runtime: mark JoinHandle as UnwindSafe (#4414)

tokio/src/runtime/task/join.rs

@@ -3,6 +3,7 @@ use crate::runtime::task::RawTask;
 use std::fmt;
 use std::future::Future;
 use std::marker::PhantomData;
+use std::panic::{RefUnwindSafe, UnwindSafe};
 use std::pin::Pin;
 use std::task::{Context, Poll};
 
@@ -150,6 +151,9 @@ cfg_rt! {
 unsafe impl<T: Send> Send for JoinHandle<T> {}
 unsafe impl<T: Send> Sync for JoinHandle<T> {}
 
+impl<T: Send> UnwindSafe for JoinHandle<T> {}
+impl<T: Send> RefUnwindSafe for JoinHandle<T> {}
+
 impl<T> JoinHandle<T> {
     pub(super) fn new(raw: RawTask) -> JoinHandle<T> {
         JoinHandle {

tokio/tests/net_types_unwind.rs → tokio/tests/unwindsafe.rs

@@ -2,6 +2,22 @@
 #![cfg(feature = "full")]
 
 use std::panic::{RefUnwindSafe, UnwindSafe};
+use tokio::task::spawn_blocking;
+
+#[tokio::test]
+async fn futures_are_unwind_safe() {
+    unwind_safe_future(|| async {
+        let _ = spawn_blocking(|| {}).await;
+    })
+    .await
+}
+
+async fn unwind_safe_future<F, Fut>(_: F)
+where
+    F: FnOnce() -> Fut,
+    Fut: std::future::Future<Output = ()> + std::panic::UnwindSafe,
+{
+}
 
 #[test]
 fn net_types_are_unwind_safe() {