Showing the changes to java/pkg/sun/management/snmp/util/SnmpTableCache.java (1 of 18352 files). Show all
Unified · Split
| @@ -0,0 +1,119 @@ | ||
| 1 | +/* | |
| 2 | + * Copyright (c) 2003, 2006, Oracle and/or its affiliates. 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. Oracle designates this | |
| 8 | + * particular file as subject to the "Classpath" exception as provided | |
| 9 | + * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| 22 | + * or visit www.oracle.com if you need additional information or have any | |
| 23 | + * 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 | +} | |