001 /* PAVLOV -- Multiple Choice Study System
002 * Copyright (C) 2000 - 2004 T.J. Willis
003 *
004 * This program is free software; you can redistribute it and/or
005 * modify it under the terms of the GNU General Public License
006 * as published by the Free Software Foundation; either version 2
007 * of the License, or (at your option) any later version.
008 *
009 * This program is distributed in the hope that it will be useful,
010 * but WITHOUT ANY WARRANTY; without even the implied warranty of
011 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
012 * GNU General Public License for more details.
013 *
014 * You should have received a copy of the GNU General Public License
015 * along with this program; if not, write to the Free Software
016 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
017 *
018 * $Header: /cvsroot/pavlov/net/sourceforge/pavlov/randommedia/MediaCache.java,v 1.4 2004/05/10 14:58:54 tj_willis Exp $
019 */
020 package net.sourceforge.pavlov.randommedia;
021
022 import java.net.URL;
023 import org.apache.log4j.*;
024
025 /**
026 * Loads and holds a bunch of audio files whose locations are specified
027 * relative to a fixed base URL.
028 * @author <a href="mailto:tj_willis@users.sourceforge.net">T.J. Willis</a>
029 * @version 1.0
030 */
031 public abstract class MediaCache extends java.util.Stack<Object> {
032 private int maxPriorityBound = 3;
033 private int normPriorityBound = 5;
034 private volatile int numLoading;
035 private int maxLoading = 10;
036 RandomURLProvider provider;
037 private Category cat
038 = Category.getInstance(MediaCache.class.getName());
039
040 /**
041 * Creates a new <code>MediaCache</code> instance.
042 *
043 * @param p a <code>RandomURLProvider</code> value
044 * @param mySize an <code>int</code> value
045 */
046 public MediaCache(RandomURLProvider p,int mySize) {
047 super();
048 provider = p;
049 assert provider!=null: "RandomURLProvider is null";
050 ensureCapacity(mySize);
051 numLoading = 0;
052 }
053
054 /**
055 * Describe <code>startLoading</code> method here.
056 *
057 * @param url an <code>URL</code> value
058 */
059 public void startLoading(URL url) {
060 if(numLoading>maxLoading) return;
061 if(url==null){
062 cat.warn("null url in startLoading");
063 return;
064 }
065 int pri = Thread.MIN_PRIORITY;
066 if(size()<=maxPriorityBound) pri = Thread.MAX_PRIORITY;
067 else if(size()<normPriorityBound) pri = Thread.NORM_PRIORITY;
068 //cat.debug(numLoading + "/" + maxLoading + ": Cache Loading: " + url + " at priority: " + pri + ": size is: " + size());
069 numLoading++;
070 //createMediaLoader(this,url,pri);
071 new MediaLoader(this, url,pri);
072 }
073
074
075 /**
076 * Describe <code>getObject</code> method here.
077 *
078 * @return an <code>Object</code> value
079 */
080 public Object getObject() {
081 if (size()<1) return null;
082 //FIXME: change this to synchronously load an object
083 //cat.debug("size is " + size());
084 manageCache();
085 return pop();
086 }
087
088 void decrementNumberLoading()
089 {
090 if(numLoading<=0) return;
091 numLoading-=1;
092 }
093
094 /**
095 * Describe <code>add</code> method here.
096 *
097 * @param obj an <code>Object</code> value
098 * @return a <code>boolean</code> value
099 */
100 public boolean add(Object obj) {
101 numLoading--;
102 return super.add(obj);
103 }
104
105 /**
106 * Describe <code>clearCache</code> method here.
107 *
108 */
109 public void clearCache()
110 {
111 super.clear();
112 // FIXME: this is unimplemented
113 //clear();
114 }
115
116 /**
117 * Describe <code>manageCache</code> method here.
118 *
119 */
120 public void manageCache()
121 {
122 int ss = size();
123 if(ss<7)
124 loadObjects(1);
125 if(ss<5)
126 loadObjects(2);
127 if(ss<3)
128 loadObjects(4);
129 }
130
131 void loadObjects(int num)
132 {
133 assert provider!=null : "loadMedia: RandomURLProvider is null";
134 for(int i=0;i<num;i++)
135 {
136 URL it = provider.getRandomURL();
137 if(it!=null)
138 startLoading(it);
139 }
140 }
141
142 abstract ContentLoader getContentLoader();
143
144 }