Feature request: actions

[Timple]

rclcpp::action is still synchronous. Which means I cannot do an icey service call in a handle_accepted callback of the action.

Is this correct?
And if yes, can this be supported? 🙂

Use-case: I have an action which needs to call several service calls.

[iv461]

Hey Tim, yes, ICEY does not have an API for actions, this is currently a known limitation.
But it is very simple to use coroutines as callbacks:

 /// A function having a co_await expression must be a coroutine, i.e. return a promise
const auto handle_accepted = [](auto goal) -> icey::Promise<void> {
            /// Here is your async/await based service call:
            auto result = co_await service_->call(req, timeout);
};
/// To be able to use coroutines as callbacks, simply wrap them inside a regular function and call them without co_await:
rclcpp_action::create_server<MyAction>(
      node, "my_action_name", ..., ..., [handle_accepted](const rclcpp_action::GoalUUID & uuid,  std::shared_ptr<const MyAction::Goal> goal)
        handle_accepteduuid, goal);
      }, ...);

In fact, this is exactly what would be required to support coroutines as callbacks in the actions API, simply wrapping the coroutine in a regular function. (see e.g. create_timer_async)

Edit: This suggestion only works with void-callbacks. I.e. it works with the handle_accepted callback, but not with other action server callbacks that return something

Also, pay attention to a big C++ footgun here: If a lambda function is a coroutine, you cannot simplify

const auto f = []() -> icey::Promise<void> {
};
f();

into

[]() -> icey::Promise<void> { }();

because this leads to use-after-free. This is because temporary lifetime extension of lambda functions is not coroutine-aware (see 1)

Feel free to ask is something is unclear.

[iv461]

Implemented a fully-featured async/await API for action client and server in #17