Support MaybeUninit
#152
Comments
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I agree this would be useful in some form, though there are issues. There is related discussion in #133 that we should consider. |
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So the straightforward user interface might look like // this is safe because `assume_init` applies to the `MaybeUninit<f64>`, but you get the buffer somehow
let mut buffer: [MaybeUninit<f64>; 4] = unsafe { MaybeUninit::uninit().assume_init() };
let recv: &mut [MaybeUninit<f64>] = &mut buffer[..]; // slice to receive into
comm.all_reduce_into(send, recv, op);
let recv: &mut [f64] = unsafe { MaybeUninit::slice_assume_init_mut(recv) }; // nightly API or can be done with transmuteI think that's pretty undesirable because that unsafe line at the bottom is easy for callers to mess up (and a bit worse without using the nightly-only experimental API). What about this? let recv: &mut [MaybeUninit<f64>] = &mut buffer[..]; // slice to receive into
let recv: &mut [f64] = comm.all_reduce_into_uninit(send, recv, op);Note that I used overly type annotations above, and in practice, you'd just write: let recv = comm.all_reduce_into_uninit(send, &mut buffer[..], op); |
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I've left the original project that needed this feature for a long time and forgot some details. But the |
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Currently,
all_reduce_intoand some other APIs only accept buffers like&mut [f32]but not&mut [MaybeUninit<f32>]. However, It's common to use&mut [MaybeUninit<f32>]as a receive buffer. We need lib support for this, as casting a uninitialized buffer to&mut [T]might be undefined behavior, see [1], [2], and [3].Note that we cannot simply implement
EquivalenceforMaybeUninit<T>whereT: Equivalence<Out = SystemDatatype>, which gives users the right to pass an uninitialized buffer as a send buffer, so that APIs likeall_reduce_intoare not safe anymore.The text was updated successfully, but these errors were encountered: