) {
200			((LinkedList) _lists.get(queue)).clear();
201	tdb	1.6	}
202			}
203
204	tdb	1.1	/**
205	tdb	1.9	* This method returns an XML textual status of the queues.
206			* It is merely for observation, and would most likely be
207			* used by a larger "monitoring" component. Information
208			* returned includes the current size of each queue, and
209			* the total items passed through.
210	tdb	1.1	*
211	tdb	1.9	* @return A String message containing status information in XML format
212	tdb	1.1	*/
213	tdb	1.9	public String xmlStatus() {
214			String status = "<queue ";
215	tdb	1.1	for(int i=0; i < _lists.size(); i++) {
216			// check for null entries
217			if(_lists.get(i) != null) {
218	tdb	1.9	status += "queue"+i+"=\""+((LinkedList) _lists.get(i)).size()+"\" ";
219	tdb	1.1	}
220			else {
221	tdb	1.13	status += "queue"+i+"=\"[deleted]\" ";
222	tdb	1.1	}
223			}
224	tdb	1.14	status += "total=\""+_count+"\"";
225			if(_maxSize != -1) {
226			status += " maxSize=\""+_maxSize+"\"";
227			}
228	tdb	1.15	status += "></queue>";
229	tdb	1.1	return status;
230	tdb	1.4	}
231
232			/**
233			* Returns the size of a given queue. A consumer can use
234			* this to see how big their queue is at any given time.
235			* they should use their queue number as the parameter.
236			*
237			* @param queue The queue number to query.
238			* @return the current size of the queue.
239	tdb	1.8	* @throws InvalidQueueException if the queue does not exist.
240	tdb	1.4	*/
241			public int queueSize(int queue) throws InvalidQueueException {
242	tdb	1.5	if (queue >= _lists.size() \|\| _lists.get(queue) == null) {
243	tdb	1.4	throw new InvalidQueueException("Requested queue "+queue+" does not exist");
244			}
245	tdb	1.5	return ((LinkedList) _lists.get(queue)).size();
246	tdb	1.4	}
247
248			/**
249			* Returns the total numer of elements to have passed
250	tdb	1.23	* through this queue. This is essentially a counter
251			* on the add method.
252	tdb	1.4	*
253	tdb	1.8	* @return the element-ometer.
254	tdb	1.4	*/
255			public int elementCount() {
256	tdb	1.5	return _count;
257	tdb	1.1	}
258
259			/**
260			* This method assigns a queue to a consumer. The idea behind
261			* this is to ensure that only 1 consumer can be associated with
262			* a given queue, otherwise the whole "blocking" thing fails
263			* miserably. Queues are created upon requested.
264			*
265			* It is IMPORTANT that removeQueue() is used when the queue is
266			* no longer required.
267			*
268			* @return An integer to be passed to the get() method.
269			*/
270	tdb	1.19	public synchronized int getQueue() {
271	tdb	1.1	int pos = -1;
272			for(int i=0; i < _lists.size(); i++) {
273			if(_lists.get(i) == null) {
274			// found a gap, re-use it
275			pos = i;
276			_lists.set(i, new LinkedList());
277			}
278			}
279			if(pos == -1) {
280			//we didn't find a gap, add at end
281			pos = _lists.size();
282			_lists.add(pos, new LinkedList());
283			}
284			return pos;
285			}
286
287			/**
288			* This method sets a entry to null in the list. This ensures
289			* that it will no longer be added to after it is no longer
290			* required be a consumer.
291			*
292			* @param queue The integer identifier for the queue, given by getQueue().
293			*/
294	tdb	1.19	public synchronized void removeQueue(int queue) {
295	tdb	1.1	_lists.set(queue, null);
296			}
297
298			/**
299	tdb	1.9	* Start a monitor on our own Queue. This will log XML
300			* statistics about our Queue to a given Queue (could be
301			* the one being monitored).
