dds_experimentation

We will check if various forms of msg with different typename and fields can be communicated across pub sub nodes. Msgs are shown below:

Msg Definition

1. Message: HelloWorld_v1.idl

Type 1	Type 2	Type 3
struct HelloWorld_v1 { unsigned long index; string message; };	struct HelloWorld_v1 { unsigned long index; string message; float value; };	struct HelloWorld_v1 { short index; string message; };

2. Message HelloWorld_v2.idl (type4 with extensibility)

Type 1	Type 2	Type 3	Type 4
struct HelloWorld_v2 { unsigned long index; string message; };	struct HelloWorld_v2 { unsigned long index; string message; float value; };	struct HelloWorld_v2 { short index; string message; };	@appendable struct HelloWorld_v2 { unsigned long index; string message; float value; };

3. Message HelloWorld_v3.idl

Type 1	Type 2	Type 3
@appendable struct HelloWorld_v3 { unsigned long index; string message; float value; sequence<double> data; };	@appendable struct HelloWorld_v3 { unsigned long index; string message; short value; };	@appendable struct HelloWorld_v3 { unsigned long index; float message; short value; };

Comparison Table

	Fast DDS	Cyclone DDS	RTI Connext
Same Type Name: HelloWorld_v1.idl with HelloWorld_v1.idl
V1T1 with V1T2	✓	✗	✓
V1T1 with V1T3	✓	✗	✗
V1T2 with V1T3	✓	✗	✗
Mismatch Type Name HelloWorld_v1.idl with HelloWorld_v2.idl
V1T1 with V2T1	✗	✗	✓
V1T1 with V2T2	✗	✗	✓
V1T1 with V2T3	✗	✗	✗
V1T1 with V2T4	✗	✗	✓
Extensibility with mismatch type name HelloWorld_v2.idl with HelloWorld_v3.idl
V2T4 with V3T1	✗	✓	✓
V2T4 with V3T2	✗	✗	✓
V2T4 with V3T3	✗	✗	✗

-fastdds is tested with fastdds/HelloWorldExample/ -cyclonedds is tested with cyclonedds/helloworld/ -rticonnext is tested with rticonnext/hello_world_example/c++11/

---

Fast DDS

Create Env

Refered to eproxima official doc

mkdir fastdds_ws
cd fastdds_ws
wget https://raw.githubusercontent.com/eProsima/Fast-DDS/master/fastrtps.repos
mkdir src
vcs import src < fastrtps.repos

Testing dynamic msg pubsub

Refered to this from eproxima

cd /fastdds_ws
source install/setup.bash 
cd src/dds_experimentation/fastdds/DynamicHelloWorldExample
mkdir build
cmake ..
make -j4

Run pub sub in 2 different terminals

# In the first one launch: 
./DDSDynamicHelloWorldExample publisher
# In the second one: 
./DDSDynamicHelloWorldExample subscriber

The msg definition is defined in the example_type.xml. The example shows the publisher publishes CustomMsgFoo and CustomMsgBar msg types. And the sub will only able to sub to one type during discovery. Note that the msg definition is parsed via dds from the pub to sub participant.

Static Types: HelloWorldExample

Generate headers from IDL

Uses fastddsgen

Quick installation, follow: https://fast-dds.docs.eprosima.com/en/latest/installation/sources/sources_linux.html#fast-dds-gen-installation

After installations and compilations, generate headers

cd dds_experimentation/fastdds/HelloWorldExample
java -jar ~/fastdds_ws/src/fastddsgen/share/fastddsgen/java/fastddsgen.jar HelloWorld_v1.idl -replace

Compile and Run pubsub

mkdir build && cd build
cmake .. && make -j4

# run 
./DDSHelloWorldExample publisher
./DDSHelloWorldExample subscriber

Testing with incompatible topic detection

Modified the HelloWorldExample script (~/Fast-DDS/examples/C++/DDS/HelloWorldExample/build), and let the publisher publishes an incompatible topic.

Provide listener class member to create_topic() function. However, currently the TopicListener::on_inconsistent_topic() callback is not working as it isn't yet being implemented (refer here).

Parsing UserDataQosPolicy

Working in progress in HellowWorldExample

---

RTI Connext

Setting up env

Install RTI:

Download and install, 6.X.X: https://www.rti.com/free-trial/dds-files. Select the provided rti license during installation via the RTI Launcher gui

on terminal

export NDDSHOME=~/rti_connext_dds-6.1.1
export PATH=${PATH}:~/rti_connext_dds-6.1.1/lib/x64Linux4gcc7.3.0

Then compile in build dir

cmake ..
make -j4

Testing with incompatible topic detection

A modified example code of listeners

After compile with cmake (cd builld && cmake .. && cmake --build .), then run:

./listeners_subscriber
./listeners_publisher

publisher temp creates an incompatible topic, which will trigger subscriber to call on_inconsistent_topic.

Printout from subscriber, notice the on_inconsistent_topic callback

youliang@youliang-XPS-13-7390:~/rticonnextdds-examples/examples/connext_dds/listeners/c++11/build$ ./listeners_subscriber
RTI Connext DDS EVAL License issued to open robotics [email protected] For non-production use only.
Expires on 01-Jul-2022 See www.rti.com for more information.
ParticipantListener: on_inconsistent_topic()!!!
 msg def::topic_listeners listeners

ReaderListener: on_subscription_matched()
ReaderListener: on_liveliness_changed()
  Alive writers: 1
SubscriberListener: on_data_on_readers()
[x: 1]
SubscriberListener: on_data_on_readers()
[x: 2]

Hello world example:

Originated from here. During build, the connextdds_add_example.cmake will generate cpp headers according to .idl.

cd hello_world_example
mkdir build cd build
cmake ..
make -j4

Run pub sub

./example_publisher
./example_subscriber

---

Cyclonedds

Install with colcon, refer to this

Testout modified helloworld code, with on_inconsistent_topic callback of cyclonedds C api, defined here

source ~/cyclonedds_ws/install/setup.bash
mkdir build
cmake ..
make -j4

Run

./HelloworldPublisher
./HelloworldSubscriber

Unfortunately, not able to trigger on_inconsistent_topic callback

The above example also shows the usage of dds's extensibility by using @appendable in 2 different .idl definitions for pub sub.

To switch sub with msg v2, set #define MSG_VERSION 2 in subscriber.c