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
• not use pointers to manage their internal structure

Only fixed-size integers (like uint8_t), float, 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, an equality comparison function for the key must be provided.

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, all dependencies need to be installed. You can find instructions in the C Examples Readme.

First you have to build the C examples:

cmake -S . -B target/ff/cc/build -DBUILD_EXAMPLES=ON -DBUILD_CXX=OFF
cmake --build target/ff/cc/build

How to Run

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

Terminal 1

./target/ff/cc/build/examples/c/blackboard/example_c_creator

Terminal 2

./target/ff/cc/build/examples/c/blackboard/example_c_opener

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.