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use alloc::sync::Arc;
/// Guarantees uniqueness only if `Weak` pointers are never created
/// from this `Arc` or clones.
pub(crate) fn is_arc_unique<M>(arc: &mut Arc<M>) -> bool {
let strong_count = Arc::strong_count(&*arc);
debug_assert_ne!(strong_count, 0, "This Arc should exist");
debug_assert!(
strong_count > 1 || Arc::get_mut(arc).is_some(),
"`Weak` pointer exists"
);
strong_count == 1
}
/// Can be used instead of `Arc::try_unwrap(arc).unwrap()`
/// when it is guaranteed to succeed.
pub(crate) unsafe fn arc_unwrap<M>(mut arc: Arc<M>) -> M {
use core::{mem::ManuallyDrop, ptr::read};
debug_assert!(is_arc_unique(&mut arc));
// Get raw pointer to inner value.
let raw = Arc::into_raw(arc);
// As `Arc` is unique and no Weak pointers exist
// it won't be dereferenced elsewhere.
let inner = read(raw);
// Cast to `ManuallyDrop` which guarantees to have same layout
// and will skip dropping.
drop(Arc::from_raw(raw as *const ManuallyDrop<M>));
inner
}
/// Can be used instead of `Arc::try_unwrap`
/// only if `Weak` pointers are never created from this `Arc` or clones.
pub(crate) unsafe fn try_arc_unwrap<M>(mut arc: Arc<M>) -> Option<M> {
if is_arc_unique(&mut arc) {
Some(arc_unwrap(arc))
} else {
None
}
}
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