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/target
/Cargo.lock

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[package]
name = "tile-buffer"
version = "0.1.0"
authors = ["Andrey Tkachenko <andrey@aidev.ru>"]
description = "Tiling Buffer useful when dealing with range requests"
keywords = ["io", "buffer", "async", "tile", "range"]
documentation = "https://docs.rs/tile-bufer"
repository = "https://github.com/andreytkachenko/tile-buffer"
license = "MIT OR Apache-2.0"
readme = "README.md"
edition = "2021"
[dependencies]
arrayvec = "0.7.4"
bytes = "1.5.0"
futures = "0.3.28"
parking_lot = "0.12.1"
pin-project-lite = "0.2.13"
tokio = "1.32.0"
[dev-dependencies]
tokio = { version = "1.32.0", features = ["full"] }

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Copyright (c) 2019 Alexey Gerasev
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# TileBuffer

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use std::{io, pin::Pin};
use futures::Future;
use tile_buffer::{AsyncRangeRead, TileBuffer};
use tokio::io::AsyncReadExt;
struct Test;
impl AsyncRangeRead for Test {
type Fut<'a> = Pin<Box<dyn Future<Output = io::Result<()>> + 'a>>
where Self: 'a;
fn total_size(&self) -> usize {
50630
}
fn range_read<'a>(&'a self, buf: &'a mut [u8], offset: usize) -> Self::Fut<'a> {
println!("range_read size {}; offset {}", buf.len(), offset);
Box::pin(async move {
let mut counter = offset;
for val in buf.iter_mut() {
*val = counter as _;
counter += 1;
}
Ok(())
})
}
}
#[tokio::main]
async fn main() {
let inner = Test;
let mut buff: TileBuffer<5, _> = TileBuffer::new_with_tile_size(inner, 1024);
let mut data = Vec::new();
let x = buff.read_to_end(&mut data).await.unwrap();
let valid = (0..50630u32).map(|x| x as u8).collect::<Vec<u8>>();
assert_eq!(x, 50630);
assert_eq!(data, valid);
}

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use std::mem::MaybeUninit;
pub(crate) trait CastExt<const N: usize, T>: Sized + Iterator<Item = T> {
fn cast(mut self) -> [T; N] {
let mut out: MaybeUninit<[T; N]> = MaybeUninit::uninit();
(0..N).for_each(|i| {
let item = self.next().expect("Array was not filled");
unsafe {
let slot = (out.as_mut_ptr() as *mut T).add(i);
slot.write(item);
};
});
unsafe { out.assume_init() }
}
}
impl<const N: usize, T, V: Sized + Iterator<Item = T>> CastExt<N, T> for V {}

