We still have a bunch of "global" C variables (static globals, static locals, maybe thread-local storage) in our code-base that break the isolation between interpreters.  I added Tools/c-globals/check-c-globals.py a while back to help identify such variables, however more have crept in.  I also did not take static locals or thread-locals into account.

To address the above, we should do the following:

1. update check-c-globals.py to identify static locals (and thread-locals)
2. deal with any identified globals
   * move them to _PyRuntimeState (or thread-locals to PyThreadState, etc.)
   * ignore them by adding them to Tools/c-globals/ignored-globals.txt
3. add check-c-globals.py to "make check"
4. (if "make check" isn't already there), ensure check-c-globals.py is run at some point in CI

Separately, we should move fields out of _PyRuntimeState into PyInterpreterState wherever possible.  That can also be done at step 2 if it's not too much work.

Also, Tools/c-globals/ignored-globals.txt is a bit out of date (some vars have been removed, renamed, or moved to another file).  That should get cleaned up.  It might also make sense to update check-c-globals.py to verify that all variables in ignored-globals.txt actually exist.

New changeset ee536b2020b1f0baad1286dbd4345e13870324af by Eric Snow in branch 'master':
bpo-36876: Add a tool that identifies unsupported global C variables. (#15877)
https://github.com/python/cpython/commit/ee536b2020b1f0baad1286dbd4345e13870324af

The new test_check_c_globals.ActualChecks test is failing with an "unexpected success" on the bolen-ubuntu buildbot (under Ubuntu 18.04.3).  I can reproduce the failure in a manually built tree.

@db3l, I'll take a look right away.

New changeset 64535fc6c0712caef0bc46be30e661f7ccf8280e by Eric Snow in branch 'master':
bpo-36876: Skip test_check_c_globals for now. (gh-16017)
https://github.com/python/cpython/commit/64535fc6c0712caef0bc46be30e661f7ccf8280e

New changeset 088b63ea7a8331a3e34bc93c3b873c60354b4fad by Eric Snow in branch 'master':
bpo-36876: Fix the globals checker tool. (gh-16058)
https://github.com/python/cpython/commit/088b63ea7a8331a3e34bc93c3b873c60354b4fad

New changeset e4c431ecf50def40eb93c3969c1e4eeaf7bf32f1 by Eric Snow in branch 'master':
bpo-36876: Re-organize the c-analyzer tool code. (gh-16841)
https://github.com/python/cpython/commit/e4c431ecf50def40eb93c3969c1e4eeaf7bf32f1

New changeset 9def81aa52adc3cc89554156e40742cf17312825 by Vinay Sajip in branch 'master':
bpo-36876: Moved Parser/listnode.c statics to interpreter state. (GH-16328)
https://github.com/python/cpython/commit/9def81aa52adc3cc89554156e40742cf17312825