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layout: Stop using Rayon in single-threaded mode (#37832)

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In layout, some parts of the code were still using parallel iterators
from Rayon even when single-thread layout was activated. This change
modifies those parts to use non-parallel iterators when
`LayoutContext::use_rayon` is not active.

Testing: It's very hard to make an automated test for this, but I've
manually
verified this by building with tracing and observing that layout runs
only on
a single thread now when loading https://servo.org.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
This commit is contained in:
Martin Robinson 2025-07-02 14:44:43 +02:00 • committed by GitHub
parent da364f7a61
commit 647122d0f6
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GPG key ID: B5690EEEBB952194
3 changed files with 197 additions and 144 deletions
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171
components/layout/construct_modern.rs
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@ -44,6 +44,90 @@ enum ModernContainerJob<'dom> {
TextRuns(Vec<ModernContainerTextRun<'dom>>),
}
impl<'dom> ModernContainerJob<'dom> {
fn finish(
self,
builder: &ModernContainerBuilder,
anonymous_info: &LazyLock<NodeAndStyleInfo<'dom>, impl FnOnce() -> NodeAndStyleInfo<'dom>>,
) -> Option<ModernItem<'dom>> {
match self {
ModernContainerJob::TextRuns(runs) => {
let mut inline_formatting_context_builder =
InlineFormattingContextBuilder::new(builder.info);
for flex_text_run in runs.into_iter() {
inline_formatting_context_builder
.push_text(flex_text_run.text, &flex_text_run.info);
}
let inline_formatting_context = inline_formatting_context_builder.finish(
builder.context,
true, /* has_first_formatted_line */
false, /* is_single_line_text_box */
builder.info.style.to_bidi_level(),
)?;
let block_formatting_context = BlockFormattingContext::from_block_container(
BlockContainer::InlineFormattingContext(inline_formatting_context),
);
let info: &NodeAndStyleInfo = anonymous_info;
let formatting_context = IndependentFormattingContext {
base: LayoutBoxBase::new(info.into(), info.style.clone()),
contents: IndependentFormattingContextContents::NonReplaced(
IndependentNonReplacedContents::Flow(block_formatting_context),
),
};
Some(ModernItem {
kind: ModernItemKind::InFlow,
order: 0,
box_slot: None,
formatting_context,
})
},
ModernContainerJob::ElementOrPseudoElement {
info,
display,
contents,
box_slot,
} => {
let is_abspos = info.style.get_box().position.is_absolutely_positioned();
// Text decorations are not propagated to any out-of-flow descendants. In addition,
// absolutes don't affect the size of ancestors so it is fine to allow descendent
// tables to resolve percentage columns.
let propagated_data = match is_abspos {
false => builder.propagated_data,
true => PropagatedBoxTreeData::default(),
};
let formatting_context = IndependentFormattingContext::construct(
builder.context,
&info,
display.display_inside(),
contents,
propagated_data,
);
if is_abspos {
Some(ModernItem {
kind: ModernItemKind::OutOfFlow,
order: 0,
box_slot: Some(box_slot),
formatting_context,
})
} else {
Some(ModernItem {
kind: ModernItemKind::InFlow,
order: info.style.clone_order(),
box_slot: Some(box_slot),
formatting_context,
})
}
},
}
}
}
struct ModernContainerTextRun<'dom> {
info: NodeAndStyleInfo<'dom>,
text: Cow<'dom, str>,
@ -137,84 +221,17 @@ impl<'a, 'dom> ModernContainerBuilder<'a, 'dom> {
.pseudo(self.context, PseudoElement::ServoAnonymousBox)
.expect("Should always be able to construct info for anonymous boxes.")
});
let mut children: Vec<ModernItem> = std::mem::take(&mut self.jobs)
.into_par_iter()
.filter_map(|job| match job {
ModernContainerJob::TextRuns(runs) => {
let mut inline_formatting_context_builder =
InlineFormattingContextBuilder::new(self.info);
for flex_text_run in runs.into_iter() {
inline_formatting_context_builder
.push_text(flex_text_run.text, &flex_text_run.info);
}
let inline_formatting_context = inline_formatting_context_builder.finish(
self.context,
true, /* has_first_formatted_line */
false, /* is_single_line_text_box */
self.info.style.to_bidi_level(),
)?;
let block_formatting_context = BlockFormattingContext::from_block_container(
BlockContainer::InlineFormattingContext(inline_formatting_context),
);
let info: &NodeAndStyleInfo = &anonymous_info;
let formatting_context = IndependentFormattingContext {
base: LayoutBoxBase::new(info.into(), info.style.clone()),
contents: IndependentFormattingContextContents::NonReplaced(
IndependentNonReplacedContents::Flow(block_formatting_context),
),
};
Some(ModernItem {
kind: ModernItemKind::InFlow,
order: 0,
box_slot: None,
formatting_context,
})
},
ModernContainerJob::ElementOrPseudoElement {
info,
display,
contents,
box_slot,
} => {
let is_abspos = info.style.get_box().position.is_absolutely_positioned();
// Text decorations are not propagated to any out-of-flow descendants. In addition,
// absolutes don't affect the size of ancestors so it is fine to allow descendent
// tables to resolve percentage columns.
let propagated_data = match is_abspos {
false => self.propagated_data,
true => PropagatedBoxTreeData::default(),
};
let formatting_context = IndependentFormattingContext::construct(
self.context,
&info,
display.display_inside(),
contents,
propagated_data,
);
if is_abspos {
Some(ModernItem {
kind: ModernItemKind::OutOfFlow,
order: 0,
box_slot: Some(box_slot),
formatting_context,
})
} else {
Some(ModernItem {
kind: ModernItemKind::InFlow,
order: info.style.clone_order(),
box_slot: Some(box_slot),
formatting_context,
})
}
},
})
.collect::<Vec<_>>();
let jobs = std::mem::take(&mut self.jobs);
let mut children: Vec<_> = if self.context.use_rayon {
jobs.into_par_iter()
.filter_map(|job| job.finish(&self, &anonymous_info))
.collect()
} else {
jobs.into_iter()
.filter_map(|job| job.finish(&self, &anonymous_info))
.collect()
};
// https://drafts.csswg.org/css-flexbox/#order-modified-document-order
children.sort_by_key(|child| child.order);