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 com.datastax.oss.driver.core;
  
  import static java.util.concurrent.TimeUnit.SECONDS;
  import static org.assertj.core.api.Assertions.fail;
  
  import com.datastax.oss.driver.api.core.CqlSession;
  import com.datastax.oss.driver.api.core.NoNodeAvailableException;
  import com.datastax.oss.driver.api.core.config.DefaultDriverOption;
  import com.datastax.oss.driver.api.core.config.DriverConfigLoader;
  import com.datastax.oss.driver.api.core.cql.AsyncResultSet;
  import com.datastax.oss.driver.api.testinfra.session.SessionRule;
  import com.datastax.oss.driver.api.testinfra.simulacron.SimulacronRule;
  import com.datastax.oss.driver.categories.ParallelizableTests;
  import com.datastax.oss.simulacron.common.cluster.ClusterSpec;
  import java.util.concurrent.CountDownLatch;
  import java.util.concurrent.atomic.AtomicReference;
  import org.junit.Before;
  import org.junit.ClassRule;
  import org.junit.Test;
  import org.junit.experimental.categories.Category;
  import org.junit.rules.RuleChain;
  import org.junit.rules.TestRule;
  
  @Category(ParallelizableTests.class)
  public class PoolBalancingIT {
  
    private static final int POOL_SIZE = 2;
    private static final int REQUESTS_PER_CONNECTION = 20;
  
    private static final SimulacronRule SIMULACRON_RULE =
        new SimulacronRule(ClusterSpec.builder().withNodes(1));
  
    private static final SessionRule<CqlSession> SESSION_RULE =
        SessionRule.builder(SIMULACRON_RULE)
            .withConfigLoader(
                DriverConfigLoader.programmaticBuilder()
                    .withInt(DefaultDriverOption.CONNECTION_MAX_REQUESTS, REQUESTS_PER_CONNECTION)
                    .withInt(DefaultDriverOption.CONNECTION_POOL_LOCAL_SIZE, POOL_SIZE)
                    .build())
            .build();
  
    @ClassRule
    public static final TestRule CHAIN = RuleChain.outerRule(SIMULACRON_RULE).around(SESSION_RULE);
  
    private CountDownLatch done;
    private AtomicReference<Throwable> unexpectedErrorRef;
  
    @Before
    public void setup() {
      done = new CountDownLatch(1);
      unexpectedErrorRef = new AtomicReference<>();
    }
  
    @Test
    public void should_balance_requests_across_connections() throws InterruptedException {
      // Generate just the right load to completely fill the pool. All requests should succeed.
      int simultaneousRequests = POOL_SIZE * REQUESTS_PER_CONNECTION;
  
      for (int i = 0; i < simultaneousRequests; i++) {
        reschedule(null, null);
      }
      SECONDS.sleep(1);
      done.countDown();
  
      Throwable unexpectedError = unexpectedErrorRef.get();
      if (unexpectedError != null) {
        fail("At least one request failed unexpectedly", unexpectedError);
      }
    }
  
    private void reschedule(AsyncResultSet asyncResultSet, Throwable throwable) {
      if (done.getCount() == 1) {
        if (throwable != null
            // Actually there is a tiny race condition where pool acquisition may still fail: channel
            // sizes can change as the client is iterating through them, so it can look like they're
            // all full even if there's always a free slot somewhere at every point in time. This will
            // result in NoNodeAvailableException, ignore it.
            && !(throwable instanceof NoNodeAvailableException)) {
          unexpectedErrorRef.compareAndSet(null, throwable);
          // Even a single error is a failure, no need to continue
          done.countDown();
        }
        SESSION_RULE
            .session()
            .executeAsync("SELECT release_version FROM system.local")
            .whenComplete(this::reschedule);
      }
    }
  }
  