Rollup merge of rust-lang#146322 - weiznich:fix/146087, r=joboet

Make Barrier RefUnwindSafe again

This commit manually implements `RefUnwindSafe` for `std::sync::Barrier` to fix rust-lang#146087. This is a fix for a regression indroduced by rust-lang@e95db59

Author: matthiaskrgr

std/src/sync/barrier.rs

@@ -1,4 +1,5 @@
 use crate::fmt;
+use crate::panic::RefUnwindSafe;
 use crate::sync::nonpoison::{Condvar, Mutex};
 
 /// A barrier enables multiple threads to synchronize the beginning
@@ -31,6 +32,9 @@ pub struct Barrier {
     num_threads: usize,
 }
 
+#[stable(feature = "unwind_safe_lock_refs", since = "1.12.0")]
+impl RefUnwindSafe for Barrier {}
+
 // The inner state of a double barrier
 struct BarrierState {
     count: usize,

std/tests/sync/barrier.rs

@@ -1,3 +1,4 @@
+use std::panic::RefUnwindSafe;
 use std::sync::mpsc::{TryRecvError, channel};
 use std::sync::{Arc, Barrier};
 use std::thread;
@@ -33,3 +34,11 @@ fn test_barrier() {
     }
     assert!(leader_found);
 }
+
+/// Asserts that `Barrier` is ref unwind safe.
+///
+/// See <https://github.com/rust-lang/rust/issues/146087>.
+const _: () = {
+    const fn check_ref_unwind_safe<T: RefUnwindSafe>() {}
+    check_ref_unwind_safe::<Barrier>();
+};