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.
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);
}
Have the c++ callback place the data in a queue. Have the python code poll the queue to extract the data.
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