/**
   * Adds a Near key.
   *
   * @param key Key.
   * @param keyBytes Key bytes.
   * @param ctx Context.
   * @throws GridException If failed.
   */
  public void addNearKey(K key, byte[] keyBytes, GridCacheContext<K, V> ctx) throws GridException {
    if (ctx.deploymentEnabled()) prepareObject(key, ctx);

    if (nearKeyBytes == null) nearKeyBytes = new ArrayList<>();

    nearKeyBytes.add(keyBytes);
  }
  /**
   * @return Collection of readers after check.
   * @throws GridCacheEntryRemovedException If removed.
   */
  public Collection<ReaderId> checkReaders() throws GridCacheEntryRemovedException {
    synchronized (mux) {
      checkObsolete();

      if (!readers.isEmpty()) {
        List<ReaderId> rmv = null;

        for (ReaderId reader : readers) {
          if (!cctx.discovery().alive(reader.nodeId())) {
            if (rmv == null) rmv = new LinkedList<ReaderId>();

            rmv.add(reader);
          }
        }

        if (rmv != null) {
          readers = new LinkedList<ReaderId>(readers);

          for (ReaderId rdr : rmv) readers.remove(rdr);

          readers = Collections.unmodifiableList(readers);
        }
      }

      return readers;
    }
  }
  /** {@inheritDoc} */
  @SuppressWarnings("all")
  @Override
  public boolean readFrom(ByteBuffer buf) {
    commState.setBuffer(buf);

    if (!super.readFrom(buf)) return false;

    switch (commState.idx) {
      case 8:
        if (commState.readSize == -1) {
          if (buf.remaining() < 4) return false;

          commState.readSize = commState.getInt();
        }

        if (commState.readSize >= 0) {
          if (nearKeyBytes == null) nearKeyBytes = new ArrayList<>(commState.readSize);

          for (int i = commState.readItems; i < commState.readSize; i++) {
            byte[] _val = commState.getByteArray();

            if (_val == BYTE_ARR_NOT_READ) return false;

            nearKeyBytes.add((byte[]) _val);

            commState.readItems++;
          }
        }

        commState.readSize = -1;
        commState.readItems = 0;

        commState.idx++;
    }

    return true;
  }
  /**
   * Adds a Near key.
   *
   * @param key Key.
   * @param keyBytes Key bytes.
   * @param ctx Context.
   * @throws GridException If failed.
   */
  public void addNearKey(K key, byte[] keyBytes, GridCacheContext<K, V> ctx) throws GridException {
    prepareObject(key, ctx);

    nearKeyBytes.add(keyBytes);
  }
  /**
   * @param nodeId Reader to add.
   * @param msgId Message ID.
   * @return Future for all relevant transactions that were active at the time of adding reader, or
   *     {@code null} if reader was added
   * @throws GridCacheEntryRemovedException If entry was removed.
   */
  @Nullable
  public GridFuture<Boolean> addReader(UUID nodeId, long msgId)
      throws GridCacheEntryRemovedException {
    // Don't add local node as reader.
    if (cctx.nodeId().equals(nodeId)) return null;

    GridNode node = cctx.discovery().node(nodeId);

    // If remote node has no near cache, don't add it.
    if (node == null || !U.hasNearCache(node, cctx.dht().near().name())) return null;

    // If remote node is (primary?) or back up, don't add it as a reader.
    if (U.nodeIds(cctx.affinity(partition(), CU.allNodes(cctx))).contains(nodeId)) return null;

    boolean ret = false;

    GridCacheMultiTxFuture<K, V> txFut;

    Collection<GridCacheMvccCandidate<K>> cands = null;

    synchronized (mux) {
      checkObsolete();

      txFut = this.txFut;

      ReaderId reader = readerId(nodeId);

      if (reader == null) {
        reader = new ReaderId(nodeId, msgId);

        readers = new LinkedList<ReaderId>(readers);

        readers.add(reader);

        // Seal.
        readers = Collections.unmodifiableList(readers);

        txFut = this.txFut = new GridCacheMultiTxFuture<K, V>(cctx);

        cands = localCandidates();

        ret = true;
      } else {
        long id = reader.messageId();

        if (id < msgId) reader.messageId(msgId);
      }
    }

    if (ret) {
      assert txFut != null;

      if (!F.isEmpty(cands)) {
        for (GridCacheMvccCandidate<K> c : cands) {
          GridCacheTxEx<K, V> tx = cctx.tm().<GridCacheTxEx<K, V>>tx(c.version());

          if (tx != null) {
            assert tx.local();

            txFut.addTx(tx);
          }
        }
      }

      txFut.init();

      if (!txFut.isDone()) {
        txFut.listenAsync(
            new CI1<GridFuture<?>>() {
              @Override
              public void apply(GridFuture<?> f) {
                synchronized (mux) {
                  // Release memory.
                  GridDhtCacheEntry.this.txFut = null;
                }
              }
            });
      } else
        // Release memory.
        txFut = this.txFut = null;
    }

    return txFut;
  }