blackboard

Blackboard

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.

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 the blackboard messaging pattern, a key-value repository in shared memory. Each communication participant can access exactly the entries it needs instead of the whole repository, making it useful for sharing a global configuration or state, for example.

Important

In addition to the shared memory related requirements mentioned above, the keys and values stored in the blackboard must be trivially copyable. To be able to store and retrieve keys in the blackboard, the key must implement __eq__.

In this example, one writer updates the values in the blackboard every second and a reader reads and prints them to the console.

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 the blackboard messaging pattern in action, open two separate terminals and execute the following commands:

Terminal 1

poetry --project iceoryx2-ffi/python run python examples/python/blackboard/creator.py

Terminal 2

poetry --project iceoryx2-ffi/python run python examples/python/blackboard/opener.py

Feel free to run multiple instances of reader processes simultaneously but note that the blackboard_creator must run first to create the blackboard service with the key-value pairs and that there can be only one writer.