78 lines
2.4 KiB
Rust
78 lines
2.4 KiB
Rust
use core::panic::{RefUnwindSafe, UnwindSafe};
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use critical_section::{CriticalSection, Mutex};
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use portable_atomic::{AtomicBool, Ordering};
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use crate::unsync;
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pub(crate) struct OnceCell<T> {
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initialized: AtomicBool,
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// Use `unsync::OnceCell` internally since `Mutex` does not provide
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// interior mutability and to be able to re-use `get_or_try_init`.
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value: Mutex<unsync::OnceCell<T>>,
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}
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// Why do we need `T: Send`?
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// Thread A creates a `OnceCell` and shares it with
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// scoped thread B, which fills the cell, which is
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// then destroyed by A. That is, destructor observes
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// a sent value.
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unsafe impl<T: Sync + Send> Sync for OnceCell<T> {}
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unsafe impl<T: Send> Send for OnceCell<T> {}
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impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for OnceCell<T> {}
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impl<T: UnwindSafe> UnwindSafe for OnceCell<T> {}
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impl<T> OnceCell<T> {
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pub(crate) const fn new() -> OnceCell<T> {
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OnceCell { initialized: AtomicBool::new(false), value: Mutex::new(unsync::OnceCell::new()) }
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}
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pub(crate) const fn with_value(value: T) -> OnceCell<T> {
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OnceCell {
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initialized: AtomicBool::new(true),
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value: Mutex::new(unsync::OnceCell::with_value(value)),
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}
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}
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#[inline]
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pub(crate) fn is_initialized(&self) -> bool {
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self.initialized.load(Ordering::Acquire)
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}
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#[cold]
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pub(crate) fn initialize<F, E>(&self, f: F) -> Result<(), E>
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where
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F: FnOnce() -> Result<T, E>,
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{
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critical_section::with(|cs| {
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let cell = self.value.borrow(cs);
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cell.get_or_try_init(f).map(|_| {
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self.initialized.store(true, Ordering::Release);
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})
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})
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}
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/// Get the reference to the underlying value, without checking if the cell
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/// is initialized.
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///
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/// # Safety
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///
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/// Caller must ensure that the cell is in initialized state, and that
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/// the contents are acquired by (synchronized to) this thread.
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pub(crate) unsafe fn get_unchecked(&self) -> &T {
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debug_assert!(self.is_initialized());
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// SAFETY: The caller ensures that the value is initialized and access synchronized.
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self.value.borrow(CriticalSection::new()).get().unwrap_unchecked()
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}
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#[inline]
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pub(crate) fn get_mut(&mut self) -> Option<&mut T> {
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self.value.get_mut().get_mut()
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}
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#[inline]
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pub(crate) fn into_inner(self) -> Option<T> {
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self.value.into_inner().into_inner()
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}
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}
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