| /* |
| * 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.accumulo.core.util; |
| |
| import java.util.ArrayList; |
| import java.util.List; |
| import java.util.concurrent.CompletableFuture; |
| import java.util.function.BiFunction; |
| import java.util.function.Supplier; |
| |
| public class CompletableFutureUtil { |
| |
| // create a binary tree of completable future operations, where each node in the tree merges the |
| // results of their children when complete |
| public static <T> CompletableFuture<T> merge(List<CompletableFuture<T>> futures, |
| BiFunction<T,T,T> mergeFunc, Supplier<T> nothing) { |
| if (futures.isEmpty()) { |
| return CompletableFuture.completedFuture(nothing.get()); |
| } |
| while (futures.size() > 1) { |
| ArrayList<CompletableFuture<T>> mergedFutures = new ArrayList<>(futures.size() / 2); |
| for (int i = 0; i < futures.size(); i += 2) { |
| if (i + 1 == futures.size()) { |
| mergedFutures.add(futures.get(i)); |
| } else { |
| mergedFutures.add(futures.get(i).thenCombine(futures.get(i + 1), mergeFunc)); |
| } |
| } |
| |
| futures = mergedFutures; |
| } |
| |
| return futures.get(0); |
| } |
| |
| } |