AST-945 Protect embedded python code by mutex

Embedded python code can not be run multi threaded. This MR protects the execution of embedded python by a mutex.

An alternative would be to use a Global Interpreter Lock (GIL), but that caused a dead lock in parallel deconvolution.

cpp/algorithms/python_deconvolution.cc

@@ -9,6 +9,8 @@
 #include <pybind11/pybind11.h>
 #include <pybind11/stl.h>
 
+#include <mutex>
+
 namespace radler::algorithms {
 
 struct PyChannel {
@@ -197,6 +199,9 @@ float PythonDeconvolution::ExecuteMajorIteration(
   size_t nFreq = dirty_set.NDeconvolutionChannels();
   size_t nPol = dirty_set.Size() / dirty_set.NDeconvolutionChannels();
 
+  static std::mutex mutex;
+  const std::lock_guard<std::mutex> lock(mutex);
+
   pybind11::object result;
 
   // A new context block is started to destroy the python data arrays asap