1 use core::panic::{RefUnwindSafe, UnwindSafe}; 2 3 use atomic_polyfill::{AtomicBool, Ordering}; 4 use critical_section::{CriticalSection, Mutex}; 5 6 use crate::unsync; 7 8 pub(crate) struct OnceCell<T> { 9 initialized: AtomicBool, 10 // Use `unsync::OnceCell` internally since `Mutex` does not provide 11 // interior mutability and to be able to re-use `get_or_try_init`. 12 value: Mutex<unsync::OnceCell<T>>, 13 } 14 15 // Why do we need `T: Send`? 16 // Thread A creates a `OnceCell` and shares it with 17 // scoped thread B, which fills the cell, which is 18 // then destroyed by A. That is, destructor observes 19 // a sent value. 20 unsafe impl<T: Sync + Send> Sync for OnceCell<T> {} 21 unsafe impl<T: Send> Send for OnceCell<T> {} 22 23 impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for OnceCell<T> {} 24 impl<T: UnwindSafe> UnwindSafe for OnceCell<T> {} 25 26 impl<T> OnceCell<T> { new() -> OnceCell<T>27 pub(crate) const fn new() -> OnceCell<T> { 28 OnceCell { initialized: AtomicBool::new(false), value: Mutex::new(unsync::OnceCell::new()) } 29 } 30 with_value(value: T) -> OnceCell<T>31 pub(crate) const fn with_value(value: T) -> OnceCell<T> { 32 OnceCell { 33 initialized: AtomicBool::new(true), 34 value: Mutex::new(unsync::OnceCell::with_value(value)), 35 } 36 } 37 38 #[inline] is_initialized(&self) -> bool39 pub(crate) fn is_initialized(&self) -> bool { 40 self.initialized.load(Ordering::Acquire) 41 } 42 43 #[cold] initialize<F, E>(&self, f: F) -> Result<(), E> where F: FnOnce() -> Result<T, E>,44 pub(crate) fn initialize<F, E>(&self, f: F) -> Result<(), E> 45 where 46 F: FnOnce() -> Result<T, E>, 47 { 48 critical_section::with(|cs| { 49 let cell = self.value.borrow(cs); 50 cell.get_or_try_init(f).map(|_| { 51 self.initialized.store(true, Ordering::Release); 52 }) 53 }) 54 } 55 56 /// Get the reference to the underlying value, without checking if the cell 57 /// is initialized. 58 /// 59 /// # Safety 60 /// 61 /// Caller must ensure that the cell is in initialized state, and that 62 /// the contents are acquired by (synchronized to) this thread. get_unchecked(&self) -> &T63 pub(crate) unsafe fn get_unchecked(&self) -> &T { 64 debug_assert!(self.is_initialized()); 65 // SAFETY: The caller ensures that the value is initialized and access synchronized. 66 crate::unwrap_unchecked(self.value.borrow(CriticalSection::new()).get()) 67 } 68 69 #[inline] get_mut(&mut self) -> Option<&mut T>70 pub(crate) fn get_mut(&mut self) -> Option<&mut T> { 71 self.value.get_mut().get_mut() 72 } 73 74 #[inline] into_inner(self) -> Option<T>75 pub(crate) fn into_inner(self) -> Option<T> { 76 self.value.into_inner().into_inner() 77 } 78 } 79