anchor.diff:  
   On peut récupérer le futur associée d'une promise
   
  +[source,c++]
   ----
   void accumulate(boost::promise<int> &p)
   {
  
positive.code: = multithreading
  
  == threads, groups
  ----
  void change_count(){]
  
  
negative.code: 
  * shared_mutex (lock par shared_lock ou unique lock)
  
  [source,c++]
  ----
    void write_acess()
    {
  