Expose libstd::sys_common::remutex

[ckaran]

I just discovered that libstd::sys_common::remutex has the ReentrantMutex type, which is not exposed in std::sync. Can you please expose it in std::sync?

[eggyal]

See also #27738

[ckaran]

@eggyal Thank you for link!

[SimonSapin]

The fact that an implementation already exists inside std may help a little but it’s not the most important point. This would add non-trivial new API surface to the standard library, so it should likely go through the RFC process to consider questions like: what are the details of new APIs? What are their semantics? Why is making these choices preferable over alternatives? Is this a commonly-used enough primitive that is should be in the standard library rather than on crates.io? etc.

[eggyal]

Is this a commonly-used enough primitive that is should be in the standard library rather than on crates.io?

Worth noting that @Amanieu's parking_lot crate provides a ReentrantMutex.

[ckaran]

@SimonSapin I agree that it should go through the RFC process, if for no other reason than the fully refine the API and ensure it is exactly what we want to expose. Unfortunately, I don't have the time to push for it (too many deadlines at work right now).

[Mark-Simulacrum]

Closing in favor of rust-lang/libs-team#193, which is tracking this API (and has an open PR).