code: /*
   * Copyright (c) 2019 the Eclipse Milo Authors
   *
   * This program and the accompanying materials are made
   * available under the terms of the Eclipse Public License 2.0
   * which is available at https://www.eclipse.org/legal/epl-2.0/
   *
   * SPDX-License-Identifier: EPL-2.0
   */
  
  package org.eclipse.milo.opcua.stack.core.util;
  
  import java.util.concurrent.CountDownLatch;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.testng.annotations.Test;
  
  import static org.testng.Assert.assertEquals;
  import static org.testng.Assert.assertFalse;
  
  public class ExecutionQueueTest {
  
      private final ExecutorService executor = Executors.newCachedThreadPool();
  
      @Test
      public void testSubmitIsLinearWhenConcurrencyIs1() {
          ExecutionQueue queue = new ExecutionQueue(executor, 1);
  
          AtomicBoolean failed = new AtomicBoolean(false);
          AtomicInteger n = new AtomicInteger(0);
  
          for (int i = 0; i < 1000000; i++) {
              final int ii = i;
  
              queue.submit(() -> {
                  int nn = n.getAndIncrement();
                  if (ii != nn) {
                      System.out.println("n=" + nn + " i=" + ii);
                      failed.set(true);
                  }
              });
          }
  
          assertFalse(failed.get());
      }
  
      @Test
      public void testWithConcurrency() throws InterruptedException {
          ExecutionQueue queue = new ExecutionQueue(executor, 4);
  
          final CountDownLatch latch = new CountDownLatch(100000);
          final AtomicInteger count = new AtomicInteger();
  
          for (int i = 0; i < 100000; i++) {
              queue.submit(() -> {
                  count.incrementAndGet();
                  latch.countDown();
              });
          }
  
          latch.await();
          assertEquals(count.get(), 100000);
      }
  
  }
  