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.
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
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````
Windows: Iterative `remove_dir_all`
This will allow better strategies for use of memory and File handles. However, fully taking advantage of that is left to future work.
Note to reviewer: It's probably best to view the `remove_dir_all_recursive` as a new function. The diff is not very helpful (imho).
Make RwLockReadGuard covariant
Hi, first time contributor here, if anything is not as expected, please let me know.
`RwLockReadGoard`'s type constructor is invariant. Since it behaves like a smart pointer to an immutable reference, there is no reason that it should not be covariant. Take e.g.
```
fn test_read_guard_covariance() {
fn do_stuff<'a>(_: RwLockReadGuard<'_, &'a i32>, _: &'a i32) {}
let j: i32 = 5;
let lock = RwLock::new(&j);
{
let i = 6;
do_stuff(lock.read().unwrap(), &i);
}
drop(lock);
}
```
where the compiler complains that &i doesn't live long enough. If `RwLockReadGuard` is covariant, then the above code is accepted because the lifetime can be shorter than `'a`.
In order for `RwLockReadGuard` to be covariant, it can't contain a full reference to the `RwLock`, which can never be covariant (because it exposes a mutable reference to the underlying data structure). By reducing the data structure to the required pieces of `RwLock`, the rest falls in place.
If there is a better way to do a test that tests successful compilation, please let me know.
Fixes#80392
Fix documentation for `with_capacity` and `reserve` families of methods
Fixes#95614
Documentation for the following methods
- `with_capacity`
- `with_capacity_in`
- `with_capacity_and_hasher`
- `reserve`
- `reserve_exact`
- `try_reserve`
- `try_reserve_exact`
was inconsistent and often not entirely correct where they existed on the following types
- `Vec`
- `VecDeque`
- `String`
- `OsString`
- `PathBuf`
- `BinaryHeap`
- `HashSet`
- `HashMap`
- `BufWriter`
- `LineWriter`
since the allocator is allowed to allocate more than the requested capacity in all such cases, and will frequently "allocate" much more in the case of zero-sized types (I also checked `BufReader`, but there the docs appear to be accurate as it appears to actually allocate the exact capacity).
Some effort was made to make the documentation more consistent between types as well.
Document Rust's stance on `/proc/self/mem`
Add documentation to `std::os::unix::io` describing Rust's stance on
`/proc/self/mem`, treating it as an external entity which is outside
the scope of Rust's safety guarantees.
`Stdio::makes_pipe`
Wrappers around `std::process::Command` may want to be able to override pipe creation. However, [`std::process::Stdio`](https://doc.rust-lang.org/std/process/struct.Stdio.html) is opaque so there's no way to tell if `Command` was told to create new pipes or not.
This is in some ways a more generic (and cross-platform) alternative to #97149. However, unlike that feature, this comes with the price of the user needing to actually create their own pipes rather than reusing the std one. So I think it stands (or not) on its own.
# Example
```rust
#![feature(stdio_makes_pipe)]
use std::process::Stdio;
let io = Stdio::piped();
assert_eq!(io.makes_pipe(), true);
```
Windows: `CommandExt::async_pipes`
Discussed in https://github.com/tokio-rs/tokio/issues/4670 was the need for third party crates to be able to force `process::Command::spawn` to create pipes as async.
This implements the suggestion for a `async_pipes` method that gives third party crates that option.
# Example:
```rust
use std::process::{Command, Stdio};
Command::new("cmd")
.async_pipes(true)
.stdin(Stdio::piped())
.stdout(Stdio::piped())
.stderr(Stdio::piped())
.spawn()
.unwrap();
```
Stabilize `Path::try_exists()` and improve doc
This stabilizes the `Path::try_exists()` method which returns
`Result<bool, io::Error>` instead of `bool` allowing handling of errors
unrelated to the file not existing. (e.g permission errors)
Along with the stabilization it also:
* Warns that the `exists()` method is error-prone and suggests to use
the newly stabilized one.
* Suggests it instead of `metadata()` to handle errors.
* Mentions TOCTOU bugs to avoid false assumption that `try_exists()` is
completely safe fixed version of `exists()`.
* Renames the feature of still-unstable `std::fs::try_exists()` to
`fs_try_exists` to avoid name conflict.
The tracking issue #83186 remains open to track `fs_try_exists`.
Documentation for the following methods
with_capacity
with_capacity_in
with_capacity_and_hasher
reserve
reserve_exact
try_reserve
try_reserve_exact
was inconsistent and often not entirely correct where they existed on the following types
Vec
VecDeque
String
OsString
PathBuf
BinaryHeap
HashSet
HashMap
BufWriter
LineWriter
since the allocator is allowed to allocate more than the requested capacity in all such cases, and will frequently "allocate" much more in the case of zero-sized types (I also checked BufReader, but there the docs appear to be accurate as it appears to actually allocate the exact capacity).
Some effort was made to make the documentation more consistent between types as well.
Fix with_capacity* methods for Vec
Fix *reserve* methods for Vec
Fix docs for *reserve* methods of VecDeque
Fix docs for String::with_capacity
Fix docs for *reserve* methods of String
Fix docs for OsString::with_capacity
Fix docs for *reserve* methods on OsString
Fix docs for with_capacity* methods on HashSet
Fix docs for *reserve methods of HashSet
Fix docs for with_capacity* methods of HashMap
Fix docs for *reserve methods on HashMap
Fix expect messages about OOM in doctests
Fix docs for BinaryHeap::with_capacity
Fix docs for *reserve* methods of BinaryHeap
Fix typos
Fix docs for with_capacity on BufWriter and LineWriter
Fix consistent use of `hasher` between `HashMap` and `HashSet`
Fix warning in doc test
Add test for capacity of vec with ZST
Fix doc test error
once cell renamings
This PR does the renamings proposed in https://github.com/rust-lang/rust/issues/74465#issuecomment-1153703128
- Move/rename `lazy::{OnceCell, Lazy}` to `cell::{OnceCell, LazyCell}`
- Move/rename `lazy::{SyncOnceCell, SyncLazy}` to `sync::{OnceLock, LazyLock}`
(I used `Lazy...` instead of `...Lazy` as it seems to be more consistent, easier to pronounce, etc)
```@rustbot``` label +T-libs-api -T-libs
Avoid `thread::panicking()` in non-poisoning methods of `Mutex` and `RwLock`
`Mutex::lock()` and `RwLock::write()` are poison-guarded against panics,
in that they set the poison flag if a panic occurs while they're locked.
But if we're already in a panic (`thread::panicking()`), they leave the
poison flag alone.
That check is a bit of a waste for methods that never set the poison
flag though, namely `get_mut()`, `into_inner()`, and `RwLock::read()`.
These use-cases are now split to avoid that unnecessary call.
