001 /** 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.activemq.memory; 018 019 /** 020 * Maintains a simple linked list of CacheEntry objects. It is thread safe. 021 * 022 * 023 */ 024 public class CacheEntryList { 025 026 // Points at the tail of the CacheEntry list 027 public final CacheEntry tail = new CacheEntry(null, null); 028 029 public CacheEntryList() { 030 tail.next = tail; 031 tail.previous = tail; 032 } 033 034 public void add(CacheEntry ce) { 035 addEntryBefore(tail, ce); 036 } 037 038 private void addEntryBefore(CacheEntry position, CacheEntry ce) { 039 assert ce.key != null && ce.next == null && ce.owner == null; 040 041 synchronized (tail) { 042 ce.owner = this; 043 ce.next = position; 044 ce.previous = position.previous; 045 ce.previous.next = ce; 046 ce.next.previous = ce; 047 } 048 } 049 050 public void clear() { 051 synchronized (tail) { 052 tail.next = tail; 053 tail.previous = tail; 054 } 055 } 056 057 public CacheEvictor createFIFOCacheEvictor() { 058 return new CacheEvictor() { 059 public CacheEntry evictCacheEntry() { 060 CacheEntry rc; 061 synchronized (tail) { 062 rc = tail.next; 063 } 064 return rc.remove() ? rc : null; 065 } 066 }; 067 } 068 069 public CacheEvictor createLIFOCacheEvictor() { 070 return new CacheEvictor() { 071 public CacheEntry evictCacheEntry() { 072 CacheEntry rc; 073 synchronized (tail) { 074 rc = tail.previous; 075 } 076 return rc.remove() ? rc : null; 077 } 078 }; 079 } 080 081 }