Add sync option to -Z threads to force synchronization on one thread#156198
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rust-bors[bot] merged 1 commit intorust-lang:mainfrom May 8, 2026
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Add sync option to -Z threads to force synchronization on one thread#156198rust-bors[bot] merged 1 commit intorust-lang:mainfrom
sync option to -Z threads to force synchronization on one thread#156198rust-bors[bot] merged 1 commit intorust-lang:mainfrom
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r? @folkertdev rustbot has assigned @folkertdev. Use Why was this reviewer chosen?The reviewer was selected based on:
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folkertdev
requested changes
May 6, 2026
Comment on lines
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1089
| pub(crate) fn parse_threads(slot: &mut Option<usize>, v: Option<&str>) -> bool { | ||
| let n = match v { | ||
| Some("sync") => { | ||
| *slot = Some(1); | ||
| return true; | ||
| } | ||
| None => false, | ||
| Some(s) => match s.parse().ok() { | ||
| Some(0) => std::thread::available_parallelism().map_or(1, NonZero::<usize>::get), | ||
| Some(i) => i, | ||
| None => return false, | ||
| }, | ||
| None => return false, | ||
| }; | ||
|
|
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| // We want to cap the number of threads here to avoid large numbers like 999999 and compiler panics. | ||
| // This solution was suggested here https://github.com/rust-lang/rust/issues/117638#issuecomment-1800925067 | ||
| *slot = slot.clone().min(MAX_THREADS_CAP); | ||
| ret | ||
| let n = n.min(MAX_THREADS_CAP); | ||
| *slot = (n > 1).then_some(n); | ||
| true | ||
| } |
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I think this will now be clearer as
Suggested change
| pub(crate) fn parse_threads(slot: &mut Option<usize>, v: Option<&str>) -> bool { | |
| let n = match v { | |
| Some("sync") => { | |
| *slot = Some(1); | |
| return true; | |
| } | |
| None => false, | |
| Some(s) => match s.parse().ok() { | |
| Some(0) => std::thread::available_parallelism().map_or(1, NonZero::<usize>::get), | |
| Some(i) => i, | |
| None => return false, | |
| }, | |
| None => return false, | |
| }; | |
| // We want to cap the number of threads here to avoid large numbers like 999999 and compiler panics. | |
| // This solution was suggested here https://github.com/rust-lang/rust/issues/117638#issuecomment-1800925067 | |
| *slot = slot.clone().min(MAX_THREADS_CAP); | |
| ret | |
| let n = n.min(MAX_THREADS_CAP); | |
| *slot = (n > 1).then_some(n); | |
| true | |
| } | |
| pub(crate) fn parse_threads(slot: &mut Option<usize>, v: Option<&str>) -> bool { | |
| let Some(s) = v else { return false }; | |
| // Configures to use synchronization despite only using one thread. | |
| if s == "sync" { | |
| *slot = Some(1); | |
| return true; | |
| } | |
| let n = match s.parse().ok() { | |
| Some(0) => std::thread::available_parallelism().map_or(1, NonZero::<usize>::get), | |
| Some(i) => i, | |
| None => return false, | |
| }; | |
| // We want to cap the number of threads here to avoid large numbers like 999999 and compiler panics. | |
| // This solution was suggested here https://github.com/rust-lang/rust/issues/117638#issuecomment-1800925067 | |
| let n = n.min(MAX_THREADS_CAP); | |
| *slot = (n > 1).then_some(n); | |
| true | |
| } |
maybe with another comment on the (n > 1).then_some(n) line.
Collaborator
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Reminder, once the PR becomes ready for a review, use |
Contributor
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@bors r+ rollup |
Contributor
JonathanBrouwer
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May 7, 2026
Add `sync` option to `-Z threads` to force synchronization on one thread This adds a `sync` option to `-Z threads` to force synchronization while still using one thread. This is useful to measure overhead of synchronization without the noise of additional threads.
rust-bors Bot
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May 7, 2026
…uwer Rollup of 4 pull requests Successful merges: - #149468 (Skipping borrowck because of trivial const) - #152487 (core: drop unmapped ZSTs in array `map`) - #153759 (Add a suite of ChunkedBitSet union/subtract/intersect test scenarios) - #156198 (Add `sync` option to `-Z threads` to force synchronization on one thread)
rust-bors Bot
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May 7, 2026
…uwer Rollup of 6 pull requests Successful merges: - #156061 (Support `-Cpanic=unwind` on WASI targets) - #151753 (Experiment: Reborrow traits) - #156280 (Add regression test for closure return ICE) - #152487 (core: drop unmapped ZSTs in array `map`) - #153759 (Add a suite of ChunkedBitSet union/subtract/intersect test scenarios) - #156198 (Add `sync` option to `-Z threads` to force synchronization on one thread)
rust-timer
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May 8, 2026
Rollup merge of #156198 - Zoxc:threads-sync, r=folkertdev Add `sync` option to `-Z threads` to force synchronization on one thread This adds a `sync` option to `-Z threads` to force synchronization while still using one thread. This is useful to measure overhead of synchronization without the noise of additional threads.
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This adds a
syncoption to-Z threadsto force synchronization while still using one thread. This is useful to measure overhead of synchronization without the noise of additional threads.