content: /*
   *  Licensed to the Apache Software Foundation (ASF) under one or more
   *  contributor license agreements.  See the NOTICE file distributed with
   *  this work for additional information regarding copyright ownership.
   *  The ASF licenses this file to You under the Apache License, Version 2.0
   *  (the "License"); you may not use this file except in compliance with
   *  the License.  You may obtain a copy of the License at
   *
   *      https://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.
   *
   */
  package org.apache.tools.ant.types.resources;
  
  import java.util.ConcurrentModificationException;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  import java.util.Set;
  import java.util.WeakHashMap;
  
  import org.apache.tools.ant.types.Resource;
  
  /**
   * Helper class for ResourceCollections to return Iterators
   * that fail on changes to the object.
   * @since Ant 1.7
   */
  /*package-private*/ class FailFast implements Iterator<Resource> {
      private static final WeakHashMap<Object, Set<FailFast>> MAP = new WeakHashMap<>();
  
      /**
       * Invalidate any in-use Iterators from the specified Object.
       * @param o the parent Object.
       */
      static synchronized void invalidate(Object o) {
          Set<FailFast> s = MAP.get(o);
          if (s != null) {
              s.clear();
          }
      }
  
      private static synchronized void add(FailFast f) {
          MAP.computeIfAbsent(f.parent, k -> new HashSet<>()).add(f);
      }
  
      private static synchronized void remove(FailFast f) {
          Set<FailFast> s = MAP.get(f.parent);
          if (s != null) {
              s.remove(f);
          }
      }
  
      private static synchronized void failFast(FailFast f) {
          Set<FailFast> s = MAP.get(f.parent);
          if (!s.contains(f)) {
              throw new ConcurrentModificationException();
          }
      }
  
      private final Object parent;
      private Iterator<Resource> wrapped;
  
      /**
       * Construct a new FailFast Iterator wrapping the specified Iterator
       * and dependent upon the specified parent Object.
       * @param o the parent Object.
       * @param i the wrapped Iterator.
       */
      FailFast(Object o, Iterator<Resource> i) {
          if (o == null) {
              throw new IllegalArgumentException("parent object is null");
          }
          if (i == null) {
              throw new IllegalArgumentException("cannot wrap null iterator");
          }
          parent = o;
          if (i.hasNext()) {
              wrapped = i;
              add(this);
          }
      }
  
      /**
       * Fulfill the Iterator contract.
       * @return true if there are more elements.
       */
      @Override
      public boolean hasNext() {
          if (wrapped == null) {
              return false;
          }
          failFast(this);
          return wrapped.hasNext();
      }
  
      /**
       * Fulfill the Iterator contract.
       * @return the next element.
       * @throws NoSuchElementException if no more elements.
       */
      @Override
      public Resource next() {
          if (wrapped == null || !wrapped.hasNext()) {
              throw new NoSuchElementException();
          }
          failFast(this);
          try {
              return wrapped.next();
          } finally {
              if (!wrapped.hasNext()) {
                  wrapped = null;
                  remove(this);
              }
          }
      }
  
      /**
       * Fulfill the Iterator contract.
       * @throws UnsupportedOperationException always.
       */
      @Override
      public void remove() {
          throw new UnsupportedOperationException();
      }
  
  }
  
  