/**
   * Starts multi-update lock. Will wait for topology future is ready.
   *
   * @return Topology version.
   * @throws IgniteCheckedException If failed.
   */
  public AffinityTopologyVersion beginMultiUpdate() throws IgniteCheckedException {
    IgniteBiTuple<IgniteUuid, GridDhtTopologyFuture> tup = multiTxHolder.get();

    if (tup != null)
      throw new IgniteCheckedException("Nested multi-update locks are not supported");

    top.readLock();

    GridDhtTopologyFuture topFut;

    AffinityTopologyVersion topVer;

    try {
      // While we are holding read lock, register lock future for partition release future.
      IgniteUuid lockId = IgniteUuid.fromUuid(ctx.localNodeId());

      topVer = top.topologyVersion();

      MultiUpdateFuture fut = new MultiUpdateFuture(topVer);

      MultiUpdateFuture old = multiTxFuts.putIfAbsent(lockId, fut);

      assert old == null;

      topFut = top.topologyVersionFuture();

      multiTxHolder.set(F.t(lockId, topFut));
    } finally {
      top.readUnlock();
    }

    topFut.get();

    return topVer;
  }
  /**
   * Ends multi-update lock.
   *
   * @throws IgniteCheckedException If failed.
   */
  public void endMultiUpdate() throws IgniteCheckedException {
    IgniteBiTuple<IgniteUuid, GridDhtTopologyFuture> tup = multiTxHolder.get();

    if (tup == null)
      throw new IgniteCheckedException("Multi-update was not started or released twice.");

    top.readLock();

    try {
      IgniteUuid lockId = tup.get1();

      MultiUpdateFuture multiFut = multiTxFuts.remove(lockId);

      multiTxHolder.set(null);

      // Finish future.
      multiFut.onDone(lockId);
    } finally {
      top.readUnlock();
    }
  }