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root/i-scream/experimental/server/Queue/Queue.java

Comparing experimental/server/Queue/Queue.java (file contents):
Revision 1.2 by tdb, Thu Dec 28 03:49:15 2000 UTC vs.
Revision 1.7 by tdb, Mon Feb 12 02:27:56 2001 UTC

#	Line 1 | Line 1
1		//---PACKAGE DECLARATION---
2	+	//package uk.ac.ukc.iscream.util;
3
4		//---IMPORTS---
5		import java.util.LinkedList;
#	Line 14 | Line 15 | import java.util.NoSuchElementException;
15		* @author  $Author$
16		* @version $Id$
17		*/
18	<	class Queue {
18	>	public class Queue {
19
20		//---FINAL ATTRIBUTES---
21
#	Line 25 | Line 26 | class Queue {
26
27		//---STATIC METHODS---
28
29	<	//---CONSTRUCTORS---
30	<
30	<	/**
31	<	* This constructor sets up a given number of queues, all of which
32	<	* will be populated with data using the add() method. It is very
33	<	* important that the correct number is given, otherwise redundant
34	<	* queues will build up with large amounts of data in them.
35	<	*
36	<	* @param consumers The number of queues to be created.
37	<	*/
38	<	public Queue(int consumers) {
39	<	// constuct and initialise the queues
40	<	_lists = new LinkedList[consumers];
41	<	for(int i=0; i < _lists.length; i++) {
42	<	_lists[i] = new LinkedList();
43	<	}
44	<	}
45	<
46	<	/**
47	<	* This constructor is intended for an environment with a single
48	<	* consumer. This should be used in conjunction with the no-args
49	<	* get() method.
50	<	*/
51	<	public Queue() {
52	<	// call the proper constructor
53	<	this(1);
54	<	}
55	<
29	>	//---CONSTRUCTORS---
30	>
31		//---PUBLIC METHODS---
32
33		/**
#	Line 62 | Line 37 | class Queue {
37		* @param o An Object to be added to the queues.
38		*/
39		public void add(Object o) {
40	<	for(int i=0; i < _lists.length; i++) {
41	<	int s = _lists[i].size();
42	<	synchronized(this) {
43	<	// add() does the same thing, but this ensures behaviour
44	<	_lists[i].addLast(o);
45	<	}
46	<	// if the queue was empty before the add it is possible
72	<	// that a consumer is waiting... so we notify them
73	<	if (s == 0) {
74	<	synchronized(_lists[i]) {
75	<	_lists[i].notifyAll();
40	>	for(int i=0; i < _lists.size(); i++) {
41	>	// skip over any gaps left in the list
42	>	if(_lists.get(i) != null) {
43	>	int s = ((LinkedList) _lists.get(i)).size();
44	>	synchronized(this) {
45	>	// add() does the same thing, but this ensures behaviour
46	>	((LinkedList) _lists.get(i)).addLast(o);
47		}
48	+	// if the queue was empty before the add it is possible
49	+	// that a consumer is waiting... so we notify them
50	+	if (s == 0) {
51	+	synchronized(((LinkedList) _lists.get(i))) {
52	+	((LinkedList) _lists.get(i)).notifyAll();
53	+	}
54	+	}
55		}
56		}
57		// we keep track of the total additions for the status() method
#	Line 84 | Line 62 | class Queue {
62		* This method returns an object from the front of a given queue.
63		* It will block until data exists in the queue if required.
64		*
65	+	* @param The queue to retrieve data from.
66		* @return The object from the front of the queue.
67	+	* @throws InvalidQueueException if the queue does not exist.
68		*/
69	<	public Object get(int queue) {
69	>	public Object get(int queue) throws InvalidQueueException {
70	>	// make sure queue exists
71	>	if (queue >= _lists.size() || _lists.get(queue) == null) {
72	>	throw new InvalidQueueException("Requested queue "+queue+" does not exist");
73	>	}
74		// block if the queue is empty
75	<	if (_lists[queue].size() == 0) {
76	<	synchronized(_lists[queue]) {
77	<	try { _lists[queue].wait(); } catch(Exception e) {}
75	>	if (((LinkedList) _lists.get(queue)).size() == 0) {
76	>	synchronized(((LinkedList) _lists.get(queue))) {
77	>	try { ((LinkedList) _lists.get(queue)).wait(); } catch(Exception e) {}
78		}
79		}
80		// get an item, it should never be null due to the blocking above
81		Object o = null;
82		synchronized(this) {
83		try {
84	<	o = _lists[queue].removeFirst();
84	>	o = ((LinkedList) _lists.get(queue)).removeFirst();
85		}
86		catch (NoSuchElementException e) {
87		// This should never happen !
