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use crate::loom::cell::UnsafeCell;
use std::collections::VecDeque;
use std::marker::PhantomData;
/// This type is like VecDeque, except that it is not Sync and can be modified
/// through immutable references.
pub(crate) struct VecDequeCell<T> {
inner: UnsafeCell<VecDeque<T>>,
_not_sync: PhantomData<*const ()>,
}
// This is Send for the same reasons that RefCell<VecDeque<T>> is Send.
unsafe impl<T: Send> Send for VecDequeCell<T> {}
impl<T> VecDequeCell<T> {
pub(crate) fn with_capacity(cap: usize) -> Self {
Self {
inner: UnsafeCell::new(VecDeque::with_capacity(cap)),
_not_sync: PhantomData,
}
}
/// Safety: This method may not be called recursively.
#[inline]
unsafe fn with_inner<F, R>(&self, f: F) -> R
where
F: FnOnce(&mut VecDeque<T>) -> R,
{
// safety: This type is not Sync, so concurrent calls of this method
// cannot happen. Furthermore, the caller guarantees that the method is
// not called recursively. Finally, this is the only place that can
// create mutable references to the inner VecDeque. This ensures that
// any mutable references created here are exclusive.
self.inner.with_mut(|ptr| f(&mut *ptr))
}
pub(crate) fn pop_front(&self) -> Option<T> {
unsafe { self.with_inner(VecDeque::pop_front) }
}
pub(crate) fn push_back(&self, item: T) {
unsafe {
self.with_inner(|inner| inner.push_back(item));
}
}
/// Replaces the inner VecDeque with an empty VecDeque and return the current
/// contents.
pub(crate) fn take(&self) -> VecDeque<T> {
unsafe { self.with_inner(|inner| std::mem::take(inner)) }
}
}
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