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.samza.runtime;
  
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Map;
  import java.util.concurrent.CompletableFuture;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ExecutorService;
  import java.util.stream.Collectors;
  import org.apache.beam.runners.core.DoFnRunner;
  import org.apache.beam.runners.samza.SamzaPipelineOptions;
  import org.apache.beam.sdk.state.TimeDomain;
  import org.apache.beam.sdk.transforms.DoFn;
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  import org.apache.beam.sdk.values.KV;
  import org.apache.beam.sdk.values.WindowedValue;
  import org.checkerframework.checker.nullness.qual.Nullable;
  import org.joda.time.Instant;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * This {@link DoFnRunner} adds the capability of executing the {@link
   * org.apache.beam.sdk.transforms.DoFn.ProcessElement} in the thread pool, and returns the future to
   * the collector for the underlying async execution.
   */
  public class AsyncDoFnRunner<InT, OutT> implements DoFnRunner<InT, OutT> {
    private static final Logger LOG = LoggerFactory.getLogger(AsyncDoFnRunner.class);
  
    // A dummy key to represent null keys
    private static final Object NULL_KEY = new Object();
  
    private final DoFnRunner<InT, OutT> underlying;
    private final ExecutorService executor;
    private final OpEmitter<OutT> emitter;
    private final FutureCollector<OutT> futureCollector;
    private final boolean isStateful;
  
    /**
     * This map keeps track of the last outputFutures for a certain key. When the next element of the
     * key comes in, its outputFutures will be chained from the last outputFutures in the map. When
     * all futures of a key have been complete, the key entry will be removed. The map is bounded by
     * (bundle size * 2).
     */
    private final Map<Object, CompletableFuture<Collection<WindowedValue<OutT>>>> keyedOutputFutures;
  
    public static <InT, OutT> AsyncDoFnRunner<InT, OutT> create(
        DoFnRunner<InT, OutT> runner,
        OpEmitter<OutT> emitter,
        FutureCollector<OutT> futureCollector,
        boolean isStateful,
        SamzaPipelineOptions options) {
  
      LOG.info("Run DoFn with " + AsyncDoFnRunner.class.getName());
      return new AsyncDoFnRunner<>(runner, emitter, futureCollector, isStateful, options);
    }
  
    private AsyncDoFnRunner(
        DoFnRunner<InT, OutT> runner,
        OpEmitter<OutT> emitter,
        FutureCollector<OutT> futureCollector,
        boolean isStateful,
        SamzaPipelineOptions options) {
      this.underlying = runner;
      this.executor = options.getExecutorServiceForProcessElement();
      this.emitter = emitter;
      this.futureCollector = futureCollector;
      this.isStateful = isStateful;
      this.keyedOutputFutures = new ConcurrentHashMap<>();
    }
  
    @Override
    public void startBundle() {
      underlying.startBundle();
    }
  
    @Override
    public void processElement(WindowedValue<InT> elem) {
      final CompletableFuture<Collection<WindowedValue<OutT>>> outputFutures =
          isStateful ? processStateful(elem) : processElement(elem, null);
  
      futureCollector.addAll(outputFutures);
    }
  
    private CompletableFuture<Collection<WindowedValue<OutT>>> processElement(
        WindowedValue<InT> elem,
        @Nullable CompletableFuture<Collection<WindowedValue<OutT>>> prevOutputFuture) {
  
      final CompletableFuture<Collection<WindowedValue<OutT>>> prevFuture =
          prevOutputFuture == null
              ? CompletableFuture.completedFuture(Collections.emptyList())
              : prevOutputFuture;
  
      // For ordering by key, we chain the processing of the elem to the completion of
      // the previous output of the same key
      return prevFuture.thenApplyAsync(
          x -> {
            underlying.processElement(elem);
  
            return emitter.collectOutput().stream()
                .map(OpMessage::getElement)
                .collect(Collectors.toList());
          },
          executor);
    }
  
    private CompletableFuture<Collection<WindowedValue<OutT>>> processStateful(
        WindowedValue<InT> elem) {
      final Object key = getKey(elem);
  
      final CompletableFuture<Collection<WindowedValue<OutT>>> outputFutures =
          processElement(elem, keyedOutputFutures.get(key));
  
      // Update the latest outputFuture for key
      keyedOutputFutures.put(key, outputFutures);
  
      // Remove the outputFuture from the map once it's complete.
      // This ensures the map will be cleaned up immediately.
      return outputFutures.thenApply(
          output -> {
            // Under the condition that the outputFutures has not been updated
            keyedOutputFutures.remove(key, outputFutures);
            return output;
          });
    }
  
    /** Package private for testing. */
    boolean hasOutputFuturesForKey(Object key) {
      return keyedOutputFutures.containsKey(key);
    }
  
    @Override
    public <KeyT> void onTimer(
        String timerId,
        String timerFamilyId,
        KeyT key,
        BoundedWindow window,
        Instant timestamp,
        Instant outputTimestamp,
        TimeDomain timeDomain) {
      underlying.onTimer(timerId, timerFamilyId, key, window, timestamp, outputTimestamp, timeDomain);
    }
  
    @Override
    public void finishBundle() {
      underlying.finishBundle();
    }
  
    @Override
    public <KeyT> void onWindowExpiration(BoundedWindow window, Instant timestamp, KeyT key) {
      underlying.onWindowExpiration(window, timestamp, key);
    }
  
    @Override
    public DoFn<InT, OutT> getFn() {
      return underlying.getFn();
    }
  
    private Object getKey(WindowedValue<InT> elem) {
      KV<?, ?> kv = (KV<?, ?>) elem.getValue();
      if (kv == null) {
        return NULL_KEY;
      } else {
        Object key = kv.getKey();
        return key == null ? NULL_KEY : key;
      }
    }
  }
  