/* * Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */package sun.management.snmp.util;import com.sun.jmx.snmp.SnmpOid;import java.io.Serializable;import java.util.Comparator;import java.util.Arrays;import java.util.TreeMap;import java.util.List;import java.util.Iterator;import java.lang.ref.WeakReference;/** * This abstract class implements a weak cache that holds table data. * <p>The table data is stored in an instance of * {@link SnmpCachedData}, which is kept in a {@link WeakReference}. * If the WeakReference is null or empty, the cached data is recomputed.</p> * * <p><b>NOTE: This class is not synchronized, subclasses must implement * the appropriate synchronization when needed.</b></p> **/public abstract class SnmpTableCache implements Serializable { /** * Interval of time in ms during which the cached table data * is considered valid. **/ protected long validity; /** * A weak refernce holding cached table data. **/ protected transient WeakReference<SnmpCachedData> datas; /** * true if the given cached table data is obsolete. **/ protected boolean isObsolete(SnmpCachedData cached) { if (cached == null) return true; if (validity < 0) return false; return ((System.currentTimeMillis() - cached.lastUpdated) > validity); } /** * Returns the cached table data. * Returns null if the cached data is obsolete, or if there is no * cached data, or if the cached data was garbage collected. * @return a still valid cached data or null. **/ protected SnmpCachedData getCachedDatas() { if (datas == null) return null; final SnmpCachedData cached = datas.get(); if ((cached == null) || isObsolete(cached)) return null; return cached; } /** * Returns the cached table data, if it is still valid, * or recompute it if it is obsolete. * <p> * When cache data is recomputed, store it in the weak reference, * unless {@link #validity} is 0: then the data will not be stored * at all.<br> * This method calls {@link #isObsolete(SnmpCachedData)} to determine * whether the cached data is obsolete, and { * {@link #updateCachedDatas(Object)} to recompute it. * </p> * @param context A context object. * @return the valid cached data, or the recomputed table data. **/ protected synchronized SnmpCachedData getTableDatas(Object context) { final SnmpCachedData cached = getCachedDatas(); if (cached != null) return cached; final SnmpCachedData computedDatas = updateCachedDatas(context); if (validity != 0) datas = new WeakReference<SnmpCachedData>(computedDatas); return computedDatas; } /** * Recompute cached data. * @param context A context object, as passed to * {@link #getTableDatas(Object)} **/ protected abstract SnmpCachedData updateCachedDatas(Object context); /** * Return a table handler that holds the table data. * This method should return the cached table data if it is still * valid, recompute it and cache the new value if it's not. **/ public abstract SnmpTableHandler getTableHandler();}
/*
* Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package sun.management.snmp.util;
import com.sun.jmx.snmp.SnmpOid;
import java.io.Serializable;
import java.util.Comparator;
import java.util.Arrays;
import java.util.TreeMap;
import java.util.List;
import java.util.Iterator;
import java.lang.ref.WeakReference;
/**
* This abstract class implements a weak cache that holds table data.
* <p>The table data is stored in an instance of
* {@link SnmpCachedData}, which is kept in a {@link WeakReference}.
* If the WeakReference is null or empty, the cached data is recomputed.</p>
*
* <p><b>NOTE: This class is not synchronized, subclasses must implement
* the appropriate synchronization when needed.</b></p>
**/
public abstract class SnmpTableCache implements Serializable {
/**
* Interval of time in ms during which the cached table data
* is considered valid.
**/
protected long validity;
/**
* A weak refernce holding cached table data.
**/
protected transient WeakReference<SnmpCachedData> datas;
/**
* true if the given cached table data is obsolete.
**/
protected boolean isObsolete(SnmpCachedData cached) {
if (cached == null) return true;
if (validity < 0) return false;
return ((System.currentTimeMillis() - cached.lastUpdated) > validity);
}
/**
* Returns the cached table data.
* Returns null if the cached data is obsolete, or if there is no
* cached data, or if the cached data was garbage collected.
* @return a still valid cached data or null.
**/
protected SnmpCachedData getCachedDatas() {
if (datas == null) return null;
final SnmpCachedData cached = datas.get();
if ((cached == null) || isObsolete(cached)) return null;
return cached;
}
/**
* Returns the cached table data, if it is still valid,
* or recompute it if it is obsolete.
* <p>
* When cache data is recomputed, store it in the weak reference,
* unless {@link #validity} is 0: then the data will not be stored
* at all.<br>
* This method calls {@link #isObsolete(SnmpCachedData)} to determine
* whether the cached data is obsolete, and {
* {@link #updateCachedDatas(Object)} to recompute it.
* </p>
* @param context A context object.
* @return the valid cached data, or the recomputed table data.
**/
protected synchronized SnmpCachedData getTableDatas(Object context) {
final SnmpCachedData cached = getCachedDatas();
if (cached != null) return cached;
final SnmpCachedData computedDatas = updateCachedDatas(context);
if (validity != 0) datas = new WeakReference<SnmpCachedData>(computedDatas);
return computedDatas;
}
/**
* Recompute cached data.
* @param context A context object, as passed to
* {@link #getTableDatas(Object)}
**/
protected abstract SnmpCachedData updateCachedDatas(Object context);
/**
* Return a table handler that holds the table data.
* This method should return the cached table data if it is still
* valid, recompute it and cache the new value if it's not.
**/
public abstract SnmpTableHandler getTableHandler();
}