Question

I am developing a program that use DirectShow to grab audio data from media files. DirectShow use thread to pass audio data to the callback function in my program, and I let that callback function call another function in Python.

I use Boost.Python to wrapper my library, the callback function :

class PythonCallback { private:     object m_Function; public:     PythonCallback(object obj)         : m_Function(obj)     {}      void operator() (double time, const AudioData &data) {         // Call the callback function in python         m_Function(time, data);     }  }; 

Here comes the problem, a thread of DirectShow calls my PythonCallback, namely, call the function in Python. Once it calls, my program just crash. I found this should be threading problem. Then I found this document:

http://docs.python.org/c-api/init.html

It seems that my program can’t call to Python’s function from thread directly, because there is Global Interpreter Lock. The python’s GIL is so complex, I have no idea how it works. I’m sorry, what I can do is to ask. My question is. What should I do before and after I call a Python function from threads?

It may looks like this.

void operator() (double time, const AudioData &data) {     // acquire lock     m_Function(time, data);     // release lock } 

Thanks. Victor Lin.

Answer 1

Take a look at PyGILState_Ensure()/PyGILState_Release(), from PEP 311 http://www.python.org/dev/peps/pep-0311/

Here is an example taken from the PEP itself:

void SomeCFunction(void) {     /* ensure we hold the lock */     PyGILState_STATE state = PyGILState_Ensure();     /* Use the Python API */     ...     /* Restore the state of Python */     PyGILState_Release(state); }