firefox-main/servo/components/style/rule_tree/source.rs (file symbol)

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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
#![deny(unsafe_code)]
use crate::derives::*;
use crate::properties::PropertyDeclarationBlock;
use crate::shared_lock::{Locked, SharedRwLockReadGuard};
use servo_arc::{Arc, ArcBorrow};
use std::io::Write;
use std::ptr;
/// A style source for the rule node. It is a declaration block that may come from either a style
/// rule or a standalone block like animations / transitions / smil / preshints / style attr...
///
/// Keeping the style rule around would provide more debugability, but also causes more
/// pointer-chasing in the common code-path, which is undesired. If needed, we could keep it around
/// in debug builds or something along those lines.
#[derive(Clone, Debug)]
pub struct StyleSource(Arc<Locked<PropertyDeclarationBlock>>);
/// A borrowed version of `StyleSource`.
///
/// This is what we use during selector matching, so that we only need to touch the refcount of
/// the declarations when we actually insert them in the rule tree.
#[derive(Clone, Copy, Debug, MallocSizeOf)]
pub struct StyleSourceBorrow<'a>(ArcBorrow<'a, Locked<PropertyDeclarationBlock>>);
// The declaration block is measured as part of the stylesheet (or as part of whatever object owns
// it, like the element for the style attribute).
malloc_size_of::malloc_size_of_is_0!(StyleSource);
impl PartialEq for StyleSource {
fn eq(&self, other: &Self) -> bool {
Arc::ptr_eq(&self.0, &other.0)
}
}
impl<'a> PartialEq for StyleSourceBorrow<'a> {
fn eq(&self, other: &Self) -> bool {
ArcBorrow::ptr_eq(&self.0, &other.0)
}
}
impl<'a> StyleSourceBorrow<'a> {
/// Creates a borrowed style source from a borrowed declaration block.
#[inline]
pub fn from_declarations(decls: ArcBorrow<'a, Locked<PropertyDeclarationBlock>>) -> Self {
Self(decls)
}
/// Creates an owned style source from this borrow, bumping the refcount.
#[inline]
pub fn to_owned(&self) -> StyleSource {
StyleSource(self.0.clone_arc())
}
#[inline]
pub(super) fn key(&self) -> ptr::NonNull<()> {
ptr::NonNull::from(self.0.get()).cast()
}
/// Read the style source guard, and obtain thus read access to the underlying property
/// declaration block.
#[inline]
pub fn read<'b>(&self, guard: &'b SharedRwLockReadGuard) -> &'b PropertyDeclarationBlock
where
'a: 'b,
{
self.0.get().read_with(guard)
}
}
impl StyleSource {
#[inline]
pub(super) fn key(&self) -> ptr::NonNull<()> {
ptr::NonNull::from(&*self.0).cast()
}
/// Borrows this style source.
#[inline]
pub fn borrow(&self) -> StyleSourceBorrow<'_> {
StyleSourceBorrow(self.0.borrow_arc())
}
/// Creates a StyleSource from a PropertyDeclarationBlock.
#[inline]
pub fn from_declarations(decls: Arc<Locked<PropertyDeclarationBlock>>) -> Self {
Self(decls)
}
pub(super) fn dump<W: Write>(&self, guard: &SharedRwLockReadGuard, writer: &mut W) {
let _ = write!(writer, " -> {:?}", self.read(guard).declarations());
}
/// Read the style source guard, and obtain thus read access to the
/// underlying property declaration block.
#[inline]
pub fn read<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> &'a PropertyDeclarationBlock {
self.0.read_with(guard)
}
/// Returns the declaration block if applicable, otherwise None.
#[inline]
pub fn get(&self) -> &Arc<Locked<PropertyDeclarationBlock>> {
&self.0
}
/// Marks this block as part of the rule tree.
#[inline]
pub fn mark_in_rule_tree(&self) {
use std::sync::atomic::Ordering;
if self.0.is_static() {
// For static pointers, it doesn't matter whether we might be in the rule tree or not,
// because those are not mutable.
return;
}
// SAFETY: We're only accessing a relaxed atomic inside the locked object, which we know
// is alive. In theory, we could/should track that boolean outside of the
// Locked<PropertyDeclarationBlock>, but that is kind of a PITA.
#[allow(unsafe_code)]
unsafe {
// Load before storing: the flag is never cleared, so after the first mark every
// store is redundant, and an unconditional store would still take the cache line
// exclusive and invalidate it for every other thread reading this block.
let immutable = &self.0.read_unchecked().immutable;
if !immutable.load(Ordering::Relaxed) {
immutable.store(true, Ordering::Relaxed);
}
}
}
}