/*
    * 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
    *
    *      https://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.commons.lang3.builder;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.concurrent.Callable;
  import java.util.concurrent.CopyOnWriteArrayList;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.Future;
  import java.util.concurrent.TimeUnit;
  
  import org.apache.commons.lang3.AbstractLangTest;
  import org.apache.commons.lang3.concurrent.UncheckedFuture;
  import org.junit.jupiter.api.Test;
  
  /**
   * Tests concurrent access for the default {@link ToStringStyle}.
   * <p>
   * The {@link ToStringStyle} class includes a registry to avoid infinite loops for objects with circular references. We
   * want to make sure that we do not get concurrency exceptions accessing this registry.
   * </p>
   * <p>
   * This test passes but only tests one aspect of the issue.
   * </p>
   *
   * @see <a href="https://issues.apache.org/jira/browse/LANG-762">[LANG-762] Handle or document ReflectionToStringBuilder
   *      and ToStringBuilder for collections that are not thread safe</a>
   */
  class ToStringStyleConcurrencyTest extends AbstractLangTest {
  
      static class CollectionHolder<T extends Collection<?>> {
          T collection;
  
          CollectionHolder(final T collection) {
              this.collection = collection;
          }
      }
  
      private static final List<Integer> LIST;
      private static final int LIST_SIZE = 100000;
      private static final int REPEAT = 100;
  
      static {
          LIST = new ArrayList<>(LIST_SIZE);
          for (int i = 0; i < LIST_SIZE; i++) {
              LIST.add(Integer.valueOf(i));
          }
      }
  
      @Test
      void testArrayList() throws InterruptedException {
          testConcurrency(new CollectionHolder<>(new ArrayList<>()));
      }
  
      private void testConcurrency(final CollectionHolder<List<Integer>> holder) throws InterruptedException {
          final List<Integer> list = holder.collection;
          // make a big array that takes a long time to toString()
          list.addAll(LIST);
          // Create a thread pool with two threads to cause the most contention on the underlying resource.
          final ExecutorService threadPool = Executors.newFixedThreadPool(2);
          try {
              // Consumes toStrings
              final Callable<Integer> consumer = () -> {
                  for (int i = 0; i < REPEAT; i++) {
                      // Calls ToStringStyle
                      new ToStringBuilder(holder).append(holder.collection);
                  }
                  return Integer.valueOf(REPEAT);
              };
              final Collection<Callable<Integer>> tasks = new ArrayList<>();
              tasks.add(consumer);
              tasks.add(consumer);
              final List<Future<Integer>> futures = threadPool.invokeAll(tasks);
              UncheckedFuture.on(futures).forEach(UncheckedFuture::get);
          } finally {
              threadPool.shutdown();
              threadPool.awaitTermination(1, TimeUnit.SECONDS);
          }
      }
  
     @Test
     void testCopyOnWriteArrayList() throws InterruptedException {
         testConcurrency(new CollectionHolder<>(new CopyOnWriteArrayList<>()));
     }
 
     @Test
     void testLinkedList() throws InterruptedException {
         testConcurrency(new CollectionHolder<>(new LinkedList<>()));
     }
 }