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