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feat: add scheduler::flush() to replace sleep(Duration::ZERO) in tests #4044

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Merged
Madoshakalaka merged 3 commits into from
Mar 7, 2026
Merged

feat: add scheduler::flush() to replace sleep(Duration::ZERO) in tests #4044

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6f2cd3e
feat: add scheduler::flush() to replace sleep(Duration::ZERO) in tests
Madoshakalaka Mar 5, 2026
d0b8270
chore: tidy it up
Madoshakalaka Mar 5, 2026
9279fb5
refactor: use poll_fn for flush(), unify signature across targets
Madoshakalaka Mar 5, 2026
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6 changes: 3 additions & 3 deletions .github/workflows/main-checks.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -103,8 +103,8 @@ jobs:
- name: Run tests - yew
run: |
cd packages/yew
CHROMEDRIVER=$(which chromedriver) cargo test --features csr,hydration,ssr --target wasm32-unknown-unknown
GECKODRIVER=$(which geckodriver) cargo test --features csr,hydration,ssr --target wasm32-unknown-unknown
CHROMEDRIVER=$(which chromedriver) cargo test --features csr,hydration,ssr,test --target wasm32-unknown-unknown
GECKODRIVER=$(which geckodriver) cargo test --features csr,hydration,ssr,test --target wasm32-unknown-unknown

- name: Run tests - yew-router
run: |
Expand Down Expand Up @@ -252,7 +252,7 @@ jobs:
- name: Run WASI tests for yew
run: |
RUST_LOG=info
cargo test --features ssr,hydration --target wasm32-wasip1 -p yew
cargo test --features ssr,hydration,test --target wasm32-wasip1 -p yew

example-runnable-tests-on-wasi:
name: Example Runnable Tests on WASI
Expand Down
4 changes: 2 additions & 2 deletions packages/yew/Makefile.toml
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
[tasks.native-test]
command = "cargo"
args = ["test", "--features", "csr,ssr,hydration"]
args = ["test", "--features", "csr,ssr,hydration,test"]

[tasks.wasm-test]
command = "wasm-pack"
Expand All @@ -10,7 +10,7 @@ args = [
"--headless",
"--",
"--features",
"csr,hydration,ssr",
"csr,hydration,ssr,test",
]

[tasks.ssr-test]
Expand Down
119 changes: 119 additions & 0 deletions packages/yew/src/scheduler.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,34 @@
use std::cell::RefCell;
use std::collections::BTreeMap;
use std::rc::Rc;
#[cfg(any(test, feature = "test"))]
mod flush_wakers {
use std::cell::RefCell;
use std::task::Waker;

thread_local! {
static FLUSH_WAKERS: RefCell<Vec<Waker>> = Default::default();
}

#[cfg(all(
target_arch = "wasm32",
not(target_os = "wasi"),
not(feature = "not_browser_env")
))]
pub(super) fn register(waker: Waker) {
FLUSH_WAKERS.with(|w| {
w.borrow_mut().push(waker);
});
}

pub(super) fn wake_all() {
FLUSH_WAKERS.with(|w| {
for waker in w.borrow_mut().drain(..) {
waker.wake();
}
});
}
}

/// Alias for `Rc<RefCell<T>>`
pub type Shared<T> = Rc<RefCell<T>>;
Expand Down Expand Up @@ -207,6 +235,8 @@ pub(crate) fn start_now() {
LOCK.with(|l| {
if let Ok(_lock) = l.try_borrow_mut() {
scheduler_loop();
#[cfg(any(test, feature = "test"))]
flush_wakers::wake_all();
}
});
}
Expand All @@ -232,6 +262,11 @@ mod arch {
IS_SCHEDULED.store(is, Ordering::Relaxed)
}

#[cfg(any(test, feature = "test"))]
pub(super) fn is_scheduled() -> bool {
check_scheduled()
Comment thread
WorldSEnder marked this conversation as resolved.
}

/// We delay the start of the scheduler to the end of the micro task queue.
/// So any messages that needs to be queued can be queued.
pub(crate) fn start() {
Expand Down Expand Up @@ -260,10 +295,94 @@ mod arch {
pub(crate) fn start() {
super::start_now();
}

#[cfg(any(test, feature = "test"))]
#[allow(dead_code)]
pub(super) fn is_scheduled() -> bool {
false
}
}

pub(crate) use arch::*;

/// Flush all pending scheduler work, ensuring all rendering and lifecycle callbacks complete.
///
/// On browser WebAssembly targets, the scheduler defers its work to the microtask queue.
/// This function registers a waker that is notified when `start_now()` finishes draining all
/// queues, providing proper event-driven render-complete notification without arbitrary sleeps.
///
/// On non-browser targets, the scheduler runs synchronously so this simply drains pending work.
///
/// Use this in tests after mounting or updating a component to ensure all rendering has
/// completed before making assertions.
#[cfg(all(
any(test, feature = "test"),
target_arch = "wasm32",
not(target_os = "wasi"),
not(feature = "not_browser_env")
))]

@WorldSEnder WorldSEnder Mar 5, 2026

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Could these three lines be moved into the function for a uniform signature (and documentation) across targets.

