Not sure if this is still part of the issue. Around 15 to 16 minutes starts talking about Dave Beazley's research into GIL.
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I'm sure there are a number of people on here that know more about cpython than I do.
I understand this is less of an issue now with python 3 but still exists in python 2.7x which renpy uses.
I did notice they suggest writing code that works with python 2 and 3 for renpy. Wonder if they plan to switch?
Anyway I'll leave it to the more informed to answer beyond this.