Mercurial > jdk8-mips64-public > nashorn / file revision

 /*

  * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 /*

  * This file is available under and governed by the GNU General Public

  * License version 2 only, as published by the Free Software Foundation.

  * However, the following notice accompanied the original version of this

  * file, and Oracle licenses the original version of this file under the BSD

  * license:

  */

 /*

    Copyright 2009-2013 Attila Szegedi

    Licensed under both the Apache License, Version 2.0 (the "Apache License")

    and the BSD License (the "BSD License"), with licensee being free to

    choose either of the two at their discretion.

    You may not use this file except in compliance with either the Apache

    License or the BSD License.

    If you choose to use this file in compliance with the Apache License, the

    following notice applies to you:

        You may obtain a copy of the Apache License at

            http://www.apache.org/licenses/LICENSE-2.0

        Unless required by applicable law or agreed to in writing, software

        distributed under the License is distributed on an "AS IS" BASIS,

        WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or

        implied. See the License for the specific language governing

        permissions and limitations under the License.

    If you choose to use this file in compliance with the BSD License, the

    following notice applies to you:

        Redistribution and use in source and binary forms, with or without

        modification, are permitted provided that the following conditions are

        met:

        * Redistributions of source code must retain the above copyright

          notice, this list of conditions and the following disclaimer.

        * 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.

        * Neither the name of the copyright holder nor the names of

          contributors may be used to endorse or promote products derived from

          this software without specific prior written permission.

        THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS

        IS" AND ANY EXPRESS 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 COPYRIGHT HOLDER

        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.

 */

 package jdk.internal.dynalink.support;

 import java.lang.ref.Reference;

 import java.lang.ref.SoftReference;

 import java.security.AccessController;

 import java.security.PrivilegedAction;

 import java.util.Map;

 import java.util.WeakHashMap;

 import java.util.concurrent.ConcurrentHashMap;

 import java.util.concurrent.ConcurrentMap;

 /**

  * A dual map that can either strongly or weakly reference a given class depending on whether the class is visible from

  * a class loader or not.

  *

  * @author Attila Szegedi

  * @param <T> the type of the values in the map

  */

 public abstract class ClassMap<T> {

     private final ConcurrentMap<Class<?>, T> map = new ConcurrentHashMap<>();

     private final Map<Class<?>, Reference<T>> weakMap = new WeakHashMap<>();

     private final ClassLoader classLoader;

     /**

      * Creates a new class map. It will use strong references for all keys and values where the key is a class visible

      * from the class loader, and will use weak keys and soft values for all other classes.

      *

      * @param classLoader the classloader that determines strong referenceability.

      */

     protected ClassMap(ClassLoader classLoader) {

         this.classLoader = classLoader;

     }

     /**

      * Compute the value associated with the given class. It is possible that the method will be invoked several times

      * (or even concurrently) for the same class parameter.

      *

      * @param clazz the class to compute the value for

      * @return the return value. Must not be null.

      */

     protected abstract T computeValue(Class<?> clazz);

     /**

      * Returns the value associated with the class

      *

      * @param clazz the class

      * @return the value associated with the class

      */

     public T get(final Class<?> clazz) {

         // Check in fastest first - objects we're allowed to strongly reference

         final T v = map.get(clazz);

         if(v != null) {

             return v;

         }

         // Check objects we're not allowed to strongly reference

         Reference<T> ref;

         synchronized(weakMap) {

             ref = weakMap.get(clazz);

         }

         if(ref != null) {

             final T refv = ref.get();

             if(refv != null) {

                 return refv;

             }

         }

         // Not found in either place; create a new value

         final T newV = computeValue(clazz);

         assert newV != null;

         final ClassLoader clazzLoader = AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() {

             @Override

             public ClassLoader run() {

                 return clazz.getClassLoader();

             }

         }, ClassLoaderGetterContextProvider.GET_CLASS_LOADER_CONTEXT);

         // If allowed to strongly reference, put it in the fast map

         if(Guards.canReferenceDirectly(classLoader, clazzLoader)) {

             final T oldV = map.putIfAbsent(clazz, newV);

             return oldV != null ? oldV : newV;

         }

         // Otherwise, put it into the weak map

         synchronized(weakMap) {

             ref = weakMap.get(clazz);

             if(ref != null) {

                 final T oldV = ref.get();

                 if(oldV != null) {

                     return oldV;

                 }

             }

             weakMap.put(clazz, new SoftReference<>(newV));

             return newV;

         }

     }

 }