CP.25: gsl::joining_thread missing implementation in Guidelines support library

Problem

CP.25 says "Prefer gsl::joining_thread over std::thread". However there is no implementation of gsl::joining_thread in Microsoft GSL. Hence the rule CP.25 is incorrect.

Workaround

For projects using C++20, CP.25 could be reworded to "Prefer std::jthread to std::thread".
For projects using C++11 & higher, there should be a workaround to handle this broken rule.

The textbook "C++ Concurrency in action - Practical Multithreading" by Anthony Williams, Chapter 2: "Managing threads", Section 2.3: "Transferring ownership of a thread" under Listing 2.6: "scoped_thread and example usage" mentions an example implementation of scoped_thread class which could be a useful workaround to handle this scenario for projects lesser than C++20 version.

Rainer Grimm's blog also mentions about this workaround.

Action item

It would be nice to incorporate the above workarounds or a better solution to address the incorrect CP.25 rule. If this workarounds are okay for reviewers, I can support in creating a pull request to edit the rule. Let me know your valuable thoughts on this.

Thanks,
Honey

Honey Sukesan

Start with the CP.25 rule and its linked C++ Core Guidelines text; compare its recommendation with std::jthread for C++20 and the pre-C++20 workaround described in the issue. Done means the rule no longer recommends an unavailable gsl::joining_thread and clearly addresses supported language versions.