Method await_suspend

example/python.cpp:219–263

  template<typename T>
  bool await_suspend(std::coroutine_handle<T> h)
  {
    asio::any_io_executor exec;
    if constexpr (requires (T & p) {p.get_executor();})
      exec = h.promise().get_executor();
    else
      exec = cobalt::this_thread::get_executor();

    auto loop = get_loop();
    auto task = getattr(loop, "create_task")(target);

    struct wrapper
    {
      asio::any_io_executor exec;
      mutable cobalt::unique_handle<void> awaiter;
      py_awaitable * res;

      void operator()(py::object t) const
      {
        res->extract_result(t);
        asio::dispatch(exec, std::move(awaiter));
      }
    };

    if (py::cast<bool>(getattr(task, "done")()))
    {
      extract_result(task);
      return false;
    }

    getattr(task, "add_done_callback")(py::cpp_function(wrapper{
          std::move(exec),
          cobalt::unique_handle<void>{h.address()},
          this
        }));

    if constexpr (requires (T & p) {p.get_cancellation_slot();})
      h.promise().get_cancellation_slot().
      assign([c = getattr(task, "cancel")](asio::cancellation_type ct) {
        py::gil_scoped_acquire lock;
        c();
      });

    return true;
  }

  void extract_result(py::object task)
  {