Writing an asynchronous publisher
==========================================

Sometimes, it is required to publish infromation at a fixed frequency in the background 
independently from the main process. In such cases, we can utlise the async functionaality 
in C++ for concurrent programming.

.. code-block:: c
  
    #include "PositionPubSubTypes.h"
    #include "domain_participant.h"
    #include "geometry_msgs/msgs/Position.h"
    #include "publisher.h"
    #include <chrono>
    #include <future>

    std::atomic_bool close_flag{};

    void async_publisher(const int delay_ms, DDSPublisher *pub) {

      // create message of position
      cpp_msg::Position pos_msg;

      while (!close_flag) {

        pos_msg.x = 1;
        pos_msg.y = 2;
        pos_msg.z = 3;

        pub->publish(pos_msg);
        std::this_thread::sleep_for(std::chrono::milliseconds(delay_ms));
      }
    }

    int main() {

      // Create participant. Arguments: Domain id, Name
      DefaultParticipant dp(0, "sample_participant");

      // Create publisher with msg type and topic name
      DDSPublisher position_pub(idl_msg::PositionPubSubType(), "position",
                                dp.participant());

      // start asynchronous publisher
      auto async_pub =
          std::async(std::launch::async, async_publisher, 100, &position_pub);

      std::cin.ignore();

      // set close_flag and wait for asynchronous publisher to close
      close_flag = true;
    }