aoqi@0: /*
aoqi@0:  * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
aoqi@0:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
aoqi@0:  *
aoqi@0:  * This code is free software; you can redistribute it and/or modify it
aoqi@0:  * under the terms of the GNU General Public License version 2 only, as
aoqi@0:  * published by the Free Software Foundation.  Oracle designates this
aoqi@0:  * particular file as subject to the "Classpath" exception as provided
aoqi@0:  * by Oracle in the LICENSE file that accompanied this code.
aoqi@0:  *
aoqi@0:  * This code is distributed in the hope that it will be useful, but WITHOUT
aoqi@0:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
aoqi@0:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
aoqi@0:  * version 2 for more details (a copy is included in the LICENSE file that
aoqi@0:  * accompanied this code).
aoqi@0:  *
aoqi@0:  * You should have received a copy of the GNU General Public License version
aoqi@0:  * 2 along with this work; if not, write to the Free Software Foundation,
aoqi@0:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
aoqi@0:  *
aoqi@0:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
aoqi@0:  * or visit www.oracle.com if you need additional information or have any
aoqi@0:  * questions.
aoqi@0:  */
aoqi@0: 
aoqi@0: package com.sun.istack.internal;
aoqi@0: 
aoqi@0: import java.util.concurrent.ConcurrentLinkedQueue;
aoqi@0: import java.lang.ref.WeakReference;
aoqi@0: 
aoqi@0: /**
aoqi@0:  * Pool of reusable objects that are indistinguishable from each other,
aoqi@0:  * such as JAXB marshallers.
aoqi@0:  *
aoqi@0:  * @author Kohsuke Kawaguchi
aoqi@0:  */
aoqi@0: public interface Pool<T> {
aoqi@0: 
aoqi@0:     /**
aoqi@0:      * Gets a new object from the pool.
aoqi@0:      *
aoqi@0:      * <p>
aoqi@0:      * If no object is available in the pool, this method creates a new one.
aoqi@0:      */
aoqi@0:     @NotNull T take();
aoqi@0: 
aoqi@0:     /**
aoqi@0:      * Returns an object back to the pool.
aoqi@0:      */
aoqi@0:     void recycle(@NotNull T t);
aoqi@0: 
aoqi@0:     /**
aoqi@0:      * Default implementation that uses {@link ConcurrentLinkedQueue}
aoqi@0:      * as the data store.
aoqi@0:      *
aoqi@0:      * <h2>Note for Implementors</h2>
aoqi@0:      * <p>
aoqi@0:      * Don't rely on the fact that this class extends from {@link ConcurrentLinkedQueue}.
aoqi@0:      */
aoqi@0:     public abstract class Impl<T> implements Pool<T> {
aoqi@0: 
aoqi@0:         private volatile WeakReference<ConcurrentLinkedQueue<T>> queue;
aoqi@0: 
aoqi@0:         /**
aoqi@0:          * Gets a new object from the pool.
aoqi@0:          *
aoqi@0:          * <p>
aoqi@0:          * If no object is available in the pool, this method creates a new one.
aoqi@0:          *
aoqi@0:          * @return
aoqi@0:          *      always non-null.
aoqi@0:          */
aoqi@0:         public final @NotNull T take() {
aoqi@0:             T t = getQueue().poll();
aoqi@0:             if(t==null) {
aoqi@0:                 return create();
aoqi@0:             }
aoqi@0:             return t;
aoqi@0:         }
aoqi@0: 
aoqi@0:         /**
aoqi@0:          * Returns an object back to the pool.
aoqi@0:          */
aoqi@0:         public final void recycle(T t) {
aoqi@0:             getQueue().offer(t);
aoqi@0:         }
aoqi@0: 
aoqi@0:         private ConcurrentLinkedQueue<T> getQueue() {
aoqi@0:             WeakReference<ConcurrentLinkedQueue<T>> q = queue;
aoqi@0:             if (q != null) {
aoqi@0:                 ConcurrentLinkedQueue<T> d = q.get();
aoqi@0:                 if (d != null) {
aoqi@0:                     return d;
aoqi@0:                 }
aoqi@0:             }
aoqi@0:             // overwrite the queue
aoqi@0:             ConcurrentLinkedQueue<T> d = new ConcurrentLinkedQueue<T>();
aoqi@0:             queue = new WeakReference<ConcurrentLinkedQueue<T>>(d);
aoqi@0: 
aoqi@0:             return d;
aoqi@0:         }
aoqi@0: 
aoqi@0:         /**
aoqi@0:          * Creates a new instance of object.
aoqi@0:          *
aoqi@0:          * <p>
aoqi@0:          * This method is used when someone wants to
aoqi@0:          * {@link #take() take} an object from an empty pool.
aoqi@0:          *
aoqi@0:          * <p>
aoqi@0:          * Also note that multiple threads may call this method
aoqi@0:          * concurrently.
aoqi@0:          */
aoqi@0:         protected abstract @NotNull T create();
aoqi@0:     }
aoqi@0: }