Python plugin multithreading support #7
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The classes PythonInterpreter, PythonGuard, PythonObject and PythonTuple were added to wrap Python's C API into C++ friendly interfaces.
Replace PyGILState* API by PyEval_{Acquire,Release}Thread API.
This is necessary since only the latter supports sub-interpreters in
Python 3.12.
This configuration is especially designed to be used when embedding the python interpreter in another application.
Use PyErr_GetRaisedException if available and wrap in PythonObjects for correct PyObject* reference cleanup. Additionally, add bool cast to PythonException and PyObject.
For this, PythonException::occurred() is introduced to check if the error indicator is set in Python. PythonObject::to<std::string>() is added to allow formatting of the exception. PythonInterpreter::call() was modified to handle exceptions raised during execution of the called function.
Since some of the required functionality is not supported, it was supersided by own python C API wrappers. This is to avoid weird bugs due to GIL and Python's internal global states and the Boost.Python library and custom functions interfering with each other.
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This PR introduces multi-threading support for different instances of
PythonPlugin.Previously, due to the global state used internally in the CPython library, two different plugins could not be used thread-safely.
This is achieved by using the Global Interpreter Lock (GIL) and (for Python 3.12 or newer) different sub-interpreters.
However, sub-interpreters are poorly documented and thus the implementation might not be perfect and still have some thread-unsafe calls.
Resolves #6