/**
   * Concat arrays in one.
   *
   * @param arrays Arrays.
   * @return Summary array.
   */
  public static int[] concat(int[]... arrays) {
    assert arrays != null;
    assert arrays.length > 1;

    int len = 0;

    for (int[] a : arrays) len += a.length;

    int[] r = Arrays.copyOf(arrays[0], len);

    for (int i = 1, shift = 0; i < arrays.length; i++) {
      shift += arrays[i - 1].length;
      System.arraycopy(arrays[i], 0, r, shift, arrays[i].length);
    }

    return r;
  }
  /**
   * Grabs local events and detects if events was lost since last poll.
   *
   * @param ignite Target grid.
   * @param evtOrderKey Unique key to take last order key from node local map.
   * @param evtThrottleCntrKey Unique key to take throttle count from node local map.
   * @param evtTypes Event types to collect.
   * @param evtMapper Closure to map grid events to Visor data transfer objects.
   * @return Collections of node events
   */
  public static Collection<VisorGridEvent> collectEvents(
      Ignite ignite,
      String evtOrderKey,
      String evtThrottleCntrKey,
      final int[] evtTypes,
      IgniteClosure<Event, VisorGridEvent> evtMapper) {
    assert ignite != null;
    assert evtTypes != null && evtTypes.length > 0;

    ConcurrentMap<String, Long> nl = ignite.cluster().nodeLocalMap();

    final long lastOrder = getOrElse(nl, evtOrderKey, -1L);
    final long throttle = getOrElse(nl, evtThrottleCntrKey, 0L);

    // When we first time arrive onto a node to get its local events,
    // we'll grab only last those events that not older than given period to make sure we are
    // not grabbing GBs of data accidentally.
    final long notOlderThan = System.currentTimeMillis() - EVENTS_COLLECT_TIME_WINDOW;

    // Flag for detecting gaps between events.
    final AtomicBoolean lastFound = new AtomicBoolean(lastOrder < 0);

    IgnitePredicate<Event> p =
        new IgnitePredicate<Event>() {
          /** */
          private static final long serialVersionUID = 0L;

          @Override
          public boolean apply(Event e) {
            // Detects that events were lost.
            if (!lastFound.get() && (lastOrder == e.localOrder())) lastFound.set(true);

            // Retains events by lastOrder, period and type.
            return e.localOrder() > lastOrder
                && e.timestamp() > notOlderThan
                && F.contains(evtTypes, e.type());
          }
        };

    Collection<Event> evts = ignite.events().localQuery(p);

    // Update latest order in node local, if not empty.
    if (!evts.isEmpty()) {
      Event maxEvt = Collections.max(evts, EVTS_ORDER_COMPARATOR);

      nl.put(evtOrderKey, maxEvt.localOrder());
    }

    // Update throttle counter.
    if (!lastFound.get())
      nl.put(evtThrottleCntrKey, throttle == 0 ? EVENTS_LOST_THROTTLE : throttle - 1);

    boolean lost = !lastFound.get() && throttle == 0;

    Collection<VisorGridEvent> res = new ArrayList<>(evts.size() + (lost ? 1 : 0));

    if (lost) res.add(new VisorGridEventsLost(ignite.cluster().localNode().id()));

    for (Event e : evts) {
      VisorGridEvent visorEvt = evtMapper.apply(e);

      if (visorEvt != null) res.add(visorEvt);
    }

    return res;
  }
  /** @throws Exception If failed. */
  private void doTest() throws Exception {
    System.gc();
    System.gc();
    System.gc();

    try {
      useCache = true;

      startGridsMultiThreaded(GRID_CNT);

      useCache = false;

      Ignite ignite = startGrid();

      final IgniteDataStreamer<Integer, String> ldr = ignite.dataStreamer(null);

      ldr.perNodeBufferSize(8192);
      ldr.receiver(DataStreamerCacheUpdaters.<Integer, String>batchedSorted());
      ldr.autoFlushFrequency(0);

      final LongAdder8 cnt = new LongAdder8();

      long start = U.currentTimeMillis();

      Thread t =
          new Thread(
              new Runnable() {
                @SuppressWarnings("BusyWait")
                @Override
                public void run() {
                  while (true) {
                    try {
                      Thread.sleep(10000);
                    } catch (InterruptedException ignored) {
                      break;
                    }

                    info(">>> Adds/sec: " + cnt.sumThenReset() / 10);
                  }
                }
              });

      t.setDaemon(true);

      t.start();

      int threadNum = 2; // Runtime.getRuntime().availableProcessors();

      multithreaded(
          new Callable<Object>() {
            @SuppressWarnings("InfiniteLoopStatement")
            @Override
            public Object call() throws Exception {
              ThreadLocalRandom8 rnd = ThreadLocalRandom8.current();

              while (true) {
                int i = rnd.nextInt(ENTRY_CNT);

                ldr.addData(i, vals[rnd.nextInt(vals.length)]);

                cnt.increment();
              }
            }
          },
          threadNum,
          "loader");

      info("Closing loader...");

      ldr.close(false);

      long duration = U.currentTimeMillis() - start;

      info("Finished performance test. Duration: " + duration + "ms.");
    } finally {
      stopAllGrids();
    }
  }