anchor.diff:  
   
   %% API
  --export([start_link/2, run/2, cancel/1, is_running/1]).
  +-export([start_link/2, run/2, cancel/1, is_running/1, get_compacting_pid/1]).
   
   %% gen_server callbacks
   -export([init/1, terminate/2, code_change/3]).
  
positive.code:     unlink(Pid),
      exit(Pid, kill),
      {reply, ok, State#st{pid=undefined}};
  handle_call(is_running, _From, #st{pid=Pid}=State) when is_pid(Pid) ->
      {reply, true, State};
  handle_call(is_running, _From, State) ->
  
negative.code: is_running(Pid) ->
      gen_server:call(Pid, is_running).
  
  get_compacting_pid(Pid) ->
      gen_server:call(Pid, get_compacting_pid).
  
  init({Index, Module}) ->
      process_flag(trap_exit, true),
  