Round trip and Flood in C

authors:Stefanos Florescu date:March 2020

The Roundtrip demonstrator has two different experiments. The first experiment sets up one main master hub and three hubs. The master hub sends the value 1 and starts measuring time upon sending the message. This message travels from hub to hub with each hub adding 1 until it returns to the master. Upon arrival of the modified integer from the third hub at the master, the clock is stopped and the time it took for the roundtrip is displayed.

Similarly to the simple roundtrip experiment, the flood experiment has the same setup of master and three hubs. The only difference is that the master now sends a bunch of messages at the same time. The hubs read the messages one by one, process them (by adding 1) and pass them on. The master will start measuring time from the moment he sends his first message and up to the moment he receives the last message from the last hub.

More information on these demonstrators can be found in the Backlog.

Building and running the executables

Make sure your local repo is up to date with the HighTech-nl repo and move into the directory /dds-demonstrators/src/demonstrators/RoundTrip/C:

$ mkdir build
$ cd build
$ cmake ..
$ make

Also, after the build directory has been initialized using the cmake .. command, the two scripts run_roundtrip.sh and run_flood.sh can be used to compile the executables and run the experiments. These two scripts are similar with the only differences being that they call different executables. For example the run_roundtrip.sh includes the following:

#!/bin/bash

cmake --build $PWD/build/
echo "Deleting old log file."
rm $PWD/roundtrip.log

echo "Running Roundtrip Demonstrator...press ^C to exit"
./build/Hub_roundtrip topic_2 topic_3 &
./build/Hub_roundtrip topic_3 topic_4 &
./build/Hub_roundtrip topic_4 topic_1 &
./build/Master_roundtrip topic_1 topic_2 > roundtrip.log

The master will output all his measurements into the .log file in each respective case. Furthermore, the first argument passed to each Hub/Master executable is the topic name on which that entity will be listening on, while the second argument is the topic on which that entity will write to. In order to see the output of the experiment simply open the respective .log file.

Note

The Master/Hub can be executed on different nodes, such as Raspberry Pis and PCs. See Setting up Raspberry Pi network for details on how to connect to the Raspberry Pis.

Note

In the case of the flood experiment, the number of samples the Master will send can be defined in the Master_flood.c file by changing the #define FLOOD_SAMPLES number.

Running the Round trip in a Docker Container

Similarly to what we described above, the Round trip and Flood experiments can be executed from a Docker Container. First make sure you follow the guide on how to build the Docker Image which can be found in the Docker Guide: How to create and run a Docker Image under “Building Demo Image”. First create a new container using:

$ docker run -it --network="host" --name <container name> <image name>

You can open another terminal/Powershell and have as many processes on that container as you want using per terminal:

$ docker exec -it <existing container name> bash

Navigate into the Roundtrip/ directory and either experiment using:

$ ./docker_run_roundtrip.sh
$ ./docker_run_flood.sh

Warning

Due to the networking issue of the Docker Desktop (see in Docker Guide: How to create and run a Docker Image under “Running Docker Containers” for more info) on Windows/MacOS we need to change the DDS networking interface in the docker_cyclonedds_config.xml in /root/. The video in Matrix Board Communication in C shows how this is done. On a Linux machine this is not required and your container will communicate over the network.