text: /*
   * Copyright DataStax, Inc.
   *
   * Licensed 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.loadbalancing.LoadBalancingPolicy;
  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 com.datastax.oss.driver.internal.core.loadbalancing.DefaultLoadBalancingPolicy;
  import com.datastax.oss.driver.shaded.guava.common.collect.Iterators;
  import edu.umd.cs.findbugs.annotations.NonNull;
  import edu.umd.cs.findbugs.annotations.Nullable;
  import java.util.AbstractCollection;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.Queue;
  import java.util.concurrent.atomic.AtomicInteger;
  import net.jcip.annotations.ThreadSafe;
  
  /**
   * A specialized, thread-safe queue implementation for {@link
   * LoadBalancingPolicy#newQueryPlan(Request, Session)}.
   *
   * <p>All nodes must be provided at construction time. After that, the only valid mutation operation
   * is {@link #poll()}, other methods throw.
   *
   * <p>This class is not a general-purpose implementation, it is tailored for a specific use case in
   * the driver. It makes a few unconventional API choices for the sake of performance (see {@link
   * #QueryPlan(Object...)}. It can be reused for custom load balancing policies; if you plan to do
   * so, study the source code of {@link DefaultLoadBalancingPolicy}.
   */
  @ThreadSafe
  public class QueryPlan extends AbstractCollection<Node> implements Queue<Node> {
  
    private final Object[] nodes;
    private final AtomicInteger nextIndex = new AtomicInteger();
  
    /**
     * @param nodes the nodes to initially fill the queue with. For efficiency, there is no defensive
     *     copy, the provided array is used directly. The declared type is {@code Object[]} because of
     *     implementation details of {@link DefaultLoadBalancingPolicy}, but all elements must be
     *     instances of {@link Node}, otherwise instance methods will fail later.
     */
    public QueryPlan(@NonNull Object... nodes) {
      this.nodes = nodes;
    }
  
    @Nullable
    @Override
    public Node poll() {
      // We don't handle overflow. In practice it won't be an issue, since the driver stops polling
      // once the query plan is empty.
      int i = nextIndex.getAndIncrement();
      return (i >= nodes.length) ? null : (Node) nodes[i];
    }
  
    /**
     * {@inheritDoc}
     *
     * <p>The returned iterator reflects the state of the queue at the time of the call, and is not
     * affected by further modifications.
     */
    @NonNull
    @Override
    public Iterator<Node> iterator() {
      int i = nextIndex.get();
      if (i >= nodes.length) {
        return Collections.<Node>emptyList().iterator();
      } else {
        return Iterators.forArray(Arrays.copyOfRange(nodes, i, nodes.length, Node[].class));
      }
    }
  
    @Override
    public int size() {
      return Math.max(nodes.length - nextIndex.get(), 0);
    }
  
    @Override
    public boolean offer(Node node) {
      throw new UnsupportedOperationException("Not implemented");
    }
  
    @Override
    public Node remove() {
      throw new UnsupportedOperationException("Not implemented");
    }
  
    @Override
    public Node element() {
      throw new UnsupportedOperationException("Not implemented");
    }
  
    @Override
    public Node peek() {
      throw new UnsupportedOperationException("Not implemented");
    }
  }
  