io: change AsyncRead to use a ReadBuf #2758
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seanmonstar
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CI is green. |
Darksonn
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A-tokio
| let r = (*self).get_mut().read(buf); | ||
| // We can't assume the `Read` won't look at the read buffer, | ||
| // so we have to force initialization here. | ||
| let r = (*self).get_mut().read(buf.initialize_unfilled()); |
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Types like TcpStream go via this path. We will want to avoid initializing memory in cases where it is not necessary. This can be done in a later PR, but we should track it.
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I don't believe neither TcpStream nor UnixStream hit this path. They both use their own poll_read_priv, which skips PollEvented.
| pos: 0, | ||
| cap: 0, | ||
| } | ||
| let buffer = vec![0; capacity]; |
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This switches to initializing the memory. Do we want to track this to fix later?
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This switches to just using alloc_zeroed. I guessed that the cost is not likely noticeable, here in making a BufReader. If it is, we would need more complicated logic to keep a buffer: Box<[MaybeUninit<u8>]>, initialized: usize so we don't keep re-initializing it over and over.
| let n = ready!(me.inner.poll_read(cx, &mut buf[..max]))?; | ||
| let max = std::cmp::min(buf.remaining() as u64, *me.limit_) as usize; | ||
| // Make a ReadBuf of the unfulled section up to max | ||
| let mut b = unsafe { ReadBuf::uninit(&mut buf.unfilled_mut()[..max]) }; |
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Should we add a ReadBuf::take(&mut self, n: usize) -> ReadBuf<'_> that does this logic? It seems useful.
seanmonstar
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I opened #2769 to track the remaining items. Please check I didn't forget anything. |
This changes
AsyncRead::poll_readfrom being passed a&mut [u8]to be passed a&mut ReadBuf, which is a type that encapsulates the possibility of the read buffer containing uninitialized memory. For background, see #2716.