task: mark JoinHandle as UnwindSafe (#4418)

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> UnwindSafe for JoinHandle<T> {}
+impl<T> RefUnwindSafe for JoinHandle<T> {}
+
 impl<T> JoinHandle<T> {
     pub(super) fn new(raw: RawTask) -> JoinHandle<T> {
         JoinHandle {

tokio/tests/unwindsafe.rs

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