allow to construct BytesMut with custom alignment #601
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| // # Safety | ||
| // + as long as `capacity % align == 0` it prevent `RawVec::drop` to cause `SIGSEGV` | ||
| // because `RawVec::drop` will create new Layout during free, | ||
| // `RawVec<u8>` will use `Layout::<u8>::array(capacity)` | ||
| // to free instead of our alignment | ||
| Vec::from_raw_parts(ptr, 0, capacity) |
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The documentation for from_raw_parts says the following:
T needs to have the same alignment as what ptr was allocated with. (T having a less strict alignment is not sufficient, the alignment really needs to be equal to satisfy the dealloc requirement that memory must be allocated and deallocated with the same layout.)
Since the vector is using alignment 1, passing it a pointer of larger alignment is incorrect.
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ok, I see errors in miri.
and now I don't think it's possible without custom drop handling,
like making list of structs with alignment by list of power of two e.g. #[repr(align($align))] struct Align$align([0u8;$align]) and then pass custom struct on BytesMut::drop to make it aligned, and should I make it?
if you don't think please close my pr and my last question: can you make BytesMut::from_vec public to allow me to pass my illegal vec please?
| let ptr = std::alloc::alloc(layout); | ||
| if ptr.is_null() { | ||
| // handle null ptr here because it might cause a problem at `BytesMut::from_vec` | ||
| panic!("Not enough memory"); |
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You should call alloc::alloc::handle_alloc_error to handle OOM errors, since panicking may cause unexpected results in low-memory environments.
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Close for now. I have no idea to archive aligned drop and ensure share ref able to drop aligned yet. If anyone have idea please comment 😄 . |
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My use-case is the same as yours, @Wireless4024: I need an aligned buffer to use I just submitted PR #684, which gives one way in which it might be possible to create a |
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BytesMut::with_capacity_alignedto allocate BytesMut with custom alignmentfix #600