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 | } | ||