@Madoshakalaka Madoshakalaka Mar 5, 2026

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Done, both targets now use pub async fn flush()

pub fn flush() -> Flush {
Flush { _priv: () }
}

/// Future returned by [`flush()`] that resolves when the scheduler finishes all pending work.
///
/// On each poll, this future eagerly drains any currently-queued scheduler work via
/// `start_now()`. It then checks whether the scheduler has been re-scheduled (via
/// `IS_SCHEDULED`), which indicates that spawned microtasks (e.g., from Suspense futures
/// resolving) will trigger more work. If so, it re-registers its waker and yields, allowing
/// those microtasks to execute before the next poll. This loop continues until the scheduler
/// is truly idle.
#[cfg(all(
any(test, feature = "test"),
target_arch = "wasm32",
not(target_os = "wasi"),
not(feature = "not_browser_env")
))]
#[derive(Debug)]
pub struct Flush {
_priv: (),
}

#[cfg(all(
any(test, feature = "test"),
target_arch = "wasm32",
not(target_os = "wasi"),
not(feature = "not_browser_env")
))]
impl std::future::Future for Flush {
type Output = ();

fn poll(
self: std::pin::Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
) -> std::task::Poll<()> {
start_now();

if arch::is_scheduled() {
flush_wakers::register(cx.waker().clone());
std::task::Poll::Pending
} else {
std::task::Poll::Ready(())
}
}
}

@WorldSEnder WorldSEnder Mar 5, 2026

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This future could be simply implemented with std::future::poll_fn.

@Madoshakalaka Madoshakalaka Mar 5, 2026

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Good call, done.

/// Flush all pending scheduler work, ensuring all rendering and lifecycle callbacks complete.
///
/// On non-browser targets, the scheduler runs synchronously so this simply drains pending work.
#[cfg(all(
any(test, feature = "test"),
not(all(
target_arch = "wasm32",
not(target_os = "wasi"),
not(feature = "not_browser_env")
))
))]
pub async fn flush() {
start_now();
}

impl Scheduler {
/// Fill vector with tasks to be executed according to Runnable type execution priority
///
Expand Down
47 changes: 19 additions & 28 deletions packages/yew/tests/hydration.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ use yew::platform::time::sleep;
use yew::prelude::*;
use yew::suspense::{use_future, Suspension, SuspensionResult};
use yew::virtual_dom::VNode;
use yew::{component, Renderer, ServerRenderer};
use yew::{component, scheduler, Renderer, ServerRenderer};

wasm_bindgen_test::wasm_bindgen_test_configure!(run_in_browser);

Expand Down Expand Up @@ -62,12 +62,12 @@ async fn hydration_works() {
.unwrap()
.set_inner_html(&s);

sleep(Duration::ZERO).await;
scheduler::flush().await;

Renderer::<App>::with_root(gloo::utils::document().get_element_by_id("output").unwrap())
.hydrate();

sleep(Duration::ZERO).await;
scheduler::flush().await;

let result = obtain_result_by_id("output");

Expand All @@ -85,7 +85,7 @@ async fn hydration_works() {
.unwrap()
.click();

sleep(Duration::ZERO).await;
scheduler::flush().await;

let result = obtain_result_by_id("output");

Expand Down Expand Up @@ -237,7 +237,7 @@ async fn hydration_with_suspense() {
.unwrap()
.set_inner_html(&s);

sleep(Duration::ZERO).await;
scheduler::flush().await;

Renderer::<App>::with_root(gloo::utils::document().get_element_by_id("output").unwrap())
.hydrate();
Expand Down Expand Up @@ -393,7 +393,7 @@ async fn hydration_with_suspense_not_suspended_at_start() {
.unwrap()
.set_inner_html(&s);

sleep(Duration::ZERO).await;
scheduler::flush().await;

