synchronized_value

[Klaim]

Description

Adds an implementation of synchronized_value inspired by boost::thread::synchronized_value and the Concurrency TS 2's specifications. It doesnt follow these exactly for the advanced features but do so for the basic ones.

As there is a reticence to depend upon Boost, we decided it would be best to have an implementation at hand for libmamba's internals as we have many cases of tricky mutex handling. The logging split which is WIP will depon on this tool.

Supports shared mutex by using shared locking instead of normal/exclusive locking when the access is const.

Type of Change

• Bugfix
• Feature / enhancement
• CI / Documentation
• Maintenance
• Internal tooling

Checklist

• My code follows the general style and conventions of the codebase, ensuring consistency
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have run pre-commit run --all locally in the source folder and confirmed that there are no linter errors.
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.83%. Comparing base (445bf87) to head (3d9248a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3984      +/-   ##
==========================================
- Coverage   63.86%   63.83%   -0.04%     
==========================================
  Files         300      302       +2     
  Lines       38220    38353     +133     
  Branches     2853     2855       +2     
==========================================
+ Hits        24411    24481      +70     
- Misses      13742    13805      +63     
  Partials       67       67              

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[Klaim]

A note about the documentation: doxygen's autobrief generates the brief from the first line (until the first dot) of the doxygen comments, so there is no need to add @brief, no need to add an empty first line etc.
I also used the less noisy doxygen comments form (* vertical is really not helping reading) and didnt use @param when the brief already describe enough of the behavior and the parameters are constrained enough.

[Klaim]

Looks like my local VS2022 (preview) has fixes that the CI doesnt have yet. I'll do some woarkaounds.

[AntoinePrv]

Why static?

[Klaim]

that function is only used in non-evaluated context so I just wrote that to avoid having to construct a mutex. In theory we could remove the definition I think.
But tu clarify: I needed a reference to be returned, not a r-value reference, not a moved-from, not a value. Returning a temporary would have not compiled.

[Klaim]

I can confirm I can just remove the definition, I'll push the change. I suspect there might be a standard tool to get what I wnat but I didnt find it , std::declval isnt it.