Make sentinel value configurable in `library/std/src/sys_common/thread_local_key.rs`
This is an excerpt of a changeset for the QNX/Neutrino OS. To make the patch for QNX smaller and easier to review, I've extracted this change (which is OS independent). I would be surprised if no other OS is also affected.
All this patch does is to define a `const` for a sentinel value instead of using it directly at several places.
There are OSs that always return the lowest free value. The algorithm in `lazy_init` always avoids keys with the sentinel value.
In affected OSs, this means that each call to `lazy_init` will always request two keys from the OS and returns/frees the first one (with sentinel value) immediately afterwards.
By making the sentinel value configurable, affected OSs can use a different value than zero to prevent this performance issue.
On QNX/Neutrino, it is planned to use a different sentinel value:
```rust
// Define a sentinel value that is unlikely to be returned
// as a TLS key (but it may be returned).
#[cfg(not(target_os = "nto"))]
const KEY_SENTVAL: usize = 0;
// On QNX/Neutrino, 0 is always returned when currently not in use.
// Using 0 would mean to always create two keys and remote the first
// one (with value of 0) immediately afterwards.
#[cfg(target_os = "nto")]
const KEY_SENTVAL: usize = libc::PTHREAD_KEYS_MAX + 1;
```
It seems like no other OS defines `PTHREAD_KEYS_MAX` in Rusts libc, but `limits.h` on unix systems does.
available_parallelism: Gracefully handle zero value cfs_period_us
There seem to be some scenarios where the cgroup cpu quota field `cpu.cfs_period_us` can contain `0`. This field is used to determine the "amount" of parallelism suggested by the function `std:🧵:available_parallelism`
A zero value of this field cause a panic when `available_parallelism()` is invoked. This issue was detected by the call from binaries built by `cargo test`. I really don't feel like `0` is a good value for `cpu.cfs_period_us`, but I also don't think applications should panic if this value is seen.
This panic started happening with rust 1.64.0.
This case is gracefully handled by other projects which read this information: [num_cpus](e437b9d908/src/linux.rs (L207-L210)), [ninja](https://github.com/ninja-build/ninja/pull/2174/files), [dotnet](c4341d45ac/src/coreclr/pal/src/misc/cgroup.cpp (L481-L483))
Before this change, running `cargo test` in environments configured as described above would trigger this panic:
```
$ RUST_BACKTRACE=1 cargo test
Finished test [unoptimized + debuginfo] target(s) in 3.55s
Running unittests src/main.rs (target/debug/deps/x-9a42e145aca2934d)
thread 'main' panicked at 'attempt to divide by zero', library/std/src/sys/unix/thread.rs:546:70
stack backtrace:
0: rust_begin_unwind
1: core::panicking::panic_fmt
2: core::panicking::panic
3: std::sys::unix:🧵:cgroups::quota
4: std::sys::unix:🧵:available_parallelism
5: std:🧵:available_parallelism
6: test::helpers::concurrency::get_concurrency
7: test::console::run_tests_console
8: test::test_main
9: test::test_main_static
10: x::main
at ./src/main.rs:1:1
11: core::ops::function::FnOnce::call_once
at /tmp/rust-1.64-1.64.0-1/library/core/src/ops/function.rs:248:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
error: test failed, to rerun pass '--bin x'
```
I've tested this change in an environment which has the bad (questionable?) setup and rebuilding the test executable against a fixed std library fixes the panic.
Move `ReentrantMutex` to `std::sync`
If I understand #84187 correctly, `sys_common` should not contain platform-independent code, even if it is private.
Implement allow-by-default `multiple_supertrait_upcastable` lint
The lint detects when an object-safe trait has multiple supertraits.
Enabled in libcore and liballoc as they are low-level enough that many embedded programs will use them.
r? `@nikomatsakis`
Fix backoff doc to match implementation
The commit 8dddb2294310ad3e8ce0b2af735a702ad72a9a99 in the crossbeam-channel PR (#93563) changed the backoff strategy to be quadratic instead of exponential. This updates the doc to prevent confusion.