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mod cast;
mod range;
mod waker;
use std::{
future::Future,
io,
pin::Pin,
sync::Arc,
task::{ready, Context, Poll, Waker},
};
use arrayvec::ArrayVec;
use tokio::io::{AsyncRead, AsyncSeek, ReadBuf};
use waker::PollPendingQueue;
pub use range::AsyncRangeRead;
use crate::cast::CastExt;
pub const DEFAULT_TILE_SIZE: usize = 4096;
pub const MAX_TILE_COUNT: usize = 1 << TILE_COUNT_BITS;
const TILE_COUNT_BITS: usize = 5;
const TILE_COUNT_MASK: usize = MAX_TILE_COUNT - 1;
///
/// TileBuffer structure
///
pub struct TileBuffer<const N: usize, R: AsyncRangeRead + 'static> {
///
/// Array of tiles. Size of this array usually shuld not be greated than 5
tiles: [Tile<R>; N],
///
/// Mapping between relative tile index (0..N) to global tile index (0..tile_total_count)
/// example:
/// tiles: [{index: 12, data: Some}, {index: 13, data: Some}, {index: 14, data: Some}, {index: 15, data: None}]
/// tile_mapping: [12, 13, 14, 15]
///
/// means:
/// |
/// 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16
/// == XX == ++
/// | - offset pointer
/// == - buffer loaded
/// ++ - buffer is loading now
/// XX - buffer loaded and current (relative index is 1; global index is 13)
tile_mapping: [usize; N],
///
/// Pointer of the current tile.
/// example:
/// if tile_pointer is 0:
/// 0 1 2 3 4 5 6 7 8
/// X = = =
/// note: other tiles would load further data (good for sequential forward read)
///
/// example:
/// if tile_pointer is 2:
/// 0 1 2 3 4 5 6 7 8
/// = = X =
/// note: most of other tiles would keep past data (good for random seeking within some distance from current offset)
tile_pointer: usize,
/// Size of one tile in bytes
tile_size: usize,
/// Effectivly total_size / tile_size
tile_total_count: usize,
/// Current offset in bytes
offset: usize,
/// Total size in bytes
total_size: usize,
/// Pending to poll next indexes with waker
pending: Arc<PollPendingQueue>,
inner: R,
}
impl<const N: usize, R: AsyncRangeRead> TileBuffer<N, R> {
///
pub fn new(inner: R) -> Self {
Self::new_with_tile_size_and_offset(inner, DEFAULT_TILE_SIZE, N / 2)
}
///
pub fn new_with_tile_size(inner: R, tile_size: usize) -> Self {
Self::new_with_tile_size_and_offset(inner, tile_size, N / 2)
}
///
pub fn new_with_tile_size_and_offset(inner: R, tile_size: usize, tile_pointer: usize) -> Self {
assert!(N <= 32, "Maximum number of tiles cannot be greater 32!");
let total_size = inner.total_size();
let tile_total_count = total_size / tile_size;
let tile_total_count = if (total_size % tile_size) > 0 {
tile_total_count + 1
} else {
tile_total_count
};
let pending = Arc::new(PollPendingQueue::default());
Self {
tiles: (0..N)
.map(|i| {
let mut tile = Tile::new(i, tile_size, waker::create_waker(pending.clone(), i));
let offset = i * tile_size;
let length = usize::min(offset + tile_size, total_size) - offset;
tile.stage(&inner, offset, length);
tile
})
.cast(),
tile_mapping: (0..N).cast(),
tile_pointer,
tile_size,
tile_total_count,
total_size,
offset: 0,
inner,
pending,
}
}
///
/// Set new offset
/// calling that method will recalculate mappings,
/// reuse already loaded tiles and stage the ones
/// which not loaded
pub fn set_offset(&mut self, new_offset: usize) {
self.offset = if new_offset > self.total_size {
self.total_size
} else {
new_offset
};
let (tile_begin, _) = self.current_tile();
let tile_end = tile_begin + N;
let mut free: ArrayVec<usize, N> = ArrayVec::new();
// clearing previous mappings
self.tile_mapping.iter_mut().for_each(|x| *x = usize::MAX);
// map existing ones
for (idx, b) in self.tiles.iter().enumerate() {
if b.index >= tile_begin && b.index < tile_end {
self.tile_mapping[b.index - tile_begin] = idx;
} else {
free.push(idx);
}
}
// map rest ones to free buffers and stage load appropriate ranges into those buffers
for m in 0..N {
if self.tile_mapping[m] == usize::MAX {
let bindex = free.pop().unwrap();
self.tiles[bindex].index = tile_begin + m;
self.tile_mapping[m] = bindex;
let offset = (tile_begin + m) * self.tile_size;
let length = usize::min(offset + self.tile_size, self.total_size) - offset;
self.tiles[bindex].stage(&self.inner, offset, length);
}
}
}
fn poll_tiles(&mut self, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
self.pending.register_waker(cx.waker());
loop {
let Some(index) = self.pending.next_item() else {
break Poll::Pending;
};
if let Poll::Ready(val) = self.tiles[index].poll(cx) {
break Poll::Ready(match val {
Ok(_) => Ok(index),
Err(err) => Err(err),
});
}
}
}
#[inline]
fn current_tile(&self) -> (usize, usize) {
let curr_tile = self.offset / self.tile_size;
let tile_begin = if curr_tile < self.tile_pointer {
0
} else if curr_tile + self.tile_pointer < self.tile_total_count {
curr_tile - self.tile_pointer
} else if self.tile_total_count >= N {
self.tile_total_count - N
} else {
0
};
