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Java > Open Source Codes > org > archive > util > fingerprint > LongFPSetCache


1 /* Copyright (C) 2003 Internet Archive.
2  *
3  * This file is part of the Heritrix web crawler (crawler.archive.org).
4  *
5  * Heritrix is free software; you can redistribute it and/or modify
6  * it under the terms of the GNU Lesser Public License as published by
7  * the Free Software Foundation; either version 2.1 of the License, or
8  * any later version.
9  *
10  * Heritrix 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 Lesser Public License for more details.
14  *
15  * You should have received a copy of the GNU Lesser Public License
16  * along with Heritrix; if not, write to the Free Software
17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18  *
19  * LongFPSetCache.java
20  * Created on Oct 21, 2003
21  *
22  * $Header: /cvsroot/archive-crawler/ArchiveOpenCrawler/src/java/org/archive/util/fingerprint/LongFPSetCache.java,v 1.1.16.1 2007/01/13 01:31:40 stack-sf Exp $
23  */
24 package org.archive.util.fingerprint;
25
26
27
28 /**
29  * Like a MemLongFPSet, but with fixed capacity and maximum size.
30  * When an add would expand past the maximum size, an old entry
31  * is deleted via a clock/counter algorithm.
32  *
33  * @author gojomo
34  *
35  */
36 public class LongFPSetCache extends MemLongFPSet {
37     
38     private static final long serialVersionUID = -5307436423975825566L;
39
40     long sweepHand = 0;
41
42     public LongFPSetCache() {
43         super();
44     }
45
46     public LongFPSetCache(int capacityPowerOfTwo, float loadFactor) {
47         super(capacityPowerOfTwo, loadFactor);
48     }
49
50     protected void noteAccess(long index) {
51         if(slots[(int)index]<Byte.MAX_VALUE) {
52             slots[(int)index]++;
53         }
54     }
55
56     protected void makeSpace() {
57         discard(1);
58     }
59
60     private void discard(int i) {
61         int toDiscard = i;
62         while(toDiscard>0) {
63             if(slots[(int)sweepHand]==0) {
64                 removeAt(sweepHand);
65                 toDiscard--;
66             } else {
67                 if (slots[(int)sweepHand]>0) {
68                     slots[(int)sweepHand]--;
69                 }
70             }
71             sweepHand++;
72             if (sweepHand==slots.length) {
73                 sweepHand = 0;
74             }
75         }
76     }
77 }
78
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