std: split up the `thread` module #148765

joboet · 2025-11-09T20:06:07Z

Almost all functionality in std::thread is currently implemented in thread/mod.rs, resulting in a huge file with more than 2000 lines and multiple, interoperating unsafe sections. This PR splits the file up into multiple different private modules, each implementing mostly independent parts of the functionality. The only remaining unsafe interplay is that of the lifecycle and scope modules, the spawn_scoped implementation relies on the live thread count being updated correctly by the lifecycle module.

This PR contains no functional changes and only moves code around for the most part, with a few notable exceptions:

with_current_name is moved to the already existing current module and now uses the name method instead of calculating the name from private fields. The old code was just a reimplementation of that method anyway.
The private JoinInner type used to implement both join handles now has some more methods (is_finished, thread and the AsInner/IntoInner implementations) to avoid having to expose private fields and their invariants.
The private spawn_unchecked_ (note the underscore) method of Builder is now a freestanding function in lifecycle.

The rest of the changes are just visibility annotations.

I realise this PR ended up quite large – let me know if there is anyway I can aid the review process.

Edit: I've simplified the diff by adding an intermediate commit that creates all the new files by duplicating mod.rs. The actual changes in the second commit thus appear to delete the non-relevant parts from the respective file.

rustbot · 2025-11-09T20:06:12Z

r? @ChrisDenton

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rustbot · 2025-11-09T21:19:54Z

The Miri subtree was changed

cc @rust-lang/miri

RalfJung · 2025-11-10T10:29:44Z

library/std/src/thread/lifecycle.rs

Would be good to have some module-level docs for this, the name isn't exactly self-explaining.

ChrisDenton · 2025-11-10T15:23:38Z

Hm, I'm going to nominate this for @rust-lang/libs. Not because it particularly needs discussion but just for awareness. If anyone has anything they'd like to change/add about this PR I'd prefer they speak up now then have more churn after this is merged.

I've not finished considering it yet but my initial thought is that it seems to have swung a bit too heavily from (almost) everything in one file to (almost) everything in separate files. For example, JoinHandle is essentially a small shim that simply forwards to the underlying implementation and the only unsafe is the Send and Sync impls. Builder is somewhat similarly trivial.

Amanieu · 2025-11-19T03:10:26Z

This was discussed in @rust-lang/libs meeting last week. We're OK with this change, though some people had concerns that some of the logic was split across too many files.

ChrisDenton · 2025-11-26T17:25:53Z

I was convinced that this is ok. Well, I'm still a bit nervous about some of the smaller files but I'm willing to see how it goes.

@bors r+

bors · 2025-11-26T17:25:56Z

📌 Commit 693055f has been approved by ChrisDenton

It is now in the queue for this repository.

std: split up the `thread` module Almost all functionality in `std::thread` is currently implemented in `thread/mod.rs`, resulting in a *huge* file with more than 2000 lines and multiple, interoperating `unsafe` sections. This PR splits the file up into multiple different private modules, each implementing mostly independent parts of the functionality. The only remaining `unsafe` interplay is that of the `lifecycle` and `scope` modules, the `spawn_scoped` implementation relies on the live thread count being updated correctly by the `lifecycle` module. This PR contains no functional changes and only moves code around for the most part, with a few notable exceptions: * `with_current_name` is moved to the already existing `current` module and now uses the `name` method instead of calculating the name from private fields. The old code was just a reimplementation of that method anyway. * The private `JoinInner` type used to implement both join handles now has some more methods (`is_finished`, `thread` and the `AsInner`/`IntoInner` implementations) to avoid having to expose private fields and their invariants. * The private `spawn_unchecked_` (note the underscore) method of `Builder` is now a freestanding function in `lifecycle`. The rest of the changes are just visibility annotations. I realise this PR ended up quite large – let me know if there is anyway I can aid the review process. Edit: I've simplified the diff by adding an intermediate commit that creates all the new files by duplicating `mod.rs`. The actual changes in the second commit thus appear to delete the non-relevant parts from the respective file.

Rollup of 19 pull requests Successful merges: - #148048 (Stabilize `maybe_uninit_write_slice`) - #148641 (Add a diagnostic attribute for special casing const bound errors for non-const impls) - #148765 (std: split up the `thread` module) - #149074 (Add Command::get_env_clear) - #149097 (num: Implement `uint_gather_scatter_bits` feature for unsigned integers) - #149131 (optimize `slice::Iter::next_chunk`) - #149190 (Forbid `CHECK: br` and `CHECK-NOT: br` in codegen tests (suggest `br {{.*}}` instead)) - #149239 (clarify float min/max behavios for NaNs and signed zeros) - #149243 (Fix typo and clarify bootstrap change tracker entry) - #149270 (implement `Iterator::{exactly_one, collect_array}`) - #149295 (Suggest _bytes versions of endian-converting methods) - #149301 (Motor OS: make decode_error_kind more comprehensive) - #149306 (bootstrap: Miri now handles jemalloc like everything else) - #149325 (rustdoc: add regression test for #140968) - #149332 (fix rustdoc search says “Consider searching for "null" instead.” #149324) - #149349 (Fix typo in comment.) - #149353 (Tidying up UI tests [3/N]) - #149355 (Document that `build.description` affects symbol mangling and crate IDs) - #149360 (Enable CI download for windows-gnullvm) r? `@ghost` `@rustbot` modify labels: rollup

Zalathar · 2025-11-27T01:09:24Z

Failed in rollup in aarch64-msvc-1: #149361 (comment)

Unfortunately, some of these internal module paths show up in debuginfo tests that need adjustment.

