[C++-sig] X-language polymorphism and multithreading

Hans Meine hans_meine at gmx.net
Tue Jul 6 16:11:28 CEST 2010

On Saturday 03 July 2010 03:03:53 Anton Yabchinskiy wrote:
> So, I need PyGILState_Ensure/PyGILState_Release around the
> overridden method call, and PyEval_InitThreads in the module
> initialization. Am I right? Is the following code OK?

The code looks OK to me at least, but what's your problem?  (You just wrote 
"does not work"!)  Is there still a problem with the code below?

If so, I can see potential problems just due to ownership handling, for 
example you pass &data to the callbacks, but who's the owner of that data?  Is 
it possible that another thread releases the memory while the callback is 

Oh, I see another likely problematic thing:
>     void
>     on_data(const Data_Buffer& data)
>     {
>         if (override on_data = get_override("on_data")) {
>             GIL_State_Guard guard;
>             on_data(data);
>         }
>         default_on_data(data);
>     }

You're calling get_override - although I never used it, I believe it performs 
some PyObject_GetAttr or similar to check for an overridden method.  Remember: 
As soon as you're dealing with any python objects, you need the GIL!  (A 
common problem is that people don't see _GetItem oder _GetAttr as "running 
python code", although that's pushing your luck!)


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