[benschulz]

I'm not convinced this is a meaningful distinction in this context. Assuming a developer consciously creates a race which turns out to be a bug, how does it matter whether it was a data race or some other kind of race condition?

[bcoates]

In general data races can break program invariants, violate memory safety and do other undefined behavior.

In C++, data races can cause jumps to invalid addresses and the compiler will assume data races away and delete checks that are redundant in the single-thread case. The equivalent problem happens in most languages where data races are possible (two Python threads writing at once can put a value into an impossible/illegal state)

An ordinary race condition is just an observable effect of the nondeterministic progress of threads, so it's possible to have a truly benign race condition, so long as the correctness of the whole program doesn't depend on the outcome of the race. I/O causes nondeterminism anyway, so it's not really practical to avoid all ordinary races.

[benschulz]

It's possible to have truly benign data races too, e.g. lazily computing a hash of immutable data.

One of the reasons that Rust's ownership model is necessary is most data races cannot otherwise be statically detected. The compiler will be unable to apply any of its theoretical UB optimizations. It will emit its native code and you get the defined behavior of the underlying hardware. There will be no undefined behavior. If that ever changes, the bigger news, I imagine, will be that we solved the halting problem.

[steveklabnik]

Data races are undefined behavior, and race conditions are a logic error. Yes, both are bugs, and both are important to fix. But they have (at least to me) different severities.

(Worth noting that data races have a clear, unambiguous definition, and therefore are possible to eliminate through tooling. Race conditions rely on program intent or logic, and are therefore... not really.)

Also, I think it matters, generally, that we are truthful about what Rust prevents and does not prevent.

[brundolf]

> Worth noting that data races have a clear, unambiguous definition, and therefore are possible to eliminate through tooling. Race conditions rely on program intent or logic, and are therefore... not really.

This is a great point. Usually people only talk about the two categories in terms of vague severity, but this is a hard distinction which has lots of implications for how each can be dealt with.

[pjmlp]

Any kind of race can lead to data corruption, or being very drastic, possible death if the outcome is related to any computer system with direct influence over human lives like factory automation systems.

This is why I think Rust discussions about this subject don't focus enough that the language only validates a very tiny subset of races.

[benschulz]

> Data races are undefined behavior, and race conditions are a logic error. Yes, both are bugs, and both are important to fix. But they have (at least to me) different severities.

Some data races really are benign while some other race conditions can lead to data corruption or security vulnerabilities. Why then should data races be strictly more severe than data races? What am I missing?

[anp]

"This context" is the original article, which is discussing data races specifically.

[benschulz]

Actually "this context" was my previous reply. Much like I can nest a lexical scope inside a program and have it reach up and past the containing scope, I can create a new context in a discussion. Please at least try to understand my position before you reply.