[issue40572] Support basic asynchronous cross-interpreter operations.

Change by Eric Snow : -- keywords: +patch pull_requests: +19323 stage: needs patch -> patch review pull_request: https://github.com/python/cpython/pull/20012 ___ Python tracker ___

[issue40572] Support basic asynchronous cross-interpreter operations.

New submission from Eric Snow : (This is a continuation of the work from bpo-33608. That issue ended up with a lot of baggage and clutter (due to problems that have since been resolved), so we closed it. This issue is where we're picking it up fresh.) When two interpreters are cooperating,