style/rule_tree/
source.rs

1/* This Source Code Form is subject to the terms of the Mozilla Public
2 * License, v. 2.0. If a copy of the MPL was not distributed with this
3 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
4
5#![deny(unsafe_code)]
6
7use crate::properties::PropertyDeclarationBlock;
8use crate::shared_lock::{Locked, SharedRwLockReadGuard};
9use servo_arc::Arc;
10use std::io::Write;
11use std::ptr;
12
13/// A style source for the rule node. It is a declaration block that may come from either a style
14/// rule or a standalone block like animations / transitions / smil / preshints / style attr...
15///
16/// Keeping the style rule around would provide more debugability, but also causes more
17/// pointer-chasing in the common code-path, which is undesired. If needed, we could keep it around
18/// in debug builds or something along those lines.
19#[derive(Clone, Debug)]
20pub struct StyleSource(Arc<Locked<PropertyDeclarationBlock>>);
21
22impl PartialEq for StyleSource {
23    fn eq(&self, other: &Self) -> bool {
24        Arc::ptr_eq(&self.0, &other.0)
25    }
26}
27
28impl StyleSource {
29    #[inline]
30    pub(super) fn key(&self) -> ptr::NonNull<()> {
31        self.0.raw_ptr()
32    }
33
34    /// Creates a StyleSource from a PropertyDeclarationBlock.
35    #[inline]
36    pub fn from_declarations(decls: Arc<Locked<PropertyDeclarationBlock>>) -> Self {
37        Self(decls)
38    }
39
40    pub(super) fn dump<W: Write>(&self, guard: &SharedRwLockReadGuard, writer: &mut W) {
41        let _ = write!(writer, "  -> {:?}", self.read(guard).declarations());
42    }
43
44    /// Read the style source guard, and obtain thus read access to the
45    /// underlying property declaration block.
46    #[inline]
47    pub fn read<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> &'a PropertyDeclarationBlock {
48        self.0.read_with(guard)
49    }
50
51    /// Returns the declaration block if applicable, otherwise None.
52    #[inline]
53    pub fn get(&self) -> &Arc<Locked<PropertyDeclarationBlock>> {
54        &self.0
55    }
56
57    /// Marks this block as part of the rule tree.
58    #[inline]
59    pub fn mark_in_rule_tree(&self) {
60        use std::sync::atomic::Ordering;
61        if self.0.is_static() {
62            // For static pointers, it doesn't matter whether we might be in the rule tree or not,
63            // because those are not mutable.
64            return;
65        }
66        // SAFETY: We're only accessing a relaxed atomic inside the locked object, which we know
67        // is alive. In theory, we could/should track that boolean outside of the
68        // Locked<PropertyDeclarationBlock>, but that is kind of a PITA.
69        #[allow(unsafe_code)]
70        unsafe {
71            self.0
72                .read_unchecked()
73                .immutable
74                .store(true, Ordering::Relaxed);
75        }
76    }
77}
style/rule_tree/source.rs

style/rule_tree/
source.rs
