Panic guard for increase_refcount

futures-util/src/task/waker.rs

@@ -18,16 +18,29 @@ where
     }
 }
 
-// FIXME: panics on Arc::clone / refcount changes could wreak havoc on the
-// code here. We should guard against this by aborting.
-
 unsafe fn increase_refcount<T: ArcWake>(data: *const ()) {
+    struct Guard;
+
+    impl Drop for Guard {
+        fn drop(&mut self) {
+            // panicking twice to abort the program
+            panic!("panics on Arc::clone / refcount changes")
+        }
+    }
+
+    // Panics on Arc::clone / refcount changes could wreak havoc on the
+    // code here. Guard against this by aborting.
+    let guard = Guard;
+
     // Retain Arc by creating a copy
     let arc: Arc<T> = Arc::from_raw(data as *const T);
     let arc_clone = arc.clone();
     // Forget the Arcs again, so that the refcount isn't decrased
     mem::forget(arc);
     mem::forget(arc_clone);
+
+    // Forget the guard to avoid panicking.
+    mem::forget(guard);
 }
 
 // used by `waker_ref`