/**
   * Performs flush.
   *
   * @throws GridException If failed.
   */
  private void doFlush() throws GridException {
    lastFlushTime = U.currentTimeMillis();

    List<GridFuture> activeFuts0 = null;

    int doneCnt = 0;

    for (GridFuture<?> f : activeFuts) {
      if (!f.isDone()) {
        if (activeFuts0 == null) activeFuts0 = new ArrayList<>((int) (activeFuts.size() * 1.2));

        activeFuts0.add(f);
      } else {
        f.get();

        doneCnt++;
      }
    }

    if (activeFuts0 == null || activeFuts0.isEmpty()) return;

    while (true) {
      Queue<GridFuture<?>> q = null;

      for (Buffer buf : bufMappings.values()) {
        GridFuture<?> flushFut = buf.flush();

        if (flushFut != null) {
          if (q == null) q = new ArrayDeque<>(bufMappings.size() * 2);

          q.add(flushFut);
        }
      }

      if (q != null) {
        assert !q.isEmpty();

        boolean err = false;

        for (GridFuture fut = q.poll(); fut != null; fut = q.poll()) {
          try {
            fut.get();
          } catch (GridException e) {
            if (log.isDebugEnabled()) log.debug("Failed to flush buffer: " + e);

            err = true;
          }
        }

        if (err)
          // Remaps needed - flush buffers.
          continue;
      }

      doneCnt = 0;

      for (int i = 0; i < activeFuts0.size(); i++) {
        GridFuture f = activeFuts0.get(i);

        if (f == null) doneCnt++;
        else if (f.isDone()) {
          f.get();

          doneCnt++;

          activeFuts0.set(i, null);
        } else break;
      }

      if (doneCnt == activeFuts0.size()) return;
    }
  }
  /**
   * This method is called to map or split grid task into multiple grid jobs. This is the first
   * method that gets called when task execution starts.
   *
   * @param data Task execution argument. Can be {@code null}. This is the same argument as the one
   *     passed into {@code Grid#execute(...)} methods.
   * @param subgrid Nodes available for this task execution. Note that order of nodes is guaranteed
   *     to be randomized by container. This ensures that every time you simply iterate through grid
   *     nodes, the order of nodes will be random which over time should result into all nodes being
   *     used equally.
   * @return Map of grid jobs assigned to subgrid node. Unless {@link
   *     GridComputeTaskContinuousMapper} is injected into task, if {@code null} or empty map is
   *     returned, exception will be thrown.
   * @throws GridException If mapping could not complete successfully. This exception will be thrown
   *     out of {@link GridComputeTaskFuture#get()} method.
   */
  @Override
  public Map<? extends GridComputeJob, GridNode> map(
      List<GridNode> subgrid, @Nullable final Collection<Integer> data) throws GridException {
    assert !subgrid.isEmpty();

    // Give preference to wanted node. Otherwise, take the first one.
    GridNode targetNode =
        F.find(
            subgrid,
            subgrid.get(0),
            new GridPredicate<GridNode>() {
              @Override
              public boolean apply(GridNode e) {
                return preferredNode.equals(e.id());
              }
            });

    return Collections.singletonMap(
        new GridComputeJobAdapter() {
          @GridLoggerResource private GridLogger log;

          @GridInstanceResource private Grid grid;

          @Override
          public Object execute() throws GridException {
            log.info("Going to put data: " + data.size());

            GridCache<Object, Object> cache = grid.cache(cacheName);

            assert cache != null;

            Map<Integer, T2<Integer, Collection<Integer>>> putMap = groupData(data);

            for (Map.Entry<Integer, T2<Integer, Collection<Integer>>> entry : putMap.entrySet()) {
              T2<Integer, Collection<Integer>> pair = entry.getValue();

              Object affKey = pair.get1();

              // Group lock partition.
              try (GridCacheTx tx =
                  cache.txStartPartition(
                      cache.affinity().partition(affKey),
                      optimistic ? OPTIMISTIC : PESSIMISTIC,
                      REPEATABLE_READ,
                      0,
                      pair.get2().size())) {
                for (Integer val : pair.get2()) cache.put(val, val);

                tx.commit();
              }
            }

            log.info("Finished put data: " + data.size());

            return data;
          }

          /**
           * Groups values by partitions.
           *
           * @param data Data to put.
           * @return Grouped map.
           */
          private Map<Integer, T2<Integer, Collection<Integer>>> groupData(Iterable<Integer> data) {
            GridCache<Object, Object> cache = grid.cache(cacheName);

            Map<Integer, T2<Integer, Collection<Integer>>> res = new HashMap<>();

            for (Integer val : data) {
              int part = cache.affinity().partition(val);

              T2<Integer, Collection<Integer>> tup = res.get(part);

              if (tup == null) {
                tup = new T2<Integer, Collection<Integer>>(val, new LinkedList<Integer>());

                res.put(part, tup);
              }

              tup.get2().add(val);
            }

            return res;
          }
        },
        targetNode);
  }