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Don't store subclass impl/private data in an Option<T> #589
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We don't know the exact memory layout of the Option<T> in relation to T so can't easily go from a *const T to the surrounding *const Option<T>. Since nightly from 2020-02-12 using both pointer types interchangeably causes segmentation faults as their memory layouts are not actually compatible and never were, but due to some compiler changes this actually causes crashes at runtime now. See rust-lang/rust#69102 for details. As an Option<_> was only used for some paranoid runtime checks that are not really needed, simply store T directly as impl/private data of subclasses. This has the side-effect of having zero-sized impl/private data types to actually occupy zero bytes of memory, and in some other cases to save a few bytes of the allocation.
Instead of first reading it on the stack and the dropping it.
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@GuillaumeGomez This wants another bugfix release btw, it's a quite bad bug and I don't fully understand why it didn't explode from the very beginning :) |
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Indeed, thanks for coming up so quickly with this fix! 👍 |
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I have a small additional fix tomorrow, so don't do a release just yet. Tomorrow :)
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Sent from my Android device with K-9 Mail. Please excuse my brevity.
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It's a bit late for a release you know... We still have a few details to discuss about as well! |
…te/impl data for subclasses GLib aligns the type private data to two gsizes so we can't safely store any type there that requires a bigger alignment.
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👍 Thanks. |
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Thanks for reviewing :) |
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Released as 0.9.3 on crates.io |
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We don't know the exact memory layout of the Option in relation to T
so can't easily go from a *const T to the surrounding *const Option.
Since nightly from 2020-02-12 using both pointer types interchangeably
causes segmentation faults as their memory layouts are not actually
compatible and never were, but due to some compiler changes this
actually causes crashes at runtime now.
See rust-lang/rust#69102 for details.
As an Option<_> was only used for some paranoid runtime checks that are
not really needed, simply store T directly as impl/private data of
subclasses.
This has the side-effect of having zero-sized impl/private data types to
actually occupy zero bytes of memory, and in some other cases to save a
few bytes of the allocation.
CC @EPashkin @GuillaumeGomez