anchor.diff:  
       try
           %% Give workers one more chance to abort or get a lock or whatever.
  -        maybe_call_handoff_started(Module, SrcPartition, SrcNode),
  +         FoldOpts = maybe_call_handoff_started(Module, SrcPartition),
   
            Filter = get_filter(Opts),
            [_Name,Host] = string:tokens(atom_to_list(TargetNode), "@"),
  
positive.code:     end.
  
  %% @private
  %% @doc The optional call to handoff_started/2 allows vnodes one last chance to abort
  %% the handoff process. the function is passed the source vnode's partition number
  %% and node name (this node) because the callback does not have access to the full vnode
  %% state at this time. In addition the worker pid is passed so the vnode may use that
  %% information in its decision to cancel the handoff or not (e.g. get a lock on behalf
  %% of the process.
  maybe_call_handoff_started(Module, SrcPartition, SrcNode) ->
      case lists:member({handoff_started, 2}, Module:module_info(exports)) of
          true ->
              Source = {SrcPartition, SrcNode},
              WorkerPid = self(),
              case Module:handoff_started(Source, WorkerPid) of
                  true ->
                      ok;
                  max_concurrency ->
                      %% Handoff of that partition is busy or can't proceed. Stopping with
                      %% max_concurrency will cause this partition to be retried again later.
                      exit({shutdown, max_concurrency});
                  Error ->
                      exit({shutdown, Error})
              end;
          false ->
              %% optional callback not implemented, so we carry on.
              ok
      end.
  
negative.code:                                      notsent_acc=UnsentAcc0,
                                       notsent_fun=UnsentFun},
                               false,
                               FoldOpts),
  
           %% IFF the vnode is using an async worker to perform the fold
           %% then sync_command will return error on vnode crash,
  