/** Checks consistency after all operations. */
  private void consistencyCheck() {
    if (CONSISTENCY_CHECK) {
      assert lock.writeLock().isHeldByCurrentThread();

      if (node2part == null) return;

      for (Map.Entry<UUID, GridDhtPartitionMap> e : node2part.entrySet()) {
        for (Integer p : e.getValue().keySet()) {
          Set<UUID> nodeIds = part2node.get(p);

          assert nodeIds != null
              : "Failed consistency check [part=" + p + ", nodeId=" + e.getKey() + ']';
          assert nodeIds.contains(e.getKey())
              : "Failed consistency check [part="
                  + p
                  + ", nodeId="
                  + e.getKey()
                  + ", nodeIds="
                  + nodeIds
                  + ']';
        }
      }

      for (Map.Entry<Integer, Set<UUID>> e : part2node.entrySet()) {
        for (UUID nodeId : e.getValue()) {
          GridDhtPartitionMap map = node2part.get(nodeId);

          assert map != null
              : "Failed consistency check [part=" + e.getKey() + ", nodeId=" + nodeId + ']';
          assert map.containsKey(e.getKey())
              : "Failed consistency check [part=" + e.getKey() + ", nodeId=" + nodeId + ']';
        }
      }
    }
  }
  public void returnConnection(Connection connection) {
    int inFlight = connection.inFlight.decrementAndGet();

    if (connection.isDefunct()) {
      if (host.getMonitor().signalConnectionFailure(connection.lastException())) shutdown();
      else replace(connection);
    } else {

      if (trash.contains(connection) && inFlight == 0) {
        if (trash.remove(connection)) close(connection);
        return;
      }

      if (connections.size() > options().getCoreConnectionsPerHost(hostDistance)
          && inFlight <= options().getMinSimultaneousRequestsPerConnectionThreshold(hostDistance)) {
        trashConnection(connection);
      } else {
        signalAvailableConnection();
      }
    }
  }