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use std::{
fmt::{Debug, Formatter},
future::Future,
mem::replace,
pin::Pin,
};
#[cfg(feature = "hanging_detection")]
use std::{
sync::Arc,
task::{Poll, ready},
time::Duration,
};
#[cfg(feature = "hanging_detection")]
use tokio::time::{Timeout, timeout};
pub struct Event {
#[cfg(feature = "hanging_detection")]
description: Arc<dyn Fn() -> String + Sync + Send>,
event: event_listener::Event,
}
impl Event {
/// See [`event_listener::Event::new`]. May attach a description that may optionally be read
/// later.
///
/// This confusingly takes a closure ([`FnOnce`]) that returns a nested closure ([`Fn`]).
///
/// When `hanging_detection` is disabled, `description` is never called.
///
/// When `hanging_detection` is enabled, the outer closure is called immediately. The outer
/// closure can have an ephemeral lifetime. The inner closure must be `'static`, but is called
/// only when the `description` is actually read.
///
/// The outer closure allows avoiding extra lookups (e.g. task type info) that may be needed to
/// capture information needed for constructing (moving into) the inner closure.
#[inline(always)]
pub fn new<InnerFn>(_description: impl FnOnce() -> InnerFn) -> Self
where
InnerFn: Fn() -> String + Sync + Send + 'static,
{
#[cfg(not(feature = "hanging_detection"))]
return Self {
event: event_listener::Event::new(),
};
#[cfg(feature = "hanging_detection")]
return Self {
description: Arc::new((_description)()),
event: event_listener::Event::new(),
};
}
/// See [`event_listener::Event::listen`].
pub fn listen(&self) -> EventListener {
#[cfg(not(feature = "hanging_detection"))]
return EventListener {
listener: self.event.listen(),
};
#[cfg(feature = "hanging_detection")]
return EventListener {
description: self.description.clone(),
note: Arc::new(String::new),
future: Some(Box::pin(timeout(
Duration::from_secs(30),
self.event.listen(),
))),
duration: Duration::from_secs(30),
};
}
/// See [`event_listener::Event::listen`]. May attach a note that may optionally be read later.
///
/// This confusingly takes a closure ([`FnOnce`]) that returns a nested closure ([`Fn`]).
///
/// When `hanging_detection` is disabled, `note` is never called.
///
/// When `hanging_detection` is enabled, the outer closure is called immediately. The outer
/// closure can have an ephemeral lifetime. The inner closer must be `'static`, but is called
/// only when the `note` is actually read.
///
/// The outer closure allow avoiding extra lookups (e.g. task type info) that may be needed to
/// capture information needed for constructing (moving into) the inner closure.
pub fn listen_with_note<InnerFn>(&self, _note: impl FnOnce() -> InnerFn) -> EventListener
where
InnerFn: Fn() -> String + Sync + Send + 'static,
{
#[cfg(not(feature = "hanging_detection"))]
return EventListener {
listener: self.event.listen(),
};
#[cfg(feature = "hanging_detection")]
return EventListener {
description: self.description.clone(),
note: Arc::new((_note)()),
future: Some(Box::pin(timeout(
Duration::from_secs(30),
self.event.listen(),
))),
duration: Duration::from_secs(30),
};
}
/// pulls out the event listener, leaving a new, empty event in its place.
pub fn take(&mut self) -> Event {
#[cfg(not(feature = "hanging_detection"))]
return Self {
event: replace(&mut self.event, event_listener::Event::new()),
};
#[cfg(feature = "hanging_detection")]
return Self {
description: self.description.clone(),
event: replace(&mut self.event, event_listener::Event::new()),
};
}
}
impl Event {
/// see [`event_listener::Event::notify`]
pub fn notify(&self, n: usize) {
self.event.notify(n);
}
}
impl Debug for Event {
fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
let mut t = f.debug_tuple("Event");
#[cfg(feature = "hanging_detection")]
t.field(&(self.description)());
t.finish()
}
}
#[cfg(not(feature = "hanging_detection"))]
pub struct EventListener {
listener: event_listener::EventListener,
}
#[cfg(not(feature = "hanging_detection"))]
impl Debug for EventListener {
fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
f.debug_tuple("EventListener").finish()
}
}
#[cfg(not(feature = "hanging_detection"))]
impl Future for EventListener {
type Output = ();
fn poll(
self: Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
) -> std::task::Poll<Self::Output> {
let listener = unsafe { self.map_unchecked_mut(|s| &mut s.listener) };
listener.poll(cx)
}
}
#[cfg(feature = "hanging_detection")]
pub struct EventListener {
description: Arc<dyn Fn() -> String + Sync + Send>,
note: Arc<dyn Fn() -> String + Sync + Send>,
// Timeout need to stay pinned while polling and also while it's dropped.
// So it's important to put it into a pinned Box to be able to take it out of the Option.
future: Option<std::pin::Pin<Box<Timeout<event_listener::EventListener>>>>,
duration: Duration,
}
#[cfg(feature = "hanging_detection")]
impl Debug for EventListener {
fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
let mut t = f.debug_tuple("EventListener");
t.field(&(self.description)());
let note = (self.note)();
if !note.is_empty() {
t.field(¬e);
}
t.finish()
}
}
#[cfg(feature = "hanging_detection")]
impl Future for EventListener {
type Output = ();
fn poll(
mut self: Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
) -> std::task::Poll<Self::Output> {
while let Some(future) = self.future.as_mut() {
match ready!(future.as_mut().poll(cx)) {
Ok(_) => {
self.future = None;
return Poll::Ready(());
}
Err(_) => {
let note = (self.note)();
let description = (self.description)();
if note.is_empty() {
eprintln!(
"EventListener({}) is potentially hanging, waiting for {}s",
description,
self.duration.as_secs(),
);
} else {
eprintln!(
"EventListener({}) is potentially hanging, waiting for {}s from {}",
description,
self.duration.as_secs(),
note
);
}
self.duration *= 2;
// SAFETY: Taking from Option is safe because the value is inside of a pinned
// Box. Pinning must continue until dropped.
let future = self.future.take().unwrap();
self.future = Some(Box::pin(timeout(
self.duration,
// SAFETY: We can move the inner future since it's an EventListener and
// that is Unpin.
unsafe { std::pin::Pin::into_inner_unchecked(future) }.into_inner(),
)));
}
}
}
// EventListener was awaited again after completion
Poll::Ready(())
}
}
#[cfg(all(test, not(feature = "hanging_detection")))]
mod tests {
use std::hint::black_box;
use tokio::time::{Duration, timeout};
use super::*;
// The closures used for descriptions/notes should be eliminated. This may only happen at higher
// optimization levels (that would be okay), but in practice it seems to work even for
// opt-level=0.
#[tokio::test]
async fn ensure_dead_code_elimination() {
fn dead_fn() {
// This code triggers a build error when it's not removed.
unsafe {
unsafe extern "C" {
fn trigger_link_error() -> !;
}
trigger_link_error();
}
}
let event = black_box(Event::new(|| {
dead_fn();
|| {
dead_fn();
String::new()
}
}));
let listener = black_box(event.listen_with_note(|| {
dead_fn();
|| {
dead_fn();
String::new()
}
}));
let _ = black_box(timeout(Duration::from_millis(10), listener)).await;
}
}
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