title: Problems regarding Boost::Python and Boost::Threads
body: <p>Me and a friend are developing an application which uses Boost::Python. I have defined an interface in C++ (well a pure virtual class), exposed through Boost::Python to the users, who have to inherit from it and create a class, which the application takes and uses for some callback mechanism.</p>
  
  <p>Everything that far goes pretty well. Now, the function callback may take some time (the user may have programmed some heavy stuff)...  but we need to repaint the window, so it doesn't look "stuck".We wanted to use Boost::Thread for this. Only one callback will be running at a time (no other threads will call python at the same time), so we thought it wouldn't be such a great deal... since we don't use threads inside python, nor in the C++ code wrapped for python.</p>
  
  <p>What we do is calling PyEval_InitThreads() just after Py_Initialize(), then, before calling the function callback inside it's own boost thread, we use the macro PY_BEGIN_ALLOW_THREADS and, and the macro PY_END_ALLOW_THREADS when the thread has ended.</p>
  
  <p>I think I don't need to say the execution never reaches the second macro. It shows several errors everytime it runs... but t's always while calling the actual callback. I have googled a lot, even read some of the PEP docs regarding threads, but they all talk about threading inside the python module (which I don't sice it's just a pure virtual class exposed) or threading inside python, not about the main application calling Python from several threads.</p>
  
  <p>Please help, this has been frustrating me for several hours.</p>
  
  <p>Ps. help!</p>