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.io.sstable;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Iterator;
  
  import org.apache.cassandra.db.DecoratedKey;
  import org.apache.cassandra.io.sstable.format.SSTableReader;
  import org.apache.cassandra.io.util.FileUtils;
  import org.apache.cassandra.utils.CloseableIterator;
  import org.apache.cassandra.utils.IMergeIterator;
  import org.apache.cassandra.utils.MergeIterator;
  import org.apache.cassandra.utils.Throwables;
  
  /**
   * Caller must acquire and release references to the sstables used here.
   */
  public class ReducingKeyIterator implements CloseableIterator<DecoratedKey>
  {
      private final ArrayList<KeyIterator> iters;
      private volatile IMergeIterator<DecoratedKey, DecoratedKey> mi;
  
      public ReducingKeyIterator(Collection<SSTableReader> sstables)
      {
          iters = new ArrayList<>(sstables.size());
          for (SSTableReader sstable : sstables)
          {
              try
              {
                  iters.add(sstable.keyIterator());
              }
              catch (IOException ex)
              {
                  iters.forEach(FileUtils::closeQuietly);
                  throw new RuntimeException("Failed to create a key iterator for sstable " + sstable.getFilename());
              }
          }
      }
  
      private void maybeInit()
      {
          if (mi != null)
              return;
  
          synchronized (this)
          {
              if (mi == null)
              {
                  mi = MergeIterator.get(iters, DecoratedKey.comparator, new MergeIterator.Reducer<DecoratedKey, DecoratedKey>()
                  {
                      DecoratedKey reduced = null;
  
                      @Override
                      public boolean trivialReduceIsTrivial()
                      {
                          return true;
                      }
  
                      public void reduce(int idx, DecoratedKey current)
                      {
                          reduced = current;
                      }
  
                      protected DecoratedKey getReduced()
                      {
                          return reduced;
                      }
                  });
              }
          }
      }
  
      public void close()
      {
          if (mi != null)
          {
              mi.close();
          }
          else
          {
              // if merging iterator was not initialized before this reducing iterator is closed, we need to close the
              // underlying iterators manually
              Throwable err = Throwables.close(null, iters);
              if (err != null)
                  throw Throwables.unchecked(err);
          }
      }
  
      public long getTotalBytes()
      {
          maybeInit();
  
          long m = 0;
          for (Iterator<DecoratedKey> iter : mi.iterators())
          {
              m += ((KeyIterator) iter).getTotalBytes();
          }
          return m;
      }
  
      public long getBytesRead()
      {
          maybeInit();
  
          long m = 0;
          for (Iterator<DecoratedKey> iter : mi.iterators())
          {
              m += ((KeyIterator) iter).getBytesRead();
          }
          return m;
      }
  
      public boolean hasNext()
      {
          maybeInit();
          return mi.hasNext();
      }
  
      public DecoratedKey next()
      {
          maybeInit();
          return mi.next();
      }
  
      public void remove()
      {
          throw new UnsupportedOperationException();
      }
  }