(tile_begin, curr_tile - tile_begin)
}
fn current_buffer_read(&mut self, buf: &mut ReadBuf<'_>) -> Poll<usize> {
let (begin, current) = self.current_tile();
let current_tile_idx = begin + current;
let mapped = self.tile_mapping[current];
let tile = &mut self.tiles[mapped];
if tile.task.is_some() {
return Poll::Pending;
}
let begin_offset = current_tile_idx * self.tile_size;
let tile_offset = self.offset - begin_offset;
let tile_buffer_remaining = &tile.data[tile_offset..];
let upto = usize::min(buf.remaining(), tile_buffer_remaining.len());
buf.put_slice(&tile_buffer_remaining[..upto]);
Poll::Ready(upto)
}
}
impl<const N: usize, R: AsyncRangeRead> AsyncRead for TileBuffer<N, R> {
fn poll_read(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut ReadBuf<'_>,
) -> Poll<io::Result<()>> {
// TODO: use pin-project eventually
let this = unsafe { self.get_unchecked_mut() };
while let Poll::Ready(val) = this.poll_tiles(cx) {
match val {
Ok(_index) => (),
Err(err) => return Poll::Ready(Err(err)),
}
}
let remaining = buf.remaining();
while let Poll::Ready(read) = this.current_buffer_read(buf) {
this.set_offset(this.offset + read);
if read == 0 || buf.remaining() == 0 {
return Poll::Ready(Ok(()));
}
}
if remaining != buf.remaining() {
Poll::Ready(Ok(()))
} else {
Poll::Pending
}
}
}
impl<const N: usize, R: AsyncRangeRead> AsyncSeek for TileBuffer<N, R> {
fn start_seek(self: Pin<&mut Self>, position: io::SeekFrom) -> io::Result<()> {
let new_offset = match position {
io::SeekFrom::Start(offset) => offset as _,
io::SeekFrom::End(offset) => (self.total_size as i64 + offset).try_into().unwrap(),
io::SeekFrom::Current(offset) => (self.offset as i64 + offset).try_into().unwrap(),
};
unsafe { self.get_unchecked_mut() }.set_offset(new_offset);
Ok(())
}
fn poll_complete(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
Poll::Ready(Ok(self.offset as _))
}
}
struct Tile<R: AsyncRangeRead + 'static> {
index: usize,
data: Vec<u8>,
task: Option<R::Fut<'static>>,
waker: Waker,
}
impl<R: AsyncRangeRead + 'static> Tile<R> {
fn new(index: usize, tile_size: usize, waker: Waker) -> Self {
Self {
index,
data: Vec::with_capacity(tile_size),
task: None,
waker,
}
}
fn poll(&mut self, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
if let Some(fut) = self.task.as_mut() {
let mut ctx = Context::from_waker(&self.waker);
// SAFTY:
let pinned = unsafe { Pin::new_unchecked(fut) };
ready!(pinned.poll(&mut ctx))?;
drop(self.task.take());
Poll::Ready(Ok(()))
} else {
Poll::Pending
}
}
fn stage(&mut self, inner: &R, offset: usize, length: usize) {
if self.data.len() != length {
self.data.resize(length, 0);
}
let fut = inner.range_read(&mut self.data, offset);
// SAFTY: Safe because it will live within 'self lifetime
self.task = Some(unsafe { std::mem::transmute(fut) });
self.waker.wake_by_ref();
}
}
#[cfg(test)]
mod tests {
use std::{io, pin::Pin};
use super::{AsyncRangeRead, TileBuffer};
use futures::Future;
use tokio::io::{AsyncReadExt, AsyncSeekExt};
struct Test;
impl AsyncRangeRead for Test {
type Fut<'a> = Pin<Box<dyn Future<Output = io::Result<()>> + 'a>>
where Self: 'a;
fn total_size(&self) -> usize {
50630
}
fn range_read<'a>(&'a self, buf: &'a mut [u8], offset: usize) -> Self::Fut<'a> {
Box::pin(async move {
let mut counter = offset;
tokio::time::sleep(std::time::Duration::from_millis(100)).await;
for val in buf.iter_mut() {
*val = counter as _;
counter += 1;
}
Ok(())
})
}
}
#[tokio::test]
async fn sequential_read_test() {
let inner = Test;
let mut buff: TileBuffer<5, _> = TileBuffer::new_with_tile_size(inner, 1024);
let mut data = Vec::new();
let x = buff.read_to_end(&mut data).await.unwrap();
let valid = (0..50630u32).map(|x| x as u8).collect::<Vec<u8>>();
assert_eq!(x, 50630);
assert_eq!(data, valid);
}
#[tokio::test]
async fn random_read_test() {
let inner = Test;
let mut buff: TileBuffer<5, _> = TileBuffer::new_with_tile_size(inner, 1024);
let mut data = [0u8; 256];
let valid = (0u8..=255).collect::<Vec<u8>>();
let x = buff.read_exact(&mut data).await.unwrap();
assert_eq!(x, 256);
assert_eq!(data.as_slice(), valid.as_slice());
buff.seek(io::SeekFrom::Start(8448)).await.unwrap();
let x = buff.read_exact(&mut data).await.unwrap();
assert_eq!(x, 256);
assert_eq!(data.as_slice(), valid.as_slice());
buff.seek(io::SeekFrom::Start(7424)).await.unwrap();
let x = buff.read_exact(&mut data).await.unwrap();
assert_eq!(x, 256);
assert_eq!(data.as_slice(), valid.as_slice());
buff.seek(io::SeekFrom::Current(-1024)).await.unwrap();
let x = buff.read_exact(&mut data).await.unwrap();
assert_eq!(x, 256);
assert_eq!(data.as_slice(), valid.as_slice());
buff.seek(io::SeekFrom::Start(0)).await.unwrap();
buff.seek(io::SeekFrom::End(-454)).await.unwrap();
let x = buff.read_exact(&mut data).await.unwrap();
assert_eq!(x, 256);
assert_eq!(data.as_slice(), valid.as_slice());
}
}

