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.ambari.server.topology;
  
  import java.util.concurrent.Callable;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.Executors;
  import java.util.concurrent.Future;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  import java.util.function.Consumer;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import com.google.common.base.Preconditions;
  import com.google.common.base.Throwables;
  
  /**
   * Callable service implementation for executing tasks asynchronously.
   * The service repeatedly tries to execute the provided task till it successfully completes, or the provided timeout
   * interval is exceeded.
   *
   * @param <T> the type returned by the task to be executed
   */
  public class AsyncCallableService<T> implements Callable<T> {
  
    private static final Logger LOG = LoggerFactory.getLogger(AsyncCallableService.class);
  
    // task execution is done on a separate thread provided by this executor
    private final ScheduledExecutorService executorService;
  
    // the task to be executed
    private final Callable<T> task;
    private final String taskName;
  
    // the total time the allowed for the task to be executed (retries will be happen within this timeframe in
    // milliseconds)
    private final long timeout;
  
    // the delay between two consecutive execution trials in milliseconds
    private final long retryDelay;
    private final Consumer<Throwable> onError;
  
    public AsyncCallableService(Callable<T> task, long timeout, long retryDelay, String taskName, Consumer<Throwable> onError) {
      this(task, timeout, retryDelay, taskName, Executors.newScheduledThreadPool(1), onError);
    }
  
    public AsyncCallableService(Callable<T> task, long timeout, long retryDelay, String taskName, ScheduledExecutorService executorService, Consumer<Throwable> onError) {
      Preconditions.checkArgument(retryDelay > 0, "retryDelay should be positive");
  
      this.task = task;
      this.executorService = executorService;
      this.timeout = timeout;
      this.retryDelay = retryDelay;
      this.taskName = taskName;
      this.onError = onError;
    }
  
    @Override
    public T call() throws Exception {
      long startTime = System.currentTimeMillis();
      long timeLeft = timeout;
      Future<T> future = executorService.submit(task);
      LOG.info("Task {} execution started at {}", taskName, startTime);
  
      Throwable lastError = null;
      while (true) {
        try {
          LOG.debug("Task {} waiting for result at most {} ms", taskName, timeLeft);
          T taskResult = future.get(timeLeft, TimeUnit.MILLISECONDS);
          LOG.info("Task {} successfully completed with result: {}", taskName, taskResult);
          return taskResult;
        } catch (TimeoutException e) {
          LOG.debug("Task {} timeout", taskName);
          if (lastError == null) {
            lastError = e;
          }
          timeLeft = 0;
        } catch (ExecutionException e) {
          Throwable cause = Throwables.getRootCause(e);
          if (!(cause instanceof RetryTaskSilently)) {
            LOG.info(String.format("Task %s exception during execution", taskName), cause);
          }
          lastError = cause;
          timeLeft = timeout - (System.currentTimeMillis() - startTime) - retryDelay;
        }
  
        if (timeLeft <= 0) {
          attemptToCancel(future);
          LOG.warn("Task {} timeout exceeded, no more retries", taskName);
          onError.accept(lastError);
          return null;
        }
  
        LOG.debug("Task {} retrying execution in {} milliseconds", taskName, retryDelay);
        future = executorService.schedule(task, retryDelay, TimeUnit.MILLISECONDS);
      }
    }
  
    private void attemptToCancel(Future<?> future) {
      LOG.debug("Task {} timeout exceeded, cancelling", taskName);
      if (!future.isDone() && future.cancel(true)) {
        LOG.debug("Task {} cancelled", taskName);
      } else {
        LOG.debug("Task {} already done", taskName);
      }
    }
  
    public static class RetryTaskSilently extends RuntimeException {
      // marker, throw if the task needs to be retried
      public RetryTaskSilently() {
        super();
      }
      public RetryTaskSilently(String message) {
        super(message);
      }
    }
  
  }
  