sync: make Notify panic safe (#5154)

tokio/src/sync/notify.rs

@@ -13,6 +13,7 @@ use crate::util::WakeList;
 use std::cell::UnsafeCell;
 use std::future::Future;
 use std::marker::PhantomPinned;
+use std::panic::{RefUnwindSafe, UnwindSafe};
 use std::pin::Pin;
 use std::ptr::NonNull;
 use std::sync::atomic::Ordering::SeqCst;
@@ -566,6 +567,9 @@ impl Default for Notify {
     }
 }
 
+impl UnwindSafe for Notify {}
+impl RefUnwindSafe for Notify {}
+
 fn notify_locked(waiters: &mut WaitList, state: &AtomicUsize, curr: usize) -> Option<Waker> {
     loop {
         match get_state(curr) {

tokio/tests/unwindsafe.rs

@@ -3,6 +3,11 @@
 
 use std::panic::{RefUnwindSafe, UnwindSafe};
 
+#[test]
+fn notify_is_unwind_safe() {
+    is_unwind_safe::<tokio::sync::Notify>();
+}
+
 #[test]
 fn join_handle_is_unwind_safe() {
     is_unwind_safe::<tokio::task::JoinHandle<()>>();