Merge 'v1.6.1' into 'master' (#721)

src/bytes_mut.rs

@@ -1780,7 +1780,7 @@ static SHARED_VTABLE: Vtable = Vtable {
     clone: shared_v_clone,
     to_vec: shared_v_to_vec,
     to_mut: shared_v_to_mut,
-    is_unique: crate::bytes::shared_is_unique,
+    is_unique: shared_v_is_unique,
     drop: shared_v_drop,
 };
 
@@ -1843,6 +1843,12 @@ unsafe fn shared_v_to_mut(data: &AtomicPtr<()>, ptr: *const u8, len: usize) -> B
     }
 }
 
+unsafe fn shared_v_is_unique(data: &AtomicPtr<()>) -> bool {
+    let shared = data.load(Ordering::Acquire);
+    let ref_count = (*shared.cast::<Shared>()).ref_count.load(Ordering::Relaxed);
+    ref_count == 1
+}
+
 unsafe fn shared_v_drop(data: &mut AtomicPtr<()>, _ptr: *const u8, _len: usize) {
     data.with_mut(|shared| {
         release_shared(*shared as *mut Shared);