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## Summary of the Pull Request
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## References
#11083#11143
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## PR Checklist
* [ ] Closes #xxx
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [x] Tests added/passed
* [ ] Documentation updated. If checked, please file a pull request on [our docs repo](https://github.com/MicrosoftDocs/terminal) and link it here: #xxx
* [ ] Schema updated.
* [ ] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx
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## Detailed Description of the Pull Request / Additional comments
While testing the save/quit features a number of issues were found that were caused by poor synchronization on the monarch, resulting in various unexpected crashes. Because this uses std collections, and I didn't see any builtin winrt multithreaded containers I went with the somewhat heavy-handed mutex approach.
e.g.
- https://github.com/microsoft/terminal/pull/11083#issuecomment-916218353
- https://github.com/microsoft/terminal/pull/11083#issuecomment-916220521
- https://github.com/microsoft/terminal/pull/11143/#discussion_r704738433
This also makes it so that on quit peasants don't try to become the monarch, and the monarch closes their peasant last to prevent elections from happening.
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## Validation Steps Performed
Create many windows (hold down ctrl-shift-n) then use the quit action from peasants/the monarch to make sure everything closes properly.
591a67111e