Access violation in Python garbage collector (visit_decref) - how to debug?

[MRAB]

On 2019-10-04 20:32, Geoff Bache wrote:
> Hi all,
> 
> We are running Python embedded in our C++ product and are now experiencing
> crashes (access violation reading 0xffffffffff on Windows) in the Python
> garbage collector.
> 
> We got this on Python 3.6.4 originally, but I can reproduce it with both
> Python 3.6.8 and Python 3.7.4.
> 
> The chances of producing a minimal example that reproduces it reliably are
> currently small I would say. All attempts to simplify the set up seem to
> cause the problem to go away.
> Indeed I can only reproduce it by sending a fairly large amount of data 2
> or 3 times to our server - sending either half of the data does not
> reproduce it.
> 
[snip]
In my experience, it's most likely caused by incorrect refcounting, 
DECREFing too many times.