.connectionPool(ConnectionPool(connectionListener = connectionListener))
    }

  private fun loomThreadFactory(): ThreadFactory {
    val ofVirtual = Thread::class.java.getMethod("ofVirtual").invoke(null)

    return Class
      .forName("java.lang.Thread\$Builder")
      .getMethod("factory")
      .invoke(ofVirtual) as ThreadFactory
  }

   * Futures#addCallback addCallback()}.
   *
   * <p>Memory consistency effects: Actions in a thread prior to adding a listener <a
   * href="https://docs.oracle.com/javase/specs/jls/se25/html/jls-17.html#jls-17.4.5">
   * <i>happen-before</i></a> its execution begins, perhaps in another thread.
   *
   * <p>Guava implementations of {@code ListenableFuture} promptly release references to listeners

 * contract.
 *
 * <p>The {@code standard} methods and the collection views they return are not guaranteed to be
 * thread-safe, even when all of the methods that they depend on are thread-safe.
 *
 * @author Louis Wasserman
 * @since 12.0
 */
@GwtIncompatible
public abstract class ForwardingNavigableSet<E extends @Nullable Object>

import java.util.logging.Level;
import java.util.logging.Logger;
import org.jspecify.annotations.NullMarked;

/**
 * A {@code TearDownStack} contains a stack of {@link TearDown} instances.
 *
 * <p>This class is thread-safe.
 *
 * @author Kevin Bourrillion
 * @since 10.0
 */
@GwtCompatible
@NullMarked
public class TearDownStack implements TearDownAccepter {

import java.util.logging.Level;
import java.util.logging.Logger;
import org.jspecify.annotations.NullMarked;

/**
 * A {@code TearDownStack} contains a stack of {@link TearDown} instances.
 *
 * <p>This class is thread-safe.
 *
 * @author Kevin Bourrillion
 * @since 10.0
 */
@GwtCompatible
@NullMarked
public class TearDownStack implements TearDownAccepter {

        assertNotNull(threadName.get());
        // The async execution should have run on a ForkJoinPool thread, not the main thread
        assertTrue("Should run on ForkJoinPool thread: " + threadName.get(),
                threadName.get().contains("ForkJoinPool") || !threadName.get().equals(Thread.currentThread().getName()));
        pool.shutdown();
    }

    // --- Synchronous execute() test ---

    @Test

 * contract.
 *
 * <p>The {@code standard} methods and the collection views they return are not guaranteed to be
 * thread-safe, even when all of the methods that they depend on are thread-safe.
 *
 * @author Louis Wasserman
 * @since 12.0
 */
@GwtIncompatible
public abstract class ForwardingNavigableSet<E extends @Nullable Object>

 *
 * <p>Note that although your APIs should be liberal in what they accept, your methods which
 * <i>return</i> iterables should make every attempt to return ones of the robust variety.
 *
 * <p>This testing utility is not thread-safe.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible
public final class MinimalIterable<E extends @Nullable Object> implements Iterable<E> {

  // Internal methods (package-visible, but treat as only subclass-visible)

  @Override
  @Nullable V getIfCached(@Nullable Object key) {
    V value = super.getIfCached(key);
    if (value != null) {
      return value;
    }

    // Store a local reference to the cache entry. If the backing map is immutable, this,
    // in combination with immutable cache entries, will ensure a thread-safe cache.
    CacheEntry<K, V> entry;

  }

  private void drainQueue() throws Exception {
    for (HttpUrl url; (url = queue.take()) != null; ) {
      if (!fetchedUrls.add(url)) {
        continue;
      }

      Thread currentThread = Thread.currentThread();
      String originalName = currentThread.getName();
      currentThread.setName("Crawler " + url);
      try {
        fetch(url);
      } catch (IOException e) {