Comments on decisions:

• Placed reentrant lock logic directly into Tkinter 'cuz reentrant locks aren't used anywhere else, and this is easier than overhauling all 4 PyThread lock implementations. (They're also based on condition variables which don't support reentrance.)
• Pushed both fixes to the same PR 'cuz the test case based on TkinterHanders3.py detects both bugs and would fail CI otherwise
• Reentry count overflow check can probably be replaced by an assert: unless there's a bug, we'll sooner hit RecursionError or MemoryError.

Test case has code nonportable to Py2. Shall I make it portable or compose a backport by hand?

Test failures on MacOS in acyncio are caused by https://bugs.python.org/issue33531 .

GH-6972 is a backport of this pull request to the 2.7 branch.

I removed the " needs backport to 3.6" label, the 3.6 branch no longer accept bugfixes (only security fixes are accepted): https://devguide.python.org/#status-of-python-branches

This PR is stale because it has been open for 30 days with no activity.

All commit authors signed the Contributor License Agreement.

This PR is stale because it has been open for 30 days with no activity.

PR inactive since 2018, I close it.

Updated the PR branch but that doesn't show here for some reason.

To test with nonthreaded Tcl, apply the attached patch, then run PCBuild/prepare_tcltk.bat, then build and test.
tcltk_nothreads.patch