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.core;
  
  import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.List;
  import java.util.Map;
  import org.apache.beam.sdk.state.BagState;
  import org.apache.beam.sdk.state.CombiningState;
  import org.apache.beam.sdk.state.GroupingState;
  import org.apache.beam.sdk.state.ReadableState;
  import org.apache.beam.sdk.state.SetState;
  import org.apache.beam.sdk.state.State;
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  
  /** Helpers for merging state. */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class StateMerging {
    /**
     * Clear all state in {@code address} in all windows under merge (even result windows) in {@code
     * context}.
     */
    public static <K, StateT extends State, W extends BoundedWindow> void clear(
        MergingStateAccessor<K, W> context, StateTag<StateT> address) {
      for (StateT state : context.accessInEachMergingWindow(address).values()) {
        state.clear();
      }
    }
  
    /**
     * Prefetch all bag state in {@code address} across all windows under merge in {@code context},
     * except for the bag state in the final state address window which we can blindly append to.
     */
    @SuppressFBWarnings("RV_RETURN_VALUE_IGNORED_NO_SIDE_EFFECT") // just prefetch calls to readLater
    public static <K, T, W extends BoundedWindow> void prefetchBags(
        MergingStateAccessor<K, W> context, StateTag<BagState<T>> address) {
      Map<W, BagState<T>> map = context.accessInEachMergingWindow(address);
      if (map.isEmpty()) {
        // Nothing to prefetch.
        return;
      }
      BagState<T> result = context.access(address);
      // Prefetch everything except what's already in result.
      for (BagState<T> source : map.values()) {
        if (!source.equals(result)) {
          prefetchRead(source);
        }
      }
    }
  
    /** Merge all bag state in {@code address} across all windows under merge. */
    public static <K, T, W extends BoundedWindow> void mergeBags(
        MergingStateAccessor<K, W> context, StateTag<BagState<T>> address) {
      mergeBags(context.accessInEachMergingWindow(address).values(), context.access(address));
    }
  
    /**
     * Merge all bag state in {@code sources} (which may include {@code result}) into {@code result}.
     */
    public static <T> void mergeBags(Collection<BagState<T>> sources, BagState<T> result) {
      if (sources.isEmpty()) {
        // Nothing to merge.
        return;
      }
      // Prefetch everything except what's already in result.
      List<ReadableState<Iterable<T>>> futures = new ArrayList<>(sources.size());
      for (BagState<T> source : sources) {
        if (!source.equals(result)) {
          prefetchRead(source);
          futures.add(source);
        }
      }
      if (futures.isEmpty()) {
        // Result already holds all the values.
        return;
      }
      // Transfer from sources to result.
      for (ReadableState<Iterable<T>> future : futures) {
        for (T element : future.read()) {
          result.add(element);
        }
      }
      // Clear sources except for result.
      for (BagState<T> source : sources) {
        if (!source.equals(result)) {
          source.clear();
        }
      }
    }
  
    /** Merge all set state in {@code address} across all windows under merge. */
    public static <K, T, W extends BoundedWindow> void mergeSets(
        MergingStateAccessor<K, W> context, StateTag<SetState<T>> address) {
      mergeSets(context.accessInEachMergingWindow(address).values(), context.access(address));
    }
  
    /**
     * Merge all set state in {@code sources} (which may include {@code result}) into {@code result}.
     */
    public static <T> void mergeSets(Collection<SetState<T>> sources, SetState<T> result) {
      if (sources.isEmpty()) {
        // Nothing to merge.
        return;
      }
      // Prefetch everything except what's already in result.
      List<ReadableState<Iterable<T>>> futures = new ArrayList<>(sources.size());
      for (SetState<T> source : sources) {
        if (!source.equals(result)) {
          prefetchRead(source);
          futures.add(source);
        }
      }
      if (futures.isEmpty()) {
        // Result already holds all the values.
        return;
      }
      // Transfer from sources to result.
      for (ReadableState<Iterable<T>> future : futures) {
        for (T element : future.read()) {
          result.add(element);
        }
      }
      // Clear sources except for result.
      for (SetState<T> source : sources) {
        if (!source.equals(result)) {
          source.clear();
        }
      }
    }
  
    /**
     * Prefetch all combining value state for {@code address} across all merging windows in {@code
     * context}.
     */
    public static <K, StateT extends GroupingState<?, ?>, W extends BoundedWindow>
        void prefetchCombiningValues(MergingStateAccessor<K, W> context, StateTag<StateT> address) {
      for (StateT state : context.accessInEachMergingWindow(address).values()) {
        prefetchRead(state);
      }
    }
  
    /** Merge all value state in {@code address} across all merging windows in {@code context}. */
    public static <K, InputT, AccumT, OutputT, W extends BoundedWindow> void mergeCombiningValues(
        MergingStateAccessor<K, W> context,
        StateTag<CombiningState<InputT, AccumT, OutputT>> address) {
      mergeCombiningValues(
          context.accessInEachMergingWindow(address).values(), context.access(address));
    }
  
    /**
     * Merge all value state from {@code sources} (which may include {@code result}) into {@code
     * result}.
     */
    public static <InputT, AccumT, OutputT> void mergeCombiningValues(
        Collection<CombiningState<InputT, AccumT, OutputT>> sources,
        CombiningState<InputT, AccumT, OutputT> result) {
      if (sources.isEmpty()) {
        // Nothing to merge.
        return;
      }
      if (sources.size() == 1 && sources.contains(result)) {
        // Result already holds combined value.
        return;
      }
      // Prefetch.
      List<ReadableState<AccumT>> futures = new ArrayList<>(sources.size());
      for (CombiningState<InputT, AccumT, OutputT> source : sources) {
        prefetchRead(source);
      }
      // Read.
      List<AccumT> accumulators = new ArrayList<>(futures.size());
      for (CombiningState<InputT, AccumT, OutputT> source : sources) {
        accumulators.add(source.getAccum());
      }
      // Merge (possibly update and return one of the existing accumulators).
      AccumT merged = result.mergeAccumulators(accumulators);
      // Clear sources.
      for (CombiningState<InputT, AccumT, OutputT> source : sources) {
        source.clear();
      }
      // Update result.
      result.addAccum(merged);
    }
  
    private static void prefetchRead(ReadableState<?> source) {
      source.readLater();
    }
  }
  