// (roll detect).
// { ackChecksumChecker => insistentAppend => stubbornAppend =>
// insistentOpen => mask("rolltag") => roll(xx) { rollDetect =>
// escapedCusomtDfs } }
EventSink tmp = new MaskDecorator(s, "rolltag");
tmp = new InsistentOpenDecorator<EventSink>(tmp, backoff1);
tmp = new StubbornAppendSink<EventSink>(tmp);
tmp = new InsistentAppendDecorator<EventSink>(tmp, backoff2);
snk = new AckChecksumChecker<EventSink>(tmp, accum);
}