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Reduce SSR Buffers in VList #2826

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merged 1 commit into from
Aug 14, 2022
Merged

Reduce SSR Buffers in VList #2826

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2 changes: 1 addition & 1 deletion packages/yew/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,7 @@ slab = "0.4"
wasm-bindgen = "0.2"
yew-macro = { version = "^0.19.0", path = "../yew-macro" }
thiserror = "1.0"
futures = { version = "0.3", default-features = false, features = ["std"] }
futures = { version = "0.3", default-features = false, features = ["std", "async-await"] }
html-escape = { version = "0.2.9", optional = true }
implicit-clone = { version = "0.3", features = ["map"] }
base64ct = { version = "1.5.0", features = ["std"], optional = true }
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108 changes: 63 additions & 45 deletions packages/yew/src/virtual_dom/vlist.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -156,8 +156,10 @@ mod test {

#[cfg(feature = "ssr")]
mod feat_ssr {
use futures::stream::{FuturesUnordered, StreamExt};
use futures::{future, FutureExt};
use std::task::Poll;

use futures::stream::StreamExt;
use futures::{join, pin_mut, poll, FutureExt};

use super::*;
use crate::html::AnyScope;
Expand All @@ -175,52 +177,68 @@ mod feat_ssr {
[child] => {
child.render_into_stream(w, parent_scope, hydratable).await;
}
[first_child, rest_children @ ..] => {
let buf_capacity = w.capacity();
let mut child_streams = Vec::with_capacity(self.children.len() - 1);

// Concurrently render rest children into a separate buffer.
let rest_child_furs = rest_children.iter().map(|child| {
let (mut w, r) = io::buffer(buf_capacity);

child_streams.push(r);

async move {
child
.render_into_stream(&mut w, parent_scope, hydratable)
.await;
}
});

// Concurrently resolve all child futures.
let resolve_fur = if rest_children.len() <= 30 {
// 30 is selected by join_all to be deemed small.
let rest_child_furs = future::join_all(rest_child_furs);
async move {
rest_child_furs.await;
}
.left_future()
} else {
let mut rest_child_furs: FuturesUnordered<_> = rest_child_furs.collect();
async move { while rest_child_furs.next().await.is_some() {} }
.right_future()
};

let transfer_fur = async move {
// Render first child to parent buffer directly.
first_child
.render_into_stream(w, parent_scope, hydratable)
.await;

// Transfer results to parent writer.
for mut r in child_streams {
while let Some(next_chunk) = r.next().await {
w.write(next_chunk.into());
_ => {
async fn render_child_iter<'a, I>(
mut children: I,
w: &mut BufWriter,
parent_scope: &AnyScope,
hydratable: bool,
) where
I: Iterator<Item = &'a VNode>,
{
let buf_capacity = w.capacity();
let mut w = w;
while let Some(m) = children.next() {
let child_fur = async move {
// Rust's Compiler does not release the mutable reference to
// BufWriter until the end of the loop, regardless of whether an
// await statement has dropped the child_fur.
//
// We capture and return the mutable reference to avoid this.

m.render_into_stream(w, parent_scope, hydratable).await;
w
};
pin_mut!(child_fur);

match poll!(child_fur.as_mut()) {
Poll::Pending => {
let (mut next_w, next_r) = io::buffer(buf_capacity);
// Move buf writer into an async block for it to be dropped at
// the end of the future.
let rest_render_fur = async move {
render_child_iter(
children,
&mut next_w,
parent_scope,
hydratable,
)
.await;
}
// boxing to avoid recursion
.boxed_local();
Comment on lines +218 to +219
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Out of curiosity, what happens this isn't boxed? If the issue is stack overflow, is this something tail recursion can fix?

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With Rust’s async/await design, it’s not possible to recursively call async functions without boxing.

https://rust-lang.github.io/async-book/07_workarounds/04_recursion.html


let transfer_fur = async move {
let w = child_fur.await;

pin_mut!(next_r);
while let Some(m) = next_r.next().await {
w.write(m.into());
}
};

join!(rest_render_fur, transfer_fur);
break;
}
Poll::Ready(w_) => {
w = w_;
}
}
}
};
}

future::join(resolve_fur, transfer_fur).await;
let children = self.children.iter();
render_child_iter(children, w, parent_scope, hydratable).await;
}
}
}
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