import com.google.common.util.concurrent.Futures.FutureCombiner;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.DoNotMock;
import com.google.j2objc.annotations.RetainedWith;
import java.io.Closeable;
import java.util.IdentityHashMap;
import java.util.Map;
import java.util.concurrent.Callable;