import static com.google.common.collect.Sets.newConcurrentHashSet;
import static java.util.Objects.requireNonNull;
import static java.util.concurrent.atomic.AtomicIntegerFieldUpdater.newUpdater;
import static java.util.concurrent.atomic.AtomicReferenceFieldUpdater.newUpdater;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.j2objc.annotations.ReflectionSupport;