/*! \static Add a callback fired when the send of any Comm is posted */
static void on_send_cb(const std::function<void(Comm const&)>& cb) { on_send.connect(cb); }
/*! Add a callback fired when the send of this specific Comm is posted */
/*! \static Add a callback fired when the send of any Comm is posted */
static void on_send_cb(const std::function<void(Comm const&)>& cb) { on_send.connect(cb); }
/*! Add a callback fired when the send of this specific Comm is posted */