document-haness/docs/clean-architecture-backend-template/final/evidence/raw/113a-pool-lane-saturation-probe.java

package dev.caskeleton.adapter.outbound.persistence.platform.pool;

import com.zaxxer.hikari.HikariConfig;
import com.zaxxer.hikari.HikariDataSource;
import dev.caskeleton.adapter.outbound.persistence.testkit.pool.PoolMeasurement;
import dev.caskeleton.adapter.outbound.persistence.testkit.postgresql.PostgreSqlContainerFactory;
import dev.caskeleton.adapter.outbound.persistence.testkit.postgresql.PostgreSqlVersion;
import java.sql.Connection;
import java.time.Duration;
import java.time.Instant;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;
import org.testcontainers.postgresql.PostgreSQLContainer;

/** Analysis-only probe: what a real saturated Hikari pool reports, and how long acquisition waits. */
class AnalysisPoolSaturationProbe {

  private static PostgreSQLContainer container;

  @BeforeAll
  static void startServer() {
    container = PostgreSqlContainerFactory.create(PostgreSqlVersion.PG_16);
    container.start();
  }

  @AfterAll
  static void stopServer() {
    if (container != null) {
      container.stop();
    }
  }

  @Test
  void realSaturatedPoolPendingCount() throws Exception {
    try (HikariDataSource pool = pool(2, 3000L)) {
      Connection first = pool.getConnection();
      Connection second = pool.getConnection();
      CountDownLatch waiterStarted = new CountDownLatch(1);
      AtomicReference<String> waiterOutcome = new AtomicReference<>("none");
      Thread waiter =
          new Thread(
              () -> {
                waiterStarted.countDown();
                try (Connection blocked = pool.getConnection()) {
                  waiterOutcome.set("acquired");
                } catch (Exception refused) {
                  waiterOutcome.set(refused.getClass().getSimpleName());
                }
              });
      waiter.start();
      waiterStarted.await(5, TimeUnit.SECONDS);
      Thread.sleep(500L);

      var bean = pool.getHikariPoolMXBean();
      PoolMeasurement measurement =
          new PoolMeasurement(
              bean.getActiveConnections(),
              bean.getIdleConnections(),
              bean.getThreadsAwaitingConnection(),
              Duration.ZERO);
      System.out.println("realPool.active=" + measurement.active());
      System.out.println("realPool.idle=" + measurement.idle());
      System.out.println("realPool.pending=" + measurement.pending());
      System.out.println("realPool.saturated=" + measurement.saturated());

      first.close();
      waiter.join(10_000L);
      System.out.println("realPool.waiterOutcome=" + waiterOutcome.get());
      second.close();
    }
  }

  @Test
  void acquireWaitAgainstTheConfiguredTimeout() throws Exception {
    long configuredTimeoutMillis = 500L;
    try (HikariDataSource pool = pool(2, configuredTimeoutMillis)) {
      Connection first = pool.getConnection();
      Connection second = pool.getConnection();
      Instant startedAt = Instant.now();
      String outcome;
      try (Connection refused = pool.getConnection()) {
        outcome = "acquired";
      } catch (Exception failure) {
        outcome = failure.getClass().getSimpleName();
      }
      Duration waited = Duration.between(startedAt, Instant.now());
      System.out.println("acquire.configuredTimeoutMillis=" + configuredTimeoutMillis);
      System.out.println("acquire.observedWaitMillis=" + waited.toMillis());
      System.out.println("acquire.outcome=" + outcome);
      System.out.println(
          "acquire.assertedUpperBoundMillis=" + (configuredTimeoutMillis + 2000L));
      first.close();
      second.close();
    }
  }

  @Test
  void handBuiltFixtureStateVersusRealPoolState() {
    PoolMeasurement fixture = new PoolMeasurement(4, 2, 3, Duration.ofMillis(80));
    System.out.println("fixture.active=" + fixture.active());
    System.out.println("fixture.idle=" + fixture.idle());
    System.out.println("fixture.pending=" + fixture.pending());
    System.out.println("fixture.saturated=" + fixture.saturated());
    System.out.println("fixture.total=" + fixture.total());
    int concurrentThreads = 8;
    int maxRequiresNewDepth = 1;
    System.out.println(
        "formula.required=" + (concurrentThreads * (1 + maxRequiresNewDepth) + 1));
  }

  private static HikariDataSource pool(int size, long connectionTimeoutMillis) {
    HikariConfig config = new HikariConfig();
    config.setJdbcUrl(container.getJdbcUrl());
    config.setUsername(container.getUsername());
    config.setPassword(container.getPassword());
    config.setMaximumPoolSize(size);
    config.setConnectionTimeout(connectionTimeoutMillis);
    return new HikariDataSource(config);
  }
}