add Send and Sync as appropriate

src/lib.rs

@@ -50,6 +50,7 @@ where
 }
 
 impl<T> std::iter::FusedIterator for LinkerSetIter<T> where T: 'static {}
+unsafe impl<T: Send> Send for LinkerSetIter<T> {}
 
 pub struct LinkerSet<T>
 where
@@ -104,6 +105,9 @@ where
     }
 }
 
+unsafe impl<T: Send> Send for LinkerSet<T> {}
+unsafe impl<T: Sync> Sync for LinkerSet<T> {} // readonly once created
+
 #[macro_export]
 macro_rules! set_declare {
     ($set:ident, $type:ty) => {
@@ -207,6 +211,16 @@ mod test {
         let expect = HashSet::from([&AAA]);
         assert_eq!(actual, expect);
     }
+
+    #[test]
+    fn test_traits() {
+        fn require_send<T: Send>(_: T) {}
+        fn require_sync<T: Sync>(_: T) {}
+
+        require_send(set!(aaa));
+        require_sync(set!(aaa));
+        require_send(set!(aaa).iter());
+    }
 }
 
 #[cfg(test)]