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Use const initialized thread locals where possible #4677

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merged 4 commits into from
Jun 29, 2022

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a1phyr
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@a1phyr a1phyr commented May 10, 2022

Motivation

This PR uses a new feature (stabilized in Rust 1.59) to initialize some thread-local statics at compile time. This should bring better performances and code size.

Drawbacks

It adds back a build script to check the version of rustc.

@github-actions github-actions bot added the R-loom Run loom tests on this PR label May 10, 2022
@Noah-Kennedy
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I'm not entirely sure how I feel about this approach to getting by our MSRV. @Darksonn @hawkw thoughts?

@Darksonn Darksonn added the A-tokio Area: The main tokio crate label May 10, 2022
@Darksonn
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I think we have done something similar in the past for #[track_caller].

@hawkw
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hawkw commented May 10, 2022

Yeah, we've done similar things in the past, so I'm fine with introducing the build script again provided that the benefit outweighs the extra complexity.

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This looks good to me.

@Darksonn Darksonn enabled auto-merge (squash) June 29, 2022 09:01
@Darksonn Darksonn merged commit 7f92bce into tokio-rs:master Jun 29, 2022
crapStone pushed a commit to Calciumdibromid/CaBr2 that referenced this pull request Jul 18, 2022
This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [tokio](https://tokio.rs) ([source](https://github.com/tokio-rs/tokio)) | dependencies | minor | `1.19.2` -> `1.20.0` |
| [tokio](https://tokio.rs) ([source](https://github.com/tokio-rs/tokio)) | dev-dependencies | minor | `1.19.2` -> `1.20.0` |

---

### Release Notes

<details>
<summary>tokio-rs/tokio</summary>

### [`v1.20.0`](https://github.com/tokio-rs/tokio/releases/tag/tokio-1.20.0)

[Compare Source](tokio-rs/tokio@tokio-1.19.2...tokio-1.20.0)

##### 1.20.0 (July 12, 2022)

##### Added

-   tokio: add track_caller to public APIs ([#&#8203;4772], [#&#8203;4791], [#&#8203;4793], [#&#8203;4806], [#&#8203;4808])
-   sync: Add `has_changed` method to `watch::Ref` ([#&#8203;4758])

##### Changed

-   time: remove `src/time/driver/wheel/stack.rs` ([#&#8203;4766])
-   rt: clean up arguments passed to basic scheduler ([#&#8203;4767])
-   net: be more specific about winapi features ([#&#8203;4764])
-   tokio: use const initialized thread locals where possible ([#&#8203;4677])
-   task: various small improvements to LocalKey ([#&#8203;4795])

##### Fixed

##### Documented

-   fs: warn about performance pitfall ([#&#8203;4762])
-   chore: fix spelling ([#&#8203;4769])
-   sync: document spurious failures in oneshot ([#&#8203;4777])
-   sync: add warning for watch in non-Send futures ([#&#8203;4741])
-   chore: fix typo ([#&#8203;4798])

##### Unstable

-   joinset: rename `join_one` to `join_next` ([#&#8203;4755])
-   rt: unhandled panic config for current thread rt ([#&#8203;4770])

[#&#8203;4677]: tokio-rs/tokio#4677

[#&#8203;4741]: tokio-rs/tokio#4741

[#&#8203;4755]: tokio-rs/tokio#4755

[#&#8203;4758]: tokio-rs/tokio#4758

[#&#8203;4762]: tokio-rs/tokio#4762

[#&#8203;4764]: tokio-rs/tokio#4764

[#&#8203;4766]: tokio-rs/tokio#4766

[#&#8203;4767]: tokio-rs/tokio#4767

[#&#8203;4769]: tokio-rs/tokio#4769

[#&#8203;4770]: tokio-rs/tokio#4770

[#&#8203;4772]: tokio-rs/tokio#4772

[#&#8203;4777]: tokio-rs/tokio#4777

[#&#8203;4791]: tokio-rs/tokio#4791

[#&#8203;4793]: tokio-rs/tokio#4793

[#&#8203;4795]: tokio-rs/tokio#4795

[#&#8203;4798]: tokio-rs/tokio#4798

[#&#8203;4806]: tokio-rs/tokio#4806

[#&#8203;4808]: tokio-rs/tokio#4808

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about these updates again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, click this checkbox.

---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzMi4xMTEuMSIsInVwZGF0ZWRJblZlciI6IjMyLjExMS4xIn0=-->

Co-authored-by: cabr2-bot <cabr2.help@gmail.com>
Reviewed-on: https://codeberg.org/Calciumdibromid/CaBr2/pulls/1458
Reviewed-by: crapStone <crapstone@noreply.codeberg.org>
Co-authored-by: Calciumdibromid Bot <cabr2_bot@noreply.codeberg.org>
Co-committed-by: Calciumdibromid Bot <cabr2_bot@noreply.codeberg.org>
@caldwell
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I'm getting an error with tokio 1.20.0 on nightly-aarch64-apple-darwin updated - rustc 1.64.0-nightly (7fe022f5a 2022-07-24):

error[E0658]: use of unstable library feature 'thread_local_const_init'
  --> /Users/david/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.20.0/src/coop.rs:34:1
   |
34 | / thread_local! {
35 | |     static CURRENT: Cell<Budget> = const { Cell::new(Budget::unconstrained()) };
36 | | }
   | |_^
   |
   = note: see issue #84223 <https://github.com/rust-lang/rust/issues/84223> for more information
   = help: add `#![feature(thread_local_const_init)]` to the crate attributes to enable
   = note: this error originates in the macro `$crate::__thread_local_inner` (in Nightly builds, run with -Z macro-backtrace for more info)

This looks related to this change. Is this something I'm doing wrong, or is this a Tokio bug?

@Darksonn
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@caldwell The thread_local_const_init feature was stabilized in rustc 1.59.0, so it seems very weird that you would get such an error on a nightly newer than 1.59.0.

@Darksonn
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Does this compile for you?

thread_local! {
    static FOO: usize = const { 10 };
}

fn main() {
    println!("Hello, world!");
}

@caldwell
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caldwell commented Jul 25, 2022

Sigh, this was operator error: I had run rustup update but it merely downloaded a new compiler but didn't activate it like I expected. I was actually running 1.58 from December. With the latest nightly (2022-07-24) it builds just fine.

Thanks for your response and sorry about the bug spam!

@Darksonn
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Can you elaborate on how you were running it? Tokio should detect that you are on 1.58.0 and avoid using the feature. I just tried compiling with 1.58.0 myself and it worked fine.

@caldwell
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It was just cargo build, where tokio was a dependency. It also happened on a cargo install pijul (which is basically the same thing). The specific version(s) I was running:

$ rustc --version
rustc 1.59.0-nightly (532d2b14c 2021-12-03)
$ cargo version
cargo 1.58.0-nightly (294967c53 2021-11-29)

(I don't understand how those could be different.)

@Darksonn
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@caldwell I figured out what issue you ran into. See #4860 for the fix.

@caldwell
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Thanks, I appreciate your help!

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