Add a copy-on-write container.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/libstd/sync/arc.rs b/src/libstd/sync/arc.rs
index 7b94a3acc2b..5c452018b9b 100644
--- a/src/libstd/sync/arc.rs
+++ b/src/libstd/sync/arc.rs
@@ -94,6 +94,14 @@ impl<T: Send> UnsafeArc<T> {
             return &(*self.data).data as *T;
         }
     }
+
+    /// checks if this is the only reference to the arc protected data
+    #[inline]
+    pub fn is_owned(&self) -> bool {
+        unsafe {
+            (*self.data).count.load(Relaxed) == 1
+        }
+    }
 }
 
 impl<T: Send> Clone for UnsafeArc<T> {