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.Iterator;
  import java.util.concurrent.CompletableFuture;
  import java.util.concurrent.TimeUnit;
  import java.util.function.Predicate;
  import java.util.function.Supplier;
  import java.util.stream.Stream;
  import org.apache.bookkeeper.common.concurrent.FutureUtils;
  
  /**
   * A util class for supporting retries with customized backoff.
   */
  public final class Retries {
  
      private Retries() {
      }
  
      public static final Predicate<Throwable> NonFatalPredicate =
          cause -> !(cause instanceof RuntimeException);
  
      /**
       * Retry a given {@code task} on failures.
       *
       * <p>It is a shortcut of {@link #run(Stream, Predicate, Supplier, OrderedScheduler, Object)}
       * that runs retries on any threads in the provided {@code scheduler}.
       *
       * @param backoffs       a stream of backoff delays, in milliseconds.
       * @param retryPredicate a predicate to test if failures are retryable.
       * @param task           a task to execute.
       * @param scheduler      scheduler to schedule the task and complete the futures.
       * @param <ReturnT>      the return type
       * @return future represents the result of the task with retries.
       */
      public static <ReturnT> CompletableFuture<ReturnT> run(
          Stream<Long> backoffs,
          Predicate<Throwable> retryPredicate,
          Supplier<CompletableFuture<ReturnT>> task,
          OrderedScheduler scheduler) {
          return run(backoffs, retryPredicate, task, scheduler, null);
      }
  
      /**
       * Retry a given {@code task} on failures.
       *
       * <p>It will only retry the tasks when the predicate {@code retryPredicate} tests
       * it as a retryable failure and it doesn't exhaust the retry budget. The retry delays
       * are defined in a stream of delay values (in milliseconds).
       *
       * <p>If a schedule {@code key} is provided, the {@code task} will be submitted to the
       * scheduler using the provided schedule {@code key} and also the returned future
       * will be completed in the same thread. Otherwise, the task and the returned future will
       * be executed and scheduled on any threads in the scheduler.
       *
       * @param backoffs       a stream of backoff delays, in milliseconds.
       * @param retryPredicate a predicate to test if failures are retryable.
       * @param task           a task to execute.
       * @param scheduler      scheduler to schedule the task and complete the futures.
       * @param key            the submit key for the scheduler.
       * @param <ReturnT>      the return type.
       * @return future represents the result of the task with retries.
       */
      public static <ReturnT> CompletableFuture<ReturnT> run(
          Stream<Long> backoffs,
          Predicate<Throwable> retryPredicate,
          Supplier<CompletableFuture<ReturnT>> task,
          OrderedScheduler scheduler,
          Object key) {
          CompletableFuture<ReturnT> future = FutureUtils.createFuture();
          if (null == key) {
              execute(
                  future,
                  backoffs.iterator(),
                  retryPredicate,
                  task,
                  scheduler,
                  null);
          } else {
              scheduler.executeOrdered(key, () -> {
                  execute(
                      future,
                      backoffs.iterator(),
                      retryPredicate,
                      task,
                      scheduler,
                      key);
              });
          }
          return future;
      }
  
      private static <ReturnT> void execute(
          CompletableFuture<ReturnT> finalResult,
          Iterator<Long> backoffIter,
          Predicate<Throwable> retryPredicate,
          Supplier<CompletableFuture<ReturnT>> task,
          OrderedScheduler scheduler,
          Object key) {
  
          FutureUtils.whenCompleteAsync(task.get(), (result, cause) -> {
              if (null == cause) {
                  finalResult.complete(result);
                  return;
              }
              if (retryPredicate.test(cause)) {
                  if (!backoffIter.hasNext()) {
                      // exhausts all the retry budgets, fail the task now
                      finalResult.completeExceptionally(cause);
                      return;
                  }
                  long nextRetryDelayMs = backoffIter.next();
                  scheduler.scheduleOrdered(key, () -> execute(
                      finalResult,
                      backoffIter,
                      retryPredicate,
                      task,
                      scheduler,
                      key), nextRetryDelayMs, TimeUnit.MILLISECONDS);
              } else {
                  // the exception can not be retried
                  finalResult.completeExceptionally(cause);
              }
          }, scheduler, key);
      }
  
  }
  