1 /* 2 * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package com.sun.istack.internal; 27 28 import java.util.concurrent.ConcurrentLinkedQueue; 29 import java.lang.ref.WeakReference; 30 31 /** 32 * Pool of reusable objects that are indistinguishable from each other, 33 * such as JAXB marshallers. 34 * 35 * @author Kohsuke Kawaguchi 36 */ 37 public interface Pool<T> { 38 39 /** 40 * Gets a new object from the pool. 41 * 42 * <p> 43 * If no object is available in the pool, this method creates a new one. 44 */ 45 @NotNull T take(); 46 47 /** 48 * Returns an object back to the pool. 49 */ 50 void recycle(@NotNull T t); 51 52 /** 53 * Default implementation that uses {@link ConcurrentLinkedQueue} 54 * as the data store. 55 * 56 * <h2>Note for Implementors</h2> 57 * <p> 58 * Don't rely on the fact that this class extends from {@link ConcurrentLinkedQueue}. 59 */ 60 public abstract class Impl<T> implements Pool<T> { 61 62 private volatile WeakReference<ConcurrentLinkedQueue<T>> queue; 63 64 /** 65 * Gets a new object from the pool. 66 * 67 * <p> 68 * If no object is available in the pool, this method creates a new one. 69 * 70 * @return 71 * always non-null. 72 */ 73 public final @NotNull T take() { 74 T t = getQueue().poll(); 75 if(t==null) { 76 return create(); 77 } 78 return t; 79 } 80 81 /** 82 * Returns an object back to the pool. 83 */ 84 public final void recycle(T t) { 85 getQueue().offer(t); 86 } 87 88 private ConcurrentLinkedQueue<T> getQueue() { 89 WeakReference<ConcurrentLinkedQueue<T>> q = queue; 90 if (q != null) { 91 ConcurrentLinkedQueue<T> d = q.get(); 92 if (d != null) { 93 return d; 94 } 95 } 96 // overwrite the queue 97 ConcurrentLinkedQueue<T> d = new ConcurrentLinkedQueue<T>(); 98 queue = new WeakReference<ConcurrentLinkedQueue<T>>(d); 99 100 return d; 101 } 102 103 /** 104 * Creates a new instance of object. 105 * 106 * <p> 107 * This method is used when someone wants to 108 * {@link #take() take} an object from an empty pool. 109 * 110 * <p> 111 * Also note that multiple threads may call this method 112 * concurrently. 113 */ 114 protected abstract @NotNull T create(); 115 } 116 }