Stabilize `rwlock_downgrade` library feature #143191

connortsui20 · 2025-06-29T12:51:00Z

Tracking Issue: #128203

Method to be stabilized:

impl<'a, T: ?Sized> RwLockWriteGuard<'a, T> {
    pub fn downgrade(s: Self) -> RwLockReadGuard<'a, T> {}
}

I would like to point out that my documentation comment is longer than ideal, but at the same time I don't really know how else to show why downgrade is actually necessary (instead of just unlocking and relocking). If anyone has ideas for making this more concise that would be great! I have made the documentation a bit more clear.

Stabilization report: #128203 (comment)

rustbot · 2025-06-29T12:51:04Z

r? @tgross35

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Amanieu · 2025-07-01T16:04:37Z

This means that we can never go back to pthreads to back our locks, but that seems fine since the pthreads API has many issues around UB and movability.

@rfcbot merge

Amanieu · 2025-07-01T17:24:55Z

@rfcbot merge

rfcbot · 2025-07-01T17:25:04Z

Team member @Amanieu has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

connortsui20 · 2025-07-25T15:42:05Z

Gentle bump on the proposed FCP above! @BurntSushi @joshtriplett @m-ou-se

This commit is a purely cosmetic change to the documentation and ordering of items in the `rwlock.rs` file. List of changes (lots of small things): - Clean up some of the existing field doc comments - Add documentation for every field in struct definitions - Consolidate related implementation blocks (1 implementation block per guard instead of 2) - Use the lifetime name `'rwlock` instead of `'a` - Reorder implementation blocks to be consistent across the entire file (follows the order `ReadGuard`, `WriteGuard`, `MappedReadGuard`, MappedWriteGuard`) - Move simple trait implementations to the bottom of the file - Rename the `poison` field in `MappedRwLockWriteGuard` to posion_guard` - Cut off comments at 100 columns - Update the documentation of `downgrade` to match https://github.com rust-lang/pull/143191

bors · 2025-08-23T09:05:00Z

☔ The latest upstream changes (presumably #145773) made this pull request unmergeable. Please resolve the merge conflicts.

connortsui20 · 2025-08-25T09:47:31Z

@rustbot label -S-waiting-on-author

connortsui20 · 2025-08-26T19:40:13Z

Bump on the proposed FCP above! @BurntSushi @joshtriplett @m-ou-se

(link)

tgross35 · 2025-09-24T16:52:14Z

It's been a little while, nominating just to bump the fcp checkboxes and make sure there aren't any new concerns.

@rustbot label +I-libs-api-nominated

rust-rfcbot · 2025-09-30T15:14:30Z

🔔 This is now entering its final comment period, as per the review above. 🔔

rust-rfcbot · 2025-10-10T15:16:49Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

tgross35 · 2025-10-15T09:28:57Z

@bors r+

bors · 2025-10-15T09:29:00Z

📌 Commit 780319a has been approved by tgross35

It is now in the queue for this repository.

tgross35 · 2025-10-15T09:29:04Z

@bors rollup

…grade, r=tgross35 Stabilize `rwlock_downgrade` library feature Tracking Issue: rust-lang#128203 Method to be stabilized: ```rust impl<'a, T: ?Sized> RwLockWriteGuard<'a, T> { pub fn downgrade(s: Self) -> RwLockReadGuard<'a, T> {} } ``` ~~I would like to point out that my documentation comment is longer than ideal, but at the same time I don't really know how else to show why `downgrade` is actually necessary (instead of just unlocking and relocking). If anyone has ideas for making this more concise that would be great!~~ I have made the documentation a bit more clear. Stabilization report: rust-lang#128203 (comment)

