rust/library/std/src/sys/sync/rwlock, branch master

library: Migrate from `cfg_if` to `cfg_select`

2025-08-16T12:28:31+00:00

Migrate the standard library from using the external `cfg_if` crate to using the now-built-in `cfg_select` macro. This does not yet eliminate the dependency from `library/std/Cargo.toml`, because while the standard library itself no longer uses `cfg_if`, it also incorporates the `backtrace` crate, which does. Migration assisted by the following vim command (after selecting the full `cfg_if!` invocation): ``` '<,'>s/\(cfg_if::\)\?cfg_if/cfg_select/ | '<,'>s/^\( *\)} else {/\1}\r\1_ => {/c | '<,'>s/^\( *\)} else if #\[cfg(\(.*\))\] /\1}\r\1\2 => /e | '<,'>s/if #\[cfg(\(.*\))\] {/\1 => {/e ``` This is imperfect, but substantially accelerated the process. This prompts for confirmation on the `} else {` since that can also appear inside one of the arms. This also requires manual intervention to handle any multi-line conditions.

use generic Atomic type where possible

2025-04-26T23:18:08+00:00

in core/alloc/std only for now, and ignoring test files Co-authored-by: Pavel Grigorenko

update cfgs

2024-11-27T15:14:54+00:00

std: allow after-main use of synchronization primitives

2024-11-18T16:55:36+00:00

By creating an unnamed thread handle when the actual one has already been destroyed, synchronization primitives using thread parking can be used even outside the Rust runtime. This also fixes an inefficiency in the queue-based `RwLock`: if `thread::current` was not initialized yet, it will create a new handle on every parking attempt without initializing `thread::current`. The private `current_or_unnamed` function introduced here fixes this.

fix `DOWNGRADED` bit unpreserved

2024-11-16T17:31:14+00:00

Co-authored-by: Jonas Böttiger

fix memory ordering bug + bad test

2024-11-16T17:31:14+00:00

This commit fixes a memory ordering bug in the futex implementation (`Relaxed` -> `Release` on `downgrade`). This commit also removes a badly written test that deadlocked and replaces it with a more reasonable test based on an already-tested `downgrade` test from the parking-lot crate.

add safety comments for queue implementation

2024-11-16T17:31:13+00:00

add `downgrade` to `queue` implementation

2024-11-16T17:31:13+00:00

This commit adds the `downgrade` method onto the inner `RwLock` queue implementation. There are also a few other style patches included in this commit. Co-authored-by: Jonas Böttiger

modify queue implementation documentation

2024-11-16T17:31:13+00:00

This commit only has documentation changes and a few things moved around the file. The very few code changes are cosmetic: changes like turning a `match` statement into an `if let` statement or reducing indentation for long if statements. This commit also adds several safety comments on top of `unsafe` blocks that might not be immediately obvious to a first-time reader. Code "changes" are in: - `add_backlinks_and_find_tail` - `lock_contended` A majority of the changes are just expanding the comments from 80 columns to 100 columns.

add `downgrade` to `futex` implementation

2024-11-16T17:31:13+00:00