@Override
 public void run() {
   synchronized (lock) {
     // make sure we only have 5 ping in parallel
     if (shutdown || COUNTER.get() > MAX_PING) {
       return;
     }
     for (Maintainable maintainable : maintainables) {
       PeerStatistic peerStatatistic = maintainable.nextForMaintenance(runningFutures.values());
       if (peerStatatistic == null) {
         continue;
       }
       BaseFuture future;
       if (peerStatatistic.isLocal()) {
         future = peer.localAnnounce().ping().peerAddress(peerStatatistic.peerAddress()).start();
         LOG.debug(
             "maintenance local ping from {} to {}",
             peer.peerAddress(),
             peerStatatistic.peerAddress());
       } else {
         future = peer.ping().peerAddress(peerStatatistic.peerAddress()).start();
         LOG.debug(
             "maintenance ping from {} to {}", peer.peerAddress(), peerStatatistic.peerAddress());
       }
       peer.notifyAutomaticFutures(future);
       runningFutures.put(future, peerStatatistic.peerAddress());
       COUNTER.incrementAndGet();
       future.addListener(
           new BaseFutureAdapter<BaseFuture>() {
             @Override
             public void operationComplete(BaseFuture future) throws Exception {
               synchronized (lock) {
                 runningFutures.remove(future);
                 COUNTER.decrementAndGet();
               }
             }
           });
     }
   }
 }
 public FutureDone<Void> shutdown() {
   if (scheduledFuture != null) {
     scheduledFuture.cancel(false);
     // TODO: check if synchronized is really necessary here
   }
   final FutureDone<Void> futureShutdown = new FutureDone<Void>();
   synchronized (lock) {
     shutdown = true;
     final int max = runningFutures.size();
     final AtomicInteger counter = new AtomicInteger(0);
     for (BaseFuture future : runningFutures.keySet()) {
       future.addListener(
           new BaseFutureAdapter<BaseFuture>() {
             @Override
             public void operationComplete(BaseFuture future) throws Exception {
               if (counter.incrementAndGet() == max) {
                 futureShutdown.done();
               }
             }
           });
     }
   }
   return futureShutdown;
 }