This commit is an initial start at implementing the standard library for
wasm32-unknown-unknown with the experimental `atomics` feature enabled. None of
these changes will be visible to users of the wasm32-unknown-unknown target
because they all require recompiling the standard library. The hope with this is
that we can get this support into the standard library and start iterating on it
in-tree to enable experimentation.
Currently there's a few components in this PR:
* Atomic fences are disabled on wasm as there's no corresponding atomic op and
it's not clear yet what the convention should be, but this will change in the
future!
* Implementations of `Mutex`, `Condvar`, and `RwLock` were all added based on
the atomic intrinsics that wasm has.
* The `ReentrantMutex` and thread-local-storage implementations panic currently
as there's no great way to get a handle on the current thread's "id" yet.
Right now the wasm32 target with atomics is unfortunately pretty unusable,
requiring a lot of manual things here and there to actually get it operational.
This will likely continue to evolve as the story for atomics and wasm unfolds,
but we also need more LLVM support for some operations like custom `global`
directives for this to work best.
Added in #52149 the discussion in #53514 is showing how we may not want to
actually add this attribute to the atomic types. While we continue to
debate #53514 this commit reverts the addition of the `transparent` attribute.
This should be a more conservative route which leaves us the ability to tweak
this in the future but in the meantime allows us to continue discussion as well.
This allows them to be used in #[repr(C)] structs without warnings. Since rust-lang/rfcs#1649 and rust-lang/rust#35603 they are already documented to have "the same in-memory representation as" their corresponding primitive types. This just makes that explicit.
closes#45085
this commit adds an `atomic_cas` target option and an unstable `#[cfg(target_has_atomic_cas)]`
attribute to enable a subset of the `Atomic*` API on architectures that don't support atomic CAS
natively, like MSP430 and ARMv6-M.
atomic: remove 'Atomic*' from Debug output
For the same reason that we don't show `Vec { data: [0, 1, 2, 3] }`, but just the array, the `AtomicUsize(1000)` is noisy, and seeing just `1000` is likely better.
Add a generic CAS loop to std::sync::Atomic*
This adds two new methods to both `AtomicIsize` and `AtomicUsize` with optimized safe compare-and-set loops, so users will no longer need to write their own, except in *very* strange circumstances.
`update_and_fetch` will apply the function and return its result, whereas `fetch_and_update` will apply the function and return the previous value.
This solves #48384 with `x.update_and_fetch(|x| x.max(y))`. It also relates to #48655 (which I misuse as tracking issue for now)..
*note* This *might* need a crater run because the functions could clash with third party extension traits.
This adds a new method to all numeric `Atomic*` types with a
safe compare-and-set loop, so users will no longer need to write
their own, except in *very* strange circumstances.
This solves #48384 with `x.fetch_max(_)`/`x.fetch_min(_)`. It
also relates to #48655 (which I misuse as tracking issue for now).
*note* This *might* need a crater run because the functions could
clash with third party extension traits.
impl From<bool> for AtomicBool
This seems like an obvious omission from #45610. ~~I've used the same feature name and version in the hope that this can be backported to beta so it's stabilized with the other impls. If it can't be I'll change it to `1.24.0`.~~
