Runtime Interface Reflection: rclcpp

[methylDragon]

This PR is part of the runtime interface reflection subscription feature of REP-2011: ros2/ros2#1374

Description

This PR includes support for runtime type subscriptions, including:

• Edits to SubscriptionBase and executor code to allow for use of runtime type
  • This includes new pure virtual methods for SubscriptionBase that have also been implemented in all child classes
• A new RuntimeTypeSubscription subscription class that handles a subscription callback using ser_dynamic_data

[mergify]

⚠️ The sha of the head commit of this PR conflicts with #2160. Mergify cannot evaluate rules on this PR. ⚠️

[emersonknapp]

Can all these bad cases be true if ret == RCL_RET_OK?

[methylDragon]

🤔 probably not.

I might still leave in the typesupport identifier check though

[mergify]

⚠️ The sha of the head commit of this PR conflicts with #2160. Mergify cannot evaluate rules on this PR. ⚠️

[emersonknapp]

manage is an overloaded term - this is really a make_shared function to put ownership of the object into a shared pointer, right?

[methylDragon]

Yeah that's true.. I wanted it to be like a: "We are taking ownership/managing the lifetime of the pointer now)

It's a private method though, so I don't have any issues with changing the name

[emersonknapp]

The distinction here isn't clear to me between dynamic message direct and serialized.

What does this wording pattern "take as X and handle as Y" mean? Does "handle" refer to the argument type for the callback?

[methylDragon]

Yep, "handle" is for the callback.

The way it works with ROS is that a message has to be taken, then passed to a handle function that passes it to a callback. So take -> handle.

[emersonknapp]

What about a dynamic subscription that passes serialized data to the handler function? GenericDynamicSubscription, perhaps. It's what we would want in rosbag2 recording. Or is that the case for DYNAMIC_MESSAGE_FROM_SERIALIZED, I couldn't quite tell.

[methylDragon]

In that case you would want to use a serialized subscription (I.e. one that takes and handles serialized data), then use the DynamicMessage class to deserialize the serialized message into the DynamicMessage inside the callback

You probably would need to subclass that subscription so you can instantiate a DynamicMessage and have it accessible inside the callback

[methylDragon]

(Basically you just need a way to implement what the executor is doing here, in the callback)

[methylDragon]

    // Take serialized and then convert to dynamic message
    case rclcpp::SubscriptionType::DYNAMIC_MESSAGE_FROM_SERIALIZED:
      {
        std::shared_ptr<SerializedMessage> serialized_msg =
          subscription->create_serialized_message();

        // NOTE(methylDragon): Is this clone necessary? If I'm following the pattern, it seems so.
        DynamicMessage::SharedPtr dynamic_message = subscription->create_dynamic_message();
        take_and_do_error_handling(
          "taking a serialized message from topic",
          subscription->get_topic_name(),
          [&]() {return subscription->take_serialized(*serialized_msg.get(), message_info);},
          [&]()
          {

            // === <<< THIS IS THE MOST IMPORTANT LINE!!! >>> ===
            bool ret = dynamic_message->deserialize(&serialized_msg->get_rcl_serialized_message());
            // ^^^ <<< THIS IS THE MOST IMPORTANT LINE!!! >>> ^^^

            if (!ret) {
              throw_from_rcl_error(ret, "Couldn't convert serialized message to dynamic data!");
            }
            subscription->handle_dynamic_message(dynamic_message, message_info);
          }
        );
        subscription->return_serialized_message(serialized_msg);
        subscription->return_dynamic_message(dynamic_message);
        break;
      }
  }

[methylDragon]

Closing this in favor of #2176

[mergify]

⚠️ The sha of the head commit of this PR conflicts with #2160. Mergify cannot evaluate rules on this PR. ⚠️