Make `ThinBox<T>` covariant in `T`
Just like `Box<T>`, we want `ThinBox<T>` to be covariant in `T`, but the
projection in `WithHeader<<T as Pointee>::Metadata>` was making it
invariant. This is now hidden as `WithOpaqueHeader`, which we type-cast
whenever the real `WithHeader<H>` type is needed.
Fixes the problem noted in <https://github.com/rust-lang/rust/issues/92791#issuecomment-1104636249>.
fix data race in thread::scope
Puts the `ScopeData` into an `Arc` so it sticks around as long as we need it.
This means one extra `Arc::clone` per spawned scoped thread, which I hope is fine.
Fixes https://github.com/rust-lang/rust/issues/98498
r? `````@m-ou-se`````
[core] add `Exclusive` to sync
(discussed here: https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Adding.20.60SyncWrapper.60.20to.20std)
`Exclusive` is a wrapper that exclusively allows mutable access to the inner value if you have exclusive access to the wrapper. It acts like a compile time mutex, and hold an unconditional `Sync` implementation.
## Justification for inclusion into std
- This wrapper unblocks actual problems:
- The example that I hit was a vector of `futures::future::BoxFuture`'s causing a central struct in a script to be non-`Sync`. To work around it, you either write really difficult code, or wrap the futures in a needless mutex.
- Easy to maintain: this struct is as simple as a wrapper can get, and its `Sync` implementation has very clear reasoning
- Fills a gap: `&/&mut` are to `RwLock` as `Exclusive` is to `Mutex`
## Public Api
```rust
// core::sync
#[derive(Default)]
struct Exclusive<T: ?Sized> { ... }
impl<T: ?Sized> Sync for Exclusive {}
impl<T> Exclusive<T> {
pub const fn new(t: T) -> Self;
pub const fn into_inner(self) -> T;
}
impl<T: ?Sized> Exclusive<T> {
pub const fn get_mut(&mut self) -> &mut T;
pub const fn get_pin_mut(Pin<&mut self>) -> Pin<&mut T>;
pub const fn from_mut(&mut T) -> &mut Exclusive<T>;
pub const fn from_pin_mut(Pin<&mut T>) -> Pin<&mut Exclusive<T>>;
}
impl<T: Future> Future for Exclusive { ... }
impl<T> From<T> for Exclusive<T> { ... }
impl<T: ?Sized> Debug for Exclusive { ... }
```
## Naming
This is a big bikeshed, but I felt that `Exclusive` captured its general purpose quite well.
## Stability and location
As this is so simple, it can be in `core`. I feel that it can be stabilized quite soon after it is merged, if the libs teams feels its reasonable to add. Also, I don't really know how unstable feature work in std/core's codebases, so I might need help fixing them
## Tips for review
The docs probably are the thing that needs to be reviewed! I tried my best, but I'm sure people have more experience than me writing docs for `Core`
### Implementation:
The API is mostly pulled from https://docs.rs/sync_wrapper/latest/sync_wrapper/struct.SyncWrapper.html (which is apache 2.0 licenesed), and the implementation is trivial:
- its an unsafe justification for pinning
- its an unsafe justification for the `Sync` impl (mostly reasoned about by ````@danielhenrymantilla```` here: https://github.com/Actyx/sync_wrapper/pull/2)
- and forwarding impls, starting with derivable ones and `Future`
`alloc`: clean and ensure `no_global_oom_handling` builds are warning-free
Rust 1.62.0 introduced a couple new `unused_imports` warnings
in `no_global_oom_handling` builds, making a total of 5 warnings.
<details>
```txt
warning: unused import: `Unsize`
--> library/alloc/src/boxed/thin.rs:6:33
|
6 | use core::marker::{PhantomData, Unsize};
| ^^^^^^
|
= note: `#[warn(unused_imports)]` on by default
warning: unused import: `from_fn`
--> library/alloc/src/string.rs:51:18
|
51 | use core::iter::{from_fn, FusedIterator};
| ^^^^^^^
warning: unused import: `core::ops::Deref`
--> library/alloc/src/vec/into_iter.rs:12:5
|
12 | use core::ops::Deref;
| ^^^^^^^^^^^^^^^^
warning: associated function `shrink` is never used
--> library/alloc/src/raw_vec.rs:424:8
|
424 | fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> {
| ^^^^^^
|
= note: `#[warn(dead_code)]` on by default
warning: associated function `forget_remaining_elements` is never used
--> library/alloc/src/vec/into_iter.rs:126:19
|
126 | pub(crate) fn forget_remaining_elements(&mut self) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
```
</details>
This PR cleans them and ensures no new ones are introduced
so that projects compiling `alloc` without infallible allocations
do not see them (and may want to enable `-Dwarnings`).
