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.spark.structuredstreaming.translation.batch.functions;
  
  import static org.apache.beam.sdk.transforms.Materializations.MULTIMAP_MATERIALIZATION_URN;
  
  import java.util.Collection;
  import java.util.Map;
  import java.util.concurrent.Callable;
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.ExecutionException;
  import org.apache.beam.runners.core.SideInputReader;
  import org.apache.beam.sdk.annotations.Internal;
  import org.apache.beam.sdk.transforms.Materialization;
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  import org.apache.beam.sdk.transforms.windowing.GlobalWindows;
  import org.apache.beam.sdk.values.PCollectionView;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.cache.Cache;
  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.CacheStats;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableMap;
  import org.checkerframework.checker.nullness.qual.NonNull;
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * SideInputReader that caches results for costly {@link Materialization Materializations}.
   * Concurrent access is not expected, but it won't impact correctness.
   */
  @Internal
  public class CachedSideInputReader implements SideInputReader {
    private final SideInputReader reader;
    private final Map<PCollectionView<?>, Cache<BoundedWindow, Object>> caches;
  
    /**
     * Creates a SideInputReader that caches results for costly {@link Materialization
     * Materializations} if present, otherwise the SideInputReader is returned as is. Concurrent
     * access is not expected, but it won't impact correctness.
     */
    public static SideInputReader of(SideInputReader reader, Collection<PCollectionView<?>> views) {
      Map<PCollectionView<?>, Cache<BoundedWindow, Object>> caches = initCaches(views, 1000);
      return caches.isEmpty() ? reader : new CachedSideInputReader(reader, caches);
    }
  
    private CachedSideInputReader(
        SideInputReader reader, Map<PCollectionView<?>, Cache<BoundedWindow, Object>> caches) {
      this.reader = reader;
      this.caches = caches;
    }
  
    /**
     * Init caches based on {@link #shouldCache} using {@link SingletonCache} if using global window,
     * and otherwise a Guava LRU cache.
     */
    private static Map<PCollectionView<?>, Cache<BoundedWindow, Object>> initCaches(
        Iterable<PCollectionView<?>> views, int maxSize) {
      ImmutableMap.Builder<PCollectionView<?>, Cache<BoundedWindow, Object>> builder =
          ImmutableMap.builder();
      for (PCollectionView<?> view : views) {
        if (shouldCache(view)) {
          boolean isGlobal =
              view.getWindowingStrategyInternal().getWindowFn() instanceof GlobalWindows;
          builder.put(view, isGlobal ? new SingletonCache<>() : lruCache(maxSize));
        }
      }
      return builder.build();
    }
  
    private static boolean shouldCache(PCollectionView<?> view) {
      // only cache expensive multimap views
      return MULTIMAP_MATERIALIZATION_URN.equals(view.getViewFn().getMaterialization().getUrn());
    }
  
    private static Cache<BoundedWindow, Object> lruCache(int maxSize) {
      // no concurrent access expected, using separate instance per partition iterator
      return CacheBuilder.newBuilder().concurrencyLevel(1).maximumSize(maxSize).build();
    }
  
    @Override
    public <T> @Nullable T get(PCollectionView<T> view, BoundedWindow window) {
      Cache<BoundedWindow, Object> cache = caches.get(view);
      if (cache != null) {
        Object result = cache.getIfPresent(window);
        if (result == null) {
          result = reader.get(view, window);
          if (result != null) {
            cache.put(window, result);
          }
          return (T) result;
        }
      }
      return reader.get(view, window);
    }
  
    @Override
    public <T> boolean contains(PCollectionView<T> view) {
      return reader.contains(view);
    }
  
    @Override
    public boolean isEmpty() {
      return reader.isEmpty();
    }
  
    /** Caching a singleton value, ignoring any key. */
    private static class SingletonCache<K extends @NonNull Object, V extends @NonNull Object>
        implements Cache<K, V> {
      private @Nullable V value;
  
      @Override
      public @Nullable V getIfPresent(Object o) {
        return value;
      }
  
      @Override
      public void put(K k, V v) {
        value = v;
      }
  
      @Override
      public long size() {
        return value != null ? 1 : 0;
      }
  
      @Override
      public V get(K k, Callable<? extends V> callable) throws ExecutionException {
        throw new UnsupportedOperationException();
      }
  
      @Override
      public ImmutableMap<K, V> getAllPresent(Iterable<?> iterable) {
        throw new UnsupportedOperationException();
      }
  
      @Override
      public void putAll(Map<? extends K, ? extends V> map) {
        throw new UnsupportedOperationException();
      }
  
      @Override
      public void invalidate(Object o) {}
  
      @Override
      public void invalidateAll(Iterable<?> iterable) {}
  
      @Override
      public void invalidateAll() {}
  
      @Override
      public CacheStats stats() {
        throw new UnsupportedOperationException();
      }
  
      @Override
      public ConcurrentMap<K, V> asMap() {
        throw new UnsupportedOperationException();
      }
  
      @Override
      public void cleanUp() {
        value = null;
      }
    }
  }
  