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.beam.runners.dataflow.worker.windmill.state;
  
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.Future;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  import javax.annotation.Nullable;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.util.concurrent.ForwardingFuture;
  
  /**
   * A future which will trigger a GetData request to Windmill for all outstanding futures on the
   * first {@link #get}.
   */
  public class WrappedFuture<T> extends ForwardingFuture.SimpleForwardingFuture<T> {
    /**
     * The reader we'll use to service the eventual read. Null if read has been fulfilled.
     *
     * <p>NOTE: We must clear this after the read is fulfilled to prevent space leaks.
     */
    private @Nullable WindmillStateReader reader;
  
    public WrappedFuture(WindmillStateReader reader, Future<T> delegate) {
      super(delegate);
      this.reader = reader;
    }
  
    @Override
    public T get() throws InterruptedException, ExecutionException {
      if (!delegate().isDone() && reader != null) {
        // Only one thread per reader, so no race here.
        reader.performReads();
      }
      reader = null;
      return super.get();
    }
  
    @Override
    public T get(long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException {
      if (!delegate().isDone() && reader != null) {
        // Only one thread per reader, so no race here.
        reader.performReads();
      }
      reader = null;
      return super.get(timeout, unit);
    }
  }
  