[411111111111111]

From previous discussions it's my understanding the c integration is going to be the cause for the issues.

From a python perspective it wouldn't necessarily be a big change, but everything can branch out to c, and there you're going to get in trouble with shared memory.

[dwaite]

The most significant impact of this change is that python threads can run at the same time. Before, calls to C API were essentially cooperative multithreading yield points - even if you have 100 python threads, they can't run concurrently under the GIL. 99 are blocked waiting on the GIL.

C extensions have always been able to use real threading. But now there is no GIL to synchronize with the python interpreter on ingress/egress from the extension.