Software Architecture

Code Structure

Felix-star is written using in modern C++ using an object-oriented approach. All code is required to be testable even without FELIX or network hardware and code replication shall be null or minimal. As a consequence a component is often described by an abstract class that defined the interface and two derived implementations, one that interfaces with hardware, the other that emulates the dedicated hardware. To minimize runtime polymorphism, classes are templated such that they can have as member either implementation of another class.

Testing

Unit Tests

Algorithms implemented in felix-star are subject to unit testing. Unit-tests use the Catch [1] framework, are run by CTest and are kept in the unit-test folder.

Integration Tests

Integration tests run multiple process verify the interaction of executables. The framework is felix-unit-test which makes use of the supervisor orchestrator. This type of test verifies also network connectivity and can be extended to use FELIX hardware. These tests use the Python steering files stored in the test folder.

Threading Model

Felix-star applications are based on the event loop provided by the network library. Following the reactor pattern [2], the event loop reacts to events by invoking the corresponding callback function. Callback functions are executed by the event loop thread to avoid thread synchronisation. Scalability is achieved by running multiple event loops (which translated in multiple publishers or receivers). synchronisation across different event loops might be necessary, but the synchronisation point shall be encountered at the lowest possible rate.

Warning

Because callbacks are executed by the event loop thread it is not possible to implement blocking callbacks. Blocking code will stop event loop from processing further events and may lead to hanging or dead-locks.