futures_test/task/
panic_waker.rs

1use core::ptr::null;
2use futures_core::task::{RawWaker, RawWakerVTable, Waker};
3
4#[inline(always)]
5unsafe fn clone_panic_waker(_data: *const ()) -> RawWaker {
6    raw_panic_waker()
7}
8
9unsafe fn noop(_data: *const ()) {}
10
11unsafe fn wake_panic(_data: *const ()) {
12    if !std::thread::panicking() {
13        panic!("should not be woken");
14    }
15}
16
17const PANIC_WAKER_VTABLE: RawWakerVTable =
18    RawWakerVTable::new(clone_panic_waker, wake_panic, wake_panic, noop);
19
20const fn raw_panic_waker() -> RawWaker {
21    RawWaker::new(null(), &PANIC_WAKER_VTABLE)
22}
23
24/// Create a new [`Waker`] which will panic when `wake()` is called on it.
25/// The [`Waker`] can be converted into a [`Waker`] which will behave the same
26/// way.
27///
28/// # Examples
29///
30/// ```should_panic
31/// use futures_test::task::panic_waker;
32///
33/// let waker = panic_waker();
34/// waker.wake(); // Will panic
35/// ```
36pub fn panic_waker() -> Waker {
37    // FIXME: Since 1.46.0 we can use transmute in consts, allowing this function to be const.
38    unsafe { Waker::from_raw(raw_panic_waker()) }
39}
40
41/// Get a global reference to a [`Waker`] referencing a singleton instance of
42/// a [`Waker`] which panics when woken.
43///
44/// # Examples
45///
46/// ```should_panic
47/// use futures_test::task::panic_waker_ref;
48///
49/// let waker = panic_waker_ref();
50/// waker.wake_by_ref(); // Will panic
51/// ```
52pub fn panic_waker_ref() -> &'static Waker {
53    struct SyncRawWaker(RawWaker);
54    unsafe impl Sync for SyncRawWaker {}
55
56    static PANIC_WAKER_INSTANCE: SyncRawWaker = SyncRawWaker(raw_panic_waker());
57
58    // SAFETY: `Waker` is #[repr(transparent)] over its `RawWaker`.
59    unsafe { &*(&PANIC_WAKER_INSTANCE.0 as *const RawWaker as *const Waker) }
60}
61
62#[cfg(test)]
63mod tests {
64    #[test]
65    #[should_panic(expected = "should not be woken")]
66    fn issue_2091_cross_thread_segfault() {
67        let waker = std::thread::spawn(super::panic_waker_ref).join().unwrap();
68        waker.wake_by_ref();
69    }
70}
futures_test/task/panic_waker.rs

futures_test/task/
panic_waker.rs
