publish_subscribe_with_user_header

Publish-Subscribe With User Header

Caution

Every payload you transmit with iceoryx2 must be compatible with shared memory. Specifically, it must:

• be self contained, no heap, no pointers to external sources
• have a uniform memory representation, ensuring that shared structs have the same data layout
  • therefore, only ctypes and ctypes.Structure can be transferred
• not use pointers to manage their internal structure

Any other python data type, except ctypes or ctypes.Structures, will likely cause undefined behavior and may result in segmentation faults. Take a look at the publish subscribe example to see how ctypes can be transferred.

Only fixed-size integers (like ctypes.c_uint8_t), ctypes.c_float, ctypes.c_double, and the types in the iceoryx2-bb-container library are cross-language compatible!

This example illustrates a publisher-subscriber communication pattern between two separate processes with an additional user header, referred to as a CustomHeader. The publisher sends messages every second, each containing an incrementing number and the CustomHeader, which includes an additional version number and a timestamp. On the receiving end, the subscriber checks for new data every second and prints out the received payload and the user header.

How to Build

Before proceeding, a virtual environment with all dependencies needs to be created. You can find the detailed instructions in the Python Examples Readme.

poetry --project iceoryx2-ffi/python install

Then, the iceoryx2 python bindings can be built and installed into the virtual environment:

poetry --project iceoryx2-ffi/python run maturin develop --manifest-path iceoryx2-ffi/python/Cargo.toml --target-dir target/ff/python

How to Run

To observe this dynamic communication in action, open two separate terminals and execute the following commands:

Terminal 1

poetry --project iceoryx2-ffi/python run python examples/python/publish_subscribe_with_user_header/subscriber.py

Terminal 2

poetry --project iceoryx2-ffi/python run python examples/python/publish_subscribe_with_user_header/publisher.py

Feel free to run multiple instances of the publisher or subscriber processes simultaneously to explore how iceoryx2 handles publisher-subscriber communication efficiently.

Tip

You may hit the maximum supported number of ports when too many publisher or subscriber processes are running. Check the iceoryx2 config to set the limits globally or refer to the API of the Service builder to set them for a single service.