The couple `dead_code` ones may be reverted when some fallible
allocation support starts using them.
Simplify memory ordering intrinsics
This changes the names of the atomic intrinsics to always fully include their memory ordering arguments.
```diff
- atomic_cxchg
+ atomic_cxchg_seqcst_seqcst
- atomic_cxchg_acqrel
+ atomic_cxchg_acqrel_release
- atomic_cxchg_acqrel_failrelaxed
+ atomic_cxchg_acqrel_relaxed
// And so on.
```
- `seqcst` is no longer implied
- The failure ordering on chxchg is no longer implied in some cases, but now always explicitly part of the name.
- `release` is no longer shortened to just `rel`. That was especially confusing, since `relaxed` also starts with `rel`.
- `acquire` is no longer shortened to just `acq`, such that the names now all match the `std::sync::atomic::Ordering` variants exactly.
- This now allows for more combinations on the compare exchange operations, such as `atomic_cxchg_acquire_release`, which is necessary for #68464.
- This PR only exposes the new possibilities through unstable intrinsics, but not yet through the stable API. That's for [a separate PR](https://github.com/rust-lang/rust/pull/98383) that requires an FCP.
Suffixes for operations with a single memory order:
| Order | Before | After |
|---------|--------------|------------|
| Relaxed | `_relaxed` | `_relaxed` |
| Acquire | `_acq` | `_acquire` |
| Release | `_rel` | `_release` |
| AcqRel | `_acqrel` | `_acqrel` |
| SeqCst | (none) | `_seqcst` |
Suffixes for compare-and-exchange operations with two memory orderings:
| Success | Failure | Before | After |
|---------|---------|--------------------------|--------------------|
| Relaxed | Relaxed | `_relaxed` | `_relaxed_relaxed` |
| Relaxed | Acquire | ❌ | `_relaxed_acquire` |
| Relaxed | SeqCst | ❌ | `_relaxed_seqcst` |
| Acquire | Relaxed | `_acq_failrelaxed` | `_acquire_relaxed` |
| Acquire | Acquire | `_acq` | `_acquire_acquire` |
| Acquire | SeqCst | ❌ | `_acquire_seqcst` |
| Release | Relaxed | `_rel` | `_release_relaxed` |
| Release | Acquire | ❌ | `_release_acquire` |
| Release | SeqCst | ❌ | `_release_seqcst` |
| AcqRel | Relaxed | `_acqrel_failrelaxed` | `_acqrel_relaxed` |
| AcqRel | Acquire | `_acqrel` | `_acqrel_acquire` |
| AcqRel | SeqCst | ❌ | `_acqrel_seqcst` |
| SeqCst | Relaxed | `_failrelaxed` | `_seqcst_relaxed` |
| SeqCst | Acquire | `_failacq` | `_seqcst_acquire` |
| SeqCst | SeqCst | (none) | `_seqcst_seqcst` |
Rust 1.62.0 introduced a couple new `unused_imports` warnings
in `no_global_oom_handling` builds, making a total of 5 warnings:
```txt
warning: unused import: `Unsize`
--> library/alloc/src/boxed/thin.rs:6:33
|
6 | use core::marker::{PhantomData, Unsize};
| ^^^^^^
|
= note: `#[warn(unused_imports)]` on by default
warning: unused import: `from_fn`
--> library/alloc/src/string.rs:51:18
|
51 | use core::iter::{from_fn, FusedIterator};
| ^^^^^^^
warning: unused import: `core::ops::Deref`
--> library/alloc/src/vec/into_iter.rs:12:5
|
12 | use core::ops::Deref;
| ^^^^^^^^^^^^^^^^
warning: associated function `shrink` is never used
--> library/alloc/src/raw_vec.rs:424:8
|
424 | fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> {
| ^^^^^^
|
= note: `#[warn(dead_code)]` on by default
warning: associated function `forget_remaining_elements` is never used
--> library/alloc/src/vec/into_iter.rs:126:19
|
126 | pub(crate) fn forget_remaining_elements(&mut self) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
```
This patch cleans them so that projects compiling `alloc` without
infallible allocations do not see the warnings. It also enables
the use of `-Dwarnings`.
The couple `dead_code` ones may be reverted when some fallible
allocation support starts using them.
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Remove feature `const_option` from std
This is part of the effort to reduce the number of unstable features used by std. This one is easy as it's only used in one place.
Implement `Send` and `Sync` for `ThinBox<T>`
Just like `Box<T>`, `ThinBox<T>` owns its data on the heap, so it should
implement `Send` and `Sync` when `T` does.
