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vtable: Fix soundess issue of VRc::into_dyn for !Send types

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Dyn is currently Send+Sync, so `VRc<WhateverVTable, Dyn>` is also
Send+Sync. So we shouldn't really allow conversion between
`VRc<WhateverVTable, SomeThingNotSend>` to `VRc<_, Dyn>` that can be
sent between threads

This is a breaking change of the vtable crate, but also a soundness fix

Also VRc shouldn't be shared between thread if the vtable itself can't
be shared between threads
This commit is contained in:
Olivier Goffart 2024-02-21 12:26:43 +01:00
parent f932f25dea
commit 8888e547a5
1 changed files with 10 additions and 3 deletions
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13
helper_crates/vtable/src/vrc.rs
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@ -29,7 +29,8 @@ pub unsafe trait VTableMetaDropInPlace: VTableMeta {
/// This is a marker type to be used in [`VRc`] and [`VWeak`] to mean that the
/// actual type is not known.
pub struct Dyn(());
// Note the use of PhantomData to make this type not Send, as a VRc<T, Dyn> cannot be send between thread
pub struct Dyn(PhantomData<*mut ()>);
/// Similar to [`core::alloc::Layout`], but `repr(C)`
#[repr(C)]
@ -270,8 +271,14 @@ impl<VTable: VTableMetaDropInPlace, X /*+ HasStaticVTable<VTable>*/> Deref for V
}
// Safety: we use atomic reference count for the internal things
unsafe impl<VTable: VTableMetaDropInPlace + 'static, X: Send + Sync> Send for VRc<VTable, X> {}
unsafe impl<VTable: VTableMetaDropInPlace + 'static, X: Send + Sync> Sync for VRc<VTable, X> {}
unsafe impl<VTable: VTableMetaDropInPlace + Send + Sync + 'static, X: Send + Sync> Send
for VRc<VTable, X>
{
}
unsafe impl<VTable: VTableMetaDropInPlace + Send + Sync + 'static, X: Send + Sync> Sync
for VRc<VTable, X>
{
}
/// Weak pointer for the [`VRc`] where `VTable` is a VTable struct, and
/// `X` is the type of the instance, or [`Dyn`] if it is not known