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use std::io;
use futures::Future;
pub trait AsyncRangeRead {
type Fut<'a>: Future<Output = io::Result<()>>
where
Self: 'a;
/// Returns data total size
fn total_size(&self) -> usize;
/// Load `buf.len()` count of bytes from data starting from `offset` into `buf`
fn range_read<'a>(&'a self, buf: &'a mut [u8], offset: usize) -> Self::Fut<'a>;
}

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use std::{
sync::Arc,
task::{RawWaker, RawWakerVTable, Waker},
};
use arrayvec::ArrayVec;
use futures::task::AtomicWaker;
use parking_lot::Mutex;
use crate::{MAX_TILE_COUNT, TILE_COUNT_BITS, TILE_COUNT_MASK};
#[derive(Default)]
#[repr(align(32))]
pub(crate) struct PollPendingQueue {
waker: AtomicWaker,
items: Mutex<ArrayVec<usize, MAX_TILE_COUNT>>,
}
impl PollPendingQueue {
#[inline]
fn enqueue(&self, index: usize) {
self.items.lock().push(index);
self.waker.wake();
}
#[inline]
pub(crate) fn register_waker(&self, waker: &Waker) {
self.waker.register(waker)
}
#[inline]
pub(crate) fn next_item(&self) -> Option<usize> {
self.items.lock().pop()
}
}
pub(crate) fn create_waker<T>(arc: Arc<T>, index: usize) -> Waker {
assert!(index < MAX_TILE_COUNT);
assert!(std::mem::align_of::<T>() >= MAX_TILE_COUNT);
let ptr = Arc::into_raw(arc) as usize;
let raw_waker = RawWaker::new((ptr | index) as _, &TILE_BUFFER_WAKER_VTABLE);
unsafe { Waker::from_raw(raw_waker) }
}
pub(crate) fn split_ptr_and_offset<T>(ptr_with_offset: *const ()) -> (Arc<T>, usize) {
// clearing last TILE_COUNT_BITS bits
let ptr = (ptr_with_offset as usize >> TILE_COUNT_BITS) << TILE_COUNT_BITS;
(
unsafe { Arc::from_raw(ptr as _) },
// masking offset bits only
ptr_with_offset as usize & TILE_COUNT_MASK,
)
}
pub(crate) static TILE_BUFFER_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(
|ptr_with_offset| -> RawWaker {
let (arc, offset) = split_ptr_and_offset::<PollPendingQueue>(ptr_with_offset);
// cloning
let clone = arc.clone();
// forgetting original arc, to prevent drop
std::mem::forget(arc);
// making raw aligned (by 32) ptr of cloned Arc
let clone_ptr = Arc::into_raw(clone);
let res = clone_ptr as usize | offset;
RawWaker::new(res as _, &TILE_BUFFER_WAKER_VTABLE)
},
|ptr_with_offset| {
let (arc, offset) = split_ptr_and_offset::<PollPendingQueue>(ptr_with_offset);
arc.enqueue(offset);
},
|ptr_with_offset| {
let (arc, offset) = split_ptr_and_offset::<PollPendingQueue>(ptr_with_offset);
arc.enqueue(offset);
std::mem::forget(arc);
},
|ptr_with_offset| {
let (arc, _) = split_ptr_and_offset::<PollPendingQueue>(ptr_with_offset);
drop(arc)
},
);