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[BLOG] Why Rust mutexes look like they do - Cliffle
(cliffle.com)
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this post was submitted on 16 Sep 2024
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I started playing with rust last week (just converting a couple of C# projects so far), and I'm going to say that once you understand that mutexes/rwlocks are wrappers around the actual data, it (to me at least) feels better.
Don't get me wrong, it's an absolute headache for anyone that's acquired intermediate or better skill in one of the Cx languages. The paradigm shift is still hitting me hard. But this was one of the differences I actually think is an improvement in probably most use cases.
It's a massive win, and I would question the credibility of any systems programmer that doesn't recognize that as soon as they understand the wrapper arrangement. I would have to assume that such people are going around making egregious errors in how they're using mutexes in their C-like code, and are the reason Rust is such an important language to roll out everywhere.
The only time I've ever needed a
Mutex<()>so far with Rust is when I had to interop with a C library which itself was not thread safe (unprotected use of global variables), so I needed to lock the placeholder mutex each time I called one of the C functions.Actually I think in this case you're still better off using a Mutex with "data" inside. I've done this before. The idea is that you make a unit struct
MyCFuncsor whatever and then you only call the C functions from methods of that unit struct. Then you can only access those methods once you lock the Mutex and get the instance of the unit struct. It feel elegant to me.This makes a lot of sense, but the functions were Rust bindings for plain C functions, they weren't function pointers. Granted I could have put pointers to the function bindings into fields in a struct and stored that struct in the mutex, but the ability to anyhow call the bindings would still exist.
They were also plain C functions in my case, but it doesn't take too much discipline to only call it through the struct. Also, you can put the struct in a different crate which includes the C bindings to ensure that you can't call the C bindings without the struct.
Exactly. If there's only one thing I could bring from Rust into another language, it would be Mutexes. It's so nice to guarantee safe access to data.
Rust mutexes would be nice. But I think for me that one thing for me would be its enums.
But only if pattern matching were included, otherwise they would be as unpleasant as C++'s
std::variant.Wrapping a value in a mutex just makes sense. After learning a bit of Rust I made a similar mutex wrapper in C++ when I had to protect a class member in a C++ project. I just had to change the type in the declaration, and bam the compiler tells me about all places this member was accessed. Much easier than using some buggy 'find all references', potentially forgetting a few places.