#	Line 107 | Line 91 | class Queue {
91		}
92
93		/**
94	<	* This method is intended for an environment where there is
95	<	* only a single consumer. It simply gets the item from the
96	<	* first (and presumably only) queue.
94	>	* This method releases a get() method that's currently
95	>	* waiting on an empty queue. This was designed for
96	>	* shutdown() type methods that may have problems closing
97	>	* if the thread of control is waiting on a queue.
98		*
99	<	* @return The object from the front of the queue.
99	>	* @param queue the queue to release.
100		*/
101	<	public Object get() {
102	<	return get(0);
101	>	public void releaseQueue(int queue) {
102	>	synchronized(((LinkedList) _lists.get(queue))) {
103	>	((LinkedList) _lists.get(queue)).notifyAll();
104	>	}
105		}
106	+
107	+	/**
108	+	* This method erases the contents of a given queue. This
109	+	* method should be used with care. It can only empty one
110	+	* internal queue, not all of them. This must be called
111	+	* multiple times to empty all queues.
112	+	*
113	+	* @param queue the queue to empty.
114	+	*/
115	+	public void clearQueue(int queue) {
116	+	synchronized(this) {
117	+	((LinkedList) _lists.get(queue)).clear();
118	+	}
119	+	}
120
121		/**
122	<	* This method returns a textual status of the queues. It
123	<	* is merely for observation, and would most likely be used
124	<	* by a larger "monitoring" component. Information returned
125	<	* includes the current size of each queue, and the total
126	<	* items passed through.
122	>	* This method returns an XML textual status of the queues.
123	>	* It is merely for observation, and would most likely be
124	>	* used by a larger "monitoring" component. Information
125	>	* returned includes the current size of each queue, and
126	>	* the total items passed through.
127		*
128	<	* @return A String message containing status information.
128	>	* @return A String message containing status information in XML format
129		*/
130	<	public String status() {
131	<	String status = "";
132	<	for(int i=0; i < _lists.length; i++) {
133	<	status += "Queue number "+i+" contains "+_lists[i].size()+" elements";
134	<	status += "\n";
130	>	public String xmlStatus() {
131	>	String status = "<queue ";
132	>	for(int i=0; i < _lists.size(); i++) {
133	>	// check for null entries
134	>	if(_lists.get(i) != null) {
135	>	status += "queue"+i+"=\""+((LinkedList) _lists.get(i)).size()+"\" ";
136	>	}
137	>	else {
138	>	status += "queue"+i+"=\"null\" ";
139	>	}
140		}
141	<	status += "A total of "+_count+" elements have been added to the queues";
141	>	status += "total=\""+_count+"\"></queue>";
142		return status;
143		}
144
145		/**
146	+	* Returns the size of a given queue. A consumer can use
147	+	* this to see how big their queue is at any given time.
148	+	* they should use their queue number as the parameter.
149	+	*
150	+	* @param queue The queue number to query.
151	+	* @return the current size of the queue.
152	+	* @throws InvalidQueueException if the queue does not exist.
153	+	*/
154	+	public int queueSize(int queue) throws InvalidQueueException {
155	+	if (queue >= _lists.size() || _lists.get(queue) == null) {
156	+	throw new InvalidQueueException("Requested queue "+queue+" does not exist");
157	+	}
158	+	return ((LinkedList) _lists.get(queue)).size();
159	+	}
160	+
161	+	/**
162	+	* Returns the total numer of elements to have passed
163	+	* through this queue (ie. a counter on the add method).
164	+	*
165	+	* @return the element-ometer.
166	+	*/
167	+	public int elementCount() {
168	+	return _count;
169	+	}
170	+
171	+	/**
172		* This method assigns a queue to a consumer. The idea behind
173		* this is to ensure that only 1 consumer can be associated with
174		* a given queue, otherwise the whole "blocking" thing fails
175	<	* miserably.
175	>	* miserably. Queues are created upon requested.
176		*
177	+	* It is IMPORTANT that removeQueue() is used when the queue is
178	+	* no longer required.
179	+	*
180		* @return An integer to be passed to the get() method.
146	–	* @throws NoQueueException if there are no un-assigned queue's.
