Assertion failure in check_vtable_size
#1593
Comments
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This also occurs in And in |
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Example without dependencies (~130 lines) that I hit while working on #1504: use std::{
sync::{
atomic::{AtomicI64, Ordering},
Arc,
},
future::Future,
pin::Pin,
task::{Context, RawWaker, RawWakerVTable, Waker},
};
const NOOP_RAW_WAKER: RawWaker = {
#[inline]
unsafe fn clone_waker(_: *const ()) -> RawWaker {
NOOP_RAW_WAKER
}
#[inline]
unsafe fn noop(_: *const ()) {}
RawWaker::new(
std::ptr::null(),
&RawWakerVTable::new(clone_waker, noop, noop, noop),
)
};
type BoxFuture = Pin<Box<dyn Future<Output = ()>>>;
static mut GLOBAL_EXECUTOR: SpawnOnceScheduler = SpawnOnceScheduler::new();
struct SpawnOnceScheduler
{
spawner: Option<BoxFuture>,
spawnee: Option<BoxFuture>,
}
impl SpawnOnceScheduler
{
pub const fn new() -> Self {
Self {
spawner: None,
spawnee: None,
}
}
pub fn spawn(&mut self, fut: impl Future<Output = ()> + 'static) {
let _ = std::mem::replace(&mut self.spawnee, Some(Box::pin(fut)));
}
pub fn run(&mut self) {
let waker = unsafe { Waker::from_raw(NOOP_RAW_WAKER) };
let cx = &mut Context::from_waker(&waker);
let mut index = 0;
while self.spawner.is_some() || self.spawnee.is_some() {
index = (index + 1) % 2;
if index == 0 {
Self::poll_task(&mut self.spawner, cx)
} else {
Self::poll_task(&mut self.spawnee, cx)
}
}
}
fn poll_task(task: &mut Option<BoxFuture>, cx: &mut Context) {
if let Some(fut) = task.as_mut() {
match fut.as_mut().poll(cx) {
std::task::Poll::Ready(_) => {
let _ = std::mem::replace(task, None);
}
std::task::Poll::Pending => (),
}
}
}
pub fn block_on(
self: &'static mut Self,
fut: impl Future<Output = ()> + 'static,
) {
let _ = std::mem::replace(&mut self.spawner, Some(Box::pin(fut)));
self.run();
}
}
pub fn spawn<F: Future<Output = ()> + Sync + 'static>(fut: F) {
unsafe { GLOBAL_EXECUTOR.spawn(fut) }
}
pub fn spawnable_block_on(
fut: impl Future<Output = ()> + 'static,
) {
unsafe { GLOBAL_EXECUTOR.block_on(fut) }
}
struct YieldNow {
yielded: bool,
}
impl Future for YieldNow {
type Output = ();
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> std::task::Poll<Self::Output> {
if self.yielded {
cx.waker().wake_by_ref(); // For completeness. But Kani currently ignores wakers.
std::task::Poll::Ready(())
} else {
self.yielded = true;
std::task::Poll::Pending
}
}
}
pub fn yield_now() -> impl Future<Output = ()> {
YieldNow { yielded: false }
}
#[cfg_attr(kani, kani::proof)]
#[cfg_attr(kani, kani::unwind(4))]
fn nondeterministic_schedule() {
let x = Arc::new(AtomicI64::new(0)); // Surprisingly, Arc verified faster than Rc
let x2 = x.clone();
spawnable_block_on(
async move {
yield_now().await;
x2.fetch_add(1, Ordering::Relaxed);
},
);
assert_eq!(x.load(Ordering::Relaxed), 2);
}Run it like this: Result: |
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I believe this issue has similar root cause as #1395. The failure is triggered while trying to create a vtable for a generator wrapper: I.e.: This code is converting We fail because the size of |
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Reproduction steps:
That "current codegen location" is here:
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