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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
   *
   *      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
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   */
  package org.apache.cayenne.access.dbsync;
  
  import org.apache.cayenne.access.DataNode;
  import org.slf4j.Logger;
  import org.junit.After;
  import org.junit.Before;
  import org.junit.Test;
  import org.slf4j.LoggerFactory;
  
  import java.sql.SQLException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.Future;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import static org.junit.Assert.assertEquals;
  import static org.junit.Assert.assertFalse;
  import static org.mockito.Mockito.mock;
  
  public class BaseSchemaUpdateStrategy_ConcurrencyTest {
  
      private static final Logger LOGGER = LoggerFactory.getLogger(BaseSchemaUpdateStrategy_ConcurrencyTest.class);
  
      private ExecutorService threadPool;
      private DataNode dataNode;
  
      @Before
      public void before() {
          threadPool = Executors.newFixedThreadPool(2);
          dataNode = mock(DataNode.class);
      }
  
      @After
      public void after() {
          threadPool.shutdownNow();
      }
  
      @Test
      public void testUpdateSchema_Concurrency() throws InterruptedException, ExecutionException, TimeoutException {
  
          final AtomicInteger counter = new AtomicInteger();
          final AtomicBoolean errors = new AtomicBoolean(false);
  
          final BaseSchemaUpdateStrategy strategy = new BaseSchemaUpdateStrategy() {
              @Override
              protected void processSchemaUpdate(DataNode dataNode) throws SQLException {
                  counter.incrementAndGet();
              }
          };
  
          Collection<Future<?>> tasks = new ArrayList<>();
  
          for (int i = 0; i < 20; i++) {
              tasks.add(threadPool.submit(new Runnable() {
                  @Override
                  public void run() {
                      try {
                          strategy.updateSchema(dataNode);
                      } catch (Throwable e) {
                          LOGGER.error("error in test", e);
                          errors.set(true);
                      }
                  }
              }));
          }
  
          for(Future<?> f : tasks) {
              f.get(1, TimeUnit.SECONDS);
          }
  
          assertFalse(errors.get());
          assertEquals(1, counter.get());
      }
  }
  