302			*
303			* @param interval The long interval, in milliseconds, at which to take samples
304			* @param destQueue The queue to monitor to
305			* @param name A name to identify this Queue with
306			* @return whether we succeeded
307			*/
308			public boolean startMonitor(long interval, Queue destQueue, String name) {
309			if(_queueMon == null) {
310			// start a monitor
311			_queueMon = new QueueMonitor(this, destQueue, interval, name);
312			_queueMon.start();
313			return true;
314			}
315			else {
316			// already have a monitor running
317			return false;
318			}
319			}
320
321			/**
322			* Start a monitor on our own Queue. This will log XML
323			* statistics about our Queue to this Queue.
324			*
325			* @param interval The long interval, in milliseconds, at which to take samples
326			* @param name A name to identify this Queue with
327			* @return whether we succeeded
328			*/
329			public boolean startMonitor(long interval, String name) {
330			return startMonitor(interval, this, name);
331			}
332
333			/**
334			* Stop a monitor on our Queue if we have on running.
335			*
336			* @return whether we succeeded
337			*/
338			public boolean stopMonitor() {
339			if(_queueMon != null) {
340			// stop a monitor
341			_queueMon.shutdown();
342			_queueMon = null;
343			return true;
344			}
345			else {
346			// no monitor running
347			return false;
348			}
349			}
350
351			/**
352	tdb	1.1	* Overrides the {@link java.lang.Object#toString() Object.toString()}
353			* method to provide clean logging (every class should have this).
354			*
355	tdb	1.22	* This uses the uk.org.iscream.cms.server.util.FormatName class
356	tdb	1.1	* to format the toString()
357			*
358	tdb	1.8	* @return the name of this class and its CVS revision.
359	tdb	1.1	*/
360	tdb	1.3	public String toString() {
361	tdb	1.1	return FormatName.getName(
362			_name,
363			getClass().getName(),
364			REVISION);
365	tdb	1.3	}
366	tdb	1.1
367			//---PRIVATE METHODS---
368	tdb	1.14
369			/**
370			* This method removes an item from a Queue, using a method
371			* requested at construction.
372			*
373			* @param list The LinkedList from which to remove an item.
374			*/
375			private void removeQueueItem(LinkedList list) {
376			// look at our algorithm
377			// remove a random item from the list
378			if(_removeAlgorithm==RANDOM) {
379			// new Random, with a good seed
380			Random rand = new Random(System.currentTimeMillis());
381			int i = rand.nextInt(_maxSize);
382			synchronized(this) {
383			list.remove(i);
384			}
385			}
386			// remove the first item from the list
387			else if(_removeAlgorithm==FIRST) {
388			synchronized(this) {
389			list.removeFirst();
390			}
391			}
392			// remove the last item from the list
393			else if(_removeAlgorithm==LAST) {
394			synchronized(this) {
395			list.removeLast();
396			}
397			}
398			}
399
400	tdb	1.1	//---ACCESSOR/MUTATOR METHODS---
401
402			//---ATTRIBUTES---
403
404			/**
405			* The LinkedLists of queues.
406			*/
407			private LinkedList _lists = new LinkedList();
408
409			/**
410			* A counter so we know how many data items have been
411			* passed through, for statistical purposes.
412			*/
413			private int _count = 0;
414	tdb	1.9
415			/**
416			* A reference to our QueueMonitor, if we have one.
417			*/
418			private QueueMonitor _queueMon = null;
419	tdb	1.14
420			/**
421			* The maximum size of any Queue.
422			*/
423			private int _maxSize = -1;
424
425			/**
426			* The remove algorithm to use upon a Queue reaching
427			* it's maximum size.
428			*/
429			private int _removeAlgorithm = -1;
430	tdb	1.1
431			/**
432			* This is the friendly identifier of the
433			* component this class is running in.
434			* eg, a Filter may be called "filter1",
435			* If this class does not have an owning
436			* component, a name from the configuration
437			* can be placed here. This name could also
438			* be changed to null for utility classes.
439			*/
440	tdb	1.3	private String _name = null;
441	tdb	1.1
442			//---STATIC ATTRIBUTES---
443
444			}