runtime/common/src/main/java/org/apache/nemo/runtime/common/ReplyFutureMap.java

/*
 * 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.nemo.runtime.common;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Orchestrate message sender and receiver using {@link CompletableFuture} for asynchronous request-reply communication.
 *
 * @param <T> the type of successful reply
 */
public final class ReplyFutureMap<T> {

  private final ConcurrentHashMap<Long, CompletableFuture<T>> requestIdToFuture;

  public ReplyFutureMap() {
    requestIdToFuture = new ConcurrentHashMap<>();
  }

  /**
   * Called by message sender, just before a new request is sent.
   * Note that this method should be used *before* actual message sending.
   * Otherwise {@code onSuccessMessage} can be called before putting new future to {@code requestIdToFuture}.
   *
   * @param id the request id
   * @return a {@link CompletableFuture} for the reply
   */
  public CompletableFuture<T> beforeRequest(final long id) {
    final CompletableFuture<T> future = new CompletableFuture<>();
    requestIdToFuture.put(id, future);
    return future;
  }

  /**
   * Called by message receiver, for a successful reply message.
   *
   * @param id             the request id
   * @param successMessage the reply message
   */
  public void onSuccessMessage(final long id, final T successMessage) {
    requestIdToFuture.remove(id).complete(successMessage);
  }

  /**
   * Called for a failure in request-reply communication.
   *
   * @param id the request id
   * @param ex throwable exception
   */
  public void onFailure(final long id, final Throwable ex) {
    requestIdToFuture.remove(id).completeExceptionally(ex);
  }
}