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.beam.runners.dataflow.worker.util.common.worker;
  
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkNotNull;
  
  import org.apache.beam.runners.dataflow.worker.util.common.ForwardingReiterator;
  import org.apache.beam.sdk.util.common.Reiterator;
  
  /**
   * Implements a {@link Reiterator} that uses a {@link ProgressTrackerGroup.Tracker ProgressTracker}
   * to track how far it's gotten through some base {@code Reiterator}. {@link
   * ProgressTrackingReiterator#copy} copies the {@code ProgressTracker}, allowing for an independent
   * progress state.
   *
   * @param <T> the type of the elements of this iterator
   */
  public final class ProgressTrackingReiterator<T> extends ForwardingReiterator<T> {
    private ProgressTracker<T> tracker;
  
    public ProgressTrackingReiterator(Reiterator<T> base, ProgressTracker<T> tracker) {
      super(base);
      this.tracker = checkNotNull(tracker);
    }
  
    @Override
    public T next() {
      T result = super.next();
      tracker.saw(result);
      return result;
    }
  
    @Override
    protected ProgressTrackingReiterator<T> clone() {
      ProgressTrackingReiterator<T> result = (ProgressTrackingReiterator<T>) super.clone();
      result.tracker = tracker.copy();
      return result;
    }
  }
  