The simplest solution is for `std::mutex` to provide a simple, efficient mutex which is a good choice for almost any program. And it does. Niche programs can pu

The simplest solution is for `std::mutex` to provide a simple, efficient mutex which is a good choice for almost any program. And it does. Niche programs can pull in a crate. I doubt `parking_lot` would have been broadly used—maybe wouldn't even have been written—if `std` had this implementation from the start. What specifically in this comparison made you think that `parking_lot` is broadly needed? They had to work pretty hard to find a scenario in which `parking_lot` did much better in any performance metrics. And as I alluded to in another comment, `parking_lot::Mutex<InnerFoo>` doesn't have a size advantage over `std::mutex::Mutex<InnerFoo>` when `InnerFoo` has word alignment. That's the most common situation, I think. If I were to make a wishlist of features for `std::mutex` to just have, it wouldn't be anything `parking_lot` offers. It'd be stuff like the lock contention monitoring that the (C++) `absl::Mutex` has. (And at least on some platforms you can do a decent job of monitoring this with `std::mutex` by monitoring the underlying futex activity.)