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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 http://mozilla.org/MPL/2.0/. */
//! A shareable mutable container for the DOM.
use std::cell::{BorrowError, BorrowMutError, Ref, RefCell, RefMut};
use style::thread_state::{self, ThreadState};
/// A mutable field in the DOM.
///
/// This extends the API of `std::cell::RefCell` to allow unsafe access in
/// certain situations, with dynamic checking in debug builds.
#[derive(Clone, Debug, Default, MallocSizeOf, PartialEq)]
pub struct DomRefCell<T> {
value: RefCell<T>,
}
// Functionality specific to Servo's `DomRefCell` type
// ===================================================
impl<T> DomRefCell<T> {
/// Return a reference to the contents.
///
/// For use in the layout thread only.
#[allow(unsafe_code)]
pub unsafe fn borrow_for_layout(&self) -> &T {
debug_assert!(thread_state::get().is_layout());
&*self.value.as_ptr()
}
/// Borrow the contents for the purpose of script deallocation.
///
#[allow(unsafe_code)]
pub unsafe fn borrow_for_script_deallocation(&self) -> &mut T {
debug_assert!(thread_state::get().contains(ThreadState::SCRIPT));
&mut *self.value.as_ptr()
}
/// Version of the above that we use during restyle while the script thread
/// is blocked.
pub fn borrow_mut_for_layout(&self) -> RefMut<T> {
debug_assert!(thread_state::get().is_layout());
self.value.borrow_mut()
}
}
// Functionality duplicated with `std::cell::RefCell`
// ===================================================
impl<T> DomRefCell<T> {
/// Create a new `DomRefCell` containing `value`.
pub fn new(value: T) -> DomRefCell<T> {
DomRefCell {
value: RefCell::new(value),
}
}
/// Immutably borrows the wrapped value.
///
/// The borrow lasts until the returned `Ref` exits scope. Multiple
/// immutable borrows can be taken out at the same time.
///
/// # Panics
///
/// Panics if this is called off the script thread.
///
/// Panics if the value is currently mutably borrowed.
pub fn borrow(&self) -> Ref<T> {
self.try_borrow().expect("DomRefCell<T> already mutably borrowed")
}
/// Mutably borrows the wrapped value.
///
/// The borrow lasts until the returned `RefMut` exits scope. The value
/// cannot be borrowed while this borrow is active.
///
/// # Panics
///
/// Panics if this is called off the script thread.
///
/// Panics if the value is currently borrowed.
pub fn borrow_mut(&self) -> RefMut<T> {
self.try_borrow_mut().expect("DomRefCell<T> already borrowed")
}
/// Attempts to immutably borrow the wrapped value.
///
/// The borrow lasts until the returned `Ref` exits scope. Multiple
/// immutable borrows can be taken out at the same time.
///
/// Returns `None` if the value is currently mutably borrowed.
///
/// # Panics
///
/// Panics if this is called off the script thread.
pub fn try_borrow(&self) -> Result<Ref<T>, BorrowError> {
debug_assert!(thread_state::get().is_script());
self.value.try_borrow()
}
/// Mutably borrows the wrapped value.
///
/// The borrow lasts until the returned `RefMut` exits scope. The value
/// cannot be borrowed while this borrow is active.
///
/// Returns `None` if the value is currently borrowed.
///
/// # Panics
///
/// Panics if this is called off the script thread.
pub fn try_borrow_mut(&self) -> Result<RefMut<T>, BorrowMutError> {
debug_assert!(thread_state::get().is_script());
self.value.try_borrow_mut()
}
}
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