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Are there popular languages that don't have memory models which make reasoning about concurrent models easier? A language with a notion of threading and shared

Are there popular languages that don't have memory models which make reasoning about concurrent models easier? A language with a notion of threading and shared state is going to have something akin to read/write barriers built into the language memory model to tame the beast.

jcranmer 2y ago
I think tialaramex is overselling the complexity of concurrent memory models in practice, at least for end users. In reality, all modern memory models are based on the data-race-free theorem, which states that in the absence of data races--if your program is correctly synchronized--you can't tell that the hardware isn't sequentially consistent (i.e., what you naïvely expected it to do). Correct synchronization is based on the happens-before relation; a data race is defined as a write and a conflicting read or write such that neither happens-before the other. Within a thread, happens-before is just regular program order. Across a thread, the main happens-before that is relevant is that an release-store on a memory location happens-before an acquire-load on that memory location (this can be generalized to any memory location if they're both sequentially-consistent, but that's usually not necessary). The real cardinal rule of concurrent programming is to express your semantics in the highest-possible level of what you're trying to do, and find some library that does all the nitty-grityy of the implementation. Can you express it with fork-join parallelism? Cool, use your standard library's implementation of fork-join and just don't care about it otherwise.
xxpor 2y ago
C?
- tialaramex 2y ago
  C has the same model as C++ from the same era, so C11 is the C++ 11 model, C23 is C++ 20 and so on. It's C so you don't get a comprehensive set of bells, whistles and horns like the C++ standard library, but the actual model is the same. At a high level it's all the same as C++ 11, the details are not important to most people.

jcranmer 2y ago

I think tialaramex is overselling the complexity of concurrent memory models in practice, at least for end users. In reality, all modern memory models are based on the data-race-free theorem, which states that in the absence of data races--if your program is correctly synchronized--you can't tell that the hardware isn't sequentially consistent (i.e., what you naïvely expected it to do). Correct synchronization is based on the happens-before relation; a data race is defined as a write and a conflicting read or write such that neither happens-before the other. Within a thread, happens-before is just regular program order. Across a thread, the main happens-before that is relevant is that an release-store on a memory location happens-before an acquire-load on that memory location (this can be generalized to any memory location if they're both sequentially-consistent, but that's usually not necessary). The real cardinal rule of concurrent programming is to express your semantics in the highest-possible level of what you're trying to do, and find some library that does all the nitty-grityy of the implementation. Can you express it with fork-join parallelism? Cool, use your standard library's implementation of fork-join and just don't care about it otherwise.

xxpor 2y ago

tialaramex 2y ago
C has the same model as C++ from the same era, so C11 is the C++ 11 model, C23 is C++ 20 and so on. It's C so you don't get a comprehensive set of bells, whistles and horns like the C++ standard library, but the actual model is the same. At a high level it's all the same as C++ 11, the details are not important to most people.