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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.index.sai.plan;
  
  import java.util.concurrent.ForkJoinPool;
  
  import org.junit.Test;
  
  import static org.junit.Assert.assertEquals;
  
  import org.apache.cassandra.index.sai.SAITester;
  import org.apache.cassandra.index.sai.disk.IndexSearchResultIterator;
  import org.apache.cassandra.inject.Injections;
  import org.apache.cassandra.inject.InvokePointBuilder;
  
  /**
   * Test to cover edge cases related to memtable flush during query execution.
   */
  public class FlushIndexWhileQueryingTest extends SAITester
  {
      @Test
      public void testFlushDuringEqualityQuery() throws Throwable
      {
          createTable("CREATE TABLE %s (k text PRIMARY KEY, x int)");
  
          createIndex("CREATE CUSTOM INDEX ON %s(x) USING 'sai'");
  
          execute("INSERT INTO %s (k, x) VALUES (?, ?)", "a", 0);
          execute("INSERT INTO %s (k, x) VALUES (?, ?)", "b", 0);
          execute("INSERT INTO %s (k, x) VALUES (?, ?)", "c", 1);
  
          // We use a barrier to trigger flush at precisely the right time
          InvokePointBuilder initialInvokePoint = InvokePointBuilder.newInvokePoint()
                                                             .onClass(QueryViewBuilder.class)
                                                             .onMethod("build")
                                                             .atExit();
          Injections.Barrier initialBarrier = Injections.newBarrier("pause_query", 2, false)
                                                        .add(initialInvokePoint)
                                                        .build();
          InvokePointBuilder secondInvokePoint = InvokePointBuilder.newInvokePoint()
                                                             .onClass(IndexSearchResultIterator.class)
                                                             .onMethod("build")
                                                             .atEntry();
          Injections.Barrier secondBarrier = Injections.newBarrier("resume_query", 2, false)
                                                       .add(secondInvokePoint)
                                                       .build();
  
          Injections.inject(initialBarrier, secondBarrier);
  
          // Flush in a separate thread to allow the query to run concurrently
          ForkJoinPool.commonPool().submit(() -> {
              try
              {
                  initialBarrier.arrive();
                  flush();
                  secondBarrier.arrive();
              }
              catch (InterruptedException t)
              {
                  throw new RuntimeException(t);
              }
          });
  
          assertRowCount(execute("SELECT k FROM %s WHERE x = 0"), 2);
          assertEquals("Confirm that we hit the barrier (helps in case method name changed)", 0, initialBarrier.getCount());
          assertEquals("Confirm that we hit the barrier (helps in case method name changed)", 0, secondBarrier.getCount());
      }
  }
  