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.sdk.testing;
  
  import static java.util.stream.Collectors.joining;
  import static java.util.stream.Collectors.toList;
  import static org.junit.Assert.fail;
  
  import java.lang.reflect.Field;
  import java.util.List;
  import java.util.stream.Stream;
  import org.junit.rules.TestRule;
  import org.junit.runner.Description;
  import org.junit.runners.model.Statement;
  
  /**
   * Tracks the threads created during a test method execution (or class using @ClassRule) and fails
   * if some still exists after the test method execution.
   */
  public class ThreadLeakTracker implements TestRule {
    private final Field groupField;
  
    public ThreadLeakTracker() {
      try {
        groupField = Thread.class.getDeclaredField("group");
        if (!groupField.isAccessible()) {
          groupField.setAccessible(true);
        }
      } catch (final NoSuchFieldException e) {
        throw new IllegalStateException(e);
      }
    }
  
    @Override
    public Statement apply(final Statement base, final Description description) {
      return new Statement() {
        @Override
        public void evaluate() throws Throwable {
          final Thread thread = Thread.currentThread();
          final ThreadGroup threadGroup = thread.getThreadGroup();
          final ThreadGroup testGroup = new ThreadGroup(threadGroup, Long.toString(thread.getId()));
          groupField.set(thread, testGroup);
          try {
            base.evaluate();
          } finally {
            groupField.set(thread, threadGroup);
            final Thread[] threads = listThreads();
            final List<Thread> leaked =
                Stream.of(threads).filter(t -> t.getThreadGroup() == testGroup).collect(toList());
            if (!leaked.isEmpty()) {
              fail(
                  "Some threads leaked: "
                      + leaked.stream().map(Thread::getName).collect(joining("\n- ", "\n- ", "")));
            }
          }
        }
      };
    }
  
    private Thread[] listThreads() {
      final int count = Thread.activeCount();
      final Thread[] threads = new Thread[Math.max(count * 2, 16)];
      final int threadCount = Thread.enumerate(threads);
      final Thread[] array = new Thread[threadCount];
      System.arraycopy(threads, 0, array, 0, threadCount);
      return array;
    }
  }
  