J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2003-2006 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun in the LICENSE file that accompanied this code. |
| 10 | * |
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 14 | * version 2 for more details (a copy is included in the LICENSE file that |
| 15 | * accompanied this code). |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License version |
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | package sun.management.snmp.util; |
| 26 | |
| 27 | import com.sun.jmx.snmp.SnmpOid; |
| 28 | |
| 29 | import java.io.Serializable; |
| 30 | |
| 31 | import java.util.Comparator; |
| 32 | import java.util.Arrays; |
| 33 | import java.util.TreeMap; |
| 34 | import java.util.List; |
| 35 | import java.util.Iterator; |
| 36 | |
| 37 | import java.lang.ref.WeakReference; |
| 38 | |
| 39 | /** |
| 40 | * This abstract class implements a weak cache that holds table data. |
| 41 | * <p>The table data is stored in an instance of |
| 42 | * {@link SnmpCachedData}, which is kept in a {@link WeakReference}. |
| 43 | * If the WeakReference is null or empty, the cached data is recomputed.</p> |
| 44 | * |
| 45 | * <p><b>NOTE: This class is not synchronized, subclasses must implement |
| 46 | * the appropriate synchronization when needed.</b></p> |
| 47 | **/ |
| 48 | public abstract class SnmpTableCache implements Serializable { |
| 49 | |
| 50 | /** |
| 51 | * Interval of time in ms during which the cached table data |
| 52 | * is considered valid. |
| 53 | **/ |
| 54 | protected long validity; |
| 55 | |
| 56 | /** |
| 57 | * A weak refernce holding cached table data. |
| 58 | **/ |
| 59 | protected transient WeakReference<SnmpCachedData> datas; |
| 60 | |
| 61 | /** |
| 62 | * true if the given cached table data is obsolete. |
| 63 | **/ |
| 64 | protected boolean isObsolete(SnmpCachedData cached) { |
| 65 | if (cached == null) return true; |
| 66 | if (validity < 0) return false; |
| 67 | return ((System.currentTimeMillis() - cached.lastUpdated) > validity); |
| 68 | } |
| 69 | |
| 70 | /** |
| 71 | * Returns the cached table data. |
| 72 | * Returns null if the cached data is obsolete, or if there is no |
| 73 | * cached data, or if the cached data was garbage collected. |
| 74 | * @return a still valid cached data or null. |
| 75 | **/ |
| 76 | protected SnmpCachedData getCachedDatas() { |
| 77 | if (datas == null) return null; |
| 78 | final SnmpCachedData cached = datas.get(); |
| 79 | if ((cached == null) || isObsolete(cached)) return null; |
| 80 | return cached; |
| 81 | } |
| 82 | |
| 83 | /** |
| 84 | * Returns the cached table data, if it is still valid, |
| 85 | * or recompute it if it is obsolete. |
| 86 | * <p> |
| 87 | * When cache data is recomputed, store it in the weak reference, |
| 88 | * unless {@link #validity} is 0: then the data will not be stored |
| 89 | * at all.<br> |
| 90 | * This method calls {@link #isObsolete(SnmpCachedData)} to determine |
| 91 | * whether the cached data is obsolete, and { |
| 92 | * {@link #updateCachedDatas(Object)} to recompute it. |
| 93 | * </p> |
| 94 | * @param context A context object. |
| 95 | * @return the valid cached data, or the recomputed table data. |
| 96 | **/ |
| 97 | protected synchronized SnmpCachedData getTableDatas(Object context) { |
| 98 | final SnmpCachedData cached = getCachedDatas(); |
| 99 | if (cached != null) return cached; |
| 100 | final SnmpCachedData computedDatas = updateCachedDatas(context); |
| 101 | if (validity != 0) datas = new WeakReference<SnmpCachedData>(computedDatas); |
| 102 | return computedDatas; |
| 103 | } |
| 104 | |
| 105 | /** |
| 106 | * Recompute cached data. |
| 107 | * @param context A context object, as passed to |
| 108 | * {@link #getTableDatas(Object)} |
| 109 | **/ |
| 110 | protected abstract SnmpCachedData updateCachedDatas(Object context); |
| 111 | |
| 112 | /** |
| 113 | * Return a table handler that holds the table data. |
| 114 | * This method should return the cached table data if it is still |
| 115 | * valid, recompute it and cache the new value if it's not. |
| 116 | **/ |
| 117 | public abstract SnmpTableHandler getTableHandler(); |
| 118 | |
| 119 | } |