[Python-Dev] Const access to CPython objects outside of GIL? (original) (raw)

Chris Angelico rosuav at gmail.com
Wed Jul 18 14:19:53 EDT 2018

On Wed, Jul 18, 2018 at 8:18 PM, Radim Řehůřek <radim at rare-technologies.com> wrote:

Thanks for your feedback everyone. Given the overwhelmingly negative response, we'll drop this line of investigation.

If more people bring up the same request in the future (unlikely), feel free to reach out to us for some extra set of hands. Given the initial poking, I still think a "reasonable subset" might be "reasonably easy"; IMHO more a process/maintenance/ROI question than a strictly technical one.

The trouble would be defining that "reasonable subset", which would end up having a very large number of words in it. For example, accessing a Python list after any sort of size change could crash the interpreter hard (as the buffer will have been reallocated). I'm fairly sure you can safely read from a tuple so long as you retain a ref to the tuple itself, though, so you may find that there are options there.

Maybe, depending on your needs, the best solution might be to NOT access Python objects at all. Instead, have an API for changing info that is referenced outside of the GIL, and then the key info gets grabbed in a form that doesn't require Python. That would require some changes in the Python code (function calls rather than list manipulation), but would be 100% guaranteed safe. But you've probably already thought of that, so this is a case where that doesn't work :)

ChrisA

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