[issue33110] Adding a done callback to a concurrent.futures Future once it has already completed, may raise an exception, contrary to docs

Change by Sam Martin : -- keywords: +patch pull_requests: +13054 stage: -> patch review ___ Python tracker <https://bugs.python.org/issue33110> ___ ___ Py

[issue33110] Adding a done callback to a concurrent.futures Future once it has already completed, may raise an exception, contrary to docs

New submission from Sam Martin <nivek...@gmail.com>: Whilst working with concurrent.futures and ThreadPoolExecutors, my colleague and I have noted some undocumented behaviour. When adding a done_callback to a future that has already completed, we note that that callback is executed di