There is currently no way to reliably tell that a processing is finished (beside checking the available counters). With TBB, the only way is to call `g.wait_for_all()` which is a blocking call. Since we don't want to block the main thread, we can [add a task to run the flow graph in the background](https://oneapi-src.github.io/oneTBB/main/tbb_userguide/destroy_graphs_outside_main_thread.html). ```cpp void activate() { task_arena a; a.enqueue([background_task([this]() { // Construct graph (from preconstructed Body) graph g; function_node< int, int > f( g, 1, []( int i ) -> int { return spin_for(i); }); //Activate source src.activate(); g.wait_for_all(); // Set captured is_finished this->is_finished = true; }); } ... std::atomic_bool is_finished = false; ```