std: use futex in `Once`
Now that we have efficient locks, let's optimize the rest of `sync` as well. This PR adds a futex-based implementation for `Once`, which drastically simplifies the implementation compared to the generic version, which is provided as fallback for platforms without futex (Windows only supports them on newer versions, so it uses the fallback for now).
Instead of storing a linked list of waiters, the new implementation adds another state (`QUEUED`), which is set when there are waiting threads. These now use `futex_wait` on that state and are woken by the running thread when it finishes and notices the `QUEUED` state, thereby avoiding unnecessary calls to `futex_wake_all`.
Avoid repeated re-initialization of the BufReader buffer
Fixes https://github.com/rust-lang/rust/issues/102727
We accidentally removed this in https://github.com/rust-lang/rust/pull/98748. It looks so redundant. But it isn't.
The default `Read::read_buf` will defensively initialize the whole buffer, if any of it is indicated to be uninitialized. In uses where reads from the wrapped `Read` impl completely fill the `BufReader`, `initialized` and `filled` are the same, and this extra member isn't required. But in the reported issue, the `BufReader` wraps a `Read` impl which will _never_ fill the whole buffer. So the default `Read::read_buf` implementation repeatedly re-initializes the extra space in the buffer.
This adds back the extra `initialized` member, which ensures that the default `Read::read_buf` only zero-initialized the buffer once, and I've tried to add a comment which explains this whole situation.
unsafe keyword: trait examples and unsafe_op_in_unsafe_fn update
Having a safe `fn` in an `unsafe trait` vs an `unsafe fn` in a safe `trait` are pretty different situations, but the distinction is subtle and can confuse even seasoned Rust developers. So let's have explicit examples of both. I also removed the existing `unsafe trait` example since it was rather strange.
Also the `unsafe_op_in_unsafe_fn` lint can help disentangle the two sides of `unsafe`, so update the docs to account for that.
After calling libc::fork, the child process tried to access
a TLS variable when processing a panic. This caused
a memory allocation which is UB in the child.
To prevent this from happening, the panic handler will
not access the TLS variable in case `panic::always_abort`
was called before.
The EH actions stored in the LSDA follows the format of GCC except table
(even for LLVM-generated code). An missing action in the table is the
encoding for `Terminate`, see [1].
The currently code interprets it as `None`, as a workaround for #35011,
an issue that seems to occur in LLVM 3.7 and not after 3.9. These are
very old versions of LLVM and we don't support them anymore, so remove
this workaround and interpret them properly.
Note that LLVM currently does not emit any `Terminate` actions, but GCC
does. Although GCC backend currently doesn't do unwinding, removing it
preemptively would prevent future developers from wasting time to figure
out what's wrong.
[1]: https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/libsupc%2B%2B/eh_personality.cc#L522-L526
Add `AsFd` implementations for stdio lock types on WASI.
This mirrors the implementations on Unix platforms, and also mirrors the existing `AsRawFd` impls.
This is similar to #100892, but is for the `*Lock` types.
Update docs so that deprecated method points to relevant method
The docs for the deprecated 'park_timeout_ms' method suggests that the user 'use park_timeout' method instead (at https://doc.rust-lang.org/std/thread/index.html).
Making a similar change so that the docs for the deprecated `sleep_ms` method suggest that the user `use sleep` method instead.
Add a niche to `Duration`, unix `SystemTime`, and non-apple `Instant`
As the nanoseconds fields is always between `0` and `(NANOS_PER_SEC - 1)` inclusive, use the `rustc_layout_scalar_valid_range` attributes to create a niche in the nanosecond field of `Duration` and `Timespec` (which is used to implement unix `SystemTime` and non-apple unix `Instant`; windows `Instant` is implemented with `Duration` and therefore will also benefit). This change has the benefit of making `Option<T>` the same size as `T` for the previously mentioned types. Also shrinks the nanoseconds field of `Timespec` to a `u32` as nanoseconds do not need the extra range of an `i64`, shrinking `Timespec` by 4 bytes on 32-bit platforms.
r? ```@joshtriplett```
Make `std::os::fd` public.
`std::os::fd` defines types like `OwnedFd` and `RawFd` and is common
between Unix and non-Unix platforms that share a basic file-descriptor
concept. Rust currently uses this internally to simplify its own code,
but it would be useful for external users in the same way, so make it
public.
This means that `OwnedFd` etc. will all appear in three places, for
example on unix platforms:
- `std::os::fd::OwnedFd`
- `std::os::unix::io::OwnedFd`
- `std::os::unix::prelude::OwnedFd`
r? `````@joshtriplett`````
Suggest unwrapping `???<T>` if a method cannot be found on it but is present on `T`.
This suggests various ways to get inside wrapper types if the method cannot be found on the wrapper type, but is present on the wrappee.
For this PR, those wrapper types include `Localkey`, `MaybeUninit`, `RefCell`, `RwLock` and `Mutex`.
Stabilize bench_black_box
This PR stabilize `feature(bench_black_box)`.
```rust
pub fn black_box<T>(dummy: T) -> T;
```
The FCP was completed in https://github.com/rust-lang/rust/issues/64102.
`@rustbot` label +T-libs-api -T-libs
Stabilize `#![feature(mixed_integer_ops)]`
Tracked and FCP completed in #87840.
````@rustbot```` label +T-libs-api +S-waiting-on-review +relnotes
r? rust-lang/t-libs-api
