org.apache.pulsar.shade.com.spotify.futures.CombinedFutures Maven / Gradle / Ivy

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/*-
 * -\-\-
 * completable-futures
 * --
 * Copyright (C) 2016 - 2020 Spotify AB
 * --
 * Licensed 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.pulsar.shade.com.spotify.futures;

import java.util.IdentityHashMap;
import java.util.List;
import java.util.concurrent.CompletionStage;

public final class CombinedFutures {

  private static final Object NULL_PLACEHOLDER = new Object();

  private final IdentityHashMap, Object> map = new IdentityHashMap<>();

  CombinedFutures(List> stages) {
    for (final CompletionStage stage : stages) {
      Object value = stage.toCompletableFuture().join();
      if (value == null) {
        value = NULL_PLACEHOLDER;
      }
      map.put(stage, value);
    }
  }

  public  T get(CompletionStage stage) {
    final Object value = map.get(stage);
    if (value == null) {
      throw new IllegalArgumentException(
              "Can not resolve values for futures that were not part of the combine");
    }
    if (value == NULL_PLACEHOLDER) {
      return null;
    }
    return (T) value;
  }
}