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.index.sai.utils;
  
  import java.util.Iterator;
  import java.util.SortedSet;
  import java.util.concurrent.ConcurrentSkipListSet;
  
  import javax.annotation.concurrent.ThreadSafe;
  
  import org.apache.cassandra.utils.ObjectSizes;
  
  /**
   * A sorted set of {@link PrimaryKey}s.
   *
   * The primary keys are sorted first by token, then by partition key value, and then by clustering.
   */
  @ThreadSafe
  public class PrimaryKeys implements Iterable<PrimaryKey>
  {
      private static final long EMPTY_SIZE = ObjectSizes.measure(new PrimaryKeys());
      // from https://github.com/gaul/java-collection-overhead
      private static final long SET_ENTRY_OVERHEAD = 36;
  
      private final ConcurrentSkipListSet<PrimaryKey> keys = new ConcurrentSkipListSet<>();
  
      /**
       * Adds a {@link PrimaryKey} and returns the on-heap memory used if the key was added
       */
      public long add(PrimaryKey key)
      {
          return keys.add(key) ? SET_ENTRY_OVERHEAD : 0;
      }
  
      public SortedSet<PrimaryKey> keys()
      {
          return keys;
      }
  
      public int size()
      {
          return keys.size();
      }
  
      public boolean isEmpty()
      {
          return keys.isEmpty();
      }
  
      public long unsharedHeapSize()
      {
          return EMPTY_SIZE;
      }
  
      @Override
      public Iterator<PrimaryKey> iterator()
      {
          return keys.iterator();
      }
  }
  