Recursion stack for detecting cyclic imports#158035
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| thread_local! { | ||
| /// During import resolution, recursive imports can form cycles. | ||
| /// This set stores the active resolution stack for the current thread. | ||
| /// So it's essentially a recursion stack. | ||
| /// | ||
| /// The key is the address of a `NameResolution`; we only need identity, | ||
| /// not access to the value. | ||
| static ACTIVE_RESOLUTIONS: CacheRefCell<BTreeSet<*const ()>> = Default::default(); | ||
| } |
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So I already did it using TLS to show how I was thinking of a solution for parallel import resolution.
Can be easily translated to Rc<RefCell<...>> in the Resolver itself.
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…mut`. Place recursion stack in TLS ahead of parallel import resolution
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| active.remove(&self.key); | ||
| }); | ||
| } | ||
| } |
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DropGuard is possible (unstable feature though). But I don't like how I need to fill in the types:
/// We need a way to remove the resolution from the stack whenever we return, this type
/// holds that resolution key and removes it on drop.
pub(crate) type ImportCycleGuard<D: FnOnce(*const ())> = DropGuard<*const (), D>;
pub(crate) fn enter_cycle_detector(
&self,
resolution: &'ra CmRefCell<NameResolution<'ra>>,
) -> Result<ImportCycleGuard<impl FnOnce(*const ())>, ()> {
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Instead of using the
borrow_mutcounter of aRefCellfor aNameResolutionfor detecting cyclic imports during import resolution, we use an explicit recursion stack that keeps track of the current usedNameResolutions.Because of the upcoming parallelisation of the import resolution algorithm, the current way cannot used in a parallel context.
r? @petrochenkov