/*
* 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.size() == 0) {
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);
}
}