3 ms·

it doesn't. From cppreference (whose model Rust roughly follows): "Relaxed operation: there are no synchronization or ordering constraints imposed on other read

• dunkelheit 7y ago
  Still I think I am correct. The docs (https://doc.rust-lang.org/std/sync/atomic/enum.Ordering.html#variant.Relaxed https://doc.rust-lang.org/std/sync/atomic/enum.Ordering.html...) point to https://llvm.org/docs/Atomics.html#monotonic https://llvm.org/docs/Atomics.html#monotonic which states that "It essentially guarantees that if you take all the operations affecting a specific address, a consistent ordering exists." which is what I've said.
  • ComputerGuru 7y ago
    Yes, a consistent ordering exists but that ordering isn’t necessarily what you think or want it to be. The consistency is present based off the order the reads and writes were executed in; you’ll never read back a value that wasn’t at some point stored there. Which can happen with non-atomic reads/writes, where you’ll read part of one write and part of the next. Reads can still be reordered before writes, as no memory barriers are issued.
    • dunkelheit 7y ago
      Well that doesn't contradict anything that I have said :) My question remains - what do you mean by coherence? I argue that it is precisely the property that there is a consistent order of operations a single memory memory location so you can't say that Relaxed operations don't satisfy coherence.
      • frankenbee 7y ago
        Hm
      • gpderetta 7y ago
        You are correct. IIRC Coherency is the only property of relaxed atomic operations, as opposed of plain load/stores where concurrent modification and access is just UB.