publish_subscribe_dynamic_data

Publish-Subscribe With Dynamic Data (Slice Of Shared Memory Compatible Types)

This example demonstrates how to send data when the maximum data size cannot be predetermined and needs to be adjusted dynamically during the service's runtime. iceoryx2 enables the reallocation of the publisher's data segment, allowing users to send samples of arbitrary sizes.

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
• must be trivially destructible, see std::is_trivially_destructible

Data types like std::string or std::vector will cause undefined behavior and may result in segmentation faults. We provide alternative data types that are compatible with shared memory. See the complex data type example for guidance on how to use them.

Only fixed-size integers (like uint8_t), float, double, and the types in the iceoryx2-bb-container library are cross-language compatible!

This example demonstrates a robust publisher-subscriber communication pattern between two separate processes. A service with the payload type of an u8 slice is created, and every publisher can define a slice length hint they support for communication with initial_max_slice_len. The publisher sends a message with increasing size every second containing a piece of dynamic data. On the receiving end, the subscriber checks for new data every second.

The subscriber is printing the sample on the console whenever new data arrives.

The initial_max_slice_len hint and the AllocationStrategy set by the publisher will define how memory is reallocated when [Publisher::loan_slice()] or [Publisher::loan_slice_uninit()] request more memory than it is available.

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
cmake --build target/ff/cc/build

How to Run

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

Terminal 1

./target/ff/cc/build/examples/cxx/publish_subscribe_dynamic_data/example_cxx_publish_subscribe_dyn_subscriber

Terminal 2

./target/ff/cc/build/examples/cxx/publish_subscribe_dynamic_data/example_cxx_publish_subscribe_dyn_publisher

Feel free to run multiple instances of 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 run. Take a look at the iceoryx2 config to set the limits globally or at the API of the Service builder to set them for a single service.