This extends tracking issue #92791.
Refactor iter adapters with less macros
Just some code cleanup. Introduced a util `and_then_or_clear` for each of chain, flatten and fuse iter adapter impls. This reduces code nicely for flatten, but admittedly the other modules are more of a lateral move replacing macros with a function. But I think consistency across the modules and avoiding macros when possible is good.
attempt to optimise vectored write
benchmarked:
old:
```
test io::cursor::tests::bench_write_vec ... bench: 68 ns/iter (+/- 2)
test io::cursor::tests::bench_write_vec_vectored ... bench: 913 ns/iter (+/- 31)
```
new:
```
test io::cursor::tests::bench_write_vec ... bench: 64 ns/iter (+/- 0)
test io::cursor::tests::bench_write_vec_vectored ... bench: 747 ns/iter (+/- 27)
```
More unsafe than I wanted (and less gains) in the end, but it still does the job
libcore tests: avoid int2ptr casts
We don't need any of these pointers to actually be dereferenceable so using `ptr::invalid` should be fine. And then we can run Miri with strict provenance enforcement on the tests.
liballoc tests: avoid int2ptr cast
I think we don't need `ptr::from_exposed_addr` here; `ptr::invalid` should be enough for this test. (And this makes Miri less unhappy when running these tests.)
Just like `Box<T>`, we want `ThinBox<T>` to be covariant in `T`, but the
projection in `WithHeader<<T as Pointee>::Metadata>` was making it
invariant. This is now hidden as `WithOpaqueHeader`, which we type-cast
whenever the real `WithHeader<H>` type is needed.
This greatly reduces round-trips to fetch relevant extra information about the
token in proc macro code, and avoids RPC messages to create Group tokens.
This greatly reduces round-trips to fetch relevant extra information about the
token in proc macro code, and avoids RPC messages to create Punct tokens.
proc_macro/bridge: cache static spans in proc_macro's client thread-local state
This is the second part of https://github.com/rust-lang/rust/pull/86822, split off as requested in https://github.com/rust-lang/rust/pull/86822#pullrequestreview-1008655452. This patch removes the RPC calls required for the very common operations of `Span::call_site()`, `Span::def_site()` and `Span::mixed_site()`.
Some notes:
This part is one of the ones I don't love as a final solution from a design standpoint, because I don't like how the spans are serialized immediately at macro invocation. I think a more elegant solution might've been to reserve special IDs for `call_site`, `def_site`, and `mixed_site` at compile time (either starting at 1 or from `u32::MAX`) and making reading a Span handle automatically map these IDs to the relevant values, rather than doing extra serialization.
This would also have an advantage for potential future work to allow `proc_macro` to operate more independently from the compiler (e.g. to reduce the necessity of `proc-macro2`), as methods like `Span::call_site()` could be made to function without access to the compiler backend.
That was unfortunately tricky to do at the time, as this was the first part I wrote of the patches. After the later part (#98188, #98189), the other uses of `InternedStore` are removed meaning that a custom serialization strategy for `Span` is easier to implement.
If we want to go that path, we'll still need the majority of the work to split the bridge object and introduce the `Context` trait for free methods, and it will be easier to do after `Span` is the only user of `InternedStore` (after #98189).
Update `std::alloc::System` doc example code style
`return` on the last line of a block is unidiomatic so I don't think the example should be using that here
std: use an event-flag-based thread parker on SOLID
`Mutex` and `Condvar` are being replaced by more efficient implementations, which need thread parking themselves (see #93740). Therefore, the generic `Parker` needs to be replaced on all platforms where the new lock implementation will be used, which, after #96393, are SOLID, SGX and Hermit (more PRs coming soon).
SOLID, conforming to the [μITRON specification](http://www.ertl.jp/ITRON/SPEC/FILE/mitron-400e.pdf), has event flags, which are a thread parking primitive very similar to `Parker`. However, they do not make any atomic ordering guarantees (even though those can probably be assumed) and necessitate a system call even when the thread token is already available. Hence, this `Parker`, like the Windows parker, uses an extra atomic state variable.
I future-proofed the code by wrapping the event flag in a `WaitFlag` structure, as both SGX and Hermit can share the Parker implementation, they just have slightly different primitives (SGX uses signals and Hermit has a thread blocking API).
`````@kawadakk````` I assume you are the target maintainer? Could you test this for me?
Mitigate MMIO stale data vulnerability
Intel publicly disclosed the MMIO stale data vulnerability on June 14. To mitigate this vulnerability, compiler changes are required for the `x86_64-fortanix-unknown-sgx` target.
cc: ````@jethrogb````