181		*/
182	<	public int getQueue() throws NoQueueException {
183	<	if(_index < _lists.length) {
184	<	return _index++;
182	>	public int getQueue() {
183	>	int pos = -1;
184	>	for(int i=0; i < _lists.size(); i++) {
185	>	if(_lists.get(i) == null) {
186	>	// found a gap, re-use it
187	>	pos = i;
188	>	_lists.set(i, new LinkedList());
189	>	}
190		}
191	+	if(pos == -1) {
192	+	//we didn't find a gap, add at end
193	+	pos = _lists.size();
194	+	_lists.add(pos, new LinkedList());
195	+	}
196	+	return pos;
197	+	}
198	+
199	+	/**
200	+	* This method sets a entry to null in the list. This ensures
201	+	* that it will no longer be added to after it is no longer
202	+	* required be a consumer.
203	+	*
204	+	* @param queue The integer identifier for the queue, given by getQueue().
205	+	*/
206	+	public void removeQueue(int queue) {
207	+	_lists.set(queue, null);
208	+	}
209	+
210	+	/**
211	+	* Start a monitor on our own Queue. This will log XML
212	+	* statistics about our Queue to a given Queue (could be
213	+	* the one being monitored).
214	+	*
215	+	* @param interval The long interval, in milliseconds, at which to take samples
216	+	* @param destQueue The queue to monitor to
217	+	* @param name A name to identify this Queue with
218	+	* @return whether we succeeded
219	+	*/
220	+	public boolean startMonitor(long interval, Queue destQueue, String name) {
221	+	if(_queueMon == null) {
222	+	// start a monitor
223	+	_queueMon = new QueueMonitor(this, destQueue, interval, name);
224	+	_queueMon.start();
225	+	return true;
226	+	}
227		else {
228	<	throw new NoQueueException("Too many consumers, there are already "+_lists.length+" running");
228	>	// already have a monitor running
229	>	return false;
230		}
231		}
232	<
232	>
233		/**
234	+	* Start a monitor on our own Queue. This will log XML
235	+	* statistics about our Queue to this Queue.
236	+	*
237	+	* @param interval The long interval, in milliseconds, at which to take samples
238	+	* @param name A name to identify this Queue with
239	+	* @return whether we succeeded
240	+	*/
241	+	public boolean startMonitor(long interval, String name) {
242	+	return startMonitor(interval, this, name);
243	+	}
244	+
245	+	/**
246	+	* Stop a monitor on our Queue if we have on running.
247	+	*
248	+	* @return whether we succeeded
249	+	*/
250	+	public boolean stopMonitor() {
251	+	if(_queueMon != null) {
252	+	// stop a monitor
253	+	_queueMon.shutdown();
254	+	_queueMon = null;
255	+	return true;
256	+	}
257	+	else {
258	+	// no monitor running
259	+	return false;
260	+	}
261	+	}
262	+
263	+	/**
264		* Overrides the {@link java.lang.Object#toString() Object.toString()}
265		* method to provide clean logging (every class should have this).
266		*
267		* This uses the uk.ac.ukc.iscream.util.FormatName class
268		* to format the toString()
269		*
270	<	* @return the name of this class and its CVS revision
270	>	* @return the name of this class and its CVS revision.
271		*/
272	<	/*public String toString() {
272	>	public String toString() {
273		return FormatName.getName(
274		_name,
275		getClass().getName(),
276		REVISION);
277	<	}*/
277	>	}
278
279		//---PRIVATE METHODS---
280
#	Line 177 | Line 283 | class Queue {
283		//---ATTRIBUTES---
284
285		/**
286	<	* The array of lists, which the underlying queue data
181	<	* is stored in.
286	>	* The LinkedLists of queues.
287		*/
288	<	private LinkedList[] _lists;
288	>	private LinkedList _lists = new LinkedList();
289
290		/**
291		* A counter so we know how many data items have been
#	Line 189 | Line 294 | class Queue {
294		private int _count = 0;
295
296		/**
297	<	* An index of the next available queue. Used by the
193	<	* getQueue() method.
297	>	* A reference to our QueueMonitor, if we have one.
298		*/
299	<	private int _index = 0;
300	<
299	>	private QueueMonitor _queueMon = null;
300	>
301		/**
302		* This is the friendly identifier of the
303		* component this class is running in.
#	Line 203 | Line 307 | class Queue {
307		* can be placed here.  This name could also
308		* be changed to null for utility classes.
309		*/
310	<	//private String _name = <!THIS SHOULD CALL A STATIC NAME IN THE COMPONENT CLASS FOR THIS OBJECT!>;
207	<
208	<	/**
209	<	* This holds a reference to the
210	<	* system logger that is being used.
211	<	*/
212	<	//private Logger _logger = ReferenceManager.getInstance().getLogger();
310	>	private String _name = null;
311
312		//---STATIC ATTRIBUTES---
313

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