Test leaking of BinaryHeap Drain iterators
Add test cases about forgetting the `BinaryHeap::Drain` iterator, and slightly fortifies some other test cases.
Consists of separate commits that I don't think are relevant on their own (but I'll happily turn these into more PRs if desired).
Clarify docs of `RefCell`
Comparison operators only panic if the `RefCell` is mutably borrowed, and `RefCell::swap()` can also panic if swapping a `RefCell` with itself.
Use correct clock in `park_timeout` on Horizon
Horizon does not support using `CLOCK_MONOTONIC` with condition variables, so use the system time instead.
Fix UnsafeCell Documentation Spelling Error
This fixes the spelling of "deallocated" (instead of the original "deallocted") In the `cell.rs` source file. Honestly probably not worth the time to evaluate, but since it doesn't involve any code change, I figure why not?
Update the documentation of `Vec` to use `extend(array)` instead of `extend(array.iter().copied())`
Another option is to use `extend_from_slice()` (that may be faster), but I find this approach cleaner.
Fix a formatting error in Iterator::for_each docs
There is a formatting error (extra space in an assignment) in the documentation of `core::iter::Iterator::for_each`, which I have fixed in this pull request.
More inference-friendly API for lazy
The signature for new was
```
fn new<F>(f: F) -> Lazy<T, F>
```
Notably, with `F` unconstrained, `T` can be literally anything, and just `let _ = Lazy::new(|| 92)` would not typecheck.
This historiacally was a necessity -- `new` is a `const` function, it couldn't have any bounds. Today though, we can move `new` under the `F: FnOnce() -> T` bound, which gives the compiler enough data to infer the type of T from closure.
abort immediately on bad mem::zeroed/uninit
Now that we have non-unwinding panics, let's use them for these assertions. This re-establishes the property that `mem::uninitialized` and `mem::zeroed` will never unwind -- the earlier approach of causing panics here sometimes led to hard-to-debug segfaults when the surrounding code was not able to cope with the unexpected unwinding.
Cc `@bjorn3` I did not touch cranelift but I assume it needs a similar patch. However it has a `codegen_panic` abstraction that I did not want to touch since I didn't know how else it is used.
add ptr::from_{ref,mut}
We have methods to avoid almost all `as` casts around raw pointer handling, except for the initial cast from reference to raw pointer. These new methods close that gap.
(I also moved `null_mut` next to `null` to keep the file consistently organized.)
r? libs-api
Tracking issue: https://github.com/rust-lang/rust/issues/106116
Rollup of 6 pull requests
Successful merges:
- #105465 (Improve top-level docs)
- #105872 (Suggest remove last method call when type coerce with expected type)
- #106032 (std: only use LFS function on glibc)
- #106078 (Provide more context on FileCheck failures)
- #106100 (Codegen test for derived `<` on trivial newtype [TEST ONLY])
- #106109 (rustdoc: make line number CSS for doc comment and scraped the same)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
char: µoptimise UTF-16 surrogates decoding
According to Godbolt¹, on x86_64 using binary and produces slightly
better code than using subtraction. Readability of both is pretty
much equivalent so might just as well use the shorter option.
¹ https://rust.godbolt.org/z/9jM3ejbMx
According to Godbolt¹, on x86_64 using binary and produces slightly
better code than using subtraction. Readability of both is pretty
much equivalent so might just as well use the shorter option.
¹ https://rust.godbolt.org/z/9jM3ejbMx
Rollup of 8 pull requests
Successful merges:
- #105584 (add assert messages if chunks/windows are length 0)
- #105602 (interpret: add read_machine_[ui]size convenience methods)
- #105824 (str.lines() docstring: clarify that line endings are not returned)
- #105980 (Refer to "Waker" rather than "RawWaker" in `drop` comment)
- #105986 (Fix typo in reading_half_a_pointer.rs)
- #105995 (Add regression test for #96530)
- #106008 (Sort lint_groups in no_lint_suggestion)
- #106014 (Add comment explaining what the scrape-examples-toggle.goml GUI test is about)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