Rollup of 5 pull requests Successful merges: - #143191 (Stabilize `rwlock_downgrade` library feature) - #147000 (std: Add Motor OS std library port) - #147670 (some `ErrorGuaranteed` cleanups) - #147716 (Fix some comments) - #147718 (miri: use allocator_shim_contents codegen helper) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 11 pull requests Successful merges: - #143191 (Stabilize `rwlock_downgrade` library feature) - #147444 (Allow printing a fully-qualified path in `def_path_str`) - #147527 (Update t-compiler beta nomination Zulip msg) - #147670 (some `ErrorGuaranteed` cleanups) - #147676 (Return spans out of `is_doc_comment` to reduce reliance on `.span()` on attributes) - #147708 (const `mem::drop`) - #147710 (Fix ICE when using contracts on async functions) - #147716 (Fix some comments) - #147718 (miri: use allocator_shim_contents codegen helper) - #147729 (ignore boring locals when explaining why a borrow contains a point due to drop of a live local under polonius) - #147742 (Revert unintentional whitespace changes to rustfmt-excluded file) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #143191 - connortsui20:stabilize-rwlock-downgrade, r=tgross35 Stabilize `rwlock_downgrade` library feature Tracking Issue: #128203 Method to be stabilized: ```rust impl<'a, T: ?Sized> RwLockWriteGuard<'a, T> { pub fn downgrade(s: Self) -> RwLockReadGuard<'a, T> {} } ``` ~~I would like to point out that my documentation comment is longer than ideal, but at the same time I don't really know how else to show why `downgrade` is actually necessary (instead of just unlocking and relocking). If anyone has ideas for making this more concise that would be great!~~ I have made the documentation a bit more clear. Stabilization report: #128203 (comment)

Rollup of 11 pull requests Successful merges: - rust-lang/rust#143191 (Stabilize `rwlock_downgrade` library feature) - rust-lang/rust#147444 (Allow printing a fully-qualified path in `def_path_str`) - rust-lang/rust#147527 (Update t-compiler beta nomination Zulip msg) - rust-lang/rust#147670 (some `ErrorGuaranteed` cleanups) - rust-lang/rust#147676 (Return spans out of `is_doc_comment` to reduce reliance on `.span()` on attributes) - rust-lang/rust#147708 (const `mem::drop`) - rust-lang/rust#147710 (Fix ICE when using contracts on async functions) - rust-lang/rust#147716 (Fix some comments) - rust-lang/rust#147718 (miri: use allocator_shim_contents codegen helper) - rust-lang/rust#147729 (ignore boring locals when explaining why a borrow contains a point due to drop of a live local under polonius) - rust-lang/rust#147742 (Revert unintentional whitespace changes to rustfmt-excluded file) r? `@ghost` `@rustbot` modify labels: rollup

rustbot assigned tgross35 Jun 29, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jun 29, 2025

tgross35 added the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Jun 30, 2025

tgross35 mentioned this pull request Jun 30, 2025

Tracking Issue for rwlock_downgrade #128203

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Amanieu removed the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Jul 1, 2025

rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Jul 1, 2025

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Amanieu added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. and removed T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jul 1, 2025

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rfcbot removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Jul 1, 2025

rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Jul 1, 2025

connortsui20 force-pushed the stabilize-rwlock-downgrade branch from 2c39d70 to a3af141 Compare July 17, 2025 14:12

connortsui20 mentioned this pull request Jul 19, 2025

Reoganize poison::rwlock file #144175

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tgross35 added S-waiting-on-fcp Status: PR is in FCP and is awaiting for FCP to complete. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 29, 2025

connortsui20 force-pushed the stabilize-rwlock-downgrade branch from a3af141 to 9e3de55 Compare July 29, 2025 15:58

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Aug 25, 2025

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rust-rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Sep 30, 2025

Amanieu removed the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Sep 30, 2025

rustbot mentioned this pull request Oct 10, 2025

Tracking issue for release notes of #143191: Stabilize rwlock_downgrade library feature #147557

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esote mentioned this pull request Oct 11, 2025

Stabilize rwlock_downgrade feature #147563

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tgross35 approved these changes Oct 15, 2025

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bors added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Oct 15, 2025

matthiaskrgr mentioned this pull request Oct 15, 2025

Rollup of 5 pull requests #147720

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matthiaskrgr mentioned this pull request Oct 15, 2025

Rollup of 11 pull requests #147745

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bors merged commit 8d6356b into rust-lang:master Oct 16, 2025
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rustbot added this to the 1.92.0 milestone Oct 16, 2025

Stabilize rwlock_downgrade library feature #143191

Stabilize rwlock_downgrade library feature #143191

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Stabilize `rwlock_downgrade` library feature #143191

Stabilize `rwlock_downgrade` library feature #143191

connortsui20 commented Jun 29, 2025 •

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