long def, int exp) {
final CountDownLatch latch = new CountDownLatch(1);
final OperationFuture<Long> rv =
new OperationFuture<Long>(key, latch, operationTimeout);
Operation op = opFact.mutate(m, key, by, def, exp,
new OperationCallback() {
public void receivedStatus(OperationStatus s) {
rv.set(new Long(s.isSuccess() ? s.getMessage() : "-1"), s);
}
public void complete() {