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2362N/A * published by the Free Software Foundation. Oracle designates this
0N/A * particular file as subject to the "Classpath" exception as provided
2362N/A * by Oracle in the LICENSE file that accompanied this code.
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0N/A * version 2 for more details (a copy is included in the LICENSE file that
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0N/A */
0N/Apackage sun.management.snmp.util;
0N/A
0N/Aimport com.sun.jmx.snmp.SnmpOid;
0N/A
0N/Aimport java.io.Serializable;
0N/A
0N/Aimport java.util.Comparator;
0N/Aimport java.util.Arrays;
0N/Aimport java.util.TreeMap;
0N/Aimport java.util.List;
0N/Aimport java.util.Iterator;
0N/A
0N/Aimport java.lang.ref.WeakReference;
0N/A
0N/A/**
0N/A * This abstract class implements a weak cache that holds table data.
0N/A * <p>The table data is stored in an instance of
0N/A * {@link SnmpCachedData}, which is kept in a {@link WeakReference}.
0N/A * If the WeakReference is null or empty, the cached data is recomputed.</p>
0N/A *
0N/A * <p><b>NOTE: This class is not synchronized, subclasses must implement
0N/A * the appropriate synchronization when needed.</b></p>
0N/A **/
0N/Apublic abstract class SnmpTableCache implements Serializable {
0N/A
0N/A /**
0N/A * Interval of time in ms during which the cached table data
0N/A * is considered valid.
0N/A **/
0N/A protected long validity;
0N/A
0N/A /**
0N/A * A weak refernce holding cached table data.
0N/A **/
0N/A protected transient WeakReference<SnmpCachedData> datas;
0N/A
0N/A /**
0N/A * true if the given cached table data is obsolete.
0N/A **/
0N/A protected boolean isObsolete(SnmpCachedData cached) {
0N/A if (cached == null) return true;
0N/A if (validity < 0) return false;
0N/A return ((System.currentTimeMillis() - cached.lastUpdated) > validity);
0N/A }
0N/A
0N/A /**
0N/A * Returns the cached table data.
0N/A * Returns null if the cached data is obsolete, or if there is no
0N/A * cached data, or if the cached data was garbage collected.
0N/A * @return a still valid cached data or null.
0N/A **/
0N/A protected SnmpCachedData getCachedDatas() {
0N/A if (datas == null) return null;
0N/A final SnmpCachedData cached = datas.get();
0N/A if ((cached == null) || isObsolete(cached)) return null;
0N/A return cached;
0N/A }
0N/A
0N/A /**
0N/A * Returns the cached table data, if it is still valid,
0N/A * or recompute it if it is obsolete.
0N/A * <p>
0N/A * When cache data is recomputed, store it in the weak reference,
0N/A * unless {@link #validity} is 0: then the data will not be stored
0N/A * at all.<br>
0N/A * This method calls {@link #isObsolete(SnmpCachedData)} to determine
0N/A * whether the cached data is obsolete, and {
0N/A * {@link #updateCachedDatas(Object)} to recompute it.
0N/A * </p>
0N/A * @param context A context object.
0N/A * @return the valid cached data, or the recomputed table data.
0N/A **/
0N/A protected synchronized SnmpCachedData getTableDatas(Object context) {
0N/A final SnmpCachedData cached = getCachedDatas();
0N/A if (cached != null) return cached;
0N/A final SnmpCachedData computedDatas = updateCachedDatas(context);
0N/A if (validity != 0) datas = new WeakReference<SnmpCachedData>(computedDatas);
0N/A return computedDatas;
0N/A }
0N/A
0N/A /**
0N/A * Recompute cached data.
0N/A * @param context A context object, as passed to
0N/A * {@link #getTableDatas(Object)}
0N/A **/
0N/A protected abstract SnmpCachedData updateCachedDatas(Object context);
0N/A
0N/A /**
0N/A * Return a table handler that holds the table data.
0N/A * This method should return the cached table data if it is still
0N/A * valid, recompute it and cache the new value if it's not.
0N/A **/
0N/A public abstract SnmpTableHandler getTableHandler();
0N/A
0N/A}