Calling into Python from a C thread

Philip Semanchuk philip at
Tue Feb 10 10:29:15 EST 2009

On Feb 9, 2009, at 3:59 PM, Christian Heimes wrote:

> Philip Semanchuk wrote:
>> Yes, that's accurate except for the word "forgot". To forget  
>> something
>> one must first know it. =) I found the threading API documentation
>> difficult to follow, but I suppose that what I'm doing is a little
>> unusual so if it is not well-documented territory, that's what I  
>> get for
>> wandering off the map.
> I see. Apparently the threading and embedding docs don't cover your
> case. The docs at
> and should explain how
> and when to initialize Python threads. Please report a documentation  
> bug at

I read that several times and eventually got my code working. I  
wouldn't say that the documentation didn't cover my case (implementing  
a callback). I'd say that it doesn't cover *any* cases in particular.  
It's more like a list of tools for manipulating the GIL and thread  
state and an explanation of the need for them rather than a tutorial  
on how to use them. The latter is what I needed, but as I said, what  
I'm doing is atypical and I think it is reasonable to expect thin  
documentation on atypical situations.

> PS: I know a great way to learn more about Python's internal threading
> CAPI: fix your code, test it and attach a doc patch to your bug  
> report.
> *hint* :)

I will file a bug on a least one specific point which is that  
PyGILState_Ensure() acquires the GIL and PyGILState_Release() appears  
to release it; the latter point is undocumented.


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