ViewVC Help

View File | Revision Log | Show Annotations | Revision Graph | Root Listing

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 1.5 by tdb, Tue Jan 23 20:14:09 2001 UTC

#	Line 1 | Line 1
1		//---PACKAGE DECLARATION---
2	+	package uk.ac.ukc.iscream.util;
3
4		//---IMPORTS---
5		import java.util.LinkedList;
6		import java.util.NoSuchElementException;
7	<	//import uk.ac.ukc.iscream.util.*;
7	>	import uk.ac.ukc.iscream.util.*;
8
9		/**
10		* A Queue class designed to operate in a multi-threaded environment, with
#	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 85 | Line 63 | class Queue {
63		* It will block until data exists in the queue if required.
64		*
65		* @return The object from the front of the queue.
66	+	* @throws InvalidQueueException if the queue does not exist.
67		*/
68	<	public Object get(int queue) {
68	>	public Object get(int queue) throws InvalidQueueException {
69	>	// make sure queue exists
70	>	if (queue >= _lists.size() || _lists.get(queue) == null) {
71	>	throw new InvalidQueueException("Requested queue "+queue+" does not exist");
72	>	}
73		// block if the queue is empty
74	<	if (_lists[queue].size() == 0) {
75	<	synchronized(_lists[queue]) {
76	<	try { _lists[queue].wait(); } catch(Exception e) {}
74	>	if (((LinkedList) _lists.get(queue)).size() == 0) {
75	>	synchronized(((LinkedList) _lists.get(queue))) {
76	>	try { ((LinkedList) _lists.get(queue)).wait(); } catch(Exception e) {}
77		}
78		}
79		// get an item, it should never be null due to the blocking above
80		Object o = null;
81		synchronized(this) {
82		try {
83	<	o = _lists[queue].removeFirst();
83	>	o = ((LinkedList) _lists.get(queue)).removeFirst();
84		}
85		catch (NoSuchElementException e) {
86		// This should never happen !
#	Line 107 | Line 90 | class Queue {
90		}
91
92		/**
93	<	* This method is intended for an environment where there is
94	<	* only a single consumer. It simply gets the item from the
95	<	* first (and presumably only) queue.
93	>	* This method releases a get() method that's currently
94	>	* waiting on an empty queue. This was designed for
95	>	* shutdown() type methods that may have problems closing
96	>	* if the thread of control is waiting on a queue.
97		*
98	<	* @return The object from the front of the queue.
98	>	* @param queue the queue to release
99		*/
100	<	public Object get() {
101	<	return get(0);
100	>	public void releaseQueue(int queue) {
101	>	synchronized(((LinkedList) _lists.get(queue))) {
102	>	((LinkedList) _lists.get(queue)).notifyAll();
103	>	}
104		}
105
106		/**
#	Line 128 | Line 114 | class Queue {
114		*/
115		public String status() {
116		String status = "";
117	<	for(int i=0; i < _lists.length; i++) {
118	<	status += "Queue number "+i+" contains "+_lists[i].size()+" elements";
119	<	status += "\n";
117	>	for(int i=0; i < _lists.size(); i++) {
118	>	// check for null entries
119	>	if(_lists.get(i) != null) {
120	>	status += "Queue number "+i+" contains "+((LinkedList) _lists.get(i)).size()+" elements";
121	>	status += "\n";
122	>	}
123	>	else {
124	>	status += "Slot number "+i+" is currently empty";
125	>	status += "\n";
126	>	}
127		}
128		status += "A total of "+_count+" elements have been added to the queues";
129		return status;
130		}
131
132		/**
133	+	* Returns the size of a given queue. A consumer can use
134	+	* this to see how big their queue is at any given time.
135	+	* they should use their queue number as the parameter.
136	+	*
137	+	* @param queue The queue number to query.
138	+	* @return the current size of the queue.
139	+	*/
140	+	public int queueSize(int queue) throws InvalidQueueException {
141	+	if (queue >= _lists.size() || _lists.get(queue) == null) {
142	+	throw new InvalidQueueException("Requested queue "+queue+" does not exist");
143	+	}
144	+	return ((LinkedList) _lists.get(queue)).size();
145	+	}
146	+
147	+	/**
148	+	* Returns the total numer of elements to have passed
149	+	* through this queue (ie. a counter on the add method).
150	+	*
151	+	* @return the element-ometer
152	+	*/
153	+	public int elementCount() {
154	+	return _count;
155	+	}
156	+
157	+	/**
158		* This method assigns a queue to a consumer. The idea behind
159		* this is to ensure that only 1 consumer can be associated with
160		* a given queue, otherwise the whole "blocking" thing fails
161	<	* miserably.
161	>	* miserably. Queues are created upon requested.
162		*
163	+	* It is IMPORTANT that removeQueue() is used when the queue is
164	+	* no longer required.
165	+	*
166		* @return An integer to be passed to the get() method.
146	–	* @throws NoQueueException if there are no un-assigned queue's.
167		*/
168	<	public int getQueue() throws NoQueueException {
169	<	if(_index < _lists.length) {
170	<	return _index++;
168	>	public int getQueue() {
169	>	int pos = -1;
170	>	for(int i=0; i < _lists.size(); i++) {
171	>	if(_lists.get(i) == null) {
172	>	// found a gap, re-use it
173	>	pos = i;
174	>	_lists.set(i, new LinkedList());
175	>	}
176		}
177	<	else {
178	<	throw new NoQueueException("Too many consumers, there are already "+_lists.length+" running");
177	>	if(pos == -1) {
178	>	//we didn't find a gap, add at end
179	>	pos = _lists.size();
180	>	_lists.add(pos, new LinkedList());
181		}
182	+	return pos;
183		}
184	<
184	>
185		/**
186	+	* This method sets a entry to null in the list. This ensures
187	+	* that it will no longer be added to after it is no longer
188	+	* required be a consumer.
189	+	*
190	+	* @param queue The integer identifier for the queue, given by getQueue().
191	+	*/
192	+	public void removeQueue(int queue) {
193	+	_lists.set(queue, null);
194	+	}
195	+
196	+	/**
197		* Overrides the {@link java.lang.Object#toString() Object.toString()}
198		* method to provide clean logging (every class should have this).
199		*
#	Line 163 | Line 202 | class Queue {
202		*
203		* @return the name of this class and its CVS revision
204		*/
205	<	/*public String toString() {
205	>	public String toString() {
206		return FormatName.getName(
207		_name,
208		getClass().getName(),
209		REVISION);
210	<	}*/
210	>	}
211
212		//---PRIVATE METHODS---
213
#	Line 177 | Line 216 | class Queue {
216		//---ATTRIBUTES---
217
218		/**
219	<	* The array of lists, which the underlying queue data
181	<	* is stored in.
219	>	* The LinkedLists of queues.
220		*/
221	<	private LinkedList[] _lists;
221	>	private LinkedList _lists = new LinkedList();
222
223		/**
224		* A counter so we know how many data items have been
#	Line 189 | Line 227 | class Queue {
227		private int _count = 0;
228
229		/**
192	–	* An index of the next available queue. Used by the
193	–	* getQueue() method.
194	–	*/
195	–	private int _index = 0;
196	–
197	–	/**
230		* This is the friendly identifier of the
231		* component this class is running in.
232		* eg, a Filter may be called "filter1",
#	Line 203 | Line 235 | class Queue {
235		* can be placed here.  This name could also
236		* be changed to null for utility classes.
237		*/
238	<	//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();
238	>	private String _name = null;
239
240		//---STATIC ATTRIBUTES---
241

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines