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.activemq.artemis.utils.collections;
  
  import java.util.function.Supplier;
  
  /**
   * A type of linked list which maintains items according to a priority and allows adding and removing of elements at
   * both ends, and peeking.
   * <p>
   * Only {@link #size()} and {@link #isEmpty()} are safe to be called concurrently.
   */
  public interface PriorityLinkedList<E> {
  
     void addHead(E e, int priority);
  
     void addTail(E e, int priority);
  
     void addSorted(E e, int priority);
  
     E poll();
  
     /**
      * just look at the first element on the list
      */
     E peek();
  
     void clear();
  
     /**
      * @see LinkedList#setNodeStore(NodeStore)
      */
     void setNodeStore(Supplier<NodeStore<E>> supplier);
  
     E removeWithID(String listID, long id);
  
     /**
      * {@return the size of this list; safe to be called concurrently}
      */
     int size();
  
     LinkedListIterator<E> iterator();
  
     /**
      * {@return {@code true} if empty, {@code false} otherwise; safe to be called concurrently}
      */
     boolean isEmpty();
  }
  