[0.7] Storing a new item in the arena while holding a shared reference to an arena-allocated item fails #2968

winteler · 2024-09-12T21:24:37Z

Hello,

I've tried to migrate to 0.7 and I think I've stumbled upon a bug when using a generic component to read resources. The code builds without problem but a Uncaught RuntimeError: unreachable executed occurs when rendering the Suspense.

Leptos Dependencies

leptos = { version = "0.7.0-beta5", features = ["nightly"] }
leptos_axum = { version = "0.7.0-beta5", optional = true }
leptos_meta = { version = "0.7.0-beta5" }
leptos_router = { version = "0.7.0-beta5", features = ["nightly"] }

To Reproduce
Here is a minimal example to reproduce the issue. The bug depends on the children of , in this example it only occurs when let signal = RwSignal::new(0); is present in . In my code, I also got issues when an is in the children.

use leptos::prelude::*;
use leptos_meta::{provide_meta_context, MetaTags, Stylesheet, Title};
use leptos_router::{
    components::{Route, Router, Routes},
    StaticSegment,
};

pub fn shell(options: LeptosOptions) -> impl IntoView {
    view! {
        <!DOCTYPE html>
        <html lang="en">
            <head>
                <meta charset="utf-8"/>
                <meta name="viewport" content="width=device-width, initial-scale=1"/>
                <AutoReload options=options.clone() />
                <HydrationScripts options/>
                <MetaTags/>
            </head>
            <body>
                <App/>
            </body>
        </html>
    }
}

#[server]
pub async fn string_data() -> Result<String, ServerFnError> {
    Ok(String::from("hello world"))
}

#[component]
pub fn App() -> impl IntoView {
    // Provides context that manages stylesheets, titles, meta tags, etc.
    provide_meta_context();

    view! {
        // injects a stylesheet into the document <head>
        // id=leptos means cargo-leptos will hot-reload this stylesheet
        <Stylesheet id="leptos" href="/pkg/reproduce-leptos-0-7-beta5.css"/>

        // sets the document title
        <Title text="Welcome to Leptos"/>

        // content for this welcome page
        <Router>
            <main>
                <Routes fallback=|| "Page not found.".into_view()>
                    <Route path=StaticSegment("") view=HomePage/>
                    <Route path=StaticSegment("test") view=Test/>
                </Routes>
            </main>
        </Router>
    }
}

/// Renders the home page of your application.
#[component]
fn HomePage() -> impl IntoView {
    view! {
        <h1>"Welcome to Leptos!"</h1>
        <a href="/test">"Test page"</a>
    }
}

/// Renders the test page.
#[component]
fn Test() -> impl IntoView {
    // Creates a reactive value to update the button
    let count = RwSignal::new(0);
    let on_click = move |_| *count.write() += 1;
    let resource = Resource::new(
        move || (),
        move |_| string_data()
    );

    view! {
        <h1>"Welcome to Leptos!"</h1>
        <button on:click=on_click>"Click Me: " {count}</button>
        <SuspenseUnpack resource=resource let:value>
            <ValueDisplay value=value.clone()/>
        </SuspenseUnpack>
    }
}

/// Renders the resource value
#[component]
fn ValueDisplay(
    value: String,
) -> impl IntoView {
    let signal = RwSignal::new(0);
    view! {
        <div>{value}</div>
    }
}

#[component]
pub fn SuspenseUnpack<
    T: Clone + Send + Sync + 'static,
    V: IntoView + 'static,
    F: Fn(&T) -> V + Clone + Send + Sync + 'static,
>(
    resource: Resource<Result<T, ServerFnError>>,
    children: F,
) -> impl IntoView {
    let children = StoredValue::new(children);

    view! {
        <Suspense>
        {
            move || Suspend::new(async move {
                match &resource.await {
                    Ok(value) => Either::Left(children.with_value(|children| children(value))),
                    Err(_e) => Either::Right(view! { <div>"Error"</div> }),
                }
            })
        }
        </Suspense>
    }
}

Let me know if I can help in any way and thanks a lot for your work :)

The text was updated successfully, but these errors were encountered:

gbj · 2024-09-13T00:03:55Z

The issue is creation a new StoredValue of some kind (RwSignal in this case) while holding the lock on another.

Min reproduction:

#[component]
fn HomePage() -> impl IntoView {
    let stored = StoredValue::new("outer");
    stored.with_value(|outer| {
        let inner = StoredValue::new("inner");
        inner.get_value()
    })
}

In the case of your example this can be fixed pretty trivially:

                    Ok(value) => Either::Left(children.get_value()(value)),

These kinds of nested changes should be allowed from a DX perspective, it's just the new arena implementation which accidentally assumes they don't. Allowing them to work as intended probably involves adding an extra layer of indirection here by adding an additional Arc<Mutex<_>> around a StoredValue so that we can clone the StoredValue out of the arena, then work with it, rather than just taking a lock on the whole arena.

Given that I may want to refactor the way that signals etc. use StoredValue so that they are not paying that same cost.

Thanks for pointing this out.

winteler · 2024-09-17T15:31:43Z

Thanks a lot for the quick reply, the workaround indeed fixed the issue 👍

gbj added the bug Something isn't working label Sep 13, 2024

gbj added this to the 0.7 milestone Sep 13, 2024

gbj changed the title ~~[0.7] Runtime error when reading resource in generic component~~ [0.7] Storing a new item in the arena while holding a shared reference to an arena-allocated item fails Sep 17, 2024

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[0.7] Storing a new item in the arena while holding a shared reference to an arena-allocated item fails #2968

[0.7] Storing a new item in the arena while holding a shared reference to an arena-allocated item fails #2968

winteler commented Sep 12, 2024

gbj commented Sep 13, 2024

winteler commented Sep 17, 2024

[0.7] Storing a new item in the arena while holding a shared reference to an arena-allocated item fails #2968

[0.7] Storing a new item in the arena while holding a shared reference to an arena-allocated item fails #2968

Comments

winteler commented Sep 12, 2024

gbj commented Sep 13, 2024

winteler commented Sep 17, 2024