content: /*
   * 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.bookkeeper.common.util;
  
  import java.util.concurrent.CompletableFuture;
  import javax.annotation.concurrent.GuardedBy;
  import lombok.extern.slf4j.Slf4j;
  import org.apache.bookkeeper.common.concurrent.FutureUtils;
  
  /**
   * A common implementation for {@link AutoAsyncCloseable}.
   */
  @Slf4j
  public abstract class AbstractAutoAsyncCloseable implements AutoAsyncCloseable {
  
      @GuardedBy("this")
      private CompletableFuture<Void> closeFuture = null;
  
      @Override
      public synchronized boolean isClosed() {
          return null != closeFuture;
      }
  
      @Override
      public CompletableFuture<Void> closeAsync() {
          CompletableFuture<Void> savedFuture;
          synchronized (this) {
              if (null != closeFuture) {
                  return closeFuture;
              }
              closeFuture = savedFuture = FutureUtils.createFuture();
          }
          closeAsyncOnce(savedFuture);
          return savedFuture;
      }
  
      /**
       * Do the core logic of closing this instance once.
       *
       * @param closeFuture the future to complete when the instance is closed.
       */
      protected abstract void closeAsyncOnce(CompletableFuture<Void> closeFuture);
  
  }
  