/**
   * @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;
  }
    /** @param log Logger. */
    private void execute(GridLogger log) {
      try {
        log.info("Started execute.");

        // Countdown shared job latch so that the main thread know that all jobs are
        // inside the "execute" routine.
        jobLatch.countDown();

        log.info("After job latch.");

        // Await for the main thread to allow jobs to proceed.
        latch.await();

        log.info("After latch.");

        if (awaitMasterLeaveCallback) {
          latch0.await();

          log.info("After latch0.");
        } else log.info("Latch 0 skipped.");
      } catch (InterruptedException e) {
        // We do not expect any interruptions here, hence this statement.
        fail("Unexpected exception: " + e);
      }
    }
    /**
     * @param log Logger.
     * @param job Actual job.
     */
    private void onMasterLeave(GridLogger log, Object job) {
      log.info("Callback executed: " + job);

      latch0.countDown();

      invokeLatch.countDown();
    }
  /**
   * 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;
    }
  }
  /**
   * @param ctx Grid kernal context.
   * @param cacheName Cache name.
   * @param flushQ Flush queue.
   */
  public GridDataLoaderImpl(
      final GridKernalContext ctx,
      @Nullable final String cacheName,
      DelayQueue<GridDataLoaderImpl<K, V>> flushQ) {
    assert ctx != null;

    this.ctx = ctx;
    this.cacheName = cacheName;
    this.flushQ = flushQ;

    log = U.logger(ctx, logRef, GridDataLoaderImpl.class);

    discoLsnr =
        new GridLocalEventListener() {
          @Override
          public void onEvent(GridEvent evt) {
            assert evt.type() == EVT_NODE_FAILED || evt.type() == EVT_NODE_LEFT;

            GridDiscoveryEvent discoEvt = (GridDiscoveryEvent) evt;

            UUID id = discoEvt.eventNodeId();

            // Remap regular mappings.
            final Buffer buf = bufMappings.remove(id);

            if (buf != null) {
              // Only async notification is possible since
              // discovery thread may be trapped otherwise.
              ctx.closure()
                  .callLocalSafe(
                      new Callable<Object>() {
                        @Override
                        public Object call() throws Exception {
                          buf.onNodeLeft();

                          return null;
                        }
                      },
                      true /* system pool */);
            }
          }
        };

    ctx.event().addLocalEventListener(discoLsnr, EVT_NODE_FAILED, EVT_NODE_LEFT);

    // Generate unique topic for this loader.
    topic = TOPIC_DATALOAD.topic(GridUuid.fromUuid(ctx.localNodeId()));

    ctx.io()
        .addMessageListener(
            topic,
            new GridMessageListener() {
              @Override
              public void onMessage(UUID nodeId, Object msg) {
                assert msg instanceof GridDataLoadResponse;

                GridDataLoadResponse res = (GridDataLoadResponse) msg;

                if (log.isDebugEnabled()) log.debug("Received data load response: " + res);

                Buffer buf = bufMappings.get(nodeId);

                if (buf != null) buf.onResponse(res);
                else if (log.isDebugEnabled())
                  log.debug("Ignoring response since node has left [nodeId=" + nodeId + ", ");
              }
            });

    if (log.isDebugEnabled()) log.debug("Added response listener within topic: " + topic);

    fut = new GridDataLoaderFuture(ctx, this);
  }