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Nuts'n'Bolts Utilities
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/*
 * Copyright (c) 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 David Berkman
 *
 * This file is part of the SmallMind Code Project.
 *
 * The SmallMind Code Project is free software, you can redistribute
 * it and/or modify it under either, at your discretion...
 *
 * 1) The terms of GNU Affero General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at
 * your option) any later version.
 *
 * ...or...
 *
 * 2) The terms of the Apache License, Version 2.0.
 *
 * The SmallMind Code Project 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 or Apache License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * and the Apache License along with the SmallMind Code Project. If not, see
 *  or .
 *
 * Additional permission under the GNU Affero GPL version 3 section 7
 * ------------------------------------------------------------------
 * If you modify this Program, or any covered work, by linking or
 * combining it with other code, such other code is not for that reason
 * alone subject to any of the requirements of the GNU Affero GPL
 * version 3.
 */
package org.smallmind.nutsnbolts.lang;

import java.lang.ref.PhantomReference;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.reflect.Method;
import java.util.concurrent.ConcurrentHashMap;

public class LoaderAwareMethodCache {

  private final ReferenceQueue referenceQueue = new ReferenceQueue<>();
  private final ConcurrentHashMap> loaderMap = new ConcurrentHashMap<>();

  public T get (Method method) {

    return getMethodMap(method).get(method);
  }

  public T put (Method method, T value) {

    clearExpiredReferences();

    return getMethodMap(method).put(method, value);
  }

  public T putIfAbsent (Method method, T value) {

    clearExpiredReferences();

    return getMethodMap(method).putIfAbsent(method, value);
  }

  private ConcurrentHashMap getMethodMap (Method method) {

    ConcurrentHashMap methodMap;
    LoaderKey loaderKey = new LoaderKey(method.getDeclaringClass().getClassLoader());

    if ((methodMap = loaderMap.get(loaderKey)) == null) {

      ConcurrentHashMap priorMethodMap;

      if ((priorMethodMap = loaderMap.putIfAbsent(loaderKey, methodMap = new ConcurrentHashMap<>())) != null) {
        methodMap = priorMethodMap;
      }
    }

    return methodMap;
  }

  private void clearExpiredReferences () {

    Reference reference;

    while ((reference = referenceQueue.poll()) != null) {
      if (reference instanceof LoaderAwareMethodCache.LoaderKey) {
        loaderMap.remove((LoaderAwareMethodCache.LoaderKey)reference);
      }
    }
  }

  private class LoaderKey extends PhantomReference {

    private final int identityHashCode;

    public LoaderKey (ClassLoader classLoader) {

      super(classLoader, referenceQueue);

      identityHashCode = System.identityHashCode(classLoader);
    }

    @Override
    public int hashCode () {

      return identityHashCode;
    }

    @Override
    public boolean equals (Object obj) {

      return (obj instanceof LoaderAwareMethodCache.LoaderKey) && (identityHashCode == obj.hashCode());
    }
  }
}