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 java.io.IOException;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.TimeUnit;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.annotations.VisibleForTesting;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Objects;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Throwables;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.cache.CacheBuilder;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.cache.CacheLoader;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.cache.LoadingCache;
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /** A {@link ShuffleBatchReader} that caches batches as they're read. */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class CachingShuffleBatchReader implements ShuffleBatchReader {
    private final ShuffleBatchReader reader;
    @VisibleForTesting final LoadingCache<BatchRange, Batch> cache;
  
    /** Limit the size of the cache to 1000 batches. */
    private static final int MAXIMUM_BATCHES = 1000;
  
    // Ensure that batches in the cache are expired quickly
    // for improved GC performance.
    private static final long EXPIRE_AFTER_MS = 250;
  
    public CachingShuffleBatchReader(
        ShuffleBatchReader shuffleReader, int maximumBatches, long expireAfterAccessMillis) {
      this.reader = shuffleReader;
      this.cache =
          CacheBuilder.newBuilder()
              .maximumSize(maximumBatches)
              .expireAfterAccess(expireAfterAccessMillis, TimeUnit.MILLISECONDS)
              .<BatchRange, Batch>build(
                  new CacheLoader<BatchRange, Batch>() {
                    @Override
                    public Batch load(BatchRange batchRange) throws Exception {
                      final Batch batch =
                          reader.read(batchRange.startPosition, batchRange.endPosition);
                      return batch;
                    }
                  });
    }
  
    public CachingShuffleBatchReader(ShuffleBatchReader shuffleReader) {
      this(shuffleReader, MAXIMUM_BATCHES, EXPIRE_AFTER_MS);
    }
  
    public CachingShuffleBatchReader(ShuffleBatchReader shuffleReader, int maximumBatches) {
      this(shuffleReader, maximumBatches, EXPIRE_AFTER_MS);
    }
  
    @Override
    public Batch read(@Nullable ShufflePosition startPosition, @Nullable ShufflePosition endPosition)
        throws IOException {
      final BatchRange range = new BatchRange(startPosition, endPosition);
      try {
        return cache.get(range);
      } catch (RuntimeException | ExecutionException e) {
        Throwables.propagateIfPossible(e, IOException.class);
        throw new RuntimeException("unexpected", e);
      }
    }
  
    /** The key for the entries stored in the batch cache. */
    static final class BatchRange {
      protected final @Nullable ShufflePosition startPosition;
      protected final @Nullable ShufflePosition endPosition;
  
      public BatchRange(
          @Nullable ShufflePosition startPosition, @Nullable ShufflePosition endPosition) {
        this.startPosition = startPosition;
        this.endPosition = endPosition;
      }
  
      @Override
      public boolean equals(@Nullable Object o) {
        return o == this
            || (o instanceof BatchRange
                && Objects.equal(((BatchRange) o).startPosition, startPosition)
                && Objects.equal(((BatchRange) o).endPosition, endPosition));
      }
  
      @Override
      public int hashCode() {
        return Objects.hashCode(startPosition, endPosition);
      }
    }
  }
  