This issue has a long history. A change has been applied and then reverted three times in a row. Pending calls are now per-interpreter.
The issue title is "Add a cross-interpreter-safe mechanism to indicate that an object may be destroyed." but I don't understand if pending calls are expected to be used to communicate between two interpreters. Why not using a UNIX pipe and exchange bytes through it? Py_AddPendingCall() is a weird concept. I would prefer to not abuse it.
Moreover, it's unclear if this issue attempts to *share* a same object between two interpreters. I would prefer to avoid that by any possible way.
I close this issue with a complex history.
If someone wants to continue to work on this topic, please open an issue with a very clear description of what should be done and how it is supposed to be used.