espace executors
  {

  template <class Executor>
  class executor_ref : public executor
  {
    Executor& ex;
  public:
    /// type-erasure to store the works to do
    typedef  executors::work work;

    /// executor is not copyable.
    BOOST_THREAD_NO_COPYABLE(executor_ref)
    executor_ref(Executor& ex) : ex(ex) {}

    /**
     * \par Effects
     * Destroys the executor.
     *
     * \par Synchronization
     * The completion of all the closures happen before the completion of the executor destructor.
     */
    ~executor_ref() {};

    /**
     * \par Effects
     * Close the \c executor for submissions.
     * The worker threads will work until there is no more closures to run.
     */
    void close() { ex.close(); }

    /**
     * \par Returns
     * Whether the pool is closed for submissions.
     */
    bool closed() { return ex.closed(); }

    /**
     * \par Effects
     * The specified closure will be scheduled for execution at some point in the future.
     * If invoked closure throws an exception the executor will call std::terminate, as is the case with threads.
     *
     * \par Synchronization
     * Ccompletion of closure on a particular thread happens before destruction of thread's thread local variables.
     *
     * \par Throws
     * \c sync_queue_is_closed if the thread pool is closed.
     * Whatever exception that can be throw while storing the closure.
     */
    void submit(BOOST_THREAD_RV_REF(work) closure) {
      ex.submit(boost::move(closure));
    }
//    void submit(work& closure) {
//      ex.submit(closure);
//    }


    /**
     * \par Effects
     * Try to execute one task.
     *
     * \par Returns
     * Whether a task has been executed.
     *
     * \par Throws
     * Whatever the current task constructor throws or the task() throws.
     */
    bool try_executing_one() { return ex.try_executing_one(); }

  };

  class generic_executor_ref
  {
    shared_ptr<executor> ex;
  public:
    /// type-erasure to store the works to do
    typedef executors::work work