Method root

crates/wasmtime/src/runtime/type_registry.rs:396–419

Create an owning handle to the given index's associated type. This will prevent the associated type from being unregistered as long as the returned `RegisteredType` is kept alive.

(engine: &Engine, index: VMSharedTypeIndex)

    /// This will prevent the associated type from being unregistered as long as
    /// the returned `RegisteredType` is kept alive.
    pub fn root(engine: &Engine, index: VMSharedTypeIndex) -> RegisteredType {
        engine.signatures().debug_assert_contains(index);

        let (entry, ty, layout) = {
            let id = shared_type_index_to_slab_id(index);
            let inner = engine.signatures().0.read();

            let ty = inner.types[id].clone().unwrap();
            let entry = inner.type_to_rec_group[index].clone().unwrap();
            let layout = inner.type_to_gc_layout.get(index).and_then(|l| l.clone());

            // NB: make sure to incref while the lock is held to prevent:
            //
            // * This thread: read locks registry, gets entry E, unlocks registry
            // * Other thread: drops `RegisteredType` for entry E, decref
            //   reaches zero, write locks registry, unregisters entry
            // * This thread: increfs entry, but it isn't in the registry anymore
            entry.incref("RegisteredType::root");

            (entry, ty, layout)
        };

        RegisteredType::from_parts(engine.clone(), entry, index, ty, layout)
    }

    /// Construct a new `RegisteredType`.
    ///