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 com.datastax.oss.driver.internal.core.util.collection;
  
  import com.datastax.oss.driver.api.core.metadata.Node;
  import com.datastax.oss.driver.api.core.session.Request;
  import com.datastax.oss.driver.api.core.session.Session;
  import edu.umd.cs.findbugs.annotations.NonNull;
  import java.util.Iterator;
  import java.util.Queue;
  import net.jcip.annotations.ThreadSafe;
  
  /**
   * A specialized, thread-safe node queue for use when creating {@linkplain
   * com.datastax.oss.driver.api.core.loadbalancing.LoadBalancingPolicy#newQueryPlan(Request, Session)
   * query plans}.
   *
   * <p>This interface and its built-in implementations are not general-purpose queues; they are
   * tailored for the specific use case of creating query plans in the driver. They make a few
   * unconventional API choices for the sake of performance.
   *
   * <p>Furthermore, the driver only consumes query plans through calls to its {@link #poll()} method;
   * therefore, this method is the only valid mutation operation for a query plan, other mutating
   * methods throw.
   *
   * <p>Both {@link #size()} and {@link #iterator()} are supported and never throw, even if called
   * concurrently. These methods are implemented for reporting purposes only, the driver itself does
   * not use them.
   *
   * <p>All built-in {@link QueryPlan} implementations can be safely reused for custom load balancing
   * policies; if you plan to do so, study the source code of {@link
   * com.datastax.oss.driver.internal.core.loadbalancing.DefaultLoadBalancingPolicy} or {@link
   * com.datastax.oss.driver.internal.core.loadbalancing.BasicLoadBalancingPolicy}.
   *
   * @see QueryPlanBase
   */
  @ThreadSafe
  public interface QueryPlan extends Queue<Node> {
  
    QueryPlan EMPTY = new EmptyQueryPlan();
  
    /**
     * {@inheritDoc}
     *
     * <p>Implementation note: query plan iterators are snapshots that reflect the contents of the
     * queue at the time of the call, and are not affected by further modifications. Successive calls
     * to this method will return different objects.
     */
    @NonNull
    @Override
    Iterator<Node> iterator();
  
    @Override
    default boolean offer(Node node) {
      throw new UnsupportedOperationException("Not implemented");
    }
  
    @Override
    default Node peek() {
      throw new UnsupportedOperationException("Not implemented");
    }
  
    @Override
    default boolean add(Node node) {
      throw new UnsupportedOperationException("Not implemented");
    }
  
    @Override
    default Node remove() {
      throw new UnsupportedOperationException("Not implemented");
    }
  
    @Override
    default Node element() {
      throw new UnsupportedOperationException("Not implemented");
    }
  }
  