anchor.diff:  = multithreading
   
   == threads, groups
  +
  +[source,c++]
   ----
   void change_count(){]
   
  
positive.code: 
  
  * version simplifiée (avec async)
  ----
  int accumulate()
  {
  
negative.code: 
  * shared_mutex (lock par shared_lock ou unique lock)
  
  [source,c++]
  ----
    void write_acess()
    {
  