script/dom/bindings/
cell.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//! A shareable mutable container for the DOM.
6
7use std::cell::{BorrowError, BorrowMutError};
8#[cfg(not(feature = "refcell_backtrace"))]
9pub(crate) use std::cell::{Ref, RefCell, RefMut};
10
11#[cfg(feature = "refcell_backtrace")]
12pub(crate) use accountable_refcell::{Ref, RefCell, RefMut};
13use malloc_size_of::{MallocConditionalSizeOf, MallocSizeOfOps};
14
15use crate::dom::bindings::root::{assert_in_layout, assert_in_script};
16
17/// A mutable field in the DOM.
18///
19/// This extends the API of `std::cell::RefCell` to allow unsafe access in
20/// certain situations, with dynamic checking in debug builds.
21#[derive(Clone, Debug, Default, MallocSizeOf, PartialEq)]
22pub(crate) struct DomRefCell<T> {
23    value: RefCell<T>,
24}
25
26impl<T: MallocConditionalSizeOf> MallocConditionalSizeOf for DomRefCell<T> {
27    fn conditional_size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
28        self.value.borrow().conditional_size_of(ops)
29    }
30}
31
32// Functionality specific to Servo's `DomRefCell` type
33// ===================================================
34
35impl<T> DomRefCell<T> {
36    /// Return a reference to the contents.  For use in layout only.
37    ///
38    /// # Safety
39    ///
40    /// Unlike RefCell::borrow, this method is unsafe because it does not return a Ref, thus leaving
41    /// the borrow flag untouched. Mutably borrowing the RefCell while the reference returned by
42    /// this method is alive is undefined behaviour.
43    ///
44    /// # Panics
45    ///
46    /// Panics if this is called from anywhere other than the layout thread
47    ///
48    /// Panics if the value is currently mutably borrowed.
49    #[allow(unsafe_code)]
50    pub(crate) unsafe fn borrow_for_layout(&self) -> &T {
51        assert_in_layout();
52        unsafe {
53            self.value
54                .try_borrow_unguarded()
55                .expect("cell is mutably borrowed")
56        }
57    }
58
59    /// Borrow the contents for the purpose of script deallocation.
60    ///
61    /// # Safety
62    ///
63    /// Unlike RefCell::borrow, this method is unsafe because it does not return a Ref, thus leaving
64    /// the borrow flag untouched. Mutably borrowing the RefCell while the reference returned by
65    /// this method is alive is undefined behaviour.
66    ///
67    /// # Panics
68    ///
69    /// Panics if this is called from anywhere other than the script thread.
70    #[allow(unsafe_code, clippy::mut_from_ref)]
71    pub(crate) unsafe fn borrow_for_script_deallocation(&self) -> &mut T {
72        assert_in_script();
73        unsafe { &mut *self.value.as_ptr() }
74    }
75
76    /// Mutably borrow a cell for layout. Ideally this would use
77    /// `RefCell::try_borrow_mut_unguarded` but that doesn't exist yet.
78    ///
79    /// # Safety
80    ///
81    /// Unlike RefCell::borrow, this method is unsafe because it does not return a Ref, thus leaving
82    /// the borrow flag untouched. Mutably borrowing the RefCell while the reference returned by
83    /// this method is alive is undefined behaviour.
84    ///
85    /// # Panics
86    ///
87    /// Panics if this is called from anywhere other than the layout thread.
88    #[allow(unsafe_code, clippy::mut_from_ref)]
89    pub(crate) unsafe fn borrow_mut_for_layout(&self) -> &mut T {
90        assert_in_layout();
91        unsafe { &mut *self.value.as_ptr() }
92    }
93}
94
95// Functionality duplicated with `std::cell::RefCell`
96// ===================================================
97impl<T> DomRefCell<T> {
98    /// Create a new `DomRefCell` containing `value`.
99    pub(crate) fn new(value: T) -> DomRefCell<T> {
100        DomRefCell {
101            value: RefCell::new(value),
102        }
103    }
104
105    /// Immutably borrows the wrapped value.
106    ///
107    /// The borrow lasts until the returned `Ref` exits scope. Multiple
108    /// immutable borrows can be taken out at the same time.
109    ///
110    /// # Panics
111    ///
112    /// Panics if the value is currently mutably borrowed.
113    #[track_caller]
114    pub(crate) fn borrow(&self) -> Ref<'_, T> {
115        self.value.borrow()
116    }
117
118    /// Mutably borrows the wrapped value.
119    ///
120    /// The borrow lasts until the returned `RefMut` exits scope. The value
121    /// cannot be borrowed while this borrow is active.
122    ///
123    /// # Panics
124    ///
125    /// Panics if the value is currently borrowed.
126    #[track_caller]
127    pub(crate) fn borrow_mut(&self) -> RefMut<'_, T> {
128        self.value.borrow_mut()
129    }
130
131    /// Attempts to immutably borrow the wrapped value.
132    ///
133    /// The borrow lasts until the returned `Ref` exits scope. Multiple
134    /// immutable borrows can be taken out at the same time.
135    ///
136    /// Returns `None` if the value is currently mutably borrowed.
137    ///
138    /// # Panics
139    ///
140    /// Panics if this is called off the script thread.
141    pub(crate) fn try_borrow(&self) -> Result<Ref<'_, T>, BorrowError> {
142        assert_in_script();
143        self.value.try_borrow()
144    }
145
146    /// Mutably borrows the wrapped value.
147    ///
148    /// The borrow lasts until the returned `RefMut` exits scope. The value
149    /// cannot be borrowed while this borrow is active.
150    ///
151    /// Returns `None` if the value is currently borrowed.
152    ///
153    /// # Panics
154    ///
155    /// Panics if this is called off the script thread.
156    pub(crate) fn try_borrow_mut(&self) -> Result<RefMut<'_, T>, BorrowMutError> {
157        assert_in_script();
158        self.value.try_borrow_mut()
159    }
160}
161
162impl<T: Default> DomRefCell<T> {
163    /// Takes the wrapped value, leaving `Default::default()` in its place.
164    ///
165    /// # Panics
166    ///
167    /// Panics if the value is currently borrowed.
168    pub(crate) fn take(&self) -> T {
169        self.value.take()
170    }
171}
script/dom/bindings/cell.rs

script/dom/bindings/
cell.rs
