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   * 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.cassandra.db.compaction;
  
  import java.util.concurrent.CountDownLatch;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import com.google.common.util.concurrent.Uninterruptibles;
  
  import org.junit.After;
  import org.junit.Before;
  import org.junit.Test;
  
  import org.apache.cassandra.Util;
  import org.apache.cassandra.config.DatabaseDescriptor;
  
  
  import static org.assertj.core.api.Assertions.assertThat;
  import static org.junit.Assert.assertEquals;
  
  public class ValidationExecutorTest
  {
  
      CompactionManager.ValidationExecutor validationExecutor;
  
      @Before
      public void setup()
      {
          DatabaseDescriptor.clientInitialization();
          // required for static initialization of CompactionManager
          DatabaseDescriptor.setConcurrentCompactors(2);
          DatabaseDescriptor.setConcurrentValidations(2);
  
          // shutdown the singleton CompactionManager to ensure MBeans are unregistered
          CompactionManager.instance.forceShutdown();
      }
  
      @After
      public void tearDown()
      {
          if (null != validationExecutor)
              validationExecutor.shutdownNow();
      }
  
      @Test
      public void testQueueOnValidationSubmission() throws InterruptedException
      {
          CountDownLatch taskBlocked = new CountDownLatch(1);
          AtomicInteger threadsAvailable = new AtomicInteger(DatabaseDescriptor.getConcurrentValidations());
          CountDownLatch taskComplete = new CountDownLatch(5);
          validationExecutor = new CompactionManager.ValidationExecutor();
  
          ExecutorService testExecutor = Executors.newSingleThreadExecutor();
          for (int i=0; i< 5; i++)
              testExecutor.submit(() -> {
                  threadsAvailable.decrementAndGet();
                  validationExecutor.submit(new Task(taskBlocked, taskComplete));
              });
  
          // wait for all tasks to be submitted & check that the excess ones were queued
          while (threadsAvailable.get() > 0)
              TimeUnit.MILLISECONDS.sleep(10);
  
          // getActiveTaskCount() relies on getActiveCount() which gives an approx number so we poll it
          Util.spinAssertEquals(2, () -> validationExecutor.getActiveTaskCount(), 1);
          assertEquals(3, validationExecutor.getPendingTaskCount());
  
          taskBlocked.countDown();
          taskComplete.await(10, TimeUnit.SECONDS);
          validationExecutor.shutdownNow();
      }
  
      @Test
      public void testAdjustPoolSize()
      {
          // adjusting the pool size should dynamically set core and max pool
          // size to DatabaseDescriptor::getConcurrentValidations
  
          validationExecutor = new CompactionManager.ValidationExecutor();
  
          int corePoolSize = validationExecutor.getCorePoolSize();
          int maxPoolSize = validationExecutor.getMaximumPoolSize();
  
          DatabaseDescriptor.setConcurrentValidations(corePoolSize * 2);
          validationExecutor.adjustPoolSize();
          assertThat(validationExecutor.getCorePoolSize()).isEqualTo(corePoolSize * 2);
          assertThat(validationExecutor.getMaximumPoolSize()).isEqualTo(maxPoolSize * 2);
          validationExecutor.shutdownNow();
      }
  
      private static class Task implements Runnable
      {
          private final CountDownLatch blocked;
          private final CountDownLatch complete;
  
          Task(CountDownLatch blocked, CountDownLatch complete)
          {
              this.blocked = blocked;
              this.complete = complete;
          }
  
          public void run()
          {
              Uninterruptibles.awaitUninterruptibly(blocked);
              complete.countDown();
          }
      }
  }
  