this.closed = false;
        }

        boolean isAlive() {
            return resourceRef.get() != null && !closed;
        }

        long getAge() {
            return System.currentTimeMillis() - creationTime;
        }
    }

    private ResourceManager() {
        ThreadFactory threadFactory = r -> {

 *   INSTANCE;
 *   public void funnel(Person person, PrimitiveSink into) {
 *     into.putUnencodedChars(person.getFirstName())
 *         .putUnencodedChars(person.getLastName())
 *         .putInt(person.getAge());
 *   }
 * }
 * }
 *
 * @author Dimitris Andreou
 * @since 11.0
 */
@Beta
@DoNotMock("Implement with a lambda")
public interface Funnel<T extends @Nullable Object> extends Serializable {

  /**

import com.google.common.annotations.GwtCompatible;
import java.util.Iterator;

/**
 * Creates iterators to be tested.
 *
 * @param <E> the element type of the iterator.
 * @author George van den Driessche
 */
@GwtCompatible
public interface TestIteratorGenerator<E> {
  Iterator<E> get();

import java.util.Map;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

/**
 * Creates maps, containing sample elements, to be tested.
 *
 * @author George van den Driessche
 */
@GwtCompatible
@NullMarked
public interface TestMapGenerator<K extends @Nullable Object, V extends @Nullable Object>
    extends TestContainerGenerator<Map<K, V>, Map.Entry<K, V>> {

package com.google.common.collect.testing;

import com.google.common.annotations.GwtCompatible;
import java.util.Iterator;

/**
 * Adapts a test iterable generator to give a TestIteratorGenerator.
 *
 * @author George van den Driessche
 */
@GwtCompatible
public final class DerivedTestIteratorGenerator<E>
    implements TestIteratorGenerator<E>, DerivedGenerator {

 *
 * <p>This interface should not be implemented outside this package; {@link
 * PerCollectionSizeTestSuiteBuilder} constructs instances of it from a more general {@link
 * TestCollectionGenerator}.
 *
 * @author George van den Driessche
 */
@GwtCompatible
@NullMarked
public interface OneSizeTestContainerGenerator<T, E extends @Nullable Object>
    extends TestSubjectGenerator<T>, TestContainerGenerator<T, E> {

import com.google.common.annotations.J2ktIncompatible;
import java.util.Set;

/**
 * Thrown when requirements on a tester method or class conflict with each other.
 *
 * @author George van den Driessche
 */
@GwtCompatible
public class ConflictingRequirementsException extends Exception {
  private final Set<Feature<?>> conflicts;
  private final Object source;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.Set;

/**
 * Optional features of classes derived from {@code Set}.
 *
 * @author George van den Driessche
 */
@SuppressWarnings("rawtypes") // maybe avoidable if we rework the whole package?
@GwtCompatible
public enum SetFeature implements Feature<Set> {
  GENERAL_PURPOSE(CollectionFeature.GENERAL_PURPOSE);

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.List;
import java.util.Set;

/**
 * Optional features of classes derived from {@code List}.
 *
 * @author George van den Driessche
 */
@SuppressWarnings("rawtypes") // maybe avoidable if we rework the whole package?
@GwtCompatible
public enum ListFeature implements Feature<List> {
  SUPPORTS_SET,

import org.jspecify.annotations.Nullable;

/**
 * To be implemented by test generators that can produce test subjects without requiring any
 * parameters.
 *
 * @param <T> the type created by this generator.
 * @author George van den Driessche
 */
@GwtCompatible
@NullMarked
public interface TestSubjectGenerator<T extends @Nullable Object> {
  T createTestSubject();