@bors r-

joboet · 2025-11-28T14:59:18Z

@bors r=@ChrisDenton

bors · 2025-11-28T14:59:20Z

📌 Commit 17bca49 has been approved by ChrisDenton

It is now in the queue for this repository.

joboet · 2025-11-29T14:06:29Z

@bors r-
I need to rebase first...

joboet · 2025-11-29T15:01:53Z

Rebase on top of #144465.
I made a mistake while rebasing, here is the correct diff.

@rustbot ready

ChrisDenton · 2025-11-29T16:17:08Z

@bors r+

bors · 2025-11-29T16:17:10Z

📌 Commit c22b819 has been approved by ChrisDenton

It is now in the queue for this repository.

Rollup of 3 pull requests Successful merges: - #148746 (const validation: remove check for mutable refs in final value of const) - #148765 (std: split up the `thread` module) - #149454 (resolve: Identifier resolution refactorings) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #148765 - joboet:split-up-thread, r=ChrisDenton std: split up the `thread` module Almost all functionality in `std::thread` is currently implemented in `thread/mod.rs`, resulting in a *huge* file with more than 2000 lines and multiple, interoperating `unsafe` sections. This PR splits the file up into multiple different private modules, each implementing mostly independent parts of the functionality. The only remaining `unsafe` interplay is that of the `lifecycle` and `scope` modules, the `spawn_scoped` implementation relies on the live thread count being updated correctly by the `lifecycle` module. This PR contains no functional changes and only moves code around for the most part, with a few notable exceptions: * `with_current_name` is moved to the already existing `current` module and now uses the `name` method instead of calculating the name from private fields. The old code was just a reimplementation of that method anyway. * The private `JoinInner` type used to implement both join handles now has some more methods (`is_finished`, `thread` and the `AsInner`/`IntoInner` implementations) to avoid having to expose private fields and their invariants. * The private `spawn_unchecked_` (note the underscore) method of `Builder` is now a freestanding function in `lifecycle`. The rest of the changes are just visibility annotations. I realise this PR ended up quite large – let me know if there is anyway I can aid the review process. Edit: I've simplified the diff by adding an intermediate commit that creates all the new files by duplicating `mod.rs`. The actual changes in the second commit thus appear to delete the non-relevant parts from the respective file.

rustbot assigned ChrisDenton Nov 9, 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 Nov 9, 2025

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joboet force-pushed the split-up-thread branch from 1db1ae4 to d9260a8 Compare November 9, 2025 21:19

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joboet force-pushed the split-up-thread branch from e3ebbfb to 0d7d1fa Compare November 10, 2025 08:01

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RalfJung reviewed Nov 10, 2025

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library/std/src/thread/lifecycle.rs

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Would be good to have some module-level docs for this, the name isn't exactly self-explaining.

ChrisDenton added the I-libs-nominated Nominated for discussion during a libs team meeting. label Nov 10, 2025

joboet force-pushed the split-up-thread branch from 0d7d1fa to 693055f Compare November 11, 2025 09:55

Amanieu removed the I-libs-nominated Nominated for discussion during a libs team meeting. label Nov 19, 2025

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 26, 2025

Zalathar mentioned this pull request Nov 26, 2025

Rollup of 19 pull requests #149361

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std: split up the thread module (preparation)

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joboet force-pushed the split-up-thread branch from 17bca49 to 495e0c3 Compare November 29, 2025 14:55

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joboet added 4 commits November 29, 2025 15:59

std: split up the thread module

8b08da2

update references to thread implementation in tests

912f7f9

std: update broken links in thread module

9c6e0f6

update type names in debuginfo tests

c22b819

joboet force-pushed the split-up-thread branch from 495e0c3 to c22b819 Compare November 29, 2025 14:59

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matthiaskrgr mentioned this pull request Nov 29, 2025

Rollup of 3 pull requests #149462

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bors merged commit c93801c into rust-lang:main Nov 29, 2025
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rustbot added this to the 1.93.0 milestone Nov 29, 2025

std: split up the thread module #148765

std: split up the thread module #148765

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std: split up the `thread` module #148765

std: split up the `thread` module #148765

joboet commented Nov 9, 2025 •

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