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.sdk.util.construction;
  
  import java.util.HashSet;
  import java.util.Set;
  import org.apache.beam.sdk.Pipeline;
  import org.apache.beam.sdk.Pipeline.PipelineVisitor;
  import org.apache.beam.sdk.io.Read;
  import org.apache.beam.sdk.runners.TransformHierarchy.Node;
  import org.apache.beam.sdk.transforms.DoFn;
  import org.apache.beam.sdk.transforms.PTransform;
  import org.apache.beam.sdk.transforms.ParDo;
  import org.apache.beam.sdk.values.PCollection;
  import org.apache.beam.sdk.values.PValue;
  
  /**
   * Utilities for ensuring that all {@link Read} {@link PTransform PTransforms} are consumed by some
   * {@link PTransform}.
   */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class UnconsumedReads {
    public static void ensureAllReadsConsumed(Pipeline pipeline) {
      final Set<PCollection<?>> unconsumed = new HashSet<>();
      pipeline.traverseTopologically(
          new PipelineVisitor.Defaults() {
            @Override
            public void visitPrimitiveTransform(Node node) {
              unconsumed.removeAll(node.getInputs().values());
            }
  
            @Override
            public void visitValue(PValue value, Node producer) {
              String urn = PTransformTranslation.urnForTransformOrNull(producer.getTransform());
              if (PTransformTranslation.READ_TRANSFORM_URN.equals(urn)) {
                unconsumed.add((PCollection<?>) value);
              }
            }
          });
      int i = 0;
      for (PCollection<?> unconsumedPCollection : unconsumed) {
        consume(unconsumedPCollection, i);
        i++;
      }
    }
  
    private static <T> void consume(PCollection<T> unconsumedPCollection, int uniq) {
      // Multiple applications should never break due to stable unique names.
      String uniqueName = "DropInputs" + (uniq == 0 ? "" : uniq);
      unconsumedPCollection.apply(uniqueName, ParDo.of(new NoOpDoFn<>()));
    }
  
    private static class NoOpDoFn<T> extends DoFn<T, T> {
      @ProcessElement
      public void doNothing(ProcessContext unused) {}
    }
  }
  