1 /*
   2  * Copyright (c) 1997, 2017, 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.xml.internal.ws.util;
  27 
  28 import com.sun.xml.internal.ws.api.pipe.Tube;
  29 import com.sun.xml.internal.ws.api.pipe.TubeCloner;
  30 
  31 import javax.xml.bind.JAXBContext;
  32 import javax.xml.bind.JAXBException;
  33 
  34 import java.util.concurrent.ConcurrentLinkedQueue;
  35 import java.lang.ref.SoftReference;
  36 
  37 
  38 /**
  39  * General-purpose object pool.
  40  *
  41  * <p>
  42  * In many parts of the runtime, we need to pool instances of objects that
  43  * are expensive to create (such as JAXB objects, StAX parsers, {@link Tube} instances.)
  44  *
  45  * <p>
  46  * This class provides a default implementation of such a pool.
  47  *
  48  * TODO: improve the implementation
  49  *
  50  * @author Kohsuke Kawaguchi
  51  */
  52 public abstract class Pool<T> {
  53 
  54     // volatile since multiple threads may access queue reference
  55     private volatile SoftReference<ConcurrentLinkedQueue<T>> queue;
  56 
  57     /**
  58      * Gets a new object from the pool.
  59      *
  60      * <p>
  61      * If no object is available in the pool, this method creates a new one.
  62      *
  63      * @return
  64      *      always non-null.
  65      */
  66     public final T take() {
  67         T t = getQueue().poll();
  68         if(t==null)
  69             return create();
  70         return t;
  71     }
  72 
  73     private ConcurrentLinkedQueue<T> getQueue() {
  74         SoftReference<ConcurrentLinkedQueue<T>> q = queue;
  75         if (q != null) {
  76             ConcurrentLinkedQueue<T> d = q.get();
  77             if (d != null)
  78                 return d;
  79         }
  80 
  81         // overwrite the queue
  82         ConcurrentLinkedQueue<T> d = new ConcurrentLinkedQueue<T>();
  83         queue = new SoftReference<ConcurrentLinkedQueue<T>>(d);
  84 
  85         return d;
  86     }
  87 
  88     /**
  89      * Returns an object back to the pool.
  90      */
  91     public final void recycle(T t) {
  92         getQueue().offer(t);
  93     }
  94 
  95     /**
  96      * Creates a new instance of object.
  97      *
  98      * <p>
  99      * This method is used when someone wants to
 100      * {@link #take() take} an object from an empty pool.
 101      *
 102      * <p>
 103      * Also note that multiple threads may call this method
 104      * concurrently.
 105      */
 106     protected abstract T create();
 107 
 108 
 109     /**
 110      * JAXB {@link javax.xml.bind.Marshaller} pool.
 111      */
 112     public static final class Marshaller extends Pool<javax.xml.bind.Marshaller> {
 113         private final JAXBContext context;
 114 
 115         public Marshaller(JAXBContext context) {
 116             this.context = context;
 117         }
 118 
 119         @Override
 120         protected javax.xml.bind.Marshaller create() {
 121             try {
 122                 return context.createMarshaller();
 123             } catch (JAXBException e) {
 124                 // impossible
 125                 throw new AssertionError(e);
 126             }
 127         }
 128     }
 129 
 130     /**
 131      * JAXB {@link javax.xml.bind.Marshaller} pool.
 132      */
 133     public static final class Unmarshaller extends Pool<javax.xml.bind.Unmarshaller> {
 134         private final JAXBContext context;
 135 
 136         public Unmarshaller(JAXBContext context) {
 137             this.context = context;
 138         }
 139 
 140         @Override
 141         protected javax.xml.bind.Unmarshaller create() {
 142             try {
 143                 return context.createUnmarshaller();
 144             } catch (JAXBException e) {
 145                 // impossible
 146                 throw new AssertionError(e);
 147             }
 148         }
 149     }
 150 
 151     /**
 152      * {@link Tube} pool.
 153      */
 154     public static final class TubePool extends Pool<Tube> {
 155         private final Tube master;
 156 
 157         public TubePool(Tube master) {
 158             this.master = master;
 159             recycle(master);    // we'll use master as a part of the pool, too.
 160         }
 161 
 162         @Override
 163         protected Tube create() {
 164             return TubeCloner.clone(master);
 165         }
 166 
 167         /**
 168          *
 169          * @return master tubeline from pool
 170          * @deprecated Expected to be used in rare cases where access to master
 171          * tubeline is required and safe, such as Stub.close()."
 172          */
 173         @Deprecated()
 174         public final Tube takeMaster() {
 175             return master;
 176         }
 177 
 178     }
 179 }
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