Mercurial > hg > blitz_stable
diff src/com/go/trove/util/Cache.java @ 0:3dc0c5604566
Initial checkin of blitz 2.0 fcs - no installer yet.
author | Dan Creswell <dan.creswell@gmail.com> |
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date | Sat, 21 Mar 2009 11:00:06 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/com/go/trove/util/Cache.java Sat Mar 21 11:00:06 2009 +0000 @@ -0,0 +1,156 @@ +/* ==================================================================== + * 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); + } + } +}