Doc: MaybeUninit::assume_init_read Safety: warn on thread safety
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Due to `impl<T: Sync> Sync for MaybeUninit<T>`, `MaybeUninit::assume_init_read` is prone to the illegal use transferring ownership of `!Send + Sync` value across threads. This commit adds a warning on this thread safety problem to the method's Safety section. This commit also adds two code examples related to this problem.
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MaybeUninit::assume_init_read Safety: warn on thread safetyMaybeUninit::assume_init_read Safety: warn on thread safety (fix of #148083)
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MaybeUninit::assume_init_read Safety: warn on thread safety (fix of #148083)MaybeUninit::assume_init_read Safety: warn on thread safety
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Fixes #148083.
Due to
impl<T: Sync> Sync for MaybeUninit<T>,MaybeUninit::assume_init_readis prone to the illegal use transferring ownership of!Send + Syncvalue across threads. This PR adds a warning on this thread safety problem to the method's Safety section. This PR also adds two code examples related to this problem.On the bad case code example: I wish I could use something better than
MutexGuard<'_, u32>, because I wasn't able to produce Miri-detectable UB.core::sync::Exclusive<&Cell<u32>>would be nice, but it's unstable.