StefanRRichter commented on a change in pull request #8467: [FLINK-12535][network] Make CheckpointBarrierHandler non-blocking URL: https://github.com/apache/flink/pull/8467#discussion_r287978776
########## File path: flink-runtime/src/main/java/org/apache/flink/runtime/io/AvailabilityListener.java ########## @@ -0,0 +1,61 @@ +/* + * 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.flink.runtime.io; + +import org.apache.flink.annotation.Internal; + +import java.util.concurrent.CompletableFuture; + +/** + * Interface defining couple of essential methods for listening on data availability using + * {@link CompletableFuture}. For usage check out for example {@link AsyncDataInput}. + */ +@Internal +public interface AvailabilityListener { + /** + * Constant that allows to avoid volatile checks {@link CompletableFuture#isDone()}. Check + * {@link #isAvailable()} for more explanation. + */ + CompletableFuture<?> AVAILABLE = CompletableFuture.completedFuture(null); + + /** + * @return true if is finished and for example end of input was reached, false otherwise. + */ + boolean isFinished(); + + /** + * Check if this instance is available for further processing. + * + * <p>When hot looping to avoid volatile access in {@link CompletableFuture#isDone()} user of + * this method should do the following check: + * <pre> + * {@code + * AvailabilityListener input = ...; + * if (input.isAvailable() == AvailabilityListener.AVAILABLE || input.isAvailable().isDone()) { + * // do something; + * } + * } + * </pre> + * + * @return a future that is completed if there are more records available. If there are more + * records available immediately, {@link #AVAILABLE} should be returned. Previously returned + * not completed futures should become completed once there is more input available or if + * the input {@link #isFinished()}. + */ + CompletableFuture<?> isAvailable(); Review comment: There might be even another way that we can discuss here. IIRC one core problem in this PR with `CompletableFuture` is that it is a class and not an interface, so the implementation that is already completed cannot be more effcient. Did we ever consider returning a `CompletionStage` instead, which could be backed by a completable future in the cases that require waiting, and with some efficient completed implementations? All return an enum that indicates either `AVAILABLE` or `FINISHED`. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
