connextdds-py

A full Python binding for RTI Connext DDS using pybind11

Requirements

• macOS or Linux (Windows support coming soon)
• CMake 3.15+
• Python 2.7, Python 3.x with pip
• RTI Connext DDS 5.3.1, 6.0.0, 6.0.1

Installation

clone repo and submodules and cd to the project root

$ git clone --recurse-submodules https://github.com/rticommunity/connextdds-py.git
$ cd connextdds-py

set environment variables

$ export NDDSHOME=<install location of Connext Pro>
$ export CONNEXTDDS_ARCH=<target arch>
$ export LD_LIBRARY_PATH=<location of target libs>:$LD_LIBRARY_PATH
$ export NJOBS=<number of concurrent make jobs, default 1>

build and install

$ pip install .

Running the tests

To run the tests, first install pytest using pip.

$ pytest test/

If you want to run the performance test, you can run

$ python3 test/python/perf.py

You can add a number after it to indicate how many times to run it. You can also add either the -ind flag or the -all flag to choose which test you want to run. If you omit the flags, both will be executed.

Building for development

To build for development, you must have the wheel package installed. You also need all of the enviornment variables that you need for the regular install. If you already have an install of any form, run pip3 uninstall rti -y

$ python3 setup.py bdist_wheel
$ pip3 install dist/*

Building and viewing the documentation

To build the documentation, run

$ cd docs
$ make html

You must have the development build built and installed for this to work. To view the documentation, open in your web browser the file located at docs/build/html/index.html

Example

import rti.connextdds as dds
import time

participant = dds.DomainParticipant(0)
topic = dds.StringTopicType.Topic(participant, 'example')
writer = dds.StringTopicType.DataWriter(
    participant.implicit_publisher,
    topic)

while True:
    writer.write("Hello World!")
    time.sleep(1)

Features

• Python DDS API supporting DynamicData and built-in topic types
• Object oriented design based on Modern C++ API
• Supports QoS modifications in code
• Supports listeners
• Supports waitsets and all conditions
• Supports RTI Distributed Logger and integration with Python logging module

TODO

• Add unit tests
• Add API documentation
• Implement support for Request/Reply
• Implement support for Routing Service processors/adapters

Notes

• Because Python only supports generics in Python 3.5+ and there doesn't seem to be any support for them in the current version of pybind11, C++ template classes are generally implemented as nested classes for a topic data type. For example:
  • rti.connextdds.DynamicData.Topic
  • rti.connextdds.DynamicData.DataReader
  • rti.connextdds.DynamicData.DataWriter
  • etc.
• The Python GIL prevents multiple CPU cores from executing Python code in the same application in parallel. This means that if a single-threaded Python application is blocked in a native method (e.g. by calling rti.connextdds.WaitSet.wait()) then Ctrl-C may not be sufficient to break execution. Workarounds include:
  • using Python threading to ensure that the GIL is acquired when a native method releases it.
  • implement a custom signal handler
  • send a SIGQUIT via keyboard shortcut instead of SIGINT
  • kill the Python process via the command line
• SIP on macOS prevents Python from using DYLD_LIBRARY_PATH to find the target libraries, so it is recommended to put them somewhere on the standard search path (e.g. $HOME/lib)
• Getter/setter APIs have been replaced by Python properties in most cases. The exception is write-only properties, which are still normal method calls with the new value as the argument.