[Pyrex] Callbacks from threads and PyGILState_Ensure/PyGILState_Release

[Robert Bradshaw]

On Sep 13, 2007, at 12:56 AM, Stefan Behnel wrote:

> Robert Bradshaw wrote:
>> Back to the question of whether or not signatures match, I see  
>> only two
>> instance where we care about types matching.
>>
>> 1) Between pyx and pxd files. If we allow them to differ, which takes
>> precedence? It only benefits the lazy to allow mismatch here.
>
> I don't think so. As I already said, we are not talking about  
> interfaces here,
> only about implementation details. If I define a function in a .pxd  
> file
> without annotating it with "with GIL", but then I implement such a  
> function
> and say that I want it to execute "with GIL", that can be perfectly
> reasonable. I don't see much sense in the opposite, but maybe I'm  
> just missing
> something.
>
> How about disallowing "with GIL" in .pxd files and in function
> pre-declarations? That way, we avoid the problem all together.

You have a good point that it is an implementation rather than  
signature issue, and if we take this approach then disallowing "with  
GIL" in pxd files/function pre-declarations should be done. The only  
drawback I see is that as a programmer (and/or more intelligent  
future version of pyrex) I have to look in the pyx file (not just the  
pxd file) to decide if its safe to call if I don't currently have the  
GIL. This latter situation is purely hypothetical and may not be  
worth bothering with.

>> 2) When subclassing cdef classes and overriding cdef functions. In  
>> this
>> case, if one wants to use the function as a callback, it always  
>> requires
>> the GIL (due to the self parameter) and will probably save a lot of
>> mistakes to throw an error when they don't match.
>
> How would you use a method as a callback? That would require  
> passing self
> already in some way, right? So you can only do that from Python/ 
> Pyrex code
> anyway, which makes the problem a pretty special case.

If the callback was of the form

foo(void *, ...)

and the void * was user-specified, one could do that.