Use subinterpreters to handle Python-C++-Python calls

typon/include/python/builtins.hpp

@@ -394,4 +394,24 @@ namespace detail {
 }
 }
 
+#ifdef TYPON_EXTENSION
+class SubInterpreter {
+    PyThreadState* main;
+    PyThreadState* sub;
+
+public:
+    SubInterpreter() {
+        main = PyThreadState_Get();
+        sub = Py_NewInterpreter();
+    }
+
+    ~SubInterpreter() {
+        Py_EndInterpreter(sub);
+        PyThreadState_Swap(main);
+    }
+};
+#else
+using SubInterpreter = py::scoped_interpreter;
+#endif
+
 #endif // TYPON_BUILTINS_HPP

typon/trans/transpiler/phases/emit_cpp/module.py

@@ -59,7 +59,7 @@ class ModuleVisitor(BlockVisitor):
             yield f"> arg{i}"
 
         yield ") {"
-        yield "py::scoped_interpreter guard{};"
+        yield "SubInterpreter lock{};"
         yield f"return py::module_::import(\"{mod}\").attr(\"{name}\")("
         for i, argty in enumerate(fty.parameters):
             if i != 0: