private void awaitFollowup() {
            try {
                fencingFollowup.get();
            } catch (InterruptedException e) {
                throw new ConnectException("Interrupted while performing zombie fencing", e);
            } catch (ExecutionException e) {
                Throwable cause = e.getCause();
                throw ConnectUtils.maybeWrap(cause, "Failed to perform round of zombie fencing");
            }
        }
Start sending requests to the Kafka cluster to fence zombies. In rare cases, may cause blocking calls to
take place before returning, so care should be taken to ensure that this method is not invoked while holding
any important locks (e.g., while synchronized on the surrounding DistributedHerder instance).
This method must be invoked before any {@link #addCallback(Callback) callbacks can be added},
and may only be invoked once.
@throws IllegalStateException if invoked multiple times
connect/runtime/src/main/java/org/apache/kafka/connect/runtime/distributed/DistributedHerder.java