/**
   * @param cancel {@code True} to close with cancellation.
   * @throws GridException If failed.
   */
  @Override
  public void close(boolean cancel) throws GridException {
    if (!closed.compareAndSet(false, true)) return;

    busyLock.block();

    if (log.isDebugEnabled())
      log.debug("Closing data loader [ldr=" + this + ", cancel=" + cancel + ']');

    GridException e = null;

    try {
      // Assuming that no methods are called on this loader after this method is called.
      if (cancel) {
        cancelled = true;

        for (Buffer buf : bufMappings.values()) buf.cancelAll();
      } else doFlush();

      ctx.event().removeLocalEventListener(discoLsnr);

      ctx.io().removeMessageListener(topic);
    } catch (GridException e0) {
      e = e0;
    }

    fut.onDone(null, e);

    if (e != null) throw e;
  }
  /**
   * Flushes every internal buffer if buffer was flushed before passed in threshold.
   *
   * <p>Does not wait for result and does not fail on errors assuming that this method should be
   * called periodically.
   */
  @Override
  public void tryFlush() throws GridInterruptedException {
    if (!busyLock.enterBusy()) return;

    try {
      for (Buffer buf : bufMappings.values()) buf.flush();

      lastFlushTime = U.currentTimeMillis();
    } finally {
      leaveBusy();
    }
  }
  /**
   * 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;
    }
  }