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
   *
   *     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.
   */
  
  package org.apache.cassandra.simulator.utils;
  
  import java.util.Iterator;
  import java.util.Spliterator;
  import java.util.stream.Stream;
  import java.util.stream.StreamSupport;
  
  import static java.util.Spliterators.spliteratorUnknownSize;
  
  /**
   * A simple intrusive double-linked list for maintaining a list of tasks,
   * useful for invalidating queued ordered tasks
   */
  @SuppressWarnings("unchecked")
  public class IntrusiveLinkedList<O extends IntrusiveLinkedListNode> extends IntrusiveLinkedListNode
  {
      public IntrusiveLinkedList()
      {
          prev = next = this;
      }
  
      public void add(O add)
      {
          assert add.prev == null && add.next == null;
          IntrusiveLinkedListNode after = this;
          IntrusiveLinkedListNode before = prev;
          add.next = after;
          add.prev = before;
          before.next = add;
          after.prev = add;
      }
  
      public O poll()
      {
          if (isEmpty())
              return null;
  
          IntrusiveLinkedListNode next = this.next;
          next.remove();
          return (O) next;
      }
  
      public boolean isEmpty()
      {
          return next == this;
      }
  
      public Stream<O> stream()
      {
          Iterator<O> iterator = new Iterator<O>()
          {
              IntrusiveLinkedListNode next = IntrusiveLinkedList.this.next;
  
              @Override
              public boolean hasNext()
              {
                  return next != IntrusiveLinkedList.this;
              }
  
              @Override
              public O next()
              {
                  O result = (O)next;
                  next = next.next;
                  return result;
              }
          };
  
          return StreamSupport.stream(spliteratorUnknownSize(iterator, Spliterator.IMMUTABLE), false);
      }
  }
  
  