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.kafka.connect.util;
  
  import org.apache.kafka.connect.errors.ConnectException;
  
  import java.util.concurrent.CancellationException;
  import java.util.concurrent.CountDownLatch;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.Future;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  
  /**
   * An abstract implementation of {@link Callback} that also implements the {@link Future} interface. This allows for
   * operations like waiting until the callback is completed via {@link #onCompletion(Throwable, Object)}. The result
   * from the callback can be converted by concrete implementations of this class before being retrieved via
   * {@link Future#get}.
   * @param <U> the callback result type
   * @param <T> the future result type obtained after converting the callback result
   */
  public abstract class ConvertingFutureCallback<U, T> implements Callback<U>, Future<T> {
  
      private final Callback<T> underlying;
      private final CountDownLatch finishedLatch;
      private volatile T result = null;
      private volatile Throwable exception = null;
      private volatile boolean cancelled = false;
      private volatile Stage currentStage = null;
  
      public ConvertingFutureCallback() {
          this(null);
      }
  
      public ConvertingFutureCallback(Callback<T> underlying) {
          this.underlying = underlying;
          this.finishedLatch = new CountDownLatch(1);
      }
  
      public abstract T convert(U result);
  
      @Override
      public void onCompletion(Throwable error, U result) {
          synchronized (this) {
              if (isDone()) {
                  return;
              }
              
              if (error != null) {
                  this.exception = error;
              } else {
                  this.result = convert(result);
              }
  
              if (underlying != null)
                  underlying.onCompletion(error, this.result);
              finishedLatch.countDown();
          }
      }
  
      @Override
      public boolean cancel(boolean mayInterruptIfRunning) {
          synchronized (this) {
              if (isDone()) {
                  return false;
              }
              if (mayInterruptIfRunning) {
                  this.cancelled = true;
                  finishedLatch.countDown();
                  return true;
              }
          }
          try {
              finishedLatch.await();
          } catch (InterruptedException e) {
              throw new ConnectException("Interrupted while waiting for task to complete", e);
          }
          return false;
      }
  
      @Override
      public boolean isCancelled() {
          return cancelled;
      }
  
      @Override
      public boolean isDone() {
          return finishedLatch.getCount() == 0;
      }
  
      @Override
      public T get() throws InterruptedException, ExecutionException {
          finishedLatch.await();
          return result();
      }
  
      @Override
      public T get(long l, TimeUnit timeUnit)
              throws InterruptedException, ExecutionException, TimeoutException {
          if (!finishedLatch.await(l, timeUnit)) {
              Stage stage = currentStage;
              if (stage != null) {
                  throw new StagedTimeoutException(stage);
              } else {
                  throw new TimeoutException();
              }
          }
          return result();
      }
  
      @Override
      public void recordStage(Stage stage) {
          this.currentStage = stage;
      }
  
      private T result() throws ExecutionException {
          if (cancelled) {
              throw new CancellationException();
          }
          if (exception != null) {
              throw new ExecutionException(exception);
          }
          return result;
      }
  }
  