import com.google.common.util.concurrent.Futures;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Map;
import java.util.concurrent.Future;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import com.google.common.util.concurrent.Futures;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Map;
import java.util.concurrent.Future;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;