futures_test/task/
panic_waker.rs

1use core::ptr::null;
2use futures_core::task::{RawWaker, RawWakerVTable, Waker};
3
4unsafe fn clone_panic_waker(_data: *const ()) -> RawWaker {
5    raw_panic_waker()
6}
7
8unsafe fn noop(_data: *const ()) {}
9
10unsafe fn wake_panic(_data: *const ()) {
11    if !std::thread::panicking() {
12        panic!("should not be woken");
13    }
14}
15
16const PANIC_WAKER_VTABLE: RawWakerVTable =
17    RawWakerVTable::new(clone_panic_waker, wake_panic, wake_panic, noop);
18
19const fn raw_panic_waker() -> RawWaker {
20    RawWaker::new(null(), &PANIC_WAKER_VTABLE)
21}
22
23/// Create a new [`Waker`](futures_core::task::Waker) which will
24/// panic when `wake()` is called on it. The [`Waker`] can be converted
25/// into a [`Waker`] which will behave the same way.
26///
27/// # Examples
28///
29/// ```should_panic
30/// use futures_test::task::panic_waker;
31///
32/// let waker = panic_waker();
33/// waker.wake(); // Will panic
34/// ```
35pub fn panic_waker() -> Waker {
36    // FIXME: Since 1.46.0 we can use transmute in consts, allowing this function to be const.
37    unsafe { Waker::from_raw(raw_panic_waker()) }
38}
39
40/// Get a global reference to a
41/// [`Waker`](futures_core::task::Waker) referencing a singleton
42/// instance of 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
