use crate::marker::PhantomData;
use crate::mem::MaybeUninit;
use crate::panic::{RefUnwindSafe, UnwindSafe};
-use crate::pin::Pin;
use crate::sync::Once;
/// A synchronization primitive which can be written to only once.
Ok(unsafe { self.get_unchecked() })
}
- /// Internal-only API that gets the contents of the cell, initializing it
- /// in two steps with `f` and `g` if the cell was empty.
- ///
- /// `f` is called to construct the value, which is then moved into the cell
- /// and given as a (pinned) mutable reference to `g` to finish
- /// initialization.
- ///
- /// This allows `g` to inspect an manipulate the value after it has been
- /// moved into its final place in the cell, but before the cell is
- /// considered initialized.
- ///
- /// # Panics
- ///
- /// If `f` or `g` panics, the panic is propagated to the caller, and the
- /// cell remains uninitialized.
- ///
- /// With the current implementation, if `g` panics, the value from `f` will
- /// not be dropped. This should probably be fixed if this is ever used for
- /// a type where this matters.
- ///
- /// It is an error to reentrantly initialize the cell from `f`. The exact
- /// outcome is unspecified. Current implementation deadlocks, but this may
- /// be changed to a panic in the future.
- pub(crate) fn get_or_init_pin<F, G>(self: Pin<&Self>, f: F, g: G) -> Pin<&T>
- where
- F: FnOnce() -> T,
- G: FnOnce(Pin<&mut T>),
- {
- if let Some(value) = self.get_ref().get() {
- // SAFETY: The inner value was already initialized, and will not be
- // moved anymore.
- return unsafe { Pin::new_unchecked(value) };
- }
-
- let slot = &self.value;
-
- // Ignore poisoning from other threads
- // If another thread panics, then we'll be able to run our closure
- self.once.call_once_force(|_| {
- let value = f();
- // SAFETY: We use the Once (self.once) to guarantee unique access
- // to the UnsafeCell (slot).
- let value: &mut T = unsafe { (&mut *slot.get()).write(value) };
- // SAFETY: The value has been written to its final place in
- // self.value. We do not to move it anymore, which we promise here
- // with a Pin<&mut T>.
- g(unsafe { Pin::new_unchecked(value) });
- });
-
- // SAFETY: The inner value has been initialized, and will not be moved
- // anymore.
- unsafe { Pin::new_unchecked(self.get_ref().get_unchecked()) }
- }
-
/// Consumes the `OnceLock`, returning the wrapped value. Returns
/// `None` if the cell was empty.
///