Renderer::<App>::with_root(gloo::utils::document().get_element_by_id("output").unwrap())
.hydrate();
Expand Down Expand Up @@ -524,7 +524,7 @@ async fn hydration_nested_suspense_works() {
.unwrap()
.set_inner_html(&s);

sleep(Duration::ZERO).await;
scheduler::flush().await;

Renderer::<App>::with_root(gloo::utils::document().get_element_by_id("output").unwrap())
.hydrate();
Expand Down Expand Up @@ -661,12 +661,12 @@ async fn hydration_node_ref_works() {
.unwrap()
.set_inner_html(&s);

sleep(Duration::ZERO).await;
scheduler::flush().await;

Renderer::<App>::with_root(gloo::utils::document().get_element_by_id("output").unwrap())
.hydrate();

sleep(Duration::ZERO).await;
scheduler::flush().await;

let result = obtain_result_by_id("output");
assert_eq!(
Expand All @@ -682,7 +682,7 @@ async fn hydration_node_ref_works() {
.unwrap()
.click();

sleep(Duration::ZERO).await;
scheduler::flush().await;

let result = obtain_result_by_id("output");
assert_eq!(
Expand Down Expand Up @@ -754,16 +754,13 @@ async fn hydration_list_order_works() {
.unwrap()
.set_inner_html(&s);

sleep(Duration::ZERO).await;
scheduler::flush().await;

Renderer::<App>::with_root(gloo::utils::document().get_element_by_id("output").unwrap())
.hydrate();

// Wait until all suspended components becomes revealed.
sleep(Duration::ZERO).await;
sleep(Duration::ZERO).await;
sleep(Duration::ZERO).await;
sleep(Duration::ZERO).await;
scheduler::flush().await;

@Madoshakalaka Madoshakalaka Mar 5, 2026

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real proof of flush correctness


let result = obtain_result_by_id("output");
assert_eq!(
Expand Down Expand Up @@ -837,13 +834,13 @@ async fn hydration_suspense_no_flickering() {
.unwrap()
.set_inner_html(&s);

sleep(Duration::ZERO).await;
scheduler::flush().await;

Renderer::<App>::with_root(gloo::utils::document().get_element_by_id("output").unwrap())
.hydrate();

// Wait until all suspended components becomes revealed.
sleep(Duration::ZERO).await;
scheduler::flush().await;

let result = obtain_result_by_id("output");
assert_eq!(
Expand Down Expand Up @@ -950,16 +947,13 @@ async fn hydration_order_issue_nested_suspense() {
.unwrap()
.set_inner_html(&s);

sleep(Duration::ZERO).await;
scheduler::flush().await;

Renderer::<App>::with_root(gloo::utils::document().get_element_by_id("output").unwrap())
.hydrate();

// Wait until all suspended components becomes revealed.
sleep(Duration::ZERO).await;
sleep(Duration::ZERO).await;
sleep(Duration::ZERO).await;
sleep(Duration::ZERO).await;
scheduler::flush().await;

let result = obtain_result_by_id("output");
assert_eq!(
Expand Down Expand Up @@ -1180,7 +1174,7 @@ async fn hydration_with_camelcase_svg_elements() {
.unwrap()
.set_inner_html(&s);

sleep(Duration::ZERO).await;
scheduler::flush().await;

// Hydrate - this should not panic
Renderer::<App>::with_root(gloo::utils::document().get_element_by_id("output").unwrap())
Expand Down Expand Up @@ -1268,15 +1262,12 @@ async fn hydration_suspended_child_does_not_trap_sibling_slot() {
.unwrap()
.set_inner_html(&s);

sleep(Duration::ZERO).await;
scheduler::flush().await;

Renderer::<App>::with_root(gloo::utils::document().get_element_by_id("output").unwrap())
.hydrate();

sleep(Duration::ZERO).await;
sleep(Duration::ZERO).await;
sleep(Duration::ZERO).await;
sleep(Duration::ZERO).await;
scheduler::flush().await;

let result = obtain_result();

Expand Down
6 changes: 2 additions & 4 deletions packages/yew/tests/mod.rs
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Expand Up @@ -2,12 +2,10 @@

mod common;

use std::time::Duration;

use common::obtain_result;
use wasm_bindgen_test::*;
use yew::platform::time::sleep;
use yew::prelude::*;
use yew::scheduler;

wasm_bindgen_test::wasm_bindgen_test_configure!(run_in_browser);

Expand Down Expand Up @@ -36,7 +34,7 @@ async fn props_are_passed() {
)
.render();

sleep(Duration::ZERO).await;
scheduler::flush().await;
let result = obtain_result();
assert_eq!(result.as_str(), "done");
}
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