triple-buffer VS exhaustive

Great write up! I believe the colloquial name for this algorithm is a "lock-free triple buffer". Here's an implementation in Rust (I couldn't find any c/c++ examples) that has extremely thorough comments that might help completely wrap your head around the synchronization ordering. Rust uses the same semantics for atomic primitives as C11, so it should be pretty easy to match up with your implementation. I came to the same conclusion as you to solve an issue I had with passing arbitrarily large data between two threads in an RTOS system I was working with at my day job. It was an extremely satisfying moment, realizing the index variable was sufficient to communicate all the needed information between the two threads.

Rust marks cross-thread shared memory as immutable in the general case, and allows you to define your own shared mutability constructs out of primitives like mutexes, atomics, and UnsafeCell. As a result you don't get rope to hang yourself with by default, but atomic orderings are more than enough rope to devise incorrect synchronizations (especially with more than 2 threads or memory locations). To quote an earlier post of mine:

In terms of shared-memory threading concurrency, Send and Sync, and the distinction between &T and &Mutex and &mut T, were a revelation when I first learned them. It was a principled approach to shared-memory threading, with Send/Sync banning nearly all of the confusing and buggy entangled-state codebases I've seen and continue to see in C++ (much to my frustration and exasperation), and &Mutex providing a cleaner alternative design (there's an excellent article on its design at http://cliffle.com/blog/rust-mutexes/).

My favorite simple concurrent data structure is https://docs.rs/triple_buffer/latest/triple_buffer/struct.Tr.... It beautifully demonstrates how you can achieve principled shared mutability, by defining two "handle" types (living on different threads), each carrying thread-local state (not TLS) and a pointer to shared memory, and only allowing each handle to access shared memory in a particular way. This statically prevents one thread from calling a method intended to run on another thread, or accessing fields local to another thread (since the methods and fields now live on the other handle). It also demonstrates the complexity of reasoning about lock-free algorithms (https://github.com/HadrienG2/triple-buffer/issues/14).

I find that writing C++ code the Rust way eliminates data races practically as effectively as writing Rust code upfront, but C++ makes the Rust way of thread-safe code extra work (no Mutex unless you make one yourself, and you have to simulate &(T: Sync) yourself using T const* coupled with mutable atomic/mutex fields), whereas the happy path of threaded C++ (raw non-Arc pointers to shared mutable memory) leads to pervasive data races caused by missing or incorrect mutex locking or atomic synchronization.

In terms of shared-memory threading concurrency, Send and Sync, and the distinction between &T and &Mutex and &mut T, were a revelation when I first learned them. It was a principled approach to shared-memory threading, with Send/Sync banning nearly all of the confusing and buggy entangled-state codebases I've seen and continue to see in C++ (much to my frustration and exasperation), and &Mutex providing a cleaner alternative design (there's an excellent article on its design at http://cliffle.com/blog/rust-mutexes/).

My favorite simple concurrent data structure is https://docs.rs/triple_buffer/latest/triple_buffer/struct.Tr.... It beautifully demonstrates how you can achieve principled shared mutability, by defining two "handle" types (living on different threads), each carrying thread-local state (not TLS) and a pointer to shared memory, and only allowing each handle to access shared memory in a particular way. This statically prevents one thread from calling a method intended to run on another thread, or accessing fields local to another thread (since the methods and fields now live on the other handle). It also demonstrates the complexity of reasoning about lock-free algorithms (https://github.com/HadrienG2/triple-buffer/issues/14).

I suppose &/&mut is also a safeguard against event-loop and reentrancy bugs (like https://github.com/quotient-im/Quaternion/issues/702). I don't think Rust solves the general problem of preventing deadlocks within and between processes (which often cross organizational boundaries between projects and distinct codebases, with no clear contract on allowed behavior and which party in a deadlock is at fault), and non-atomicity between processes on a single machine (see my PipeWire criticism at https://news.ycombinator.com/item?id=31519951). File saving is also difficult (https://danluu.com/file-consistency/), though I find that fsync-then-rename works well enough if you don't need to preserve metadata or write through file (not folder) symlinks.

This is an analyzer that will catch this: https://github.com/nishanths/exhaustive

I believe it's in golangci-lint.

I agree linters in general are quite useful for Go though. The default suite from golangci-lint is quite good. I would also recommend enabling exhaustive if you're working with a codebase that uses "enums" (full disclosure, I contributed a bit to that project).

there’s a linter for exhaustive matching: https://github.com/nishanths/exhaustive

I tried to find that linter and found this: exhaustive

And in Go you'd use a linter, like this one.

this is AST go vet analyzer that performs just that: https://github.com/nishanths/exhaustive (too bad it can not do struct based enums..)

>> the main thing missing from Go is ADT's. After using these in Rust and Swift, a programming language doesn't really feel complete without them

What are the differences between an ADT (plus pattern matching i’d reckon?) in Rust/Swift vs the equiv in Go (tagged interfaces + switch statement)?

One has exhaustive matching at compile time, the other has a default clause (non exhaustive matching), although there’s an important nub here with respect to developer experience; it would be idiomatic in Go to use static analysis tooling (e.g. Rob Pike is on record saying that various checks - inc this one - don’t belong in the compiler and should live in go vet). I’ve been playing with Go in a side project and using golint-ci which invokes https://github.com/nishanths/exhaustive - net result, in both go and rust, i get a red line of text annotated at the switch in vscode if i miss a case.

Taking a step back, there isn’t a problem you can solve with one that you can’t solve with the other, or is there?

To take a step further back, why incomplete?

Use a linter.

For an exhaustive linter, were you referring to this? It looks pretty nice. If it's possible to check this with static analysis, is it something that could be in the compiler itself in the future?

https://github.com/nishanths/exhaustive

here, have fun. You’re gonna write some tests, make new types to satisfy interfaces for testing, and then wind up with branches for your test paths in your live code, but go for it, I guess. You know everything! I am but a simple blubbite, too dim, too dim to get it.