Multithreading is incompatible with custom formfactor

with number of threads >=2 we get a segmentation fault

added Python essential functionality labels

Accessing the Python interpreter from a multi-threaded C++ application needs extra care and detailed knowledge of the Python multi-threading mechanism.

See: Pulleyn (2000), “Embedding Python in Multi-Threaded C/C++ Applications”, Linux J. 2000, 73es, https://dl.acm.org/doi/abs/10.5555/348902.348913.