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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 1.6 by tdb, Tue Jan 30 02:13:09 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 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
#	Line 128 | Line 129 | class Queue {
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";
132	>	for(int i=0; i < _lists.size(); i++) {
133	>	// check for null entries
134	>	if(_lists.get(i) != null) {
135	>	status += "Queue number "+i+" contains "+((LinkedList) _lists.get(i)).size()+" elements";
136	>	status += "\n";
137	>	}
138	>	else {
139	>	status += "Slot number "+i+" is currently empty";
140	>	status += "\n";
141	>	}
142		}
143		status += "A total of "+_count+" elements have been added to the queues";
144		return status;
145		}
146
147		/**
148	+	* Returns the size of a given queue. A consumer can use
149	+	* this to see how big their queue is at any given time.
150	+	* they should use their queue number as the parameter.
151	+	*
152	+	* @param queue The queue number to query.
153	+	* @return the current size of the queue.
154	+	* @throws InvalidQueueException if the queue does not exist.
155	+	*/
156	+	public int queueSize(int queue) throws InvalidQueueException {
157	+	if (queue >= _lists.size() || _lists.get(queue) == null) {
158	+	throw new InvalidQueueException("Requested queue "+queue+" does not exist");
159	+	}
160	+	return ((LinkedList) _lists.get(queue)).size();
161	+	}
162	+
163	+	/**
164	+	* Returns the total numer of elements to have passed
165	+	* through this queue (ie. a counter on the add method).
166	+	*
167	+	* @return the element-ometer.
168	+	*/
169	+	public int elementCount() {
170	+	return _count;
171	+	}
172	+
173	+	/**
174		* This method assigns a queue to a consumer. The idea behind
175		* this is to ensure that only 1 consumer can be associated with
176		* a given queue, otherwise the whole "blocking" thing fails
177	<	* miserably.
177	>	* miserably. Queues are created upon requested.
178		*
179	+	* It is IMPORTANT that removeQueue() is used when the queue is
180	+	* no longer required.
181	+	*
182		* @return An integer to be passed to the get() method.
146	–	* @throws NoQueueException if there are no un-assigned queue's.
183		*/
184	<	public int getQueue() throws NoQueueException {
185	<	if(_index < _lists.length) {
186	<	return _index++;
184	>	public int getQueue() {
185	>	int pos = -1;
186	>	for(int i=0; i < _lists.size(); i++) {
187	>	if(_lists.get(i) == null) {
188	>	// found a gap, re-use it
189	>	pos = i;
190	>	_lists.set(i, new LinkedList());
191	>	}
192		}
193	<	else {
194	<	throw new NoQueueException("Too many consumers, there are already "+_lists.length+" running");
193	>	if(pos == -1) {
194	>	//we didn't find a gap, add at end
195	>	pos = _lists.size();
196	>	_lists.add(pos, new LinkedList());
197		}
198	+	return pos;
199		}
200	<
200	>
201		/**
202	+	* This method sets a entry to null in the list. This ensures
203	+	* that it will no longer be added to after it is no longer
204	+	* required be a consumer.
205	+	*
206	+	* @param queue The integer identifier for the queue, given by getQueue().
207	+	*/
208	+	public void removeQueue(int queue) {
209	+	_lists.set(queue, null);
210	+	}
211	+
212	+	/**
213		* Overrides the {@link java.lang.Object#toString() Object.toString()}
214		* method to provide clean logging (every class should have this).
215		*
216		* This uses the uk.ac.ukc.iscream.util.FormatName class
217		* to format the toString()
218		*
219	<	* @return the name of this class and its CVS revision
219	>	* @return the name of this class and its CVS revision.
220		*/
221	<	/*public String toString() {
221	>	public String toString() {
222		return FormatName.getName(
223		_name,
224		getClass().getName(),
225		REVISION);
226	<	}*/
226	>	}
227
228		//---PRIVATE METHODS---
229
#	Line 177 | Line 232 | class Queue {
232		//---ATTRIBUTES---
233
234		/**
235	<	* The array of lists, which the underlying queue data
181	<	* is stored in.
235	>	* The LinkedLists of queues.
236		*/
237	<	private LinkedList[] _lists;
237	>	private LinkedList _lists = new LinkedList();
238
239		/**
240		* A counter so we know how many data items have been
#	Line 189 | Line 243 | class Queue {
243		private int _count = 0;
244
245		/**
192	–	* An index of the next available queue. Used by the
193	–	* getQueue() method.
194	–	*/
195	–	private int _index = 0;
196	–
197	–	/**
246		* This is the friendly identifier of the
247		* component this class is running in.
248		* eg, a Filter may be called "filter1",
#	Line 203 | Line 251 | class Queue {
251		* can be placed here.  This name could also
252		* be changed to null for utility classes.
253		*/
254	<	//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();
254	>	private String _name = null;
255
256		//---STATIC ATTRIBUTES---
257

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