Bug report

Required Info:

• Operating System:
  • Ubuntu 18.04
• Installation type:
  • Source
• Version or commit hash:
  • Head
• DDS implementation:
  • Fast RTPS
• Client library (if applicable):
  • N/A

Steps to reproduce issue

Create a node that registers to an already registered topic but with a different typesupport. If we assume that the node is using rosout log, and that rosout regsiters a publisher in the /rosout topic with C typesupport. You can subscribe to the /rosout topic with a CPP typesupport.

#include <iostream>
#include "rclcpp/rclcpp.hpp"
#include <rcl_interfaces/msg/log.hpp>

class MinimalSubscriber : public rclcpp::Node
{
public:
  MinimalSubscriber()
  : Node("minimal_subscriber")
  {
    subscription_ = this->create_subscription<rcl_interfaces::msg::Log>(
      "rosout",
      [this](rcl_interfaces::msg::Log::UniquePtr msg) {
      RCLCPP_INFO(this->get_logger(), "I heard: '%s'", msg->msg.c_str());
    });
  }

private:
  rclcpp::Subscription<rcl_interfaces::msg::Log>::SharedPtr subscription_;
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  rclcpp::spin(std::make_shared<MinimalSubscriber>());
  rclcpp::shutdown();
  return 0;
}

Expected behavior

Both registered publisher and subscribers should be able to publish and receive messages for the topic.

Actual behavior

The process exits with a segfault when receiving a message on the subscribed topic.

Additional information

Two different typesupports cannot be in the same topic at the same time.
This is due to the fact that rmw_fastrtps uses the same name to register both typesupports in the FastRTPS Domain. See code

Disambiguate with a different name (appending or prepending a string) is not possible because the name of the typesupport is directly related to the name of the topic. See code and fastrtps TopicData

Probably happening in other implementations.