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 com.datastax.oss.driver.internal.core.util.concurrent;
  
  import edu.umd.cs.findbugs.annotations.NonNull;
  import io.netty.util.concurrent.Future;
  import io.netty.util.concurrent.GenericFutureListener;
  import io.netty.util.concurrent.Promise;
  import java.util.concurrent.atomic.AtomicInteger;
  import java.util.concurrent.atomic.AtomicReference;
  import net.jcip.annotations.ThreadSafe;
  
  /**
   * A thread-safe version of Netty's {@link io.netty.util.concurrent.PromiseCombiner} that uses
   * proper synchronization to trigger the completion of the aggregate promise.
   */
  @ThreadSafe
  public class PromiseCombiner {
  
    /**
     * Combines the given futures into the given promise, that is, ties the completion of the latter
     * to that of the formers.
     *
     * @param aggregatePromise The promise that will complete when all parents complete.
     * @param parents The parent futures.
     */
    public static void combine(
        @NonNull Promise<Void> aggregatePromise, @NonNull Future<?>... parents) {
      PromiseCombinerListener listener =
          new PromiseCombinerListener(aggregatePromise, parents.length);
      for (Future<?> parent : parents) {
        parent.addListener(listener);
      }
    }
  
    private static class PromiseCombinerListener implements GenericFutureListener<Future<Object>> {
  
      private final Promise<Void> aggregatePromise;
      private final AtomicInteger remainingCount;
      private final AtomicReference<Throwable> aggregateFailureRef = new AtomicReference<>();
  
      private PromiseCombinerListener(Promise<Void> aggregatePromise, int numberOfParents) {
        this.aggregatePromise = aggregatePromise;
        remainingCount = new AtomicInteger(numberOfParents);
      }
  
      @Override
      public void operationComplete(Future<Object> future) {
        if (!future.isSuccess()) {
          aggregateFailureRef.updateAndGet(
              aggregateFailure -> {
                if (aggregateFailure == null) {
                  aggregateFailure = future.cause();
                } else {
                  aggregateFailure.addSuppressed(future.cause());
                }
                return aggregateFailure;
              });
        }
        if (remainingCount.decrementAndGet() == 0) {
          Throwable aggregateFailure = aggregateFailureRef.get();
          if (aggregateFailure != null) {
            aggregatePromise.tryFailure(aggregateFailure);
          } else {
            aggregatePromise.trySuccess(null);
          }
        }
      }
    }
  }
  