Add integration with zerocopy crate - #253
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The zerocopy crate provides traits and functions for _safely_ transmuting types to/from bytes. It is an important building block for high-performance serialization in many designs. It is also a very well-maintained crate with high standards for quality and its maintainers are actively engaged with the Rust Project on advancing the goals of the Safe Transmute working group. The `zerocopy` crate defines the `FromZeroes` trait, which specifies that a type can be safely constructed from a buffer containing an all-zeroes bit pattern. This PR adds two new methods to `Bump`: `new_zeroed` and `new_slice_zeroed`. `new_zeroed` allocates space for `T` (where `T: FromZeroes`) and returns `&mut T`. This avoids the "placement new" problem in Rust, which causes problems when attempting to allocate large types in the heap, such as `[u8; 0x10000]`. For most containers, such as `Box`, the type is briefly constructed in a temporary on the stack, then a heap allocation is done, then the value is moved into the heap allocation. If `T` is large enough, it can cause stack overflow. The `Bump::new_zeroed` function avoids this problem by simply allocating space for `T` directly in the heap, then filling it with zeroes, then casting the allocation as `&mut T` and returning it. The `FromZeroes` constraint ensures that this is sound. The `new_slice_zeroed` function similarly allows allocating slices directly in a Bump.
fitzgen
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Jun 10, 2024
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Happy to take a PR that adds a zeroing allocation method, but I don't want to take a dependency on any new crates.
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It's an optional dependency, though, and the |
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The zerocopy crate provides traits and functions for safely transmuting types to/from bytes. It is an important building block for high-performance serialization in many designs. It is also a very well-maintained crate with high standards for quality and its maintainers are actively engaged with the Rust Project on advancing the goals of the Safe Transmute working group.
The
zerocopycrate defines theFromZeroestrait, which specifies that a type can be safely constructed from a buffer containing an all-zeroes bit pattern.This PR adds two new methods to
Bump:new_zeroedandnew_slice_zeroed.new_zeroedallocates space forT(whereT: FromZeroes) and returns&mut T. This avoids the "placement new" problem in Rust, which causes problems when attempting to allocate large types in the heap, such as[u8; 0x10000]. For most containers, such asBox, the type is briefly constructed in a temporary on the stack, then a heap allocation is done, then the value is moved into the heap allocation. IfTis large enough, it can cause stack overflow.The
Bump::new_zeroedfunction avoids this problem by simply allocating space forTdirectly in the heap, then filling it with zeroes, then casting the allocation as&mut Tand returning it. TheFromZeroesconstraint ensures that this is sound.The
new_slice_zeroedfunction similarly allows allocating slices directly in a Bump.