import objc in embedded python in a C++ thread - c++

Question

I am new to embedding python in C++ application. Please forgive me if this has been asked before, even though I did my homework by searching through the web.
So, here is my problem.
If I ran the embedded python code in the application's main thread, everything runs fine. But if I ran the embedded python code in the child thread ( created by main thread ), some of the python import will not work.
I made a small program here to demonstrate:
#include <iostream>
#include <boost/python.hpp>
#include <boost/thread.hpp>
using namespace boost::python;
int threadFunc ( ){
PyGILState_STATE gstate;
gstate = PyGILState_Ensure();
std::cout << "Py_GetProgramName: " << Py_GetProgramName() << std::endl;
std::cout << "Py_GetPath: " << Py_GetPath() << std::endl;
std::cout << "Py_GetExecPrefix: " << Py_GetExecPrefix() << std::endl;
object main_module = boost::python::import ( "__main__");
object main_namespace = main_module.attr("__dict__");
object objc_import = boost::python::import ( "objc" );
exec("a = 10\n", main_namespace);
exec("print a\n", main_namespace);
return 0;
}
int main( ){
Py_InitializeEx( 0 ); //
PyEval_InitThreads();
// Uncomment this will make the program work.
//object objc_import = boost::python::import ( "objc" );
PyEval_ReleaseLock();
boost::thread * theChildThread = new boost::thread (threadFunc);
while (1){
boost::this_thread::sleep( boost::posix_time::seconds(1) );
}
delete theChildThread;
Py_Finalize();
return 0;
}
The code fails when I tries to import objc in the threadFunc
object objc_import = boost::python::import ( "objc" );
By experiment different things, I find that if I do this in the main thread before starting child thread, the whole program would work ( see comments in the main function ):
//Uncomment this will make the program work.
//object objc_import = boost::python::import ( "objc" );
I am wondering what happened there. Is there anyway to without importing objc in main thread, but still make the child thread work?
Thanks,