Mercurial > hg > blitz_stable
view src/com/go/trove/util/Cache.java @ 35:6f68e94c1fb8 default tip
Add CondensedStats monitoring utility, equivalent to vmstat
author | Dominic Cleal <dominic-cleal@cdo2.com> |
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date | Thu, 05 Aug 2010 11:07:25 +0100 |
parents | 3dc0c5604566 |
children |
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/* ==================================================================== * Trove - Copyright (c) 1997-2000 Walt Disney Internet Group * ==================================================================== * The Tea Software License, Version 1.1 * * Copyright (c) 2000 Walt Disney Internet Group. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * 3. The end-user documentation included with the redistribution, * if any, must include the following acknowledgment: * "This product includes software developed by the * Walt Disney Internet Group (http://opensource.go.com/)." * Alternately, this acknowledgment may appear in the software itself, * if and wherever such third-party acknowledgments normally appear. * * 4. The names "Tea", "TeaServlet", "Kettle", "Trove" and "BeanDoc" must * not be used to endorse or promote products derived from this * software without prior written permission. For written * permission, please contact opensource@dig.com. * * 5. Products derived from this software may not be called "Tea", * "TeaServlet", "Kettle" or "Trove", nor may "Tea", "TeaServlet", * "Kettle", "Trove" or "BeanDoc" appear in their name, without prior * written permission of the Walt Disney Internet Group. * * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE WALT DISNEY INTERNET GROUP OR ITS * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. * ==================================================================== * * For more information about Tea, please see http://opensource.go.com/. */ package com.go.trove.util; import java.util.*; /****************************************************************************** * Cache is a SoftHashMap that is guaranteed to have the most recently used * entries available. Calling "get" or "put" updates the internal MRU list, * but calling "containsKey" or "containsValue" will not. * <p> * Like its base class, Cache is not thread-safe and must be wrapped with * Collections.synchronizedMap to be made thread-safe. * * @author Brian S O'Neill * @version * <!--$$Revision: 1.1 $-->, <!--$$JustDate:--> 01/05/30 <!-- $--> */ public class Cache extends SoftHashMap { private final int mMaxRecent; // Contains hard references to entries. private final UsageMap mUsageMap; /** * Construct a Cache with an amount of recently used entries that are * guaranteed to always be in the Cache. * * @param maxRecent maximum amount of recently used entries guaranteed to * be in the Cache. * @throws IllegalArgumentException if maxRecent is less than or equal to * zero. */ public Cache(int maxRecent) { if (maxRecent <= 0) { throw new IllegalArgumentException ("Max recent must be greater than zero: " + maxRecent); } mMaxRecent = maxRecent; mUsageMap = new UsageMap(); } /** * Piggyback this Cache onto another one in order for the map of recently * used entries to be shared. If this Cache is more active than the one * it attaches to, then more of its most recently used entries will be * guaranteed to be in the Cache, possibly bumping out entries from the * other Cache. */ public Cache(Cache cache) { mMaxRecent = cache.mMaxRecent; mUsageMap = cache.mUsageMap; } public Object get(Object key) { Object value = super.get(key); if (value != null || super.containsKey(key)) { adjustMRU(key, value); } return value; } public Object put(Object key, Object value) { if (value == null) { value = new Null(); } adjustMRU(key, value); return super.put(key, value); } public Object remove(Object key) { synchronized (mUsageMap) { mUsageMap.remove(key); } return super.remove(key); } public void clear() { super.clear(); synchronized (mUsageMap) { mUsageMap.clear(); } } private void adjustMRU(Object key, Object value) { synchronized (mUsageMap) { Object existing = mUsageMap.get(key); if (existing != null) { if (value == null && existing instanceof Null) { value = existing; } } else { if (!mUsageMap.containsKey(key)) { // A new entry will be put into the UsageMap, so remove // least recently used if MRU is too big. while (mUsageMap.size() >= mMaxRecent) { mUsageMap.remove(mUsageMap.lastKey()); } } } mUsageMap